THE CHEMISTRY of SOME TRIPLUOROMETHYL-PHOSPHINES . by MIRZA ARSHAD ALI BEG B..Sc

THE CHEMISTRY of SOME TRIPLUOROMETHYL-PHOSPHINES

. by

MIRZA ARSHAD ALI BEG

B..Sc.(Hons.)f M.Sc. (Karachi), 1955»

A thesis submitted in partial fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY in the Department of Chemistry.

We accept this thesis as conforming to the required standard©

THE UNIVERSITY OP BRITISH COLUMBIA June, 1961. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication' of this thesis for financial gain shall not be allowed'without my written permission.

Department of ^^R^+^C&&^ The University of British Columbia, Vancouver 8, Canada.

Date Af*Ql.tfc% /9£f GRADUATE STUDIES Wqp Pntuersttg of ^rtttsii Columbia Field of Study: Inorganic Chemistry Topics in Inorganic Chemistry H. C. Clark H. G. Heal FACULTY OF GRADUATE STUDIES Topics in Organic Chemistry L. D. Hayward D. E. McGreer A. Rosenthal R. Stewart Radiochemistry D. R. Wiles Seminar in Chemistry : R. Stewart Related Studies: PROGRAMME OF THE . Atomic Physics K. L. Erdman ! FINAL ORAL EXAMINATION Geophysics '. J. A. Jacobs Structure of Metals II V. Griffiths j FOR THE DEGREE OF E. Teghtsoonian DOCTOR OF PHILOSOPHY

of M. ARSHAD A. BEG B.Sc. (Hons), M.Sc. (Karachi) PUBLICATIONS FRIDAY, JULY 28th, 1961 at 2:30 p.m. 1. Chemistry of the Trifluoromethyl Group, Part I, Complex For• mation by Phosphines containing the trifluoromethyl group. IN ROOM 342, CHEMISTRY M. A. A. Beg and H. C. Clark, Can. J. Chem., 38, 119, 1960. 2. Chemistry of the Trifluoromethyl Group, Part II, Nickel(II) COMMITTEE IN CHARGE Complexes of Trifluoromethyl-phosphines. M. A. A. Beg and H. C. Clark, Can. J. Chem., 39, 595, 1961. Chairman: D. M. MYERS 3. Chemistry of the Trifluoromethyl Group, Part III, Phenylbistri- W. A. BRYCE J. A. JACOBS fluoromethylphosphine and related Compounds. M. A. A. Beg H. C. CLARK J. P. KUTNEY and H. C. Clark, Can. J. Chem., 39, 564, 1961. j. A. CRUMB c. A. MCDOWELL J. HALPERN R. STEWART L. G. HARRISON E. TEGHTSOONIAN External Examiner: H. J. EMELEUS, C.B.E., Ph.D., D.Sc, A.R.C.S., F.R.S. University Chemical Laboratory, Cambridge, England ABSTRACT By reaction with methyl iodide, this phosphine also forms a new phosphonium compound, methyldiphenyltrifluoromethylphosphonium CHEMISTRY OF SOME TRIFLUOROMETHYL-PHOSPHINES iodide which is readily hydrolysed by cold water with the loss of the trifluoromethyl group. One particular aspect of the chemistry of the trifluoromethyl In general, phosphines containing one trifluoromethyl group group is its high electron-withdrawing power which reduces the donor show similar properties to those of their parent compounds, tri- properties of normally strong bases. This investigation has been methylphosphine and triphenylphosphine, while those containing two concerned with the chemistry of some phosphines containing this trifluoromethyl groups are very similar in their behaviour to tristri- group. For this purpose, substituted phosphines containing methyl or fluoromethylphosphine. phenyl and trifluoromethyl groups have been prepared. For the study of their donor properties, a series of addition compounds with boron The phosphines containing more than one CF3 group do not trifluoride, platinum(II) chloride and nickel(II) salts have been form addition compounds with boron trifluoride. The phenyl-tri- prepared. fluoromethyl-phosphines form more stable complexes than the methyl- trifluoromethyl-phosphines. The reported methods for preparing the methyl-trifluoromethyl- The phosphines containing up to two trifluoromethyl groups phosphines do not produce a good yield; therefore, an attempt has form complexes with platinum(II) chloride. A complex with tristri- been made towards a better understanding of the reactions. The fluoromethylphosphine could not be obtained. Except dimethyltri- phenyl-trifluoromethyl-phosphines have been prepared by reacting fluoromethylphosphine, which forms mainly a cis isomer, the other trifluoroiodomethane with a phosphorus compound containing a P-P phosphines, CHa(CF3)2P, C6H5(CF3).,P, and (C6H5)2CF3P form main• bond. Thus, a reaction with tetraphenylcyclotetraphosphine gives ly trans isomers. The non-occurrence of the tristrifluoromethylphos- phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodo- phine complex and the production of mainly trans isomers of the phosphine, and reaction with tetraphenlydiphosphine gives diphenyl- above-mentioned phosphines has been interpreted in terms of steric trifluoromethylphosphine. The latter has also been prepared by re• phenomenon. action of trifluoroiodomethane with either triphenylphosphine or The phosphines containing more than one CF group do not diphenylchlorophosphine. S form complexes with nickel(II) salts. The nitrate complexes of These new phosphines are colorless liquids (except phenyltri- trimethylphosphine and dimethyltrifluoromethylphosphine are para• fluoromethyliodophosphine which is reddish-brown) of high boiling magnetic, while the dichloro, dibromo, diiodo, and dithiocyanato point. They are stable in air and cannot be hydrolysed with acid or complexes are diamagnetic. water, except the iodophosphine C(.HSCF3PI, which reacts with water A correlation of the various properties, for example boiling to give phenyltrifluoromethylphosphinic acid, a new oxyacid. Phenyl- points and heats of vaporization, has shown that the trifluoromethyl bistrifluoromethylphosphine can be hydrolysed with aqueous alkali substituted phosphines are not anomalous in the general family of to give fluoroform and phenylphosphonous acid. Diphenyltrifluoro- phosphines. methylphosphine, on the other hand, cannot be hydrolysed by aqueous An attempt has also been made towards a study of the infrared alkali, but reacts slowly with alcoholic potassium hydroxide to give' spectra of the phosphines and their compounds, and towards a cor• fluoroform and diphenylphosphinic acid. relation with the spectra of other phosphorus compounds. Finally, an approximate estimate of the "electronegativities" of a wide range The phosphines form a further series of new compounds by of substituted phosphines gives values which are in good agreement reaction with halogens. Phenylbistrifluoromethylphosphine reacts with the observed order of reactivities of the phosphines studied, and with iodine to form trifluoroiodomethane, but forms phenylbistri- assists in correctly placing the trifluoromethylphosphines in such a fluoromethyldibromophosphorane with bromine. This compound al• range, of compounds. so gives phenyltrifluoromethylphosphinic acid on aqueous hydrolysis, as obtained in the case of phenyltrifluoromethyliodophosphine. Be• sides forming the dibromophosphorane, diphenyltrifluoromethylphosphine is the first trifluoromethyl-phosphine known to form a diiodophosphorane. It is interesting to note that diphenyltrifluoromethylphosphine is difficult to hydrolyse, whereas the phosphoranes can be hydrolysed easily, giving fluoroform and diphenylphosphinic acid. (i)

ABSTRACT

One particular aspect of the chemistry of the tri• fluoromethyl group is its high electron-withdrawing power which reduces the donor properties of normally strong bases* This investigation has been concerned with the chemistry of some phosphines containing this group. For this purpose, substituted phosphines containing methyl or phenyl and tri• fluoromethyl groups have been prepared. For the study of their donor properties, a series of addition compounds with boron trifluoride, platinum(Il) chloride and nickel(II) salts have been prepared.

The reported methods for preparing the methyl- trifluoromethyl-phosphines do not produce a good yield; therefore, an attempt has been made towards a better under• standing of the reactions. The phenyl-trifluoromethyl- phosphines have been prepared by reacting trifluoroiodomethane with a phosphorus compound containing a P-P bond. Thus, a reaction with tetraphenylcyclotetraphosphine gives phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine, and reaction with tetraphenyldiphosphine gives diphenyltrifluoromethylphosphine. The latter has also been prepared by reaction of trifluoroiodomethane with either triphenylphosphine or diphenylchlorophosphine. (ii)

\ These new phosphines are colorless liquids (ex• cept phenyltrifluororaethyliodophosphine which is reddish- brown) of high boiling point. They are stable in air and cannot be hydrolysed with acid or water, except the iodophosphine C H CP PI, which reacts with water to give phenyl- 6 5 3 trifluoromethylphosphinic acid, a new oxyacid. Phenylbis- trifluororaethylphosphine can be hydrolysed with aqueous alkali to give fluoroform and phenylphosphonous acid. Di- phenyltrifluoromethylphosphine, on the other hand, cannot be hydrolysed by aqueous alkali, but reacts slowly with alco• holic potassium hydroxide to give fluoroform and diphenylphosphinic acid. The phosphines form a further series of new com• pounds by reaction with halogens. Phenylbistrifluoromethyl- phosphine reacts with iodine to form trifluoroiodomethane, but forms phenylbistrifluororaethyldibromophosphorane with bromine. This compound also gives phenyltrifluoromethyl• phosphinic acid on aqueous hydrolysis, as obtained in the case of phenyltrifluoromethyliodophosphine. Besides forming the dibromophosphorane, diphenyltrifluoromethylphosphine is the first trifluoromethyl-phosphine known to form a diiodophosphorane. It is interesting to note that diphenyltrifluoromethylphosphine is difficult to hydrolyse, whereas the phosphoranes can be hydrolysed easily, giving fluoroform and (iii) diphenylphosphinic acid. By reaction with methyl iodide, this phosphine also forms a new phosphonlum compound, methyldiphenyltrifluoromethylphosphonium iodide, which is readily hydrolysed by cold water with the loss of the tri• fluoromethyl group. In general, phosphines containing one trifluoro• methyl group show similar properties to those of their parent compounds, trimethylphosphine and triphenylphosphine, while those containing two trifluoromethyl groups are very similar in their behaviour to tristrifluoromethylphosphine. The phosphines containing more than one CP group 3 do not form addition compounds with boron trifluoride. The phenyl-trifluoromethyl-phosphines form more stable complexes than the methyl-trifluoromethyl-phosphines. The phosphines containing up to two trifluoro• methyl groups form complexes with platinum(Il) chloride. A complex with tristrifluoromethylphosphine could not be obtained. Except dimethyltrifluoromethylphosphine, which forms mainly a cis isomer, the other phosphines, CH^(GP^)^P, C H (CP ) P, and (C H ) CP P form mainly trans isomers. The 6 5 3 2 6 5 2 3 non-occurrence of the tristrifluoromethylphosphine complex and the production of mainly trans isomers of the above- mentioned phosphines has been interpreted in terms of steric phenomenon. (iv)

The phosphines containing more than one CF_ group j do not form complexes with nickel(II) salts. The nitrato complexes of trimethylphosphine and dimethyltrifluoromethylphosphine are paramagnetic, while the dichloro, dibromo, diiodo, and dithiocyanato complexes are diamagnetic. A correlation of the various properties, for ex• ample boiling points and heats of vaporization, has shown that the trifluoromethyl substituted phosphines are not anomalous in the general family of phosphines. An attempt has also been made towards a study of the infra-red spectra of the phosphines and their compounds, and towards a correlation with the spectra of other phos• phorus compounds. Finally, an approximate estimate of the "electronegativities" of a wide range of substituted phos• phines gives values which are in good agreement with the observed order of reactivities of the phosphines studied, and assists in correctly placing the trifluoromethyl- phosphines in such a range of compounds. ACKNOWLEDGEMENT

To Dr. H. C. Clark for his immeasurable advice and continual encouragement throughout the course of this work, I am particularly indebted. My thanks are due to Dr. W. R. Cullen and Dr. C. J. Willis, for their interest and discussions. I am obligated to Prof. C. A. McDowell for his personal interest, and to the other members of the Department for their assistance. In addition, ray gratitude is extended to the Council of Scientific and Industrial Research, Pakistan, and to the Colombo Plan Administration in Canada, for the award of a scholarship, held during the period of this research programme. (v)

CONTENTS

Chapter Page

INTRODUCTION 1 SECTION I PREPARATION AND' CHEMISTRY OP THE PHOSPHINES 1. Preparation of Methyl-trifluoromethyl Phosphines 7 2. Preparation of Phenyl-trifluoromethyl Phosphines 21 3. Properties of Phenyl-trifluoromethyl Phosphines 39 SECTION II PREPARATION AND STUDY OP THE ADDITION COMPOUNDS 4. Formation of Boron Trifluoride Complexes 59 5. Formation of Platinum(Il) Chloride Complexes 66 6. Formation of Complexes with Nickel Salts 82 SECTION III GENERAL DISCUSSION 7. Comparison of Phosphines with and without CF Group 90 3 8. Hydrolysis of the Trifluoromethyl-Phosphorus Compounds 116 9. Infra-Red Spectra of the Phosphines and Related Compounds 129

10. Conclusions 157

EXPERIMENTAL I. Experimental Methods 161 (vi) EXPERIMENTAL Page

II. Preparation of the Phosphines 163 Preparation of CP I 168 3 Preparation of Trimethylphosphine 169 Preparation of Dimethyltrifluoromethyl- phosphine 171 Preparation of Tristrifluoromethyl- phosphine 174 Preparation of MethyIbistrifluoromethyl- phosphine 177 IIIA. Preparation of Phenyl-Trifluoromethyl- Phosphines 179 Preparation of Phenylbistrifluoromethyl- phosphine 179 Interaction of Trifluoroiodomethane and Tetraphenylcyclotetraphosphine 181 Characterization of Fractions 184 Preparation of Diphenyltrifluoromethyl- phosphine 187 Interaction of Trifluoroiodomethane and Tetraphenyldiphosphine 190 Reaction of Trifluoroiodomethane and Triphenylphosphine 192 Reaction of Trifluoroiodomethane and Diphenylchlorophosphine 193 IIIB. Properties and Reactions of Phenyl- Trifluoromethyl-Phosphines 196 Phenylbistrifluoromethylphosphine 196 (vli) Page Physical Properties 196 Reactions: Hydrolysis 197 Reaction with Halogens 199 Reaction with CF^I 201 Reaction with OH I 202 3 Phenyltrifluoromethyliodophosphine 202 Hydrolysis 203 Reaction with CP I 204 3 Reaction with CP I and Hg 204 Diphenyltrifluoromethylphosphine 205 Physical Properties 205 Hydrolysis Reactions 206 Reaction with Halogens 207 Reaction with CP,I 209 3 Reaction wi th CH,I 210 3 IV. Complexes of the Phosphines 212 Boron Trifluoride Complexes 212 Reaction with: Trimethylphosphine 212 Dimethyl trif luoromethylphosphine 213 Me thylb i s tri fluo rome thylpho s phin e 215 Tristrifluoromethylphosphine 215 Phenylbistrifluoromethylphosphine 215 Diphenylbi s trifluoromethylpho sphine 215 Triphenylphosphine 217 (viii) Page

Platinum(II) Chloride Complexes 218 Bis(trimethylphosphine)dichloroplatinum(II) 219 Bis(dimethyltrifluoromethylphosphine)- dichloroplatinum(II) 221 Bis(methylbistrifluoromethylphosphine)- dichloroplatinum(II) 221 Reaction of Tristrifluoromethylphosphine with Platinum(Il) Chloride 225 Bi s(phenylbi s tri fluorome thylpho sphi ne)- dichloroplatinum(II) 227 Bis(diphenyltrifluoromethylphosphine)- dichloroplatinum(II) 229 Determination of Dipole Moments 232

Complexes of the Nickel Salts 233 Trimethylphosphine Complexes 233 Dimethyltrifluoromethylphosphine Complexes 237

Reaction with other Phosphines 240

REFERENCES 241 TABLE OP ILLUSTRATIONS Page

Fig. A. - Plot of M3^ R Vs. Boiling Point (Observed) 93 Plate No. 1« Pig. 1. Phenyltrifluoromethyliodophosphine 141 Fig. 2. Phenyltrifluoromethylphosphinic Acid 141 Plate No. 2, Fig. 3 * Dimethyltrifluoromethylphosphine 141 Fig. 4. Methylbi s tri fluoromethylpho sphine 141 Fig. 5• Phenylbistrifluoromethylphosphine 141 Fig. 6. Diphenyltrifluorome thylpho sphine 141 Plate No. Fig. 7. Methyldiphenyltrifluoromethylphosphonium iodide 147 Fig. 8. Methyltriphenylphosphonium iodide 147 Pig. 9. Methyldiphenylphosphine oxide 147 Pig. 101 Dime thylbi s tri fluoromethylpho sphonium iodide 147 Plate No. 4< Pig. 11. Trimethylphosphine-boron trifluoride 150 Pig. 12. Dimethyltri fluorome thylpho sphine-boron trifluoride 150 Pig. 13. Diphenyltrifluoromethylphosphine-boron trifluoride 150 Pig. 14. Triphenylpho sphine-boron tri fluoride 150 Plate No. 5. Pig. 15. Bis(diphenyltrifluoromethylphosphine)dichloroplatinum(II) 154 Pig. 16. Bis(phenylbistrifluoromethylphosphine)die chloroplatirium(II) 154 Pig. 17. Bis(phenylbistrifluoromethylphosphine)dichlorodibromoplatinum(ITC) 154 Plate No. 6. Pig. 18. Bis(trimethylphosphine)dichloroplatinum(II) 154 Pig. 19. Bis(dimethyltrifluoromethylphosphine)dichloroplatinum(II) 154 Fig. 20. Bis(methylbistrifluoromethylphosphine)dichloroplatinura(II) 154 INTRODUCTION

Pluorocarbon chemistry can rightly claim to have developed more rapidly than almost any other branch of chemistry. War acted as a catalyst in its rapid growth Virtually nothing was known of the chemistry of fluorocarbons in mid 1941> yet the necessary amount of the desired fluorocarbons was available when the first diffusion sepa• ration of UPg went into operation at Oak Ridge in 1943* Many chemists then quickly realized that this was a field which in the near future would span practically all branch of chemistry. The fluorocarbons are characterized- by their great thermal stability and resistance to chemical action. Compared with hydrocarbons, they are completely resistant to oxidation and do not burn. They are extremely inert and both they and their derivatives have been found to be most useful compounds. A further development of wide - 2 - interest commenced with the discovery that when the fluoro• carbon iodides are heated or exposed to ultraviolet light, fluorocarbon radicals are produced. This interesting pro• perty has been applied to the preparation of a large number of fluorocarbon derivatives with functional groups and of fluorocarbon metallic or metalloidal compounds. The most studied reactions are those using trifluoroiodomethane. In most cases, the reaction involves simple treatment of this compound with an organic compound, or if a trifluoromethyl- metalloid is desired then the metalloid or one of its com• pounds is used.

The development of fluorocarbon chemistry has therefore been on two main lines: the preparation of the perfluorocarbon compounds- containing functional groups, and the preparation of perfluorocarbon metallic or metalloidal compounds. The first comprises a large and interesting section of organic chemistry and the second started by the British school is still passing through its formative stage. The perfluorocarbon derivatives, or more specifi• cally, the trifluoromethyl compounds of a large number of metalloids and a few metals are now known. However, interest is currently centred on the trifluoromethyl derivatives of boron, tin, phosphorus, arsenic and sulphur. It is observed that the main features of the chemistry of the hetero atoms - 3 -

(metal or metalloid) are retained on the introduction of the trifluoromethyl group but there is a profound change from the properties of their aliphatic analogues. This trend results from the highly electronegative nature of the trifluoromethyl group. At the time when the first trifluoromethyl derivatives of the metalloids were being prepared, quite a large amount of information was already available regarding the organic compounds of phosphorus. The chemistry of the organo' phosphorus compounds is an old subject and was developed in the last century, mainly in Germany by Michaelis and his students, and later by Arbuzov in Russia. These workers con• centrated on the systematic synthesis of a wide variety of compounds. However, there are still many gaps in the list of characterized organo-phosphorus compounds. For instance, the phosphines and halophosphines react in general with halogens to form the phosphoranes — R^PX,. But thealkyl- phosphoranes were unknown until recently. Also, it is ex• pected that the stability of the phosphoranes should increase

in the order I but this has not been es tablished in many cases. In most cases, the diiodophospho- ranes are unknown. There may.be a number of reasons for this lack of knowledge in organophosphorus chemistry. The reactivity and toxicity of the compounds may be one of the reasons, but the - 4 - use of vacuum manipulation now provides a unique technique whereby reactive substances can be handled easily and safely. This technique not only provides a method of handling re• active substances out of contact with air, but also allows for the fractionation and preparation of pure samples. For instance, the preparation of trimethylphosphine has always presented a problem since it reacts readily in air and furthermore, the usual method of preparation gave a very low yield. The use of vacuum techniques and modified method of preparation leads to a high yield of the pure, phosphine. The availability of physical instruments e.g. the infra-red spectrophotometer etc. provides another means of testing the purity of the substances. With these- techniques, we are now in a better position to investigate organo-phosphorus com• pounds than was possible previously. It is also clear that even if the fluorocarbons had been known to the workers of the past century, they would have been severely handicapped by the. lack of suitable techniques.

Practically all the substituted phosphines were known by the last half of this century. With the discovery of the reaction of perfluoroalkyl iodides with phosphorus, a new chapter was opened and a series of compounds containing trifluoromethyl groups were prepared. The work was, however, directed towards the preparation of the analogues of the known organo-phosphorus compounds. The first in the series - 5 - was tristrifluoromethylphosphine and the two iodophosphines

(CF,)0PI and CF PI • The hydrocarbon analogues of only the

the remaining two are the chlorides (CH,)0PC1 and CH-PCl 3'2*" 3 2 which have been reported only recently. (2 2> ) The corresponding iodoaryl compounds have not yet been reported. The trifluoromethyl-phosphines are found to be quite different from the methyl and phenyl phosphines in both physical and chemical properties. Thus tristrifluoromethylphosphine boils at a lower temperature than the methyl analogue and much lower than triphenylphosphine which is of comparable mole• cular weight. Tristrifluoromethylphosphine inflames spon• taneously in air and unlike the alkyl or aryl phosphines can be hydrolysed with the cleavage of the P-C bond. This reaction can be considered a characteristic reaction of the trifluoro• methyl compounds of phosphorus and in most cases can be adopted for the identification of these compounds. Another major dif• ference from the methyl or phenyl phosphines is the inertness of the lone pair electrons on phosphorus.

Hox^ever, most of the work so far reported is mostly preparative in nature and the stage has been reached for more detailed studies. The present investigation is therefore concerned with the study of the reactivity of the trifluoro- methy-lphosphines towards standard reactants particularly with respect to their donor properties. For a reasonably wide - 6 -

study of the effect of the trifluoromethyl group it seems necessary to examine its chemistry in the environment of both methyl and phenyl groups. This has been done by pre• paring phosphines of the type RCCF^JgP and RgCF^P, where R is methyl or phenyl. The preparations of the methyl-trifluoro-

methyl phosphines (CHJ)2CFJP and CH^tCF )GP have been des• cribed previously but their reactivity has not been reported. The phenyl-trifluoromethyl phosphines (CgH^JgCF^P and CgH^CF^gP have been prepared during this investigation by making use of the reactivity of the P-P bonds. These sub• stituted phosphines have been made to react with boron trifluoride, platinum (II) chloride and a series of nickel salts.

The whole subject has been divided into three sec• tions. The first one deals with the preparation and the chemistry of the phosphines, the second is concerned with the preparation of the addition compounds, and the third deals with the general effect of the trifluoromethyl group on the chemistry of the class of compounds called phosphines. SECTION I

PREPARATION AND CHEMISTRY OP THE PHOSPHINES CHAPTER I

PREPARATION OP METHYL-TRIFLUOROMETHYL PHOSPHINES

The preparation of methyl-trifluoromethyl phos• phines has been carried out by the exchange methods,described (12) by previous workers. ' The exchange of a methyl group in trimethylphosphine for the trifluoromethyl group in trifluoro• iodomethane gives dimethyltrifluoromethylphosphine and like• wise, the exchange of a trifluoromethyl group in tristri• fluoromethyl phosphine with the methyl group in methyl iodide gives methylbistrifluoromethylphosphine. The reactions may be represented by the following equations: 2 (CH,)_ P +- CP_I > (CH_)_CF_P + (CH_) PI (1) JO 0 323' 34

(CF3)3 P + CH3I > CH^CF^P -hCF3I (2) These exchange reactions require the preparation of trimethylphosphine and tristrifluoromethylphosphine. The (3) former has been prepared by the Grignard reaction and the latter by the direct reaction of trifluoroiodomethane on (4-) phosphorus. The preparation of methyl-trifluoromethyl phosphines is quite involved and does not always give a satisfactory yield, since frequently side reactions occur which consume much of the starting material. In the present investigation the methods have been modified to improve the yields. An attempt has also been made to gain a better understanding of the mechanisms of the reactions. Trimethylphosphine: The reaction of phosphorus trichloride with methyl magnesium iodide at room temperature occurs with violence and produces largely tetramethylphos- 15) phonium chloride and phosphorus diiodide.

. 3PC15 + 4 CH3MgI > (CH^PCH- P^ 4- 4 MgCl2 (3) This indicates that a large excess of the Grignard reagent (33) is necessary and that only low yields can be expected. By stirring the reaction mixture vigorously and cooling it o intensively to - 78 , the violence of the reaction and the formation of phosphorus iodide can be reduced, as is evi• denced by the absence of the orange colour of the iodide. These conditions also prevent the escape of the phosphine as it is formed. To reduce the loss of the phosphine during distillation, the distillate may be received in a cooled flask. By taking these precautions, a yield of 60% of tri• methylphosphine has been obtained. _ 9 -

Dimethyltrifluoromethylphosphine; The reaction of trimethylphosphine with trifluoroiodomethane gives dimethyl- trifluororaethylphosphine, tetramethylphosphonium iodide and a small amount of a white solid which probably is dimethylbistrifluoromethylphosphonium iodide. The reaction starts much below room temperature with a rapid deposition of white solid. After about an hour, equilibrium appears to tee es• tablished, but further slow formation of the white solid continues.

The yield of the phosphine (CH^JgCF^P is not higher than 33% and hence it is desirable to elucidate the probable mechanism of this reaction. Ik few observations, in addition to those cited earlier are relevant in this connection. 1. Tetramethylphosphonium iodide does not react with tri• fluoroiodomethane. 2. Dimethyltrifluoromethylphosphine and trifluoroiodomethane formaan intimate and inseparable mixture in the gas phase. This probably indicates the formation of a molecular complex. 3» In the liquid phase, this mixture gives a reasonable amount of a white solid which melts at 60 and which sublimes into the vacuum system. The hydrolysis of this solid gives fluoroform, corresponding approximately to the loss of two trifluoromethyl groups from what may be dimethylbistrifluoromethylphosphonium iodide. The infrared spectrum of this solid is also consistent with this identifi• cation. 4. Trimethyltrifluoromethylphosphonium iodide which - \

- 10 -

Is a likely product of this reaction is not found among the products. 5» The quaternary compound j(CH^^CF^ljl is soluble in liquid trifluoroiodomethane and ethanol and is insoluble in carbon tetrachloride and trimethylphosphine. 6. When the reaction is carried out in carbon tetrachloride, the product is a mixture of trimethyltrifluoromethylphosphonium iodide and tetramethylphosphonium iodide. 7« The treatment of trimethyltrifluoromethylphosphonium iodide with trimethylphosphine in ethanol gives some tetramethylphosphonium iodide. The above facts may now be considered in the light of the mechanisms proposed by the earlier workers who predicted the initial formation of the quaternary compound

(CH,) CF,PJ+I. This is then suggested to react in either L 3 3 3 of the following ways. (a) By dissociation to the phosphine (CH^JgCF^P and methyl iodide. The methyl iodide so formed reacts further with trimethylphosphine to give tetramethylphosphonium iodide.

(CH3)3P +- CF3I > [(CH3)3CF3P)V > (CH3)2CF3P+ CH I

CH_I + (CH ) P > [(CH ) P]V 3 3 3 L 3 4J (b) By nucleophilic attack of the trimethylphosphine on a

+ methyl group of the quaternary compound {(CH3)3CF3P] I .

(CH3)3P: CH.3-P-CF3 ^Xm.^)^ + {Wj^^!

CH3 CH3 - 11 -

First of all, it may be pointed out that the phosphonium salt {(CH^^CF^pj+ I is quite stable and has been found to be unaffected by trifluoroiodomethane and trimethylphosphine. In view of its high stability towards these re• agents, it is surprising that it is not found in the reaction products. A simple mechanism for this reaction would be that of an acid-base type. That trimethylphosphine is quite basic is shown by its immediate reaction with boron trifluoride and ( J 3 3.2 3 3 However, such a reaction must involve the formation of some type of intermediate, probably from the nucleophilic attack of trimethylphosphine on the iodine atom of trifluoro• iodomethane. The electron withdrawing tendency of the tri• fluoromethyl group gives a positive character to iodine and makes it susceptible to nucleophilic attack. Such attack on iodine may give the intermediate?

P^cO-I'^'^-.PCCH^)^—>jj(CH3) PlfcF^} (5) This intermediate is vulnerable to further nucleophilic attack and may lead to the formation of a second intermediates

+ (CH3)3P: |CH3)3PI] OF"]—^CH^Plj^CH^PCpJ" (6) The formation of such compounds has been proposed by other workers in the study of the electrical conductance of the - 12 -

(58 59) phosphoranes ' • In the present case the attack may be-likely because of the negative nature of the trifluoro• methyl group. The next step will be the formation of a stable pentavalent compound. This may be done by (1) the transfer of a methyl group from anion to cation which would give

+ J( CH3 )3 PI J J( CH3) 2 P'— CPJ" » CH^) Pj * i" -f- (CH^) 2CF^P (7) or (2) the transfer of the iodine from the cation to the anion which would give

^)3Pjf^C^PCP3]"- > [(CH^CF^PJ V+CCH^P (8) However, since there is no evidence for the occurrence of the

+ compound j(CH3)3CF3PJ I as a reaction product, it is clear that (1) is the favoured route. This mechanism is supported by the observation (1) that trimethylamine and trifluoroiodomethane give fluoroform and tetramethylammonium iodide and no dimethyltrifluoro- methylamine is obtained. The small size of nitrogen allows

easy access of the CF3 group to the protons in the anion according to the above mechanism. This would give fluoro• form and tetramethylammonium iodide according to route (1). Added support also comes from the observation (7) noted above. This may be represented by the following scheme:

+ + |(CH3 )3 CF3PJ 1" :P (CH3 )3 > GH3) 3 CP3PJ 1( ) ^Plj~ I

+ ) > J(CH3)4PJ l" + (GH3)2CF3P (9) - 13 -

It should also be pointed out that further solvo- lytic action of. trifluoroiodomethane with the intermediate

[(CH^Pl]* £(CHJ)JPCFJJ~ would lead to the formation of the

+ quaternary compound |( CH3 ^ (CF3 )gPj I which has been found in the present investigation. This may be represented as follows:

+ |[ ( CH3) CH3 )3CF GH3 ) 4 CH3)G(CF3) 2PJ 3PlJ 3Pj"|^ j( PJV-f-j( V (10) The second quaternary compound being a derivative of a phos• phine which is a much weaker base than trimethylphosphine may then be extensively dissociated at room temperature.

+ [(CH3)2(CF3)2PJ I"^=^(CH3)2CF3P + CF3I (11)

Such dissociation would explain the ready sublimation of the white solid (CH,.)„(CF,).PI in vacuo. The above considerations lead to the conclusion that

the formation of two quaternary compounds £(CH3)^pjl and

£(CH3)2 (CF^^P] I would consume a large amount of the original

phosphine (CH3)3P and hence the yield of the desired phos•

phine (CH3)2CF3P would not be high. Methylbistrifluoromethylphosphine: This phosphine is prepared by heating tristrifluoromethylphosphine with methyl iodide to 240 . A yield of 54% is reported v but it can be slightly improved by using a small excess of methyl iodide. Although this excess tends to react with the phos•

+ phine 'CH3(CF3)2P forming the quaternary compound |(CH3)3CF3PJ I - 14 - and trifluoroiodomethane, it does insure complete reaction of the tristrifluoromethylphosphine, thus increasing the yield to 60% and at the same time avoiding the cumbersome separa• tion of the phosphines with close boiling points. o Below 235 tristrifluoromethylphosphine and methyl o iodide react only slowly, but heating to 235 or above, pro• duces trace amounts of free'iodine and a small amount of a white solid which has been identified as the phosphonium com• pound IJCH^^CP^PJ I . Some phosphorus trliodide and a black carbonaceous material are also obtained, the quantity of these two being considerably increased when the reaction is performed at higher temperature or for a longer period of time. The carbonaceous material contains no C-P bonds, sug• gesting that it possibly is the result of pyrolysis of hydrocarbons. Methylbistrifluoromethylphosphine has also been prepared by the reaction of methyl iodide and tetrakistri- 0 (7) fluoromethyldiphosphine by heating the two at 150 . It can also be prepared by heating tristrifluoromethylphosphine o and methyl mercuric iodide at 220 . The mechanism proposed by the previous authors (2) involves the initial formation of the quaternary compound jcH^CCF^J^pj I, which then undergoes pyrolysis to give methylbistrifluoromethylphosphine and trifluoroiodomethane. However, since this hypothetical compound has mixed ligands,

it would be expected to give a mixture of products (74). ^n - 15 - this case, equal amounts of methylbistrifluoromethylphosphine and dimethyltrifluoromethylphosphine together with a mixture of trifluoroiodomethane and methyl iodide would be obtained. But, when equimolar quantities of the reactants are taken, there is no evidence of the formation of dimethyltrifluoro• methylphosphine. On these considerations therefore the pos• tulated mechanism is a little doubtful. The high temperature at which this reaction is performed and the fact that methylbistrifluoromethylphosphine can also be prepared by heating (CP^J^P and methyl mercuric iodide suggest that some consideration must be given to a free radical mechanism. The homolytic fission of the C-I (8) bond in methyl iodide gives methyl radicals which would react with tristrifluoromethylphosphine. Further interaction of the methyl and trifluoromethyl radicals would produce fluoro• form and polymeric carbonaceous material. Free iodine would be formed in the course of this reaction which would react with the phosphines to give phosphorus iodide. The reaction . may be described by the following scheme.

•CK3I >-CH3 + I-

(CF3)3P+-CH3 > CH3(CF3)2P-(- -CF3 (12)

•CP34-CH3I >CF3CH3 -h I- (13)

•CH3+ CP3CH3 =>CF3H+-C2H5 (14)

CH3I-f- > higher hydrocarbons I- (15) - 16 -

A comparison of bond energies shows that the G-C bond in CF^CH^ is weaker than the C-H bond in CF^-H (90 and

102 kcals respectively) ^43) ao that; by a radical attack mechanism, equation (14) would proceed favourably. Also since the trifluoromethyl radical can abstract hydrogen from methane the latter would not be found among the products. This mechanism is borne out from the comparison with an analogous reaction of tristrifluoromethylarsine and methyl (75) iodide. The reaction has been carried out by heating and also by irradiating the mixture with ultraviolet light. The products obtained are analogous to those obtained for the phosphine under consideration. Tristrifluoromethylphosphine: The reaction of red or white phosphorus with trifluoroiodomethane tristrifluoromethylphosphine, bistrifluoromethyliodophosphine and (4,9) trifluoromethyldiiodophosphine . The yield of the phos• phines depends on the ratio of the reactants and also on the nature of phosphorus (white or red). A few observations are relevant in this connection: (1) Hexafluoroethane or higher fluorocarbons are not usually formed. But, it has been found that hexafluoroethane and phosphorus trifluoride (silicon tetfafluoride is also present if the reaction is carried out in a glass tube) are formed when the temperature of the reaction is very high (^270 ) or when the quantity of phosphorus is considerably increased. Higher temperatures - 17 - also give tetrafluoromethane. (2) The presence of iodine either free or in the form of trifluoroiodomethane appears to be essential for the reaction. Thus silver trifluoroacetate o and red phosphorus do not react at 250 , except to produce trifluoroacetic anhydride; but in the presence of iodine, trifluoromethyl-iodo-phosphines are readily formed. (3) Re• action occurs smoothly between trifluoroiodomethane and a mixture of phosphorus and phosphorus triiodide. (4) The reaction of tristrifluoromethylphosphine with iodine and the disproportionation of the iodophosphines gives a mixture of the phosphine, iodophosphines, phosphorus triiodide and tri• fluoroiodomethane . These facts suggest that the reaction requires the initial formation of a phosphorus iodide. The most easily formed iodide of phosphorus is the phosphorus diiodide.(Plg)^^ A kinetic study of the reaction between phosphorus and iodine shows the phosphorus diiodide to be formed through the follow• ing steps:^76) 4-1 >P l_ PI >P If P P I 4-P > P I 4- P 42 42 42 222 224 422

P2 4-I2-^P2I2 P2I24- I2-^P2I4 2P2I2—»P2I4+ P2

30 The diiodide (?2I^) formed is possibly the reactive species in the reaction under consideration. The attack on the re• active P-P bond by trifluoroiodomethane would give trifluoromethyl-diiodophosphine and phosphorus triiodide. - IS -

P4 4-4I2~*2^~P-t. (16) I. J- P P -h CP I \ CF PI -r- PI (17) i \ 3 f 3 2^ 3 Trifluororaethyldiiodophosphine appears to be the main reac• tion intermediate in the formation of the phosphine (CF^^P, as is evidenced by the small quantity of the former in the products and also by the reactions carried out at lower temperatures Q200 ) when only the iodophosphines are the major products. Further reaction of trifluoroiodomethane with trifluoromethyldiiodophosphine would form an inter• mediate (CF-) PI which has not been isolated but whose

0 d. 3 chlorine analogue (CF,)_PC1„ is known. The reaction of this J d 3 intermediate with a further quantity of phosphorus would give bistrifluoromethyliodophosphine and phosphorus diiodide. —P 2 CP PI 2CP3PI2-H 2CP5I >[ ( 3)2 3] 2(CF3)2PI+(PI2)2 (18) Trifluoromethyldiiodophosphine may also react further with phosphorus to give tristrifluoromethylphosphine and phosphorus diiodide.

3(CF,)PI_-f- P >(CF_)P +- 3PI0 (19) 3 2 33 2 The reaction of bistrifluoromethyliodophosphine

with CF3I would give another unstable pentavalent compound

(CP3)3PI2 which again has not been isolated but might form as a reaction intermediate. The reaction of this interme• diate with phosphorus would give tristrifluoromethylphosphine*

2 ( CF3 )2PI + 2CF3I—-> 2 [( CF3 )3 PI2]_Z!i_> 2 (CF3 )^ + (P^ )g (20) 1

- 19 -

Bistrifluoromethyliodophosphine may also react with phosphorus (as is the case with recycling) to give tristrifluoromethylphosphine and trifluoromethyldiiodophosphine.

2(CP3)2PI-hP 4(CP3) P + CP PI2 (21) The above consideration shows that the sets of re• actions (16) to (21) are all occurring in equilibrium with one another and may be represented as:

I2P — PI2 + CP3I CP3PI2^e( CP3 )2FI^=i (CP3) P-f-12 (22 ) It is also likely that only disproportionation re• actions are occurring and giving rise to the above sets of equilibria. Such reactions would involve radical intermediates. It is observed that heating of the iodophosphines individu• ally gives the same mixture of products. Hence for the for• mation of the radical intermediate, it is possible that the initial reaction involves the breaking of the P-I bond (P-C being stronger than P-I):

CP„PI0 » CP^PI + I- (25) 3 2 3 Since ordinary light can liberate free iodine from the iodo• phosphines, this formulation may be correct. The reaction of iodine would then be two-fold: (1) to react with phos• phorus to form the phosphorus iodides and (2) to react with trifluoromethyl groups to give trifluoroiodomethane. Prom (1) the trifluoromethyl radical(s);:; may be obtained which might start the above series of reactions. - 20 -

CF_PI0+ I »-CF„+-(PI0)0 or PI (24a) 3 2 3 2 2 3 CP.PL+ I >CFI-t-'PI (24b) 3 2 3 2 These might be followed by the equilibria represented by (22) Such equilibria have been noted in the case of furyl^"^ phenyl and trifluoromethyl arsenicals. In general mixed trihalides of phosphorus decompose to give its simple trihalides. As concluded in the case of phenyl ar- (12) senicals, it is likely that equilibria are attained by opposing bimolecular processes. However, only detailed equilibrium studies would establish the true mechanism. - 21 -

CHAPTER II

PREPARATION OP PHENYL-TRIFLUOROMETHYL-PHOSPHINES

The phenyl-trifluoromethyl-phosphines have been prepared by reacting trifluoroiodomethane with phenyl phosphines having a P-P bond and one or two phenyl groups attached to each phosphorus atom; viz., tetraphenyldiphosphine ;^^-p—p 0 -> and tetraphenylcyclotetra-

C^-Hc Ji phosphine b P—P 5 5 • v I I '^P-P 6 5 65

The former gives diphenyl trif luoromethylphosphine (C.-H,- )0CP_P 15 D

The cyclic structure has been established only recently^^, and until 1958 it was known as phosphobenzene.(or phosphoro- (15) benzene) CgH5P=PCgH5 . ' Tetraphenylcyclotetraphosphine is prepared "from phenyldichlorophosphine and phenylphosphine:

2C6H5PC12 + 2C6H5PH2 ^C^P) +4HC1 ,'(25) Phenyldichlorophosphine is prepared by the Friedel-Crafts reaction. By refluxing an excess of phosphorus trichloride with a mixture of benzene and aluminium chloride and treating the mixture with phosphorus oxychloride, a satisfactory yield of phenyldichlorophosphine is obtained. Phenylphosphine

(C,H PH0) may be obtained by the reduction of phenylph o 5 <- os- (20 21) phonous acid * , obtained by the hydrolysis of phenyl• dichlorophosphine. This is not a very satisfactory method (22) since the yield is often poor .... The method in current / Q"Z OA \ use involves the reduction of phenyldichlorophosphine with a suspension of lithium aluminium hydride in ether. The reaction of phenylphosphine and phenyldichlorophosphine has been carried out by refluxing the ether solution of the rea.ctants. Tetraphenylcyclotetraphosphine is deposited o after some time as a white solid melting at 148 - 150 . Trifluoroiodomethane does not dissolve tetraphenyl• cyclotetraphosphine at room temperature and there is no re• action until the tetraphosphine has melted. The solid dis- - 23 - solves at this temperature (150 ) and the reaction occurs slowly. Unreacted phosphine crystallizes when this solution is cooled. Heating to 185 gives an involatile mixture of phenylbistrifluoromethylphosphine, phenyltrifluoromethyl• iodophosphine and phenyldiiodophosphine. The volatile pro• ducts, besides trifluoroiodomethane, consist of small amounts of fluoroform, hexafluoroethane, and free iodine which always seems to be present.

The above reaction also occurs on irradiation with ultraviolet light. The process is slow as might be expected from reactions between heterogeneous phases. However, the products are the same as obtained by the heating of the reactants. The reaction most probably depends on the reactivity of the P-P bond. It may be worthwhile considering briefly the reactivity of the metal-metal or metalloid-metalloid bond (M-M bond). The M-M bond is limited to elements con• taining less than seven electrons in their'valence shell. The other elements which come close to carbon in forming such bonds are silicon, phosphorus and sulphur. The stability of the M-M bond decreases with in• creasing atomic number of M, for a series of elements in the same periodic group. Thus the diplumbanes are the least stable in group IV, while ethane is the most stable. Similarly dibismuthine is unknown whereas phosphorus forms the - 24 - di-, poly- and cyclopoly-phosphines, and some oxyacids are also known to have long P-P chains. These differences can be related to the bond energies which also decrease with in• creasing atomic number. The cleavage of the M-M bond is much easier than that of the C-G bond. The difference may be due to the following factors: (1) The atoms are much larger than car• bon. (2) They are .less electronegative. (3) They are capable of a much higher coordination number. (4) The bond energy of the M-M linkage is less than that of C-C. In fact the M-M bond energy is lower than for most M-X bonds, as (27 28) shown by the values reported in the literature ' . This indicates that in the event of an attack by X-Y, the bonds M-X and M-Y would be formed preferentially. Thus the M-M bond is a potential point of attack by a reactive species. The reactivity of the M-M bond must be largely due to the presence of an appreciable amount of pi-bonding. Such pi-bonding is possible in M-M bonds, for elements other than those in the first periodic row, since use can be made (33) of available higher orbitals . The attack by a reactive species X-Y at the M-M bond can then readily lead to the for• mation of a fourth single bond on each M atom. Such a quadruply bonded state is very common in phosphorus compounds ^ Subsequent rearrangement of this intermediate and cleavage of the remaining M-M single bond leads to the formation of the M-X and M-Y products. The following consideration bears out the above statement, Tetraraethyldiarsine reacts with halogen to give dimethylhaloarsine and with alkyl halides to give tetra- (32) methylarsonium iodide and dimethylhaloarsine . A compari• son of bond energies from the following table indicates that the As-As bond is much weaker and would be preferentially attacked in order to form the more stable As-halide and As-C bonds, As-As As-F As-Cl As-Br As-I As-H As-C 34.5 111.9 73.0 57.6 42.6 58.6 57 The tetraphenyldiphosphine is similarly known to react readily with hydrochloric acid to give diphenylphosphine and diphenylchlorophosphine. Here again a comparison of bond energies shows that the P-H and P-Cl bonds are stronger than the P-P bonds, so that the latter would be preferentially cleaved in order to form more stable bonds. P-P P-F P-Cl P-Br P-I P-H P-C 50.0 114 78.5 63.7 49 76.4 62 The mechanism of such an attack may be explained (35) by the so-called four-centre type reaction , the best ex• ample of which is the reaction of hydrogen iodide to give hy• drogen and iodine. H H H H H — H I 4- I I \ -+- (26) i i i i i — i -26-

Thus there is only a change of configuration of the atoms of the reactants to give the products and no electron transfer or ion formation is involved. Such a mechanism may well occur in the above reaction of tetramethyldiarsine.

.CH (CH ) As \ 5.3 'As—As (CH3)2As As(CH3)2

4- S OIL (CH_) Asl CH, 3 2

CHX — I CH; j I The trimethylarsine so formed would react further with methyl iodide and would form tetramethylarsonium iodide. The re• action of tetraphenyldiphosphine with hydrochloric acid may be represented similarly:

6 5 2 6 5 2 C ( H =±(C6H5)2PC1 (C H ) P-P(C H ) _ < 6V2?f °6 5l

H —-CI H CI +(C6H5)2PH

The above discussion of the cleavage of the M-M bond may now be applied to the reaction of trifluoroiodo• methane and tetraphenylcyclotetraphosphine. Two mechanisms are possible: (1) The reaction may proceed through a four- centre type mechanism in the following way:

yC6H5 /°6H5

C/-H — P—P—C^-Hj- CF, C6H5-[~f9*3 C6H5^P-P-GF3 (27)

C6H5-P-P-C6H5 I C^HC P—P i 5 \ C6H5-P-P: C6H5 - 2? -

C H H /°6E5 , 6 5 ,°6 5 -P-P 6 5 C6H5-B-B C6H5 CF, CF, (28)

C H PI C H P P C5H5-P--PN H 6 5~ ^ s °6 5- + 6 5~ 2 I H CF-4--I C.Hp- °6 5 3 6 j CF. CF3—I

C H C6H5 .CF, 6 5 °6H5 C6H5 /C6H5 C6H5-P-P-P^

P— PX

CF3 CF, CF. ^CF3 (29) CF—-I CF3

•+-CF3-I -f C6H5CF3I

C H C H C H 6 5 C6H5(CF3)2P 6 5X // 6 5 6 5 \ / p P P-P \ -» 4- (3Q) CF, CF, CF' CF. C6H5CF3PI + CF3-I CF3-I

Phenyltrifluoromethyliodophosphine disproportionates incompletely under the conditions of the experiment giving phenylbistrifluoromethylphosphine, phenyldiiodophosphine and some phenyltrifluoromethyliodophosphine. It may be thought likely that the diphosphine (C^H^CF^^ would be present* Whether this or the triphosphine is present has not been deter• mined; but a polymeric substance is obtained when the iodophos-

phine C5H5CF3PI is treated with mercury and a large excess of - 28 - trifluoroiodomethane. This requires further investigation. (2) The reaction has been shown to occur on ultra• violet irradiation of the reactants. The reaction may there• fore be thought of as proceeding through a free radical mechanism. The simultaneous breaking of the four P-P bonds is not energetically possible and hence the following scheme is suggested.

CF — I hv > -CF H- I- 3 3

CJK - P-P — C H +- -GF -+- I > C H_-P —P. D 5

V 6 5,(6 5 3 6 5 CF CJL- -P-P-C.rL. (ML.-P-P-I 3 6 5 6 5 6 5 ^ c bH 5 (31)

\H5 C6?5 I - P- P-P- P— CF„ -t- CF I —*C_.H - P-P-CX+C H (CP ) P+C H PI / / 3 3 6 5 • • o 5 6 5 3.2 6 5 2 C H C H 6 5 6 5 • * P P OP,I C H (CF LP+-C H PI -r-/ /

3 65 32 652 0 H_ C H (32) >• 6 5 6 5

The diradical CJi P—PC H_ would either recombine 6 5* -65 to form tetraphenylcyclotetraphosphine or would react further with trifluoroiodomethane to give the phosphine and iodophosphine. This mechanism does not require the formation of the diphosphine (C,H CP P) as in equation (30), and also gives the same approximate ratio of phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine as the experimental value of 2:1. The ratio would be of this order if the experimentally observed disproportionation of phenyltrifluoro• methyliodophosphine is taken into consideration. Diphenyltrifluoromethylphosphine There are two possible methods for the preparation of this phosphine: (1) Reaction involving the cleavage of P-P bond with each phosphorus having two phenyl groups attached to it: i.e., reaction with tetraphenyldiphosphine. (2) Ex• change reaction involving the exchange of a phenyl or any other group for the CF^ group. Such an exchange takes place between triphenylphosphine or diphenylchlorophosphine with CF^I. It may be pointed out that an analogous reaction to prepare phenylbistrifluoromethylphosphine is not successful. No reaction takes place between iodobenzene and tristrifluoro• methylphosphine. In view of this, the formation of diphenyltrifluoromethylphosphine from triphenylphosphine, although only in very low yield, is interesting. An alter• native exchange reaction is that between diphenylchlorophosphine and trifluoroiodomethane, where the chlorine atom is exchanged for a trifluoromethyl group. Since a convenient method for the preparation of diphenylchlorophosphine is now available, the phosphine (CgH^^CF^P has been prepared largely by this method. - 30 -

Diphenylchlorophosphine: This compound is prepared by a variety of methods, but they all give very low yield. (37) ° Pyrolysis of phenyldichlorophosphine at 300 for five days gave a 4% yield of the desired product (CgH^gPCl. The reac• tion is slow and the process has to be repeated a number of times. In this connection it is significant to note that triphenylphosphine and phosphorus trichloride do not dispro• portionate to give diphenylchlorophosphine, but rearrange- (38) ment does occur with the corresponding arsenic compounds . The reaction of triphenylphosphine with phosphorus triiodide also does not yield the corresponding diphenyl-product. The reaction of phenyldichlorophosphine with lithium phenyl (using molar quantities) does not give diphenylchlorophos• phine, but produces triphenylphosphine instead. Diphenylchlorophosphine is obtained in good yield (39) from diphenylphosphinodithioic acid . The acid is prepared by refluxing a mixture of phosphorus pentasulphide, benzene and aluminium chloride. The hydrolysis of the product so obtained gives diphenylphosphinodithioic acid, which separates into the benzene layer as a green solution. Chlorine is passed through this green solution when diphenyltrichloro- phosphorane separates as orange yellow crystals. Red phos- (40) phorus is added. to the solid crystalline product and slowly heated to distil off the solvent and phosphorus trichloride. Vacuum distillation of the residual mixture gives diphenyl- - 31 - chlorophosphine of high purity in excellent yield. If the heating in the last stage is carried out too vigorously, the phosphorane disproportionates to give phenyldichlorophosphine and hence heating has to be done only slowly, so that the phosphorane does react with phosphorus. The reactions may be represented as follows: A1C1_

C H VlO+ 6 6 2^(06H5)2PSSH (33) (C H ) PSSH4-3CL > (C H ) PCL+S G14-HC1 (34) 652 2 65_2 3 2

3(CCH LHC14-2P > 3(C HJPC1-T-2PC1 (35) 6523 652 3 Diphenylphosphine: This compound is prepared by (41) the reduction of diphenylchlorophosphine with lithium metal . (42) The previously described method involves the treatment of diphenylchlorophosphine with zinc and subsequent hydrolysis of the product with water. This gives a low yield of the phosphine (C-H ) PH. The effectiveness of lithium, compared 6 5 2 with zinc, is probably because the reaction with lithium occurs at room temperature but that with zinc has to be carried out at elevated temperatures. Further, the hydrolysis of the more polarised Li-P bond would occur more readily than that of the Zn-P bond. Tetraphenyldiphosphine: This phosphine is prepared by the direct reaction of diphenylphosphine and diphenyl- (41,42) chlorophosphine . - 32 -

(C.HKPH-MC H ) PCI 9- (C H ) P- P(C H ) + HC1 (36) 652 652 652 652

The reaction is preferably carried out in a high boiling sol• vent, since refluxing the mixture of reactants seems to be necessary to obtain a better yield of the pure product. Tetraphenyldiphosphine is obtained as a white crystalline o solid melting at 120 . The thermal decomposition of tetraphenylcyclotetra- (14*15) phosphine is reported to give tetraphenyldiphosphine, but in both reports, the latter has not been isolated and only indirect evidence of its formation is cited. It has (43) recently been reported that phenyldichlorophosphine reacts with lithium metal to give the dilithium adduct C^R-P—PCJEL, o 5| | 6 5

Li Li the intermediate product being tetraphenylcyclotetraphosphine. The last compound also gives a disodiura adduct(•'•^^which has (23) been used for the preparation of diphenyldimethyldiphosphine. In the present investigation this method has been studied in an attempt to obtain the diphosphine (C L).P-P(C H ) , by 6 5 2 6 5 2 treating the sodium adduct with iodobenzene but no positive results have been obtained. The details of the procedure have been described in the experimental section. Interaction of trifluoroiodomethane and tetraphenyl• diphosphine : Trifluoroiodomethane reacts with the diphosphine only at elevated temperatures. Like tetraphenylcyclotetra• phosphine, the diphosphine is also insoluble in trifluoroiodomethane at room temperature and no reaction occurs below the melting point of the diphosphine. The reaction is slow even o above this temperature until about 185 • Heating at this temperature produces diphenyltrifluoromethylphosphine and diphenyliodophosphine. The products are involatile liquids which can be separated from one another by extraction with petroleum ether which dissolves diphenyltrifluoromethylphos• phine only and leaves the diphenyliodophosphine as a thick red liquid. Among the volatile products of reaction are small amounts of fluoroform and free iodine, besides unreacted trifluoroiodomethane. The reaction has also been performed by irradiating the two reactants with ultraviolet light. The reaction is slow but the products are the same as obtained above. The reaction may be represented by equation (37).

(C H ) P P(C H ) + CF I >(C H ) CP P4 6 5 2 - 6 5 2" " 3 ~ 6 5 2 3 " (C6V2PI (3?)

The mechanism of the reaction appears to be a simple four- centre type, as discussed previously.

(C6H5)2CF5P (37a Wz *rP(06H5,2 (C6H5)2PI CF^-I 3

The reaction may also proceed by a free radical mechanism. The energy of ultraviolet radiation is much larger than the P-P bond energy, so the initial step in the reaction may be

the breaking of the P-P bond to give the radicals (C,rHt-)0P*. b 5 <~ - 34 -

Trifluoroiodomethane also undergoes homolytic fission of the C-I bond under these conditions. The reaction would then proceed by the intercombination of the radicals as shown by the following scheme.

CP,— I ^v >.CF,+ I- 3 3

652 3 6523 652

A comparison of bond energies shows why the tri• fluoromethyl radical would combine with phosphorus rather than recombine with iodine. The same reason may explain why

the phosphorus radical (CJi_ )0P« does not recombine to give 0 5 the P-P bond. P-P P-C P-I C-I

50 62 48 55 Thus the P-C bond energy being higher than P-P, diphenyltrifluoromethylphosphine would be formed preferentially and the remaining radicals (CgH^JgP-and I-would form diphenyliodophosphine. Interaction of trifluoroiodomethane and triphenylphosphine: As mentioned earlier diphenyltrifluoromethylphosphine can also be prepared by the reaction of trifluoro• iodomethane and triphenylphosphine. The reactants mix readily at room temperature without reacting. This solution - 35 -

o becomes yellow on gradual heating and, on heating to 185 for four hours, diphenyl trif luoromethylphosphine in 20%' yield, diphenyliodophosphine and some trifluoromethylbenzene are pro• duced. The last named compound is separated in vacuum and the phosphine (CgHp-^CF^P is extracted with petroleum ether. o At higher temperatures: e.g., 215 * only diphenyliodophosphine and trifluoromethylbenzene are obtained. The reaction most probably proceeds by a free radi• cal mechanism. The reaction may be initiated by the attack of the CF_ radical on one of the P-phenyl bonds and may then 3 proceed as shown by equations 38 - 38b.

A CF3— I vCF^ •+• I-

(C6H5)2P— C6H5+CF5 > (C6H5)2CF5P4- -CgH (38)

•C6H54-CF3 I ^C6H5CF3 + I- (38ai>

(C6H5)2P— C6H54- I > (C6H5)2PI + .C6H5 (38b)

A C-C bond being stronger than a P-C bond, radical attack would give trifluoromethylbenzene and reactions 38a and 38b would be favoured. This may be the reason why the yield of' diphenyltrifluoromethylphosphine is particularly low at higher temperatures. The other possible mechanism would be the formation of the quaternary compound (C.H_)„CF P+I as an intermediate. I 6 5 3 3_j This does not seem very likely in view of the products which have been obtained. The formation of iodobenzene which would be very likely according to this mechanism has not been ob• served. Moreover, it does not explain the formation of trifluoromethylbenzene. The formation of diphenyliodobenzene alone and no (CgH^^CF^P at higher temperatures is also not explained by this mechanism. Interaction of trifluoroiodomethane and diphenylchlo• rophosphine: The reaction of diphenylchlorophosphine with trifluoroiodomethane also produces diphenyltrifluoromethyl• phosphine. Diphenylchlorophosphine is soluble in trifloro- iodomethane but reaction does not occur unless the reactants are heated to a high temperature. In these investigations, o the reaction was conducted at 205 for 12 hours. The reaction is slow, for at the end of this period some diphenylchloro• phosphine is recovered. The reaction occurs in an approxi• mate ratio of 1:1 of the reactants, the major products being diphenyltrifluoromethylphosphine, diphenyliodophosphine and phenyltrifluoromethylchlorophosphine. Reasonable amounts of trifluorochloromethane and trifluoromethylbenzene and traces of hexafluoroethane and fluoroform are also obtained. The required phosphine is separated by extracting : with petroleum ether, but final purification by vacuum distillation is not satisfactory and, in the present investigation, has been effected by vapor phase chromatography. - 37 -

The formation of trifluorochloromethane has been found to be suppressed by using a large excess of trifluoro• iodomethane. Longer heating gives lower yield of diphenyltrifluoromethylphosphine and^increase in the yield of phenyltrifluoromethylchlorophosphine and trifluoromethylbenzene. The reaction probably proceeds by a free radical mechanism. Of the three ligands attached to phosphorus in diphenylchlorophosphine, the P-Cl bond, because of its higher polarity, would be the centre of attack by a trifluoro• methyl radical. The reaction may then proceed by the follow• ing scheme. CP^—I ^ vCF^-f- I-

(C.H_)_P— Cl-h«CF_ MC^H_)0P —CF,+ C1- (39) 652 3 652 3 CI- -+- CF^I - - ^ CF^Cl -h !• (39a)

(C6H5)2PC14-CF3 _ > C6H5'CP3+C6H5PC1 (40)

CgH5PCl -+-CP31 — > CgH5 (CP3 ) PCI + I • (40a)

(CgH5)2PCH-CF3I -> CP3CH-(CgH5)2PI (41) The last step (41) is a four-centre type reaction and possibly is much faster than the other possible reactions, hence the observation that the diphenyliodophosphine is always found in fairly large amounts. Prolonged heating might also involve the dissociation of trifluorochloromethane and hence suppress

the formation of the phosphine (CgHc)2CF3P by equation (39)« - 38 -

It is also possible that the reaction proceeds through the formation of an intermediate quinquevalent compound. The intermediate, having mixed ligands, would dissociate in more than one way. CI I ^1 (C6H5)2PC1 H- CFjI

H CF, C6 5 CI

(C6H5)2P—I CF3I (CgHgJgCF^P + CFjCl + Ig (41)

TF3

A * (C6H5)CF3PCl-f C6H5C^I2 (42)

A ^(C6H5)2PI CF3C1 (43)

It is difficult to say which of these reactions would be favoured. However, experimental observations show that reaction (43) occurs under all conditions, whereas reactions (41) and (42) depend on particular experimental conditions. In these reactions trifluorochloromethane also enters into reaction, and hence the quantity obtained is relatively small. " !

- 39 -

CHAPTER III

PROPERTIES OF PHENYL-TRIFLUOROMETHYL PHOSPHINES

PHENYLBISTRIFLUOROMETHYLPHOSPHINE Physical properties: Phenylbistrifluoromethylphosphine is o a colourless oily liquid which boils at 148-50 . Its vapor pressure equation is given by log P(ram) - 7.5606 - 1985, (I) ~^ -1 whence the latent heat of vaporization is 9054 cal mole and the Trouton's constant is 21.37. This last value is normal and shows that the phosphine is not associated. o The boiling point is 42 below that of the methyl analogue o

CgH5(CH3)2P and is 10 below the phosphine CgH^PHg. The compound is unaffected by air and moisture and is quite stable on heating to high temperatures in a sealed tube. The pyrolysis of the phosphine is slow at o o 200 but somewhat faster at 300 . The products of pyrolysis - 40 - are silicon tetrafluoride, trifluoromethylbenzene and traces of fluoroform. The presence of trifluoromethylbenzene in• dicates that the decomposition starts x^ith the fission of the P-CF^ bond to give the trifluoromethyl group and the subsequent reaction of this radical on the P-phenyl bond gives trifluoromethylbenzene. Silicon tetrafluoride is usually found in the pyrolysis of the trifluoromethyl com- (63) pounds . Phenylbistrifluoromethylphosphine is not dis• solved by water even at high temperatures. It is, however, soluble in organic solvents from which it can be recovered unchanged. Chemical Properties: 1. Hydrolysis: (a) Phenylbistri- fluoromethylphosphine is quite stable towards water. How- ever, prolonged heating at 110 gives fluoroform, phenyl- o (44.) phosphonous acid M.Pt.69 and traces of benzene. The reaction is extremely slow and may be represented by equation (44).

C,H_(CF„)oP-r-2Ho0 > C,H_PH( 0) 0H+ 2CF_H (44) 6532 2 o5 3 The traces of benzene are possibly due to pyrolysis rather than hydrolysis. (b) The phosphine is remarkably stable towards acid hydrolysis. It does not react at all with hydrochloric

o o acid up to 110 ; but prolonged heating at 185 gives fluoro• form in traces. This might again be due to pyrolysis rather than hydrolysis. - 41 -

(c) Phenylbistrifluoromethylphosphine can be hydro• lysed easily with aqueous sodium hydroxide. The rate of evolution of fluoroform decreases after some time and the o reaction is best carried out at elevated temperatures (80 ). The products of hydrolysis are fluoroform and the sodium salt of phenyl phosphonous acid. A solution of the latter, when acidified gives phenylphosphonous acid CgHpjPH(0)0H. This reaction has been discussed at length in chapter 80 The stability of phenylbistrifluoromethylphosphine in air, compared with tristrifluoromethylphosphine which in• flames in air, is of interest since only one phenyl group is responsible for this difference. The oxidation of tris• trifluoromethylphosphine in air is rapid but tristrifluoro- (45) methylphosphine oxide is not a reaction product . In its oxidation in air, tristrifluoromethylphosphine resembles trimethylphosphine (which is also oxidized readily but gives the oxide.J The ready oxidation of phosphines can be related to their basicities which decrease with the substitution of electronegative groups. As this substitution takes place, the lohe pair electrons become decreasingly available. Thus, whereas trimethylphosphine forms an oxide by reacting with atmospheric oxygen, trichloromethylphosphine (CI^ClXP does (46) not . Similarly, phenyldiethylarsine CJL^ C0EL )^As 0 5 2 5 2 - 42 - gives the arsine oxide, but the phenylbis(2-cyanoethyl)-

arsine CrEc(CnH.CN)_As is not affected by atmospheric air. op d 4 .2 The stability of the cyanoarsine has been ascribed to the (46) inductive effect of the CgH^CN group and this might be extended to most compounds of this type. Extension of this explanation to phenylbistri- (47) fluoromethylphosphine and arsine would indicate that the trifluoromethyl group being more electronegative should be responsible for their stability. The reactivity of tristrifluoromethylphosphine, however, contradicts this. It is possible that some factor other than the inductive effect is responsible for the instability of the tristrifluoromethylphosphine in air. An answer to this probably lies in the structure of the phosphines. The P-C bond distances in trimethylphosphine and tristrifluoromethylphosphine are 1.87 and 1.92A respectively^^] Since the bond energy de- (30) creases with increasing interatomic distances, the P-C bond in tristrifluoromethylphosphine may be somewhat more sus• ceptible to attack than the bond in trimethylphosphine. Furthermore, the suppressed availability of the phosphorus lone pair electrons might cause preferential attack on the P-C bond in tristrifluoromethylphosphine rather than forming an oxide. It is also quite likely that the difference in reactivity of the two phosphines may be related to the small amount of pi-bonding character present in the P-C bond in - 43 -

(CH_) P. This has been calculated to be 0-1 pi-bond per 3 3 sigma bond or 0-3 pi-bond per phosphorus atom in the phos- (34) phine . This pi-bond character is lost with increasing interatomic distance and may therefore not be present in tristrifluoromethylphosphine. Hence the stability of phenylbistrifluoromethylphosphine may be related to the reduced basicity of the phosphine resulting from the presence of the electronegative trifluoro• methyl groups, together with the conjugation effect of the (54) phenyl group . This latter allows some pi-bond character to the P-C bonds and confers additional stability to the compound. Its stability can be compared with the much higher reactivity of methylbistrifluoromethylphosphine where no conjugation is possible. The reaction with hydrochloric acid can be explained on the same lines. Both tristrifluoromethylphosphine and phenylbistrifluoromethylphosphine are unaffected by hydro• chloric acid even at high temperatures. These two phosphines are very weak bases and hence reaction with acid might not be expected. In the reaction with hydrochloric acid, it would be the nucleophilic attack on the proton that would start the reaction. The reduced availability of the un• shared electrons would restrict such an attack. It has been shown that the basicity towards proton and trimethylbdron is (53) of the same order . As will be shown later, phenylbistri- - 44 - fluoromethylphosphine and tristrifluoromethylphosphine fail to form any complex with boron trifluoride. It is therefore not very surprising that hydrochloric acid does not affect the two phosphines. (The same argument may be extended to methylbistrifluoromethylphosphine.) 2. Reaction with halogens; (a) Reaction with iodine: Phenylbistrifluoromethylphosphine does not react with iodine at room temperature. The usual method of re• acting a phosphine and a halogen in a carbon tetrachloride solution does not give phenylbistrifluoromethyldiiodo- o phosphorane. No reaction occurs up to 150 but the iodine vapor appears to react slowly above this temperature. The trifluoromethyl groups are almost quantitatively cleaved giving trifluoroiodomethane and phenyldiiodophosphine. Traces of benzene, fluoroform and crystals of phosphorus triiodide are also present among the products. The reaction may be represented as • C-H (CF_)P-h2l » C H PI + 2CP I (45) 6532 2 652 3 The presence of fluoroform and benzene is most likely due to the presence of moisture on iodine. The absence of phenyltrifluoromethyliodophosphine among the reaction products is interesting since it shows that the formation of this compound in the reaction of tetraphenylcyclotetraphosphine and trifluoroiodomethane is not due - 45 - to secondary reaction between phenylbistrifluoromethylphosphine and iodine and this gives support to the mechanism postulated earlier* (b) Reaction with bromine: Phenylbistrifluoro• methylphosphine reacts readily with bromine and forms phenylbistrifluoromethyldibromophosphorane which is an orange yellow crystalline solid.

C6H5(CP3)2P-hBr2 > C6H5(CP3)2PBr2 (46)

This compound is very reactive towards moisture but is quite stable in a dry atmosphere. But when it is treated with water, one equivalent of fluoroform is evolved and a white solid is formed. This solid has been identified

as phenyltrifluoromethylphosphinic acid €gH^(CP3)P(0)OH o which melts at 84-86 .

CfoH5(CF3 )APBrA-+- 2H0H—^ C^H^CF^ ) P( 0) OH + CF3 H-t- 2HBr (47) The formation of dihalophosphoranes by trifluoro• methyl phosphines is interesting since they do not react with hydrochloric acid and do not form an oxide readily. It may be noted that phosphines as a class form phosphoranes. This indicates that the reactivity in terms of basicity of the phosphines is not related to the ease of phosphorane formation. It is possible that this phenomenon is due to the different mechanism of reaction. The difference in reaction mechanism seems to be - 46 - obvious from the nature of the attacking species. The hydro• chloride formation would involve the nucleophilic attack of the phosphines on the protons, whereas phosphorane formation involves the electrophilic attack of the halogen atom on the lone pair electrons of phosphorus. Thus the reduced availa• bility of the lone pair electrons would not give a hydro• chloride but would not be concerned in the event of an electrophilic attack. The reaction might proceed through an intermediate tetrahedral structure formation. Such a structure is incap• able of independent existence and is more susceptible to further electrophilic attack and to the ultimate formation of the phosphorane. This type of structure has been postu• lated in various reaction mechanisms: e.g., in the reaction (55) between a phosphite (RO)„P and alkyl halide and its subsequent dealkylation^^. The primary step is suggested to be the formation of the intermediate phosphonium compound and the subsequent approach of the anion from behind, as in Walden inversion, is responsible for dealkylation. These results are also confirmed by the electrical conductivity of (57) the compounds PCl^ and PBr^ in nitrobenzene • Similarly the conductance of (C,-Hr-0)„PBro has been shown to involve + -(58,59) species such as (C6Ho50) 0 3PB$r dan d (C H 0) PBr 6 5 3 5 The non-occurrence of phenylbistrifluoromethyldi- iodophosphorane CgH^CF^^P^ is in accord with the general - 47 - stability of the phosphoranes. It may be pointed out that phosphorus pentaiodide is not known. This might be because of the larger size of the anions and the lower bond energy of the P-halogen bond. Moreover, the electronegativity dif• ference between phosphorus and iodine is too small to allow the attainment of the maximum covalency of phosphorus. If electron-withdrawing groups are present, the P-halogen bonds in the phosphoranes become weaker (in the order p\ci^Br^I) (61) as in the case of trifluoromethyl-bromophosphoranes . Consequently the tristrifluoromethyldiiodophosphorane is not known. It is, however, possible that such a phosphorane is formed as an intermediate which by the usual mode of decom• position gives trifluoroiodomethane, since the attack of iodine on the P-CF^ bond seems less likely. The formation of a stable phenylbistrifluoromethyldibromophosphorane is as would be expected. The hydrolysis reactions of this phosphorane provide an interesting link between the trifluoromethyl and aryl phosphines. Alkaline hydrolysis of phenylbistrifluoromethyldibromophosphorane gives fluoroform and phenylphosphonic: acid but the aqueous hydrolysis gives phenyltrifluoromethylphosphinic acid, C„H (CF )P(0)OH. The loss of only one trifluoromethyl group 6 5 3 by aqueous hydrolysis is observed in the case of tristrifluo• romethylphosphine oxide and tristrifluoromethyldichlorophosphorane. - 48 -

(CP ) PO+-H 0 ^ (CP ) P(0)OH f CP H 3 3 2 3 2 3 (CP ) PCI 4-H 0 > (CF ) P(0)OH •+- CP H 3 3 2 2 3 2 3 The mechanism of hydrolysis will be discussed later but it is interesting to note the stability of the other trifluirrro- methyl group in the phosphinic acid towards aqueous hydrolysis. The hydrolysis of the aryl-dihalophosphoranes gives (62) the corresponding oxide . The difference between the phenyl and trifluoromethyl phosphines is therefore obvious. This reaction leads to the conclusion that the behaviour of phenylbistrifluoromethyldibromophosphorane is more like that of tristrifluoromethyldichlorophosphorane rather than that of the arylphosphoranes, and is in conformity with the general conclusions derived later. The infra-red spectrum of the acid shows that phenyltrifluoromethylphosphinic acid is a fairly weak acid. The weaker acidity of this acid, compared with bistrifluoro• methylphosphinic acid, might be due to the presence of the phenyl group. The electron-withdrawing tendency of the tri• fluoromethyl group is satisfied- to some extent due to the drift of electrons from the phenyl ring and hence the acid is not strong. 3. (a) Reaction with methyl iodide: Phenylbistri- fluoromethylphosphine does not react with methyl iodide at o room temperature nor up to 100 . The two compounds, however, - 49 -

o are miscible. Decomposition occurs on heating to 230 and the products are trifluoroiodomethane and fluoroform, and a black involatile product which might be due to carbonization. How• ever, neither methylphenyltrifluoromethylphosphine nor di- methylphenyltrifluoromethylphosphonium iodide is among the reaction products. This observation is in accord with the basicity of the phosphine, since stable phosphonium compounds are formed by fairly basic phosphines. (b) Reaction with trifluoroiodomethane:. Phenyl• bis trif luoromethylphosphine does not react with trifluoro- o iodomethane when the two are heated to 230 . Among the re• action products are fluoroform and trifluoromethylbenzene, but no tristrifluoromethylphosphine is formed. The absence of tristrifluoromethylphosphine can be attributed to the poor basicity of the phosphine CgH^CF^JgP, whereby the nucleophilic attack on iodine is not likely. However, as noted above, the pyrolysis of this phosphine starts above 200 . This cleaves the phenyl group which in turn reacts with trifluoroiodomethane to form trifluoromethylbenzene. One noted feature of this reaction is the conversion of both trifluoroiodomethane and the phosphine into fluoroform. PHENYLTRIFLU0R0METHYLI0D0PH0SPHINE Physical properties: Phenyltrifluoromethyliodophosphine is o a reddish brown liquid boiling at 112-114 at 20 mm. It is not very stable in air, particularly moist air in which it - 50 - fumes. It dissolves in the common organic solvents and also in water. The aqueous solution is highly acidic. It reacts with most of the polar solvents since it cannot be recovered on evaporation of these solutions. At high temperatures there o is extensive disproportionation. When heated to 220 it gives phenylbistrifluoromethylphosphine and traces of tri• fluoroiodomethane, benzene, fluoroform and phosphorus triiodide. Chemical properties: 1. Hydrolysis with alkali; Phenyltri- fluoromethyliodophosphine reacts readily with an alkaline solution and gives fluoroform and sodium phenylphosphonate.

C,-H (CF„ )PI+- JNaOH ^CrHr.P0(0Na)o+- CF,HHTaI+- Ho0 (47) o 5 3 o 5 «- 3 d. Hydrolysis with water; Phenyltrifluoromethyliodo• phosphine reacts with water to give an acidic solution. Evaporation of this solution gives phenyltrifluoromethyl- phinic acid and a small amount of phenyltrifluoromethyl- phosphin2C H e(C accordinF )PI+2 g HOtHo equatio>2 C^n H (48)(CF_)P. (0H) 6 5 3 L s 5 3

> CCH_(CF_)P(0)0H + C,.H1_(CF,)PH+2HI (48) o 5 3 6 5 3 The acid so obtained is identical with the phosphinic acid obtained on hydrolysis of phenylbistrifluoromethyldibromo- o phosphorane (its M.Pt. is.84-86 and its silver salt melts o at 294-96 ). Phenyltrifluoromethylphosphine (CgH^CF^JPH), formed in the hydrolysis, has been characterized only by its infra• red spectrum which showed strong absorption at 2300 cm"! this being characteristic for a P-H bond. The other absorptions - 51 - characteristic of the phenyl and trifluoromethyl groups were of course present. The formation of the phosphinic acid CJE._(CF,)P(0)0H o 5 j and the phosphine CJEL (CF,)PH'is consistent with the reactions o 5 j of the halophosphinesIt is the spontaneous oxidation- reduction of the apparently unstable intermediate phosphinous acid which leads to the formation of the observed products. 2. Reaction with trifluoroiodomethane: The iodophosphine CgH^CF^JPI dissolves in trifluoroiodomethane. There is extensive disproportionation of the iodophosphine o at 200 and phenylbistrifluoromethylphosphine and phosphorus triiodide are formed, and trifluoroiodomethane is recovered quantitatively. The other products are small amounts of benzene and fluoroform. 5. Reaction with trifluoroiodomethane and mercury: Phenyltrifluoromethyliodophosphine reacts with trifluoro• iodomethane (large excess) in the presence of mercury. The products obtained are phenylbistrifluoromethylphosphine and a thick liquid. This could not be characterized properly but it contains no iodides. The details of the attempts to characterize it appear in the experimental section, from which it appears to be a polymerised product of phosphorus containing the phenyl and trifluoromethyl groups. - 52 -

DIPHENYLTRIFLUOROMETHYLPHOSPHINE Physical properties: This phosphine is a thick oily liquid* Its odour, unlike other phosphines is not too obnoxious. It o boils at 255-57 • The vapor pressure is given by the equation: Log P = 7-781 - 2598 (II) (mm; —FJT— whence the latent heat of vaporization is 11,850 cal mole and the Trouton's constant is 22-3, 'showing it to be non- o associated. The boiling point is 28 below the methyl analogue o and 24 below the secondary phosphine (CgH^JgPH. Diphenyltrifluoromethylphosphine is heavier than water and insoluble in it. It dissolves in organic solvents and can be recovered unchanged from its solutions. It is quite stable in air and moisture, and is not decomposed easily on heating in a sealed tube. It suffers only partial o decomposition on heating to 300 for 24 hours. Only mild carbonization takes place, and small amounts of silicon tetrafluoride, fluoroform and benzene are formed, with 85% recovery of the phosphine. Chemical properties: 1. (a) Hydrolysis:. Diphenyltriflruoro- o methylphosphine does not react with water even up to 120 . o It also does not react with hydrochloric acid (up to 150 ) which shows that the basicity of this phosphine is also low. It cannot be hydrolysed with aqueous sodium hydroxide even up o to 80 . Only a trace of fluoroform is obtained when the o alkaline solution is heated with the phosphine to 100 . - 53 -

1. (b) Hydrolysis with alcoholic potassium hydroxide; The phosphine can be hydrolysed with alcoholic potassium hydroxide. The reaction, however, is slow (even 6 at 80 ) and is only 78% complete in 96 hours. The residual solution from this reaction gives diphenylphosphinic acid o (M.Pt.193 ) on acidification. The reaction may be repre• sented by equation (49)«

(C,HC L CP„P-|-20H > (C6H5)2CP5P(0H)2 ^(C6H5)2P(0)OH 6 5 £ 3

-f CF3H (49)

2. Reaction with halogens: (a) with iodine: Diphenyltrifluoromethylphosphine reacts with iodine to give

diphenyltrifluoromethyldiiodophosphorane (CgH^)2CF3PI2, which is a thick brown-black oily liquid, stable in air and x-jater. o it is not decomposed by heating up to 200 . Trifluoroiodo• methane, the expected product of decomposition (as in the

case of CgHr(CP3)2P is not obtained. Hydrolysis of this com• pound by aqueous sodium hydroxide gives fluoroform quanti• tatively and sodium diphenylphosphinate.

(C6H5)2CF3P-f-I2 >• (C6H5)2CP3PI2 (50)

(C6H5)2CF3PI2+-2NaOH > ( CgH^ )2?( 0) 0H+CF3H + 2NaI (51)

2(b) Reaction with bromine: Diphenyltrifluoro- methylphosphine reacts vigorously with bromine and the reaction is exothermic. Diphenyltrifluoromethyldibromophosphorane

(OgHpj)2CF3PBrv>-.is obtained as an orange coloured oil which - 54 - is not affected by air and moisture. It is insoluble in water and hydrochloric acid and does not react with them up to 80 . However, it can be readily hydrolysed with aqueous sodium hydroxide and evolves fluoroform quantitatively. The other product of this hydrolysis is also diphenylphosphinic acid which is obtained on acidifying the alkaline solution. The reactions are similar to those represented by equations (50) and (51). The ready hydrolysis of the phosphoranes with alkaline solutions is interesting in view of the reluctance observed in the case of the phosphine (CgHpj ^CF-^P. This has been discussed in chapter 8 on the basis of formation of a trigonal bipyramidal intermediate. The formation of the diiodophosphorane is not surprising since the corresponding triphenyldiiodophosphorane is known^68! Th e stability of the iodophosphoranes decreases if the iodine content in the phosphorane is raised, particu• larly if electron attracting groups are present. Thus (CF^J^P does not form (CF^J^P^ and (CgH^JgPI^ Is not yet known. The stabilizing influence should therefore be that of the electron- releasing groups like the alkyl group or the conjugation effect of the phenyl group. Thus the properties of diphenyltrifluoromethylphosphine are determined more by the presence of the phenyl groups than by the character of the trifluoro- - 55 - methyl group. This is further revealed by the stability of the dibromo-phosphorane'; towards water which should have given the phosphinic acid if the trifluoromethyl-"character was predominant. 5(a) Reaction with trifluoroiodomethane: Diphenyl- trifluoromethylphosphine is not miscible with GPÎ at low temperatures, but they form a homogeneous solution at room o temperature. There is no reaction up to 200 except that traces of fluoroform are obtained, and a small amount of diphenyliodophosphine separates from the reaction mixture. The reaction is extremely slow. This observation is in accord with the expected be• haviour of a poorly basic phosphine. Since the phosphine does not react with hydrochloric acid, it might indicate that a nucleophilic attack on the iodine atom of CFÎ is not very likely. It may be pointed out again that the basicity of such phosphines demands the attack of electrophilic groups which could use the lone pair electrons. Apparently CPÎ fails to fulfil this condition. However, if a high enough temperature is employed pyrolysis might give some of the observed products. 5(b) Reaction with methyl iodide: Diphenyltri- fluoromethylphosphine is miscible with methyl iodide at room temperature but no reaction occurs unless the mixture is - 56 - heated to 100 . At this temperature, an orange colored oil slowly separates. This oil can be crystallized by dissolving in ethanol and treating this solution with a large excess of ether. Methyldiphenyltrifluoromethylphosphonium iodide so obtained is a yellow crystalline solid melting at 123-26 , and is quite stable in air. Methyldiphenyltrifluoromethylphosphonium iodide reacts readily with cold water to lose the trifluoromethyl group quantitatively. The resulting aqueous solution is highly acidic, due to the formation of hydriodic acid, accord• ing to equation (53). Treatment of the aqueous solution with silver oxide precipitates silver iodide and evaporation of the filtrate gives methyldiphenylphosphine oxide.

(C6H5)2CF3+CH3I OH (CJI ) CF P I (52) 3 6 5 2 5

CH_(C.H ) CF P V-t-HOH >CH,(C H ) P04-CF H+-HI (53) f 3 6 5.2 3 3 6 5.2 3 The reaction with methyl iodide seems interesting since the phosphine does not react with hydrochloric acid, and these two reactions have been correlated with the basi• city of the phosphines^\ it is likely that the difference arises because of the nature of the attacking group. It has been suggested by Baker and Ingold that the primary step in the reaction of alkyl halides is the anionization of the halogen atom R-CH^^^Hal. The methylene group so obtained provides a reactive centre and is compar• able with the halogens in its tendency to capture an electron. - 57 -

This type of anionization is not possible for trifluoro• methyl halides since in their case the reaction occurs by a

nucleophilic attack on the relatively positive iodine atom0 The non-occurrence of a hydrochloride of diphenyltrifluoromethylphosphine can be explained if it is noted that the phenylphosphines form only weak hydrochlorides which can be readily hydrolysed, and the trifluoromethylphosphines do not form any hydrochlorides. It may therefore be said that the correlation of basicity with the reaction of phos• phines with alkyl halides does not hold in the case of phenyl-trifluoromethyl-phosphines. This relation will be discussed in detail in chapter 7«

The aqueous hydrolysis of methyldiphenyltrifluoro• me thyphosphoniurn iodide resembles that of the aryl-phosphonium compounds. Thus methyltriphenylphosphonium iodide on hydrolysis with potassium hydroxide gives benzene, methyldiphenylphosphine oxide and potassium iodide.

CH (C H ) P +I + KOH > C H + CH (C H ) PO-J-KI (54) 3 >6v 5 3 _ 6 6 3 6 5.2 Phenoxydiphenylmethyl- and phenoxydiphenylbenzylphosphonium iodides are hydrolysed by heating with water, and the more (67) electronegative phenoxy group forms phenol . C^H CH C H 6 5X / ,.2 6 5

IT HOH >(CCH_.)0(CCH_GH ')P0: -j-GcE OH-f-HI 6 5' 6 5 2-' 65 C6H5 ^OC6E5 (55) - 58 -

C H CH 6 5\ / 3 XP f-f HOH- -CH (C H ) P04-C H OH-HHI (56) 3 6 5.2 6 5 C^H •r oc H 6 5- 65

The electronegative nature of the trifluoromethyl group is very much apparent when it is found that the phosphonium compound CH (C^H) CF P I hydrolyses at room L 3 6 5 2 3 temperature. Equation (53) may be represented by the following scheme.

CH C H t CH C H X 3 / 6 5 3X / 6 5 P. 1 + HOH- OH^ + HI CF. C H CF C H 6 5 6 5 J

CH CCH_ + C H \/65 6 5 P. OH ->CH - PO 4- CF H 3 3 CF. CJS C H • 6 5 6 5

The instability Of the intermediate hydroxide gives the observed products. Thus in the hydrolysis of phosphonium compounds, the CF^ group is more easily hydro• lysed than a phenoxy group and the order of ease of

O0 H C H CH C H CH e hydrolysis is CF^) g 5) g 5^ ) 6 5 2 SECTION II

PREPARATION AND STUDY OP THE ADDITION COMPOUNDS - 59 -

CHAPTER IV

FORMATION OF BORON TRIFLUORIDE COMPLEXES

In the previous chapters the relation between the availability of the lone pair of electrons on the phosphorus atom and the basicities of the phosphines has been discussed. The basicity could be further examined by studying the ease of formation of their addition compounds with strong electron acceptors such as boron trifluoride and platinum (II) chloride. The study of the reactions with the last two compounds pro• vides an insight into the coordination chemistry of these bases. The addition compounds of phosphines with boron com• pounds (Lewis acids) result from sigma-bond formation be• tween phosphorus and boron. On the other hand, the bond between phosphorus and platinum in the products of the re• actions between the phosphines and platinum (II) chloride is multiple in character and involves dn-d-jTbonding in addi• tion to the P-Pt sigma-bond. - 60 -

The ease of formation of the addition compounds formed by Lewis acids depends on more than one factor, i^uite a few cases are complex and involve the inductive, steric as well as the hybridization effects. Whereas electro• negativity demands in agreement with most observations that boron trifluoride be a better acceptor than the other boron halides (BF^ BCT ^ BBr ), it has been shown that relative acid strength increases in the order BF

a base like pyridine(70) ijh^g ^as frQen explained on the basis of increasing pi-bonding in the B-X bond in the series BF^, BCl^ and BBr^. This would place BF^ in the same posi• tion as BH in acid strength, as is shown by their acid 3 strength towards trimethylamine. Thus coordination chemistry becomes very involved if all acceptors are considered at once, since frequently their acid strengths show unusual relationships which cannot be explained by one single effect. Since a monotonic series of generalized acids and bases (73) cannot be established , the usual practice is to take one of the acids as a reference acid and to study the relative stability of its addition compounds*' *' . Boron trifluoride has been chosen as the reference acid for the present investigation. The addition compounds have been prepared by combining the reactants in molar ratios and allowing them to react slowly. In most cases, reaction occurred below room temperatur-e. - 61 -

The relative stabilities have been estimated by measuring the saturation pressures of the compounds, since (73) according to Brown , the less stable compound,compared with another of closely similar structure and molecular weight, exhibits the higher saturation pressure. The results . are only qualitative but for establishing relative stabili- (7D ties such results have been considered adequate Trimethylphosphine-boron trifluoride: This com- (6) pound has been previously reported . It is easily prepared by the direct reaction of trimethylphosphine and boron tri• fluoride. The reaction is spontaneous and occurs much below room temperature. Trimethylphosphine-boron trifluoride is a o white crystalline solid, which melts at 126-130 . It is easily decomposed in moist air and by polar solvents giving trimethylphosphine. As is true of the other boron trifluoride addition compounds, the trimethylphosphine complex is not soluble in non-polar solvents. The saturation pressure of the compound is given by equation(i11) . Log P(mm) = 8.460 - 2627 (III) T Dimethyltrifluoromethyl-boron trifluoride: This compound is also obtained easily when the phosphine reacts with boron trifluoride. When so prepared it is a thick oil. This compound is more easily decomposed in air, absorbing water, - 62 - and by polar solvents, than its trimethylphosphine analogue. The saturation pressure of the compound is given by the equation (iv)l log P(mm) = 10.354 - 2146 (IV) T Diphenyltrifluoromethylphosphine-boron trifluoride: This compound is formed by the interaction of the phosphine (CgHj-JgCF^P and boron trifluoride, but the reaction is slow and occurs at room temperature when the former has melted. The reaction can be carried out in a non-polar solvent with the deposition of the complex in the form of an oil. This complex is quite stable at room temperature but is decom• posed slowly by moisture - and readily by polar solvents. The saturation pressure of this addition compound is given by equation log P(mm) = 6.609 - 1755 (v) T Triphenylphosphine-boron trifluoride: The reaction has been carried out by passing boron trifluoride through a petroleum ether solution of triphenylphosphine, with the in• stantaneous deposition of triphenylphosphine-boron trifluoride in the form of a white crystalline solid which melts at 128- o 130 . This compound is quite stable in air and shows the same solubility behaviour toward polar and non-polar solvents as its analogues. - 63 -

The saturation pressure of this compound is given by equation (VI). Log p(ram) = 3.840 - 972 (VI) T Boron trifluoride does not react with tristrifluoro• methylphosphine, methylbistrifluoromethylphosphine, and phenylbistrifluoromethylphosphine. The reactions have been o attempted at -78 by direct treatment of the reactants, but in all cases reactants were r.ecovered quantitatively. It has already been' said that the bonding between phosphorus and boron is a sigma-bond, and that it is in• fluenced by more than one factor. One of the factors, which has been found very important in the present investigation, is the electronegativity of groups attached to the Lewis base. As mentioned earlier, electron withdrawing electro• negative groups would reduce the availability of the lone pair electrons. The high electronegativity of the trifluoro• methyl group has already been discussed. Thus it would be expected that as the basicity and consequently the availa• bility of the lone pair electrons decreases with the intro• duction of trifluoromethyl groups, the stability of the boron trifluoride addition compounds would decrease. The relative volatilities given by the vapour pressure equations show the following order of stability: (CH ) P.BP \ (CP ) 3 3 trifluoromethyl series, while in the phenyl-trifluoromethyl series - 64 -

JcJIfCF LP.BF \ (CF ) P.BF i. The same equations give 1 6 5V 3 2 3/ 3 3 3J the following order for the alkyl and aryl-trifluoromethyl-

phosphines : (C6H5)3P.BF3^ (CH5)3P.BF3^> (CgH JgCF P.BF^

(CH3)2 CF3P. BF3 ){C(CF3)2 P. BF^ CH3 ( CF3)g P. BF^ (CF^)^. BF^

The above comparison shows that the phenyl- phosphines form more stable complexes than the methyl- phosphines. This order is different from that expected from the basicities of the phosphines. Thus, whereas the methyl-phosphines form a hydrochloride and a quaternary salt readily, the phenyl-phosphines do it with difficulty. However, in both the phenyl and methyl series, the replace• ment of a trifluoromethyl group with negative inductive effect will greatly reduce the basicity of the phosphine and hence lower the stability of the addition compound. The pi-character of the P-C bonds discussed earlier is gradually lost as the more electronegative trifluoro• methyl group is introduced, and is almost absent in tristrifluoromethyl-phosphine. This effect leads to the decreased availability of the lone pair electrons. It is therefore not surprising that the boron trifluoide complexes of phosphines with more than one trifluoromethyl group have not been found. Added confirmation of this view comes from the finding that the adduct (CF^J^P.BH^ also does not exist^?) r^he borine adducts, it may be pointed out, are more stable than those of boron trifluoride. - 65 -

Steric effects may also be thought of as being responsible for the non-occurrence of the complexes of phosphines with more than one trifluoromethyl group. Steric interactions would be greatest in tristrifluoromethylphosphine, o for which the CPC angle has b een found to be 100 with all the CE^ groups on the same side of the phosphorus atom. It is known that a certain amount of rearrangement occurs from the planar configuration of BP to the tetrahedral environ- 5 ment of B in an addition compound of BF,. Hence, the steric interference of the CF, group with F atoms on B must be quite small. For phosphines having two trifluoromethyl groups this interaction would be smaller still. Although the amount of such interference is difficult to determine quantitatively, it certainly would be very small in the case of trifluoro-methyl-phosphines, and is unlikely to be responsible for the non-occurrence of the adducts under consideration. - 66 -

CHAPTER V

FORMATION OF PLATINUM(II) CHLORIDE COMPLEXES

It has already been said at the beginning of this section that the bond between phosphorus and platinum in phosphine-platinum(II) chloride complexes will be multiple in character, involving d-n-C/TT bonding in addition to sigma- bonding. This will give considerable additional stability, and hence phosphines which are otherwise poor donors towards boron trifluoride may form stable compounds with platinum(Il) chloride. The preparation of these compounds has been effected either by direct reaction of the phosphine with (78) platinura(Il) chloride or by the method of Jensen , which consists of treating an aqueous solution of potassium chloroplatinite, K^PtCl^, with an alcoholic or acetone solution of the phosphine. The ratio of phosphine to platinum(II) chloride usually taken for reaction has been 2:1. - 67 -

Bis(trimethylphosphine)dichloroplatinum( XL ): (79) This compound has been reported previously and has been shown to occur in two forms, cis and trans. The direct re• action is a slow process in this particular preparation. The solid obtained is usually a mixture of yellow and white solids, trans and cis isomers, which can be separated easily by extracting with ether, which does not dissolve the white solid. The formation of the yellow isomer can be checked by using an excess of trimethylphosphine. The preparation proceeds more rapidly in benzene solution, and in this case the formation of the yellow isomer can be suppressed by excess of phosphine. The yield in both these cases, however, is low. It can be improved by treating the phosphine with potassium chloroplatinite, when only the white isomer is obtained and in 41$ yield. The bis(trimethylphosphine)dichloroplatinum( JH. ) so obtained is the cis isomer as shown by its high dipole o moment of 13.1D. It melts at 324-326 with decomposition. o It dissociates rapidly above 200 . Its dissociation pressure is given by the equation log Pmm = 6.510 - 2108 (17TT) T ; The heat of dissociation is obtained as 9*59 kcal mole-'*'. The compound (CH ) P PtCl is not very stable 3 3 2 2 and seems to decompose on standing in air, particularly in moist air. Treatment with water, in which it is insoluble, causes slow decomposition and evolution of trimethylphos• phine. It is insoluble in ether and non-polar solvents, but is fairly soluble in polar solvents. Heating an alcoholic solution also decomposes the compound. Bis(dimethyltrifluoromethylphosphine)dichloroplatinum(II): This compound is prepared by reacting plati• num^ II") ) chloride with dimethyltrifluoromethylphosphine in the ratio of' 1:2. The reactio.h is sloitf but gives an excel• lent yield of the addition compound (CH, ) CP PL2 PtCl , 3 2 3 J 2* which is pale yellow. Recrystallization gives white needle- shaped crystals and a small amount of a pale yellow product. The white needle-shaped crystals of bis(dimethyltrifluoromethylphosphine)dichloroplatinum(II) have a dipole moment of 9.2 D showing the compound to be the cis isomer. (The small amount of the yellow product is possibly the trans isomer.) This compound, (CH ) CF P PtCl , melts at 188-190 3 2 3 2 2 with decomposition which is rapid above the melting point. The dissociation pressure of the compound is given by equa• tion (VIII): log P(rnm) = 7.969 - 2438 (VIIK) T .... whence the heat of dissociation is 11.31 kcal mole - 69

Bis(dimethyltrifluoromethylphosphine)dichloroplatinum (II) is quite stable in air and is not affected by moisture. It dissolves in polar solvents which do not react with it, but is insoluble in ether, carbon tetra• chloride, and benzene. Gold water does not react with it. Treatment with bollihg xtfater does not give the phosphine (CH^CF^P as in the case of (CH ) P -PtCl , but gives 33 \2. 2" fluoroform instead. The evolution of fluoroform is slow and not quantitative, even after 2 4 hours. Hydrolysis with alkali gives fluoroform almost quantitatively. This may be contrasted with the reaction of the phosphine (CH ) CF P itself, which is not hydrolysed by alkali. The 3 2 3 complex dissolves in methyl iodide, but can be recovered un• changed. This may be contrasted with most of the mercury iodide complexes of the phosphines and arsines, which on (80) treatment with methyl iodide form quaternary compounds. It is also unaffected by trifluoroiodomethane. Bi s(methylb i s tri fluo rome thylpho sphin e)di chloroplatinum (II): This compound is prepared by the direct re• action of methylbistrifluoromethylphosphine and dichloro- platihum (II). JThe reaction is slow, but takes place more quickly in the presence of excess phosphine, preferably in the liquid phase. The reaction product is extracted with carbon tetrachloride, which on evaporation deposits fine yellow crystals of the addition compound CH (CF )0P 3 3 d. - 70 -

The complex so obtained is the trans isomer as determined by the dipole moment which is 0.0D. It melts at 0 85-87 and is slightly dissociated below its melting point. o The dissociation Is very rapid above 140 . (.This, therefore furnishes a good method of obtaining the pure phosphine.) The dissociation pressure is given by the equation log P(mm) = 4,885 - 1258 (TJC) T whence the heat of dissociation is 5»76 kcal mole"-1-. The compound is soluble in organic solvents and only slightly so in boiling water. It is quite stable to• wards water, unlike the addition compounds of the other rnethyl-phosphines. Treatment with aqueous sodium hydroxide gives only 50/&fluoroform. It dissolves in methyl iodide and trifluoroiodomethane but is recovered unchanged in each case. Tristrifluoromethylphosphine does not react with dichloroplatinum (II) at room temperature nor when heated o to 200 . Reaction of the two in methanol or butanol gives a golden.yellow solution and some colourless crystals which are yery unstable and cannot be isolated. Evaporation of the solvent gives a resinous product but not the addition

compound (CP3)3P 2Ptci2. Bis(phenylbis trifluoromethylphosphine)dichloro• platinum (II); This compound can be prepared by direct trea

ment of the phosphine CgH^CF^gP with platinum (II) chlorid - 71 - at room temperature but the process is slow. It can be o accelerated by heating the reactants at 100 in a sealed tube. The reaction produces greenish crystals which ban be recrystallized from acetone. This product is completely soluble in non-polar solvents suggesting that it is homo• geneous and just one isomer. However, the reaction of an acetone solution of the phosphine CgH^CF^^P with an aqueous solution of potassium chloroplatinite gives a small amount of an insoluble white solid on extraction of the product with non-polar solvents. The two products also differ in their melting points. The main component (greenish o solid) melts at 134-36 , and is the trans.isomer as deter• mined by its dipole moment which is found to be 0.0D. The small amount of white solid on the other hand melts with decomposition above 300 . From its solubility and melting point it may be said, by analogy, that the latter has the cis configuration. Bis(phenylbistrifluoromethylphosphine)dichloroplatinum (II) is a very stable solid. It is not affected by water;;- or organic solvents. It is soluble in methyl iodide and trifluoroiodomethane, producing a yellow solution, but is recovered unchanged from these solutions. It can, how• ever, be hydrolysed easily with aqueous sodium hydroxide which gives fluoroform quantitatively. - 72 -

The addition compound C6H5(CP3)2P PtCl0 reacts with halogens to give new solid products. Two equivalents of the halogen are absorbed in the reaction. The bromo- compound which results is an orange coloured substance, and the iodo-compound is brown. Both are quite stable in air, insoluble in non-polar solvents, but soluble in polar solvents. Hydrolysis of the bromo-compound gives two equi• valents of fluoroform, and thermal decomposition produces pure phosphine. By analogy with the reaction of the triethylphosphine derivative (CQ^H^J^P^PtClg wni°h takes up , two equivalents of ammonia to give |Ptj(C2H^ ^PJ-gCNH^)^ Gig*

the compounds under consideration may be Jpt-£(CgH,_) (CF^^PJvjB^J Cl2

and Pt{< (CcH(CFjX 0Pkl Cl„. However further study in this '6 V 3 2 J 2 2j 2' connection is needed in order to elucidate their structure. Chemical reactions have sometimes been used to prove the structures of platinum complexes. They are known to be effective in the case of bis(triphenylphosphine)dichloropla-

(83) tinum (II, )s which has been obtained only in the cis form (c78.) This proof of structure is less ambiguous for complexes con• taining two strongly trans directing groups like the phos• phines, and the other two ligands having a weak trans effect (82) like chlorine • However, the results must be treated with caution, and physical methods are still better suited for the • elucidation of the configuration. - 73 -

The chemical method consists in treating the complex (R^PjgPtCl^ with a bidentate ligand: e.g., ethylenediammine, which would form a complex only if the positions are avail• able for chelate formation. This is better suited for com• plexes with a cis structure and would not be effective for those with a trans configuration. This method was applied to the phenylbistrifluoro• methylphosphine complex but no complex of the type jpt£cgH^(CP^ )gP^2en Gig was obtained. From this observation and the dipole moment value of 0.0D, it may be concluded that the compound has a trans configuration. Bis(diphenyltrifluoromethylphosphine)dichloroplatinum (II): This compound is prepared by reacting an acetone solution of diphenyltrifluoromethylphosphine with an aqueous solution of potassium chloroplatinite. The product so obtained is a resinous substance which can be crystal• lized by treatment of its acetone solution with a large excess of water. Bis(diphenyltrifluoromethylphosphine)- dichloroplatinum (II) is thus obtained as a pale yellow powder. Extraction with ether ^ives a small amount (r^5%) of white solid, and from its solubility and colour this is possibly the cis isomer, o The main product (pale yellow) melts at 63-65 and from its dipole moment, which is found to be 0.0D, it has the trans configuration. It is quite stable to air and moisture. It is soluble in practically all organic solvents, but is insoluble in water. It is not affected by boiling water nor by cold aqueous alkali. The compound, however, is slowly hydrolysed by heating with alcoholic potassium hydroxide. It also dissolves in methyl iodide and trifluoroiodomethane, but the two iodides do not seem to react with the complex which is recovered unchanged.. Bis(diphenyltrifluoromethylphosphine)dichloro- platlnum(II ) reacts with two equivalents of bromine to give a yellow solid. The reaction is analogous to that of the phenylbistrifluoromethylphosphine complex, and the product is possibly bis(diphenyltrifluoromethylphosphine)- dibromo.dichloroplatinum^n).This compound can be readily and quantitatively hydrolysed with aqueous alkali. This may be contrasted with the. difficulty, of hydrolysis of the phosphine (C6H5^2CP3P and its addition compound (CgH^CF^P gPtClg, and may be compared with the ready hydrolysis of diphenyl- trifluoromethyldibrpmophosphorane. Thermal decomposition of bis(diphenyltrifluoromethylphosphine)dibromodichloro- platinum(I2L ) gives the phosphine (CgH^ ^CF-^P, and also supports the above formulation.

Treatment of the addition compound j( CgH,- ^CF^P 2Ptci2 with iodine gives the corresponding iodo-compound which is a brown solid. This compound also can be hydrolysed easily and quantitatively by alkali, and in all respects is similar to - 75 - the analogous halogen compounds described above.

(06H5)2CP3P PtC1 Treatment of the addition compound 2 2 with ethylenediammine as the chemical test for the structure of the complex caused no reaction, showing (if the test is applicable) that the pale yellow solid is a trans isomer. As has already been stated, these studies with platinum( JUL) chloride would further reveal the donor proper• ties of the phosphines. This is because platinum enjoys a favourable position in coordination chemistry, this property being due to the following factors: (1) Pi-bonding is facile since the 5d levels are close to 6s and 6p. This gives additional stability to the complexes. (2) Hybridization of 6p and 5d orbitals produces pi- x xz type orbitals which form the pi-bond. Platinum is therefore in a better position than boron tri• fluoride to form complexes. Thus even phosphines of highly electronegative character which do not form an addition com• pound with boron trifluoride may do so with platinum( XL,) c'hloride. Phosphorus trifluoride is an example of this type of phosphorus derivative. An examination of phosphorus trifluoride, which behaves similarly to the above phosphines in its reaction towards boron trifluoride and platinum( XL. ) chloride, seems - 76 - useful. It Is known that phosphorus in phosphorus tri• fluoride uses its 3d and 3d orbitals to form A-rr-drr zy yz bonds with metals. The formation of such a bond is further

supported by the symmetry of the PF^ molecule (C37//)> in which the two orbitals 3d and 3d are in a doubly degenerate system of pi-symmetry . The molecules of tri• methylphosphine and tristrifluoromethylphosphine (and hence probably the other phosphines) have been shown to have the same symmetry^8] It is therefore quite surprising that no complex formation is observed in the case of tristri• fluoromethylphosphine. An examination of the mechanism of formation of these complexes seems desirable. The bonding in complexes of the type (R P) PtCT 3 2 2 consists of a sigma-bond formed by the donation of lone pair electrons from phosphorus to platinum, and a pi-bond which is the result of the overlapping of the d-or dp-hybrid orbi• tal of platinum with the vacant d-orbital of phosphorus. From the properties of the tristrifluoromethylphosphine it is apparent that the sigma-bond will be very weak. The complex, if it forms, would be stabilized by strong pi- bonding only. The formation of the square planar complexes of platinum(lt. ) salts has been suggested to occur through a (354 trigonal-bipyramidal activated complex . This transition state is stabilized by the ligands with pi-bond character. It would therefore be expected that the phosphines, which have some pi-bonding character already, would stabilize -li• the transition state more than those which have none. In platinum(H.V) complexes, the greatest degree of pi-bonding is attained wien the pi-bonding ligands are cis (133)/ to one another ,. Thus if the phosphines are cis to one another, they compete with the chloro groups for the d orbitals (d and d taking P-Pt-P as the y axis) of plati- xy yz num. However, when they are trans, the same d orbital (dyZ) would be used: i.e., the phosphines would compete with one another. Since chlorine has a smaller tendency to form a pi-bond than phosphorus, the cis isomer of the platinum compound would be more stable than the trans. However, among the alkyl phosphines, as the series is ascended from methyl to n-propyl, the trans isomer becomes increasingly stable. The stabilization of the trans isomer has been attributed to steric effects The larger trifluoromethyl groups may also be giving rise to the same phenomenon, and hence it may be expected that the trifluoromethyl-phosphines would give mainly trans isomers. Thus, whereas electro• negativity demands that a cis structure be more stable (since the pi-bond strength is increased as in phosphorus tri- (87) (78) fluoride and triphenylphosphlne ,) steric effect would give a trans isomer for tristrifluoromethylphosphine. The compound (CF ) P PtCl would, however, be 3 3 . 2 2 very unstable as is revealed by the comparison of the heat of dissociation of the complexes, (CH ) CF P ptci ,AH = 11.3 3 2 3 - 2 2' kcal mole 1 and CH (CF ) P PtCl2, AH = 5.8 kcal mole'-l. . 3 3 2 - 78 -

The value of AH is seen to decrease with substitution of trifluoromethyl groups. Extrapolation of this value would indicate that the AH for (CF ) P PtCl^ would be much too -.33. 2 2 low, and hence it is not surprising that it has not been isolated by the common methods. It might, however, be use• ful to try a displacement reaction:

(R P) PtCl + 2(CF ) P. (CF ) P 0PtCl -f- 2R P 3 2 2 3 3 3 3 3 2 2 in order to establish the non-occurrence of the complex. From the results already mentioned, it is found that all trifluoromethyl substituted phosphines, except dimethyltrifluoromethylphosphine, give the trans isomers. The1 stability of cis(C H )_,CF P 3 2 3 ^PtClg as compared with cis (CH,) P PtCl is as would be expected on the basis of 3 3 2 2 electronegativity. Thus, the replacement of one methyl group by a more electronegative trifluoromethyl group appears to give.greater stability to the complex by causing a greater increase in pi-bonding than is offset by the reduction in strength of the sigma-bond. This may be seen by a reduction in the dipole moment by the substitution of one trifluoro• methyl group, (CH ) P PtCl ,A =13.1 D, (CH ) CF P PtCl >Lb =9.2 D 3 3 2 2 3 2 3 2 2

As the number of trifluoromethyl groups is increased, steric effect which is absent in (CH,)_CF„P becomes more im- 3 2 3 portant, and hence only the trans isomer is obtained for CH (CF ) P PtCl . Steric effect and not the reduced 3 3 2 2 2 basicity of the phosphine is possibly the main reason for the stability of the trans isomer. Thus a comparison with phosphorus trifluoride shows that cis (PF ) PtCl is more . - 3 2 • 2 stable than the trans isomer. Whereas phosphorus trifluoride (88) forms Ni(PF ) , tristrifluoromethylphosphine replaces only two carbon monoxide molecules from nickel carbonylv . The formation of the platinum(II) chloride complex thus seems to be independent of the basic character of the phos• phine, and depends on steric effects instead. In the case of the phenyl phosphines it is known that triphenylphosphine gives only the cis compound. Data on mixed phosphines (RgR'P) is unfortunately lacking* How• ever, tri-n-butylarsine gives a trans isomer, but phenyldi- n-butylarsine shifts the equilibrium towards cis structure - . This is explained as partly due to steric effects and partly to electronic effects. The phenyl group, being rigid, occupies les3 space in the immediate neighbourhood of M (M = P,As) than an alkyl group. Hence when the steric effect is not operative, the more stable cis structure will be obtained. The stability will be enhanced by the electro• negativity of the phenyl group, which will increase the strength of the pi-bond between phosphorus and platinum. - 30 -

It is somewhat surprising to find that in the case of phenyl-trifluoromethyl-phosphines, mostly the trans isomers are obtained. This indicates that the replacement of a phenyl group by a CP group shifts the equilibrium towards 3 the trans isomer. The stability of the trans isomer would increase with the number of trifluoromethyl groups by the consideration of the larger size of the CF, group. The cis- 3 trans isomerization equilibrium studies indicate that the trans isomer of bis(triphenylphosphine)dichloroplatinum (II) is unstable. In this connection, it is • interesting to notethat

the melting point of the complexes increase(C sH wit) ChF Pth ePTC1 number .652 3 _ 2 2 o meltof trifluoromethys at 65 whereal sgroups—th (C H (CeF comple) P PtCx l melts at 134-136 . L 6 5 3 2 J 2 2 It may therefore be concluded that the replacement of a phenyl or methyl group by a trifluoromethyl group results mainly in the formation of a trans isomer. The possibility of phosphine-catalyzed isomerization (85) may not be ruled out . This depends on the mechanism of attack of the phosphine on the intermediate trigonal- bipyramidal structure. The first step in this mechanism is the replacement of a chloro group by the catalyst phosphine, and the second, which is through the ;same, intermediate, gives the appropriate isomer and the catalyst. The occur• rence of the cis or the trans isomer would, however, depend on the stability of the structure and the trans effect of the phosphine. - 81 -

The conclusion from the above discussion is that the substitution of trifluoromethyl group tends to favour the formation of the trans isomer. Explanation on the basis of steric phenomenon is the more probable one. Any tendency towards the formation of even a weak sigma-bond would give a complex with platinum( ZEE ), and the steric effect of the large trifluoromethyl groups would favour the placing of the phosphines trans to one another. - 82 -

CHAPTER VI

FORMTION OF COMPLEXES WITH NICKEL SALTS

It was pointed out in the last chapter that platinum( H ) forms complexes with a variety of ligands (145) because the double bonding postulated by Chatt et. al. is particularly facilitated due to the closeness of the energy level 5d to 6s and 6p. Nickel, however, does not enjoy this favourable position and hence the amount of double bonding is not at all comparable. Whereas the con• figuration of platinum and palladium complexes Is invariably planar, that of nickel is either planar or tetrahedral, depending on the ligands. The former structure is much more common than the latter which is quite rare. The tetra• hedral structure is produced by the more electronegative ligands, since in these cases the "purely ionic" bonds - 83 - formed with the co-ordinated ions will lead to a structure in which there is the greatest separation of charge. Thus as the bonds become more ionic they will more likely give rise to the tetrahedral structure. It Is therefore found that the attachment of the ligands to nickel through four oxygens tends to be tetrahedral whereas a planar structure is found for the ligands attached through sulphur, the difference being due to the higher electronegativity of (90) oxygen , The energy difference between the orbitals giving rise to the two configurations is quite small and hence the balance between the two is very delicately poised. Thus small structural differences In the ligands and changes in environment may lead to a change in configuration. In most cases, however, nickel forms an octa• hedral structure, either through co-ordination with the solvent if in solution or through polymerisation if in a (94) solid state . This has been explained on the basis of crystal field theory which shows a gain of 15-30 kcals in (134) going from a tetrahedral configuration to octahedral • This also explains why the tetrahedral structure is so rare. In the case or triphenylphosphine<91> however, it has been shown that nickel does form tetrahedral com• plexes, Steric effect is supposedly responsible for pre• venting an octahedral configuration (steric repulsion of (C_H ) P molecules would prevent polymerization) and the 653 weak crystal field strength of triphenylphosphine will not give a planar structure. Some distortion of the tetra- - 84 - hedron would be expected according to Jahn-Teller effect, (91) however this distortion would not be large . While discussing the formation of complexes be• tween trifluoromethyl-phosphines and platinum (II) chloride, it has been found that the electronegativity and steric effect of the CF group were mainly responsible for the 3 different observations. The same factors of size and elec• tronegativity have been noted above as being responsible for the occurrence of tetrahedral complexes of nickel. It might therefore be expected that the trifluoromethyl- phosphines would also form tetrahedral nickel complexes. An examination of the reactions of (CH ) P, 3 3 (CH ) CF P, CH (CF ) P, C H (CF ) P and (CF ) P 323 3. 32 6532 3.3 has shown that only the first two form stable complexes and the remaining phosphines do not react with nickel(II) salts, NiX , where X is CI", Br", I", SCN*, and No The compounds have been prepared by direct reaction in the presence of excess phosphine. The complexes with dimethyltrifluoromethylphosphine are not as stable as those of trimethylphosphine, and hence have been used without puri• fication for further study. Trimethylphosphine complexes were recrystallized from butanol. The reaction in both cases occurs in the ratio of 1:2 of NiX to phosphine. - 85 -

The properties of the phosphine complexes are given in the following table: Compound Magnetic Moment Colour Absorption Maxima

(Me P) Ni(NO ) 3.17 Dark red 4850(m ,3950(s), 3 2 3 2 3325(s

(Me5P)2NiCl2 Diamagnetic Crimson 5320(s ,3880(m), 3650(m ,2650(s). (Me P) NiBr 5400 (m ,3800(m), 3 2 2 2700(s ,2425(w).

(Me P) Nil Dark brown 5175(m ,3875(W"), 3 2 2 2850(v ),2600(a). (Me P) NI(SCN) Orange yellow 4600(sh),3550(vs), 3 2 2 2975(s ,2600(B). 5550(w ,4850(s), (Me2CP P)2NIXN03)2 2,93 Dark red 4150(s ,3270(s). 4800(w ,4050 (Me2CP3P)2NiCl^ Diamagnetic Pink (m), 3450 ('s ,2550(s). 4875 ,3950(a), (Me2CP P)2N1Bp2 " Black (s 2625(s ,2400(a). 3750 ,3550 (Me2CP3P)2NiI2 " Dark brown (m (m), 3140(m ,2280(a).

(Me2CP^P)2Ni(SCN)2 " Yellow 4600(m ,3675(vs), 2550((ss ) N.Bo s = strong; w = weak; vs = very strong; sh = shoulder.

Dinitratoniokel(II) Complexes: The isolation of the dinitrato complexes of both the phosphines is difficult since they cannot be precipitated from their solutions and hence they have been studied only in solution. These nitrato com- - 86 - plexes are very reactive towards moisture and are readily decomposed by Xi/ater and other solvents. Warming the bis (di• methyl trif luoromethylphosphine)dinitrato-nickel( II) with water gave traces of fluoroform and the phosphine (CH ) CF P. 3 2 3 Warming of the trimethylphosphine analogue with water gave trimethylphosphine. Dichloronickel(Il) Complexes: The dichloro complexes of the phosphines (CH ) P and (CH )„CF P are more 3 3 3 2 3 stable than the nitrato analogues. The reaction with dimethyltrifluoromethylphosphine is slow and is difficult to carry out in solution, since the solvents hydrolyse the phosphine (CH„) CF P. Trimethylphosphine, on the other hand, 3 2 3 reacts readily and the complex can be recrystallized from suitable solvents. There is a change in colour in different solvents which is probably due to co-ordination in solution. The aqueous solution is pink but the colour fades gradually on standing, with the evolution of the phosphine (CH ) P. 3 3 Dibromonickel(II) Complexes: The dibromo complexes of (CH ) P and (CH ) CF P are somewhat more stable than their 3 3 3 2 3 dichloro analogues, as judged by their behaviour* towards water and other solvents. Bis(dimethyltrifluoromethylphosphine) dibromonickel(II) shoxi/s the same behaviour as the dichloro compound in that it is formed slowly and is decomposed readily by moisture and other solvents. The bis(trimethylphosphine) - 37 - dibromonickel, however, is quite stable and decomposes only

slowly in moist air;. : Diiodo- and Dithiocyanatonickel(II) Complexes: The diiodo and dithiocyanato complexes of these phosphines are quite stable and are unaffected by moist air and cold water in which they are practically insoluble. The complexes dis• solve on inarming with water but the corresponding phosphines are slowly given off. The behaviour of the iodo complexes as well as of the other salts (chloride, bromide, thiocyanate, and nitrate) towards acids and bases are interesting in that the colour of the solution which is usually pink is lost in acid solutions but is restored when neutralized by bases. Their colours are stable in neutral solutions only.

The' above observations, though qualitative, reveal the general trend of the stability of the complexes which is in the order NO <^ CI ^ Br ^ I ^SCN. A similar 3 (92) relationship has been noted in the case of palladium complexes It has been explained on the basis of an increasing amount of pi-bonding in the Ni-X bond. Another factor noticeable in the above order of stability is the decreasing ^electronegativity of the anion. As was pointed out in the beginning, electronegativity differ• ences are likely to cause differences in configuration. Since the nitrate ion is more electronegative than the other anions - 38 -

studied, it (NO. ) is likely to form a more ionic bond. The 3 net effect would be an arrangement with greatest separation of like charges given by a tetrahedral structure. In terms of crystal field theory the nitrate ion does not have enough perturbing power to cause spin pairing and thus give rise to diamagnetic compounds. On the other hand, the halo• gen and the thiocyanate ions have sufficiently high ligand field strength and hence the complexes are diamagnetic. This is in keeping with the empirical relationship between the magnetic properties and the structure of compounds of (93) this type . It may be mentioned that magnetic moment though not the best guide to the structure is one of the best criteria for a tetrahedral configuration, since salts with this structure are paramagnetic and those with planar structure are diamagnetic. However, the reverse is not true; i.e., all paramagnetic complexes of nickel are not tetrahedral since octahedral complexes also exhibit para• magnetism. It is therefore necessary that the structure be definitely established, usually by X-ray methods. In the present investigation, the dinitrato com- olexes of the phosphines (CH ) P and (CH ) CP P have been 3 3 '323 found to be paramagnetic. Since the other dinitrato complexes (95) (of trie thy Iphosphine and triphenylphosphine)have been es• tablished to have tetrahedral configuration it is reasonable - 89' -

to assume that the above complexes have a tetrahedral structure ..also. The fact that no complexes of the nickel salts, with methylbistrifluoromethylphospbine, phenylbistrifluoro- phosphine, and tristrifluoromethylphosphine could be ob• tained is consistent with the observation that nickel(II) with a larger difference between the 3

GENERAL DISCUSSION CHAPTER VII

COMPARISON OP THE PHOSPHINES WITH AND WITHOUT CP, GROUPS

Physical Properties: The phosphines as a class are reactive substances. They are all malodourous. The trifluoromethyl group produces a change in odour and it is found that phenylbistrifluoromethylphosphine and diphenyltrifluoromethylphosphine are not so obnoxious as the corres• ponding phenylphosphines. Phosphines occur in all the three physical states: the hydrides, i.e., the primary and secondary phosphines (lower alkyl and trifluoromethyl sub• stituted) are gases, the tertiary phosphines containing the lower alkyl, trifluoromethyl, and some aryl groups are oily liquids, and those with higher alkyl and/or aryl groups are crystalline solids. Practically all of them solidify into a glass when cooled in liquid nitrogen,x^hich is characteristic of most phosphorus compounds. Usually the boiling points of substances increase with increasing molecular weight, but in the case of polar compounds this relationship between molecular weight and boiling point does not seem to hold. This is particularly true for the perfluoro compounds. It has been found that the boiling point in these cases is correlated with polarizability rather than molecular weight^-^l An excellent re• lationship is given by the equation: %

Tb = KM Rm where T^ is the boiling point, M is the molecular weight, R is the molar refractivity and K Is a constant depending m ° on the particular class of compound. The following table (97) gives some values of K C - OH N - - CI - Br - I K 11.6 12.3 12.75 13.6 15.05 The value of K can be found from the above rela• tionship but unfortunately no data is available for the phosphines. However from the values of triethylphosphine

C H- 1.44C 6p anld d s - 0,801), phenyldiethylphosphine ( ^9 5Jo 2 6A 5 <" ftD 1.5458, d = 0.954) and (C25 H2 ) (4-MeC 6H 4 )P = 1.5428, d = 0.9373). - 92 -

R is found from Lorentz-Lorentz equation: m

• R ^ *D - ' M M = : • -3- " D + 2. and hence an average value of 11.8 for K can be calculated, Assuming the value of K = 11.8, the refractivity equivalent of the different groups may be calculated. The

following table gives the values of Rm for the different groups»

H CH, C H P 3 6 5 Equivalents 1.1 5.65 22.5 7.1 (9-5 for PH,,' PH , -3 2 and PH) From these values the equivalent for the trifluoro- (97) methyl group may be calculated . It is found to be 37«9 for one CF group, 42.9 for two and 47*4 for three groups. '•3 It may be mentioned that the refractivity of an element is a constitutive property and hence depends on the environment. The values obtained above are therefore very approximate but give close agreement with the observed boiling points. The following table shows this. Phosphine Boiling Point Phosphine Boiling Point Calculated Observed Calculated Observed

(CH3) P 37.0 37.8 360 360 (°6H5)3P

(CH )2PH 24 21.1 (C6H5)2PH 289 280

(CH )PH - 10 -14 ,C6H5PH2 155 160 3 2 - 93 -

Phosphine Boiling Point Phosphine Boiling Point Calculated Observed Calculated Observed - 87 -87 CH (C H ) P 305 283 PH3 3 6 5 2 192 (CP3)2PH - 2 1.0 (CH,) C H P 195.9 3 2 6 5

(CP )PH2 - 28 -25.5 CE3(CH3)2P 38 46.9

(CF3)3P 17 17.0 (CP ) CH P 26 35.2 3 2 3

CP (C H ) P 257 255 (CF,) CJi P 159 150 3 6 5 2 3265 The agreement between the calculated and the ob• served values is found to deviate within reasonable limits. This may be expected obviously from the nature of the approxi• mation — particularly the value of atomic refractivity of the different groups. This is found to vary widely and obviously requires further examination. However, for the present it is sufficient to say that the boiling points of the phosphines are not a function of molecular weight alone but depend on the polarizability of the groups attached to it. A plot 3/ . of M 'c/ R^ against the observed boiling points gives a straight line as shown in fig. ( A )• The deviations may again be attributed to environmental effects. The relationship discussed above is excellent in that it correlates the methyl, phenyl, and trifluoromethyl groups, at the same time indicating that the trifluoromethyl- phosphines are not uniquely different from other phosphines but, rather, fit the general pattern. The low boiling points of the fluorocarbons are thought to be due to low intermolecular forces^^and large intramolecular forces. Such forces -93- 3/2 Flg* A*

Plot of M ~/Rm Vs. Boiling Point (Observed).

14. (CP ) CH P 15. CP (C H ) P 16. (CF ) C_H P - 94 - make the fluorocarbon molecules inflexible and therefore prevent free rotation* This restriction would be responsible for lowering the boiling points. The same might be true of the trifluoromethyl-phosphines in which the trifluoromethyl group would be responsible for the low intermolecular forces, resulting in their higher vapor pressure compared with the methyl analogues. The other properties of the phosphines are also related in a similar manner. Thus the latent heat of vapori• zation is lower for the trifluoromethyl-phosphines than the methyl- or phenyl-phosphines. The following table gives the values of the latent heats for the phosphines: Phosphines Lv (cal/mole) Phosphines Lv (cal/mole)

PH 3489 P(CF ) CH 6310 3 3 2 3 PH(CH L 6270 PCF (CH ) 6950 3 2 3 3 2 P(CH^) 6943 PtCF^CgH 9054 P(CF ) 5890 PCF (C H) 11850 3 3 3 6 5 2

Unfortunately the values for all the phosphines are not reported and so it is difficult to correlate this property. However, it is possible to say a little about the trifluoromethyl-phosphines whose values are known. Since the heat of vaporization is a measure of the forces acting between the molecules of the same species, it is possible to understand the low vapor pressures exhibited by trifluoromethyl- phosphines . - 95 -

The heat of vaporization is empirically related to polarizability of the substanceThe force preventing a molecule from leaving the surface of the liquid does not depend on the mass and hence it is possible to see why the heat of vaporization would not depend on the molecular weight. Larger molecules are easily deformed. Their effective area is greater and hence the energy required for transformation into vapor would be large. Thus heat of vaporization would depend on the molecular size and the deformability of the molecule, both of these factors being a measure of polariz• ability. The fluorocarbons have been considered as "stiff molecules" ^"^and hence the molecular size would not enter into the overall deformability of the fluorocarbons. The large trifluoromethyl groups may behave likewise and hence the properties would be similar*

The lower heat of vaporization of the trifluoro• methyl-phosphines may also be explained on the basis of the concept of interpenetration^^] according to which the hydrocarbon molecules interpenetrate one another,whereas fluorocarbons do not do so or do it to a negligible amount. Thus for vaporization of interpenetrated molecules energy would be required: (1) to free the molecules from their interpenetrated condition and, (2) for transformation of the phase; i.e., for bringing it from the liquid surface to a i - 96 -

vapor state. In the case of non-interpenetrated molecules only (2) would be involved and hence the energy of vaporization would be low. Extension of this phenomenon to the trifluoromethylphosphine would show that this concept applies very well. The trifluoromethyl group is large, compact, and more electronegative. The first two factors would prevent interpenetration and the electronegativity would cause repulsion, so that the net effect would be a lower heat of vaporization. It is significant in this connection to notice the close values of AH^ of trimethylphosphine and dimethyltrifluoro•

methylphosphine (6943 and 6950 cal/mole). This indicates that some amount of interpenetration has been promoted by the re• pulsive action of the trifluoromethyl group which causes intermeshing of the methyl groups. This effect would be absent in the phosphine with two trifluoromethyl groups. This also explains the higher boiling point of dimethyltrifluoromethylphosphine compared with trimethylphosphine. The above discussion of the application of the concept of interpenetration to the phosphines would suggest that the trifluoromethyl phosphines would not be associated and would have the normal values of Trouton's constant.

Phosphine' (CF„) P (CF )CH P CF (CH,)-P (CH7) P Z 3'3 3^3 3^^ -> 3 Trouton's Constant 20.3 20.5 21.7 22.3

Phosphine (CH ) PH (CP ) C H P CP (C H )P 3 2 3 2 6 5 3 6 5 Titojaton • s Cons tant 21.2 18.7 21.3 22 - 97 -

Although the values are not significantly different, the above table shows that progressive replacement of the different groups gradually lowers the Trouton's constant. Thus tristrifluoromethylphosphine and methylbistrifluoromethyl• phosphine have normal values. Trimethylphosphine and phenylbistrifluoromethylphosphine are probably associated more than dimethyltrifluoromethylphosphine, phenylbis trifluoromethyl• phosphine, and dimethylphosphine. It is interesting to note that the values for CF^CH^gP and (CE^)^P are quite close, showing that the former is associated,and this might be the reason for its higher boiling point, compared with the latter.

Chemical Properties: The phosphines in general are insoluble in water under normal conditions, thus showing no tendency towards hydration. They are, however, soluble in organic solvents. The primary and the secondary phos• phines dissolve to a small extent in water. The trifluoro• me thylpho sphines conform with the general behaviour of the phosphines towards solvents under ordinary conditions, but at high temperatures they usually react with the solvent and lose the trifluoromethyl group. The loss of the trifluoro• methyl group will be considered later,but for the present,it is sufficient to say that the P-CP bond is in some way more 3 susceptible to attack. Phosphines as a class are basic in nature. How• ever, phosphine PH is very weakly basic. The basicity rises 3 with the degree and type of substitution. The order of - 98 - basicity is primary ^secondary <^ tertiary I For the tertiary phosphines, introduction of electron-withdrawing groups reduces it. Thus the order of basicity is alkyl^ aryl ^ trifluoromethyl. This can be seen from the reaction with hydrochloric acid and the ease of hydrolysis of the salt so formed. Thus CH PH forms crystalline salts with HC1 3 2 and HI; C H PH is sparingly soluble in HC1 but forms a salt 6 5 2 with HI. The same is the case with secondary phosphines. The salt of (CH ^PH and HC1 is stable,but that of (CgH^PH is decomposed easily by water. The same order is applicable to the tertiary phosphines: (CH ) P-HC1 is quite stable, 3 3 (C H ) P»HC1 is decomposed on diluting the acid solution and 653 tristrifluoromethylphosphine does not form a salt at all. However, this possibly reflects the stability of the hydro• chloride rather than the reactivity of the phosphine. The phosphines In general show additive properties. The lower members (hydrides and alkyl substituted) can be

oxidized readily in air. The aryl phosphines are oxidized only by strong oxidizing agents or in the presence of catalysts. The trifluoromethyl-phosphines do not form an oxide directly and like the aryl phosphines require an intermediate compound. Direct reaction with atmospheric oxygen breaks the P - CP 3 bond and does not give any oxide. The possible explanation for this phenomenon has been given previously with respect to the reduced amount of pi-bonding character, which is exhibited in their reactions mentioned in SectionH. - 99 -

The mixed methyl phosphines RR^P have properties intermediate between the two extremes e.g. (CH^P and (CF ) P , exhibiting the properties of the predominant j J> J group. Thus methylbistrifluoromethylphosphine resembles tristrifluoromethylphosphine rather than trimethylphosphine, and dimethyltrifluoromethylphosphine resembles trimethyl• phosphine rather than tristrifluoromethylphosphine. Dimethyl- fluoromethylphosphine and trimethylphosphine react slowly with air to give the oxide, but tristrifluoromethylphosphine and methylbistrifluoromethylphosphine inflame in air and no oxide is formed in the presence of excess air. The mixed phenyl-phosphines, on the other hand, retain the inductive and mesomeric effects of the benzene ring. Thus the presence of one phenyl group is sufficient to stabilize the phosphine C^H^CF^^P completely so that it does not react with atmospheric oxygen. The effect can also o be noted in the rise In the boiling point from 17 for tristrifluoromethylphosphine to 150 for phenyIbistrifluoro- methylphosphine. The stability has been considered in Section I and has been thought to be due to the conjugation effect together with the electron-withdrawing tendency of the trimethyl group. The effect may be represented as: F F

P_cOpD c—F 15 F - 100 -

Thus,the electron-withdrawing tendency being satisfied by thee drift of electrons from the phenyl groups, the pi-bonding character is restored to a certain extent and the P-CF, bond 3 is stabilized. It may be worthwhile estimating this effect. It has been shown previously in Chapter 2 that an increase in the bond distance increases the reactivity, and the bond lengths in P-CH, and P-CF have been noted as 1.87 and 1.93 3 3 respectively. The bond shortening has been attributed to (3D pi-bonding . It has been shown that for the formation of such bonds, the relative electronegativities of the bound (102) atoms or groups are not critical . An estimate can be (101) made of the bond shortening due to pi-bonding . This gives a bond shortening of 0.054A for 0.1 pi-bond or for a 10% pi-bonding character. This is just the amount of bond lengthening observed in (CF ) P It would therefore be 3 3

expected that the P-CFJ , bond energy would be short of 10% of the pi-bonding energ y (50 kcal) attributed to phosphorus(-3 ] giving a value of 57 kcal mole-1 for the P-CF bond. The 3 total loss of energy due to the presence of CF groups would .1 3 then be 15 kcal mole , which is sufficiently significant to alter the character of. the phosphine concerned. A reaction which is common to all phosphines is the reaction with halogens. This is surprising in view of the - 101 - fact that some of the phosphines react only reluctantly with hydrochloric acid. As has been said previously, this is possibly because of the mechanism of reaction. In the case of reaction with hydrochloric acid a nucleophilic attack of the lone pair on the proton is involved, whereas in the case of the reaction with halogens an electrophilic attack of the halogens on the lone pair electrons takes place. The phosphines usually react vigorously with the halogens and form the phosphoranes R^PX^• The formation of phosphoranes is possible only under controlled conditions; otherwise a replacement reaction occurs in which one of the groups is substituted by the halogen atom forming a halophosphine. The mechanism of formation of the halophosphine, however, involves the formation of a phosphorane:

+ - R P+X - (R XP) X 3 2 3

uncontrolled (R XP)+X -> R XP+ RX > 3 The ease of reaction with the halogens is in the order (P) ^ CI ^ Br ^ I. (The' fluorine compounds have not been fully studied,) The chlorides are the most stable, whereas the iodides are in most cases quite unstable and are not known. The non-occurrence of most iodophosphoranes i, is possibly due to steric factors as well as to the lower electronegativity of iodine. The promotion energy to match - 102 -

the s-, p-, and d- orbitals demands that the ligands be electro• negative. Large ligands have high polarizability; consequently, their size would prevent a close packing. This is possibly the reason why PI does not occur. However, the iodo-phos- 5 phoranes of the phosphines with a certain amount of pi-bonding would be expected to be formed. The alkyl and aryl phosphines (68) (tertiary) are found to give the cUiodophosphorane . The trifluoromethyl-phosphines do not form the iodo-compounds

(except (CJEL)0CF P) and this gives further support to the o 5 2 3 argument that they are devoid of any pi-character. It has already been said that the formation of halophosphines takes place through the formation of an inter• mediate phosphorane. This reaction may be considered a decomposition of the phosphorane since it takes place only on heating, with a rearrangement of bonds such that more stable compounds are formed. This type of reaction occurs probably because it Is irreversible; i.e., reactions of the type

R PX + RX—-*R PX do not take place. (;Obviously the addition 2 3 2 reactions with phosphorus tr-ihalides are not possible. How• ever, gradual replacement of the halogen atom increases the tendency towards addition reaction and with diphenylchloro• phosphine and benzyl halide we do get (C H ) C H PCI .) 652772 The phosphoranes are an interesting series of com• pounds. In their reactions they resemble the phosphonium compounds. Their conductivity in solutions indicate that they - 103 -

are ionic in nature with the structure PX X or + 4, R„PX" R PX They can be hydrolysedI easileasilL y with the for• •3 - 3 3 matio— n of an "oxide R^PO. The trifluoromethyl-phosphoranes differ from the others in this respect. Their aqueous hy- (103) drolysis usually produces an acid .

H20 (CF ) PCI (CF ) P(0)0H+ CF H 3 3 2 3 2 3 NaOH (CF 5)3PC12 J£a > (CF )P(0)(0Na) + 2CF H 3 2 3

2H90 (CP3)2PCI3 d ' > (CF ) P(0)0H + 3HC1

The mixed phosphoranes R2R PX2 exhibit intermediate properties. (C.H LCF PBr is resistant to aqueous hydro- 6 5 2 3 2 lysis and in this respect resembles (CgH^J^PBr^ showing that the effect of the phenyl groups is still predominant. C H (CF LPBr on the other hand gives C H (CF )P(0)0H on 65322 653 aqueous hydrolysis and is similar to the hydrolysis of (CF ) PCI . The methyl-trifluoromethyl-phosphoranes have 3 3 2 not.been prepared but they are expected to behave similarly. The alkaline hydrolysis of the phosphoranes (other than trifluoromethyl) invariably gives the oxide. The trifluoromethyl-phosphoranes, however, give acids, de• pending upon the number of trifluoromethyl groups displaced. Thermal-decomposition of the phosphoranes gives a halophosphine and an alkyl or aryl or trifluoromethyl halide. - 104 -

R PX > R PX +• RX 3 2 2

R2PX3 > RPX2 +- RX RPX > PX 4- RX 4 3 ^ These reactions suggest that a structure with more (61) X than R is more stable ; i.e., R„PX„ should be more stable 2 3 than R PX^. A detailed study has not been made in this con- 3 2 (60) nection but whatever evidence is available, suggests that R_PX is covalent and R PX„ ionic in nature. 23 32 The thermal cleavage of R from R^R PX^ possibly depends on the nature of the group, the weakly bonded group being cleaved more easily. Thus in (C H ) CP PBr , tri- 6 5 2 3 2 fluoromethylbromide is lost easily. This is comparable with the analogous arsenic compounds. The formation of halophosphines on reaction of the phosphine with halogens Is an interesting reaction since these compounds are well suited for the synthesis of other compounds, and their polymers. This reaction may be com• pared with the formation of a phosphorane and its subsequent decomposition into halophosphine and a halide of the attached group. The hydrogen of the primary and secondary phosphine (69b) can be replaced easily by halogens . Tertiary phosphines have to be heated In order to produce the halophosphine. Irifluoromethyl-phosphines differ from the other phosphines in their reactions with iodine. They react with iodine cleaving all the trifluoromethyl groups to give trifluoro• iodomethane. - 105 -

The halophosphines are reactive compounds, due to the presence of the halogen atom. Thus most of their re• actions are similar to those of the trihalides of phosphorus. (104) The R PX compounds are more reactive than RPX^ . The 2 2 reactive group being halogen, the halophosphines can easily be oxidized in air. If the other groups attached to phos• phorus are also reactive, oxidation occurs explosively. The trifluoromethyl-iodo-phosphines decompose in this manner since the bond energies of P-I and P-CF are both lower than P-0. However, in the presence of stabilizing groups like the higher alkyl and phenyl groups, they are quite stable. The oxidation of such halophosphines gives the corresponding phosphonyl halides RPOXg or RgPOX. The hydrolysis reactions are discussed in the next chapter, but it is sufficient to say here that the trifluoromethyl-halo-phosphines give fluoroform and phosphorous acid whereas the other halophosphines give the corresponding phosphine and the acid. Like the phosphines, the halophosphines add halogens to give the pentavalent compounds. RPX + X >• RPX R PX + X > R PX 2 2 4 2 2 2 3 The monohalophosphines being more like the ter• tiary phosphines, show a greater tendency towards such reactions than the dihalophosphines, which behave more like the trihalides of phosphorus. - 106 -

The reactivity of the halogen atoms in the halophosphines can be seen from their replacement by the other halogen or pseudo-halogen atoms. The exchange of a halogen atom with an organic group by reacting with organoraetallic compounds is utilized for the preparation of higher sub• stituted halophosphines. Another important reaction utiliz• ing this property is the Wurtz reaction. The metals usually employed for this reaction are lithium, sodium, and mercury. The phosphines react with alkyl halides to form quaternary compounds. The formation of the quaternary com• pound depends on the basicity of the phosphine. However, the stability of the quaternary compound does not depend only on the base strength of the phosphine. The two pro• perties depend on different factors, the strength depending on polar effects while stability can depend to a large ex- (66) tent on stereochemical effects . Thus the lower members react spontaneously whereas with bulky groups heating is necessary for formation of the quaternary compound. The stability also depends on the polarity of the bond. A hydrochloride will be hydrolyzed easily if the polarity of P-H is greater than the other bonds. In the case of groups with positive inductive effect -j-I, (e.g., the alkyl groups) the polarity would be lower than for groups with negative inductive effect. Consequently, the hydrochloride of tri- - 107 - phenylphosphine would not be as strong as that of trimethyl• phosphine. Similarly, phosphines with two trifluoromethyl groups have not been found to form quaternary salts, but quaternary salts for phosphines with one trifluoromethyl group have geen isolated. The phosphonium salts undergo thermal decomposition giving the organic halide RX and the phosphine R P. The -,. 3 decomposition of a phosphonium compound with mixed groups

[RR'^'.I "**X is much more complicated in that it may occur in several ways. It is Sufficient here to say that the ease of elimination of the various radicals depends on their (74) relative affinity for a negative charge . On this basis the electron attracting groups head the scale. Thus In a phosphonium salt with mixed groups the more electronegative groups will cleave more easily. However it has been found that the decomposition of such compounds gives a mixture of halides of the different radicals present in it. The posi• tion in the scale for the trifluoromethyl group cannot be determined at this stage since the thermal decomposition of . + - (CH ) CP P I has not been studied, but the decomposition 3 3 3 of the phosphonium compound CH,(C H )0CF P I gives a mix- • -> 6 5 2 3 ture of methyl iodide, fluoroform, and benzene. The formation of complexes is a characteristic property of the phosphines. A large variety of such com- - 108 - plexes are known. The simplest are the carbon.disulphide and p-benzoquinone adducts. For the formation of such an adduct it is desirable that the carbon atom be in a conjugated sys- O S tem (such as in p-benzoquinone (u) and carbon disulphide C ). 6 s It is imperative that attached atoms are such that they create an electron deficiency on the carbon atom. Thus carbon di• oxide does not form an adduct nor does dimethyl- y pyrone^^) However the chief criterion is the availability of the lone pair electrons. The alkyl phosphines form carbon disulphide and p-benzoquinone adducts. Triphenylphosphine does not form a CS^ adduct but forms a p-benzoquinone addition com• pound. The difference is due possibly to the structure factors (108) and to the mechanism of reaction • The mixed phosphines with more alkyl groups (Alk C II P) form CS„ adducts but no 2 6 5 2 compound with p-benzoquinone is reported. The phosphines Alk(CgH,-)2P have also been reported as not forming CS^ or p-benzoquinone adducts. The trifluoromethyl-phosphines do not form any compound with carbon disulphide. The phosphines form a series of addition compounds with metal halides, particularly mercury halides, but also with copper, silver, gold, cadmium, zinc, boron, aluminium, tin, cobalt, nickel, palladium, platinum, and various other transition metals. A discussion of complex formation with the metal halides mentioned above would become very involved if they were discussed individually. Since in all cases ;. - 109 -

the Influence of the electronegative ligand on coordinating property of the phosphine is apparent, it will be easier to start with strong acceptors—boron and aluminium halides— and then consider the other metals. However, a full dis• cussion is handicapped by the lack of information about the trifluoromethyl-phosphines.

The formation of complexes with boron trifluoride has been discussed in chapter 4 where It was shown that the Inductive, steric, and hybridization effects were all res• ponsible for their formation and stability. The Inductive and steric effects were considered mainly responsible for the occurrence of the complexes discussed, and the steric factor would be ignored in those cases. The steric and hy• bridization effects do play an important part in the chemi• stry of the other phosphine-boron compounds. It is known that the change of the group can cause a change in hybridi• zation of the phosphorus or boron atoms. Substitution of hydrogen by methyl on the phosphine is an example. The elec• tron releasing methyl group would cause higher hybridization effect; in other words trimethylphosphine would be more highly hybridized than phosphine. Since trimethylphosphine would not require as much energy as phosphine to be promoted to the completely hybridized state, the latter would be a (109) weaker base . The effect Is related to the bond angles which are: - 110 -

Phosphine: PR, P(GH ) P(CP ) 3 o V 33 o Bond angle: 93.5 100.4 99.6^2,5 The acid-base reaction involves (1) the promotion energy to a state of complete tetrahedral hybridization and

(2) energy for the formation of the sigma-bond. The differ• ence in hybridization energy is seen to explain the behaviour of phosphine and trimethylphosphine, but does not explain the Inertness of the lone pair electrons of (CF^j^P where the inductive effect is now much more important.

It was pointed out earlier that the different reference acids would indicate different stability relation• ships and since a raonotonic scale of such relationships is difficult to establish the different acids should be con• sidered separately. Some of the obvious differences are: PP.BP is not known but F,P.BH has been prepared. BH 3 3 3 3 3 is, however, a very strong acceptor. Phosphine (PH ) forms 3 1:1 complex and also 1:2 complex with BP^, PH^BP^, and PH (BP ) . It forms 1:1 complexes with boron trichloride, 3 3 2 tribromide, borane, BH^ and boron trimethyl.

Dimethylphosphine (CH )0PH forms a complex with 3 2 BH . This addition compound (CH ) PH.BH loses hydrogen at

3 o r 3 2 3

150 [

Methylphosphine (CH )PH also forms a 1:1 complex CH PH .BH • 3 2 3 2 3 - Ill -

Triphenylphosphines form complexes with most of the boron compounds but they have not been investigated—only the compounds with BG1 ^115^and B(CiI ) ^116^have been reported 3 653 and the compound with BP has been prepared during this 3 investigation. The addition compounds with phosphines bearing mixed groups have also not been reported so that a correlation with respect to the phosphines cannot be attempted beyond whatever has been mentioned already. The study with the aluminium salts has also not been explored fully. Complexes of only the raethyl-phosphines have been prepared showing the general trend that the elec• tron releasing alkyl groups increase the donor properties of the phosphines. Compounds of gallium, indium and thallium alkyls have also been prepared but not with a variety of phosphines. The application of the above study to the tran• sition metal halides would also show the same trend—the electronegative groups would decrease the donor properties of the phosphine. In the case of transition metals the noted difference is the ability to form a dir- dir bond. Such bonding alloi^s complex formation by a wide range of phosphines. The addition compounds of the phosphines with the dihalides of the various metals are generally of two types: the rationof the phosphine to the metal halide may be 1:1 or 2:1, The 1:1 complexes are usually dimers with bridged structures. In the case of copper and silver (Cu(l), Ag(l)) it - 112 - has been shown that the 1:1 complexes are four-fold macro- (110,111) molecules of the formula R P —>MI 3 4 The above complexes are known only for a small group of the alkyl phosphines. The data on phenyl-phosphines is scanty. However;dimethylphenylpbosphine and diethylphenyl- phosphine have been studied. The former gives both 2:1 and 1:1 complexes whereas the latter gives only 1:1 complexes with copper(l)and silver(l). The trif luoromethyl-phosphines do not form any complexes with silver iodide, except dimethyltrifluoromethylphosphine which gives an unstable 1:1 complex. However complexes with diethyl p-trifluoromethylphenylphos• phine have been prepared and they are 1:1 for copper(l) iodide and 2:1 for silver iodide . These 2:1 complexes are more

stable than the 1:1. This is considered to be due to the solubility and concentration of the complex in the medium. However, it has been shown in the case of platinum(II) chloride that electronegative ligands on the tertiary phosphines en• hance the pi-bonding character since there would be a drift of electrons towards the ligand therefore forming stronger bonds. This increased amount of pi-bonding might be res- (113) ponsible for making a 2:1 complex more stable . The trifluoromethylphosphines have no tendency to form even a weak sigma-bond wfth these metal halides and hence the question of the stabilizing influence of 7r-bonding does not arise. - 113 -

The complexes of the phosphines with the halides of mercury, particularly mercuric iodide and chloride have been studied much more extensively than the other metal halides of the same group. Practically all phosphines with even a slight amount of pi-character seem to give a mer• curic iodide complex. The trifluoromethyl-phosphine com• plexes have not been isolated but qualitative tests show that unstable complexes can be produced for dimethyltrifluoromethylphosphine and diphenyltrifluoromethylphosphine. The other trifluoromethylphosphines (CF^) P, (CF^CH^P and (CF ) C H P do not seem to react with mercuric iodide 3 2 6 5 but this would require a systematic study. Further confir• mation of the strong coordination tendency of mercury halides towards the phosphines comes from the stable com• plexes of diethyl-p-trifluoromethylphenylphosphines. Since the electron-withdrawing tendency of a p-trifluoromethyl- phenyl group would be approximately comparable to the trifluoromethyl group itself, it is reasonable to conclude that complex formation by phosphines is possible if there is some amount of pi-bonding character present. This view would be found to be generally applicable. Knowledge of the complexes of the phosphines with other transition metals is extremely scattered and not - 114 - much, is known about them. However nickel, palladium, and platinum form a group of important complexes. The unique position of platinum compared with palladium and nickel has already been mentioned. The compounds of metals of higher transition series are invariably planar since elec• tron pairing, according to ligand field theory, can occur .readily. The other factors governing the configuration are the steric effect, electronegativity, and the Jahn- Teller effect. The addition compounds of the trialkyl-phosphines with platinum(II) and palladium(II) occur both in 2:1 and 1:1 ratio. For platinum(II) the phenyl-phosphines and trifluoromethyl-phosphines have been reported to form only the 2:1 type of compounds. The complexes with phenyl- phosphines and palladium have not been reported. The com• plexes of the 1:1 type are bridged through the halogen a toms: R P CI CI 3 \ / \ / Pt _Pt CI CI PR^

Their configuration permits them to exhibit geo• metrical isomerism. Thus both types, viz. 2:1 and 1:1, occur in cis and trans forms. According to the generaliza• tion made in chapter 5» phosphines with higher alkyl and/or - 115 - trifluoromethyl groups give mainly trans-isomers. The phenyl and/or lower alkyl substituted phosphines give mainly cis- isomers. It would be observed from the above discussion that the trifluoromethyl group exhibits the properties of a pseudo-halogen. The high electronegativity makes it resemble the halogens but because of its volume it does not quite fit into that series. The main difference is that, unlike the halide ions, the trifluoromethyl anion does not exist as a stable entity. - 116 -

CHAPTER VIII

HYDROLYSIS OF THE TRIFLUOROMETHYL-PHOSPH0RUS COMPOUNDS

Trifluoromethyl compounds as a class are suscep• tible to hydrolytic attack. The hydrolysis reaction usually goes to- completion with the quantitative liberation of fluoroform. Several trifluoromethyl compounds are, however, known in which the M-CF bond Is resistant to hydrolytic 3 attack. Only one compound of phosphorus, trifluoromethylphosphonic acid, is known in which the fluoroform is not liberated easily, - although it is evolved slowly on heating o to 150 . It has been proposed that the lengthening of the M-CF^ bond is responsible for the ease of hydrolysis as r 11,7; r-

observed in the case of the trifluoromethyl compounds of the group V elements ^"^l In the other cases where hydrolysis is difficult, as for example in perfluoroalkyl halides, the bonds are either normal or shorter than those observed for the corresponding alkyl compounds. However, instances to the contrary are also known in which the M-CP bond is 3 longer than the corresponding M-CH bond and still the hydro- 3 lysis is difficult. One such compound is CF,SF . The follow- 3 5 ing observations are relevant in the discussion of the ease of hydrolysis as observed in the case of P-CF compounds. 3 - 1. The P-CP bond lacks pi-character thus reducing the 3 bond energy of this bond compared with P-CH and P-CHH . 3 6 5 2. The trifluoromethyl group acts as a pseudohalogen group, so that its behaviour in the case of phosphorus com• pounds would be like the trihalides. 3. The behaviour as a pseudohalogen group is supported by its high electronegativity and high electron-withdrawing (142) effect, obtained from the o~ value given by Taft . The following table gives the values of electronegativity of groups and their o~ value and shows its similarity to the other electronegative groups. Group Electron-withdrawing Electro- power negativity CH . 0.00 2.34b 3 H 0.49e 2.10°

6 5 d C C H 0.60®a 2.70 OCH I M.46 2.92a 3 - 118 -

Group Electron-withdrawing Electro- power

2.38 3.10 OC6H5 I 2.38 2.68

Br 2.80 2.94

01 2.94 3.19 CP 2.81f 3.3^ 3 P 3.08 3.93

CC1 2.65f 2.85b 3 f « ^ t> CBr 2.50 2.6 3 a calculated from (142a) by multiplying with 2.8. b (140), C C&Q), d ( 5h), e (142), f (105), g (106) 4« The ease of hydrolysis for the phosphorus halides is known to increase as the electronegativity of the halogens decreases. However, the above table would indicate that the ease of hydrolysis would be better understood if the electron- withdrawing power is also taken into consideration. 5. whereas the bond energy and the electronegativity values do not differentiate between the ease of hydrolysis of P-CP and P-I on the one hand and P-CH and P-C H on the 3 3 6 5 other, the electron-withdrawing power does Indicate the diffi• culty that could arise in the hydrolysis of the latter bonds. This difference is further seen by the comparison of the heat of formation of the various compounds that might be expected in the hydrolysis reactions. - 119 -

Compound AH CH 17.88 4 a CF 220 4 CF H I69a 3 C^H , 19-82 6 . § CO— 161.63

HF(aq) 78.66 NaF 135.9 (aq) PH 2.21 3 H,PO, x 232.2 3 3(aq) CF 117a 3

a = (143)

The above table indicates why the methyl and the phenyl groups would be difficult to hydrolyse l whereas the hydrolysis of the CF, group would be easy. This table also indicates the 3 possibility of a closely similar reaction by which a fluoride and a carbonate could be formed. There are quite a few tri• fluoromethyl compounds which hydrolyse In this manner. This difference has been attributed to a different mechanism of reactio^ (118n .) In the case of substituted phosphines it has been Observed that their hydrolysis is much easier when they are oxidized to the pentavalent state. This is possibly because of the structure of the quinquevalent compound; viz., trigonal bipyramidal. Radioactive exchange studies indicate that the - 120 - equatorial positions in the phosphoranes are different in (119-121) behaviour from the apical positions . The difference is indicated by the hydrolysis of tristrifluoromethyldichlorophosphorane and bistrifluoromethyltrichlorophosphorane. The trifluoromethyl groups of the former are supposed to be in the equatorial position and can be hydrolysed easily, but in the latter they are in the apical position so that hydro• lysis does not remove the trifluoromethyl groups and the P-Cl bonds are replaced instead. However, these examples are meant to reveal only the difference in behaviour due to position of the group. It is observed from the reactions of the phosphoranes that unless points of more favourable attack are present in the equatorial position, the apical positions are first attacked giving an unstable intermediate.

PX + 2H 0 > [PX (OH) 1 +- 2HX If groups like methyl or phenyl are present, this intermediate is stabilized by losing a water molecule and forming an oxide,

PX3(OH)2 X P0 4- H 0 3 ^2 but if electron withdrawing groups are present, the reaction goes further and such groups are lost.

X P(0H) -> X2P0(0H)+HX 3 2 The foregoing mechanism is supported in particular by the observation that (1) phosphoranes formed from phos• phines which cannot be hydrolysed easily are themselves rapidly hydrolysed with the loss of the more electron with• drawing groups, and (2) hydrolysis of the phosphines usually - 121 - gives phosphorus in the pentavalent state. The latter obser• vation therefore outlines the general mechanism of hydrolysis of the phosphines:. 1. Promotion to the intermediate penta• valent state, followed by (2) Rearrangement to give a stable structure. • This mechanism may now be considered in the light of experimental facts. 1. Phosphines: (a) Tristrifluoromethylphosphine is not hydrolysed by water at room temperature but can be hydrolysed at high tem• peratures or by alkaline solutions. The CF groups are 3 probably replaced step by step, losing one CF„ at a time. 3 The reaction is base-catalysed since an excess of base is not necessary for the completion of the reaction. The reac• tion possibly proceeds through the formation of an inter• mediate of the. type (CP ) PH(OH) which being an unstable 3 3 compound loses a CP group and forms bistrifluoromethyl- 3 phosphinous acid (CF^^POH. The latter is unstable in water and gives fluoroform and trifluoromethyl-phosphonous acid CP P(OH) which in turn is hydrolysed by water to give fluoro- 3 2 form and phosphorous acid. The reaction may be respresented (118) as follows : OH (CP ) P + H- OH > (CP ) PH(OH) •(CF ) POH+CP H 3 2 3 3 3 3.3

(CP ) POH -—" ( CP ) P(0)H4-H0H — > 3 2 3.2 - 122 -

H H

(CP ) P (CP ) P OH + H 3.2 \ 0 OH 0

H20 CP P(OH) -t-CP OH' CP P(OH) + CPH 3 <- 3 2 3

H CP_H CF,P = 0 +• C H CP,P=0 H2( + 3 3 V 3 0H ^OH •> H3PO

The intermediates postulated above would be ob• tained only in the presence of weak alkaline solution or with water, but when strong alkaline solutions are used fluoroform Is liberated immediately and quantitatively, since in this case the nucleophilic attack would proceed more rapidly.

(b) Diphenyl-tri fluorome thylpho sphlne and Dimethyltrifluoromethylphosphine: These phosphines are

not hydrolysed easily. It is interesting to note that the hydrolysis of diphenyl-trifluoromethylarsine is also diffi- (47) cult « It is possible that the pi-bonding character due to the presence of two methyl or phenyl groups stabilizes

the P-CP bonds in the above compounds, making it more 3 difficult to remove the CP group. However, when the lone 3 pair of electrons on the phosphorus atom is used for the

formation of a coordinate bond or to give a pentavalent compound, it is found that the CP„ group is easily lost. 3 - 123 -

Thus In the case of dimethyltrifluoromethylphosphine, hydro• lysis is facilitated by the addition of bromine to it. Similarly, hydrolysis of bis(dimethyltrifluoromethylphosphine)- dichloroplatinum(II) gives fluoroform almost quantitatively«, The reaction of diphenyltrifluoromethyldibromophosphorane gives diphenylphosphinic acid and so does the platinum com• plex (C,_H ) CP P PtCl 6 5 2 3 J2 2 The reactions of these phosphines most probably

occur by the following scheme:

(C H ) CF P +- 2 (OH)" > (C H ) CP P(OH) -> CF H4- (CX )_P(0)OH 6523 65*3 2 3 o 5 The formulation of the intermediate as (CgH ^CF^PfOH^ is consistent with the fact that the reaction does not occur unless there is an excess of alkali present. (This may be contrasted with the hydrolysis of (CF_) P where the Inter- ^H 3 3 mediate is formulated as (CF,)_P since in this case the 5 3 ^GH reaction is base-catalysed and requires only one equivalent of the alkaline solution.). It is significant that the

C H CF Br iS n vo 3e<3i b phosphorane ( g ^ )2 3^ 2 °*' ^^ ^ 7 water* The hydrolysis of the platinum compound

(CH^CF^P PtCl by water to give fluoroform Is Interest- 2 2 Ing. The corresponding reaction does not occur with the complex of the phenyl-phosphine (C H ) CP P. Probably this 6 5 2 3 is due to the cis structure of the complex and'the higher basicity of the phosphine which allows the coordination - 124- -

with water forming the transition complex o ptcl {<°V2 y}2 2 This intermediate would be quite unstable and give the pentavalent compound (CH )_CP P which would split off a

N L 323 0H_ molecule of Eluorofomu The phosphine (C H ) CP P on the 6 5 2 3 other hand forms a trans complex and its weaker basicity would not permit the above reaction.

(c) Phenylbj s tri fluo romethylpho sphine and

Me thylb i s tri fluorome thylpho sphi n e: These phosphines are not hydrolysed by water at ordinary temperatures, but the latter o is hydrolysed slowly above 110 giving fluoroform and phenylphosphonous acid. Since the reaction product is the same as that obtained from the hydrolysis of tristrifluoro• methylphosphine, the reaction may be represented by the same scheme: /H C H (CP ) p+HOH- C H (CP ) P C^H^ (CF^JPOHJ -j- CP^H 6 5 3 2 6 5 3 2 N)H

HOH CgH (CP^) P (OH) C^H (CP^) P (0) H

H H / / C H (CP )P:0 : ±: C H (CP )P-0H 6 5 3 * 6 5 3 V OH OH

H / C H P=0 ^=±CH P(0H) 4- CP H 6 5 v • 65 2 3 OH 125 -

The above scheme is supported by the fact that the phosphinous acids are usually unstable and rearrange. It is not necessary that the reaction must proceed through the formation of the phosphinous acid and it Is equally likely that after the formation of the intermediate, the attack on the P-CF„ bond 3 Is much more facile and hence fluoroform is eliminated by the following scheme: HOH CCH_(CF ) P4-H0H C H (CF ) P 6 5 3 2 6 5 3 2 NQH H CH (OH) P >C H P=0 -h 2CF H 6 5 OH 6 5 S0H 3

This reaction would take place particularly in the alkaline solutions.

The hydrolysis of the phosphorane C H (CF ) PBr 6 5 3 2 2 has already been mentioned as proceeding through the forma• tion of the intermediate C H (CF ) P(OH) and HBr and the 6 5 3 2 2 disproportionation of the intermediate gives the phosphinic acid C H (CF )P(0)OH. In the presence of alkali, the hydro- 6 5 3 lysis product will be phenylphoaphonic acid C H PO(GH) . 6 5 2 C H (CF )P(0)ONa + NaOH—^C H PO(ONa) + CF H 6 5 3 6 5 2 3

A similar product has been obtained from the hydrolysis of bis trif luorome thyl phosphinic acid.. - 126 -

The hydrolysis of methylbistrifluoromethyldihalo- phosphorane has not been reported, but It is of interest to

find that the hydrolysis of bis(raethylbistrifluoromethyl• phosphine )dichloroplatinura( II ) gives only one equivalent of

fluoroform. The products have not been fully investigated

but since no fluorides are obtained, it is possible that the

reaction gives the phosphinic acid CH CP P(0)OH which might 3 3 be stable to alkali.

2. Halophosphines:

(a) Alkyl and Aryl-halophosphines: These compounds

hydrolyse to give, by simultaneous oxidation-reduction, two

products—a secondary phosphine and a phosphinic acid.

This can be explained on the basis of the above mechanism

as follows: (J) R PX4-H 0 > R P—OH ->R POH + HX 2 2 2 ^X 2 (II) R POH >R PH -f- R P(0)OH 2 2 2

In this connection it may be noted that in halophosphines

the initial attack is on the P-halogen bond with the elimin•

ation of a hydrogen halide, this being due to the higher

electronegativity of the halogens. The second step is a

rearrangement leading to the self-oxidation-reduction

process and hence the observed products. It Is only in

rare cases that the phosphinous acid R P(OH) is obtained (69c) since they usually are unstable. - 127 -

(b) Trifluoromethylhalophosphinea: The high electron- withdrawing power of the trifluoromethyl group gives a positive character to the iodine atom, thus making the latter more susceptible to attack, whereas in the case of the more electronegative halogen atoms the reaction is the same as observed for the alkyl halophosphines. By contrast with the hydrocarbon analogues the trifluoromethylhalophos- phines hydrolyse to give the phosphinous acid as required by the first step above. The stability of the phosphinous acid has been attributed to the high electron-withdrawing power of the trifluoromethyl group which reduces the ten- (122) dency of the lone pair electrons to bond with a proton , and hence the second step does not occur. However, the hydrolysis of this acid has been shown to take place under (123) certain conditions and has been discussed above in connection with the hydrolysis of (CP ) P. 3 3 (c) Phenyl trif luoromethyliodophosphine: No members of the alkyltrifluoromethylhalophosphlne have so far been reported. However, phenyltrifluoromethyliodophosphine, prepared during this investigation, hydrolyses with water according to the mechanism postulated under (2a) and gives the phosphinic acid CJK (CP )P(0)OH. However, as expected, 65 3 the hydrolysis with alkali produces the phosphonic acid CJ PO(OH) according to the following mechanism: 6 5 2 F C OH

/ C H (CF )PI+30H- \ •C H PO(OH) +- CF H-PHI C H-lP-OH 6 5 ,2 3 6 5. 3_ 6 5 \ |_ OH

The phosphoniura compounds containing alkyl or aryl groups yield a hydrocarbon containing the more electro• negative group and the corresponding phosphine oxide. Of the two phosphoniura compounds containing one CF group, + -3 the hydrolysis of only one, CH (C H ) CF P I , has been 3 6 5 2 3 studied and has been discussed already. - 129 -

CHAPTER IX

INFRA-RED SPECTRA OF THE PHOSPHINES

AND RELATED COMPOUNDS

The study of the infra-red spectra of organophosphorus compounds is of recent origin, and hence most of the assignments are only in the tentative stage. How• ever, the spectra of a large number of such compounds have been listed in this investigation, and an attempt will therefore be made in this chapter to give an approximate correlation of observed absorption bands.

It is well known that the different modes of vibration of a molecule give rise to characteristic group - 130 -

frequencies^^4] A detailed study of the vibration spectra within a group R, in compounds R-X, shows that a regular shift in wavelength is obtained as the electronegativity and the position in the periodic table of X changes^^5)

A comparison for the different elements can be found in the literature^^*^but the following table shows thie shishif; t in (126) the C-F stretching frequency of CF -X compounds 3 CF CF 01 CF Br CF I CF H 4 3 3 3 3 Frequency 1265 1210 1207 1185 1160 Electro• negativity of X 4.0 3.0 2,8 2.5 2.1

Such shifts are sufficiently consistent and from these the structure of compounds can often be deduced, Trimethylphosphine and tristrifluoromethylphos• phine both have C symmetry, so that if the frequencies 3v of one of them are assigned those of the other can at least approximately be assigned. Fortunately the spectra of (127) trimethylphosphine has been thoroughly investigated , and is supported by the assignment of the frequencies for (128) phosphine and dimethylphosphine (CH ) PH • The symmetry of the (CH ) P molecule requires 22 fundamental 3 3 vibrations. Of these, half would be doubly degenerate (E) and of the other half of the A species, four are forbidden

(A^). The remaining seven consist of two P-C skeletal modes which take care of the stretching and bending of - 131 -

this bond and the other five are the methyl group modes.

Out of the eleven E type vibrations, two are skeletal and the remaining are methyl group modes. The following table (127) gives the complete assignment of the frequencies .

Species A

CH asymmetric stretching 2970

T?2 CH symmetric stretching 2850

CH asymmetric bending 1417

CH symmetric bending 1310 v_ CH rocking or wagging 960 5 3 Vg P-C symmetric stretching 652 P-C symmetric bending

v0-v,, species A , forbidden o M 2 Species E

V,av/3 CH asymmetric stretching 2970

vIH_ CH symmetric stretching 2920

vlev/c CH asymmetric bending 1430

V,7 CH symmetric bending 1298

v,9 CH rocking or wagging 1067 3

v/tf CH^ rocking or wagging 947

•Vju P-C asymmetric stretching 717, 707

T^, P-C asymmetric bending

VA^ CH^ twisting - 132 -

The choice between symmetric and asymmetric modes is only tentative. However the interesting conclusion is that the absorption near 700 cm 'has been assigned to P-C asymmetric stretching vibration. For some time in the past, this assignment was tentative only although it was thought (129) to occur in this region . However, since C-C vibration occurs at 1100 cm ' and Si-C occurs near 800 cm"' , it is certain that P-C would occur above 800 cm"' . This is borne out by the above assignment.

In order to make' correlations for the trifluoromethylphosphines, it is necessary to know the assignments for the trifluoromethyl compounds. Fortunately some of the trifluoromethylhalides have been worked oxxt^^l These halide molecules have C, symmetry^and would give rise 3v to six infra-red active fundamental bands. Three vibra• tions would be of the species and would consist of symmetrical stretching vibration of the CE group, the 3 stretching vibration of the C-X bond and the symmetrical deformation of the CF group. The other three would be the 3 doubly degenerate vibrations of the E species and consist of the antisymmetrical CF stretching mode and two rocking 3 or bending modes. The following table gives the detailed assignments for CF I. 3 - 133 -

Band Strength Assignment Band Strength Assignment

265 (calc) E ¥- 2v A, v 1443 2 3 1

286 (()calc) v 1605 ¥ t fV. E 3 A l 1 5 449,456,461 W- v2-v3 Ax 1724 W

540 M v5 E 1818 ¥ V*2 Al

562,572,576 M 2v3 Al 1868 2v +V A ¥- 2 3 l

777 W vrv3 ^ 1855 ¥-

735,741,747 S v A 1916 W V E 2 l V 2

808 V +V A +A +E 1961 v4+vrv3 w 5 6 1 2 ¥ = E

918 ¥ + E 2137 W 2V A Wl V 1 l 1067,1073 2096 ¥- v^-V^V A 1078 S-b vl Ai L j k 2242 ¥ VA+V1 E 1019,1026 4 J-

1030 S 2203 W- E W^3

1193 W 2V2-V3 Ax 2231 " ¥ 2v4 A1+E

1185 St T4 E 2433 ¥- 2vi"V3 Al

1269 M v E 3401 W- A E V 5 ^l i"

1332 ¥ v +- E 3496 W- 3v4 A1+A2+E 1 6 W 1359 v A V 3 l

The fundamental hands are at 265, 286, 540, 743, 1076 and -i 1185 cm « The last two correspond to the symmetrical and antisymmetrical stretching vibrations of the CP group. The 3 vibrations at 540 and 743 are due to CP deformation and the 3 calculated absorption at 265 and 286 would be for C-I

stretching. - 134 -

Before considering the trifluoromethylphosphines, the CP group itself may be considered in the light of the 3 above. The CP group itself gives rise to four fundamental 3 vibrations: two symmetrical vibrations corresponding to stretching and deformation, and two antisymmetrical vibra• tions corresponding to similar modes. The atom or group bonded to the CP group would also give rise to two vibra- 3 tions — symmetrical stretching of. CP -X and the rocking of

• s-r 3 the X against CP . The result of the study of the CP -X 3 3 stretching vibrations shows that the interaction between the two modes of vibrations is small and hence it is con• cluded that the CP group is a "stiff or rigid group^3"*"! 3 This would imply that the fundamental vibrations- due to a CF group would not be greatly different from molecule to 3 molecule. This is indeed found to be the case in most of the compounds studied. Since for a full treatment of the spectra, the mathematical discussion becomes very involved, approximations have been suggested. The following table gives the observed bands. (CH,j P Strength (CH ) P Strength 3 3 3 3 2970 (M) 1298 (W) 2920 (M) 1067 (W) 2850 (M) 960 (M) 1430 (M) 947 (W) 1417 (M) 653 (M)

1310 (M) - 135 -

(4) CP PI 3 2

Abs. Strength

1272 M 1157 S 1142 S 1111 s 1072 M 737 S

(4)

(CF )2P I

Abs. Strength Abs. Strength

2252 M 1119 M 2217 S 1029 M 1273 M 951 W 1256 ¥ 854 W 1203 S 798 M 1183 M 748 S 1162 S 746 S 1131 S 714 W

(4) (CP ) P - 3 3

Abs. Strength Abs. Strength

2444 W 1492 ¥ 2298 M 1390 M 22 42 M 1345 M 1934 ¥ 1308 M 1904 ¥ 1277 M 1798 ¥ 1230 S 1751 M 1183 S 1680 ¥ 1153 S 1647 W 1127 S 1587 ¥ - 136 -

(CP ) P 3 3 (Continued)

Abs. Strength Abs. Strength

1041 M 844 W 1023 M 797 W 966 M 754 S 923 M 726 M

As in trimethylphosphine, the trifluoromethylphosphines will have vibrations corresponding to the skeletal and trifluoromethyl group stretching and bending vibrations* Since the P-I stretching vibration lies outside the scale of the common instruments 300 cm , the diiodophosphine CP PI might serve as the best starting point. In trifluoro- 3 2 iodomethane, the absorptions at 1076 and 1185 are considered as the symmetrical and antisyrametrical vibrations of the CP group. By analogy, the absorption at 1111 cm 'in 3 CP^PI^ may be assigned to the symmetrical vibrations and tKose at 1142 and 1157 may be taken as corresponding to the doubly degenerate vibration at 1185 observed in CP I. The - 137 -

-I absorption at 737 cm may be taken as due to the CP defor- 3 mation mode, since the same appears in compounds other than those containing phosphorus. However, the P-C stretching vibration is also expected to appear in this same range. A detailed study is necessary to settle this point but the presence of this vibration in a large number of compounds not containing phosphorus does indicate that it is a CF 3 deformation mode. The remaining absorptions observed in CF,PI_ are possibly the combination modes. 3 2 As more trifluoromethyl groups are attached to phosphorus, the spectra will become complicated because the skeletal vibrations would come into play. Moreover a split• ting of the characteristic frequency would be expected because of the presence of two equivalent groups. Such splitting is observed in molecules with two or more equi• valent bonds. The splitting depends on the resonance or coupling between the equivalent bonds. And, in general, the larger the coupling the larger is the splitting. In the case of trimethylphosphine the characteristic stretch• ing frequencies occur at 2970, 2920 and 2850 cm 1 Similar - 138 - splitting would be expected in the case of bistrifluoro- mehtyl and tristrifluoromethyl-phosphines. It is observed that for two CF, groups the splitting is into three bands, 3 and for three CF groups it is split into four bands. In 3 the absence of mathematical treatment, it is difficult to assign a particular band to a definite mode. All that can be said is that the bands at 1203, 1162 and 1131 cm"'ob• served for (CF,) PI are due to the stretching vibrations of the CF, group. Similarly, in the case of (CF ) P there are 3 3 3 four strong absorption maxima at 1230, 1183, 1153 and 1127, and again these are due to the stretching vibrations of three CF groups. 3 _i The absorption for (CF,) P at 754 cm is strong 5 3 and may be attributed to the antisymmetric deformation mode. Since the difference in the symmetric and antisymmetric deformation modes is quite large and since calculations for the branching of a parallel deformation band does not indi• cate a splitting into submaxima of more than 15 to 20 cm ' , the other band of medium intensity at 726 may be attributed to the P-C stretching vibration. The rest of the bands may be connected with the different combination bands, as shown in the case of CF_I. 3 The above discussion of the vibration spectra of

CF^PIg, (CF^JgPI and (CF^P simplifies the correlation for - 139 -

the methyl-trifluoromethyl phosphines. Since (CH^) P and (CF,) P both have the same symmetry, the other phosphines, 5,3 via., (CH ) CF P and CH (CF ) P, are also expected to have 3.2 3 ,3 3.2 the same symmetry, and hence the same relations should apply. The following table gives the absorption maxima of the methyl-trifluoromethyl phosphines.

(CH3)3P

Abs. Intensity Abs. Intensity 2970 M 1298 ¥ 2920 M 1067 M 2850 M 960 M 1430 M 947 ¥ 1417 M 940 ¥ + 1310 M 653 M

Abs. Intensity Abs. Intensity

2995 M 1175 VS 2934 • M 1125 VS 2840 M 1118 VS 2290 ¥ 955 M 2240 •w 906 M r+" 1440 M 876 M 1425 W 755 ¥ 1378 ¥ 745 W 1310 ¥ 725 M 1305 ¥ 680 ¥ 1295 - 140 -

CH (CP ) P 3 3.2

Abs. Intensity Abs. Intensity

2985 W 1203 VS 2934 ¥ 1167 VS 2825 ¥ 1143 s 2290 ¥ 1115 vs 1465 M 912 M 1375 M 892 1307 M 821,836 ¥ 1283 M 750,745 M 705 M

One of the characteristic features of the spectra of these phosphines is that the shapes of the bands at 900-960 in the three phosphines is the same; for(CH ) P 3.3 at 960 and 947, for (CH ) CP P at 955 and 906, and for • 3.2 3_| CH (CF ) P at 912 and 892 cm i This has been attributed •'-'^ - — - - -s - - - the stretching modes of the trifluoromethyl group are as expected from the above consideration. Thus for the phos• phine (CH ) CF P the bands at 1118 and 1125 may be attri- 3.2 3 buted to symmetrical stretching, and the bands at 1175 (by analogy with CF I) to the antisymmetrical mode. 3 Similarly for CH (CF ) P, the bands at 1115, 1167 and _| 3 3.2 1203 cm may be attributed to splitting, due to two CF 3 groups. The asymmetric deformation of the trifluoromethyl groups occur for (CH^CF P at 725, and for CH (CF ) P-at 745 and 750 cm"1. - 141 -

A third feature which is noticeable is the shifting of the

P-C stretching vibration with successive introduction of

the CP groups. These bands are well marked, and can be 3 easily distinguished from the CP^ deformation vibrations.

Thus for (CH ) P, it is at 653, for (CH )_CP P at 680, and 3 3 3 2 3 for CH (CP ) P at 705. Another feature of the spectra of 3 3 2 these phosphines is the diminution in the intensity of the

CH stretching frequency with the successive replacement of 3 groups, as would be expected. For the phenyl-trifluoromethyl phosphines, the same methods may be applied. However the behaviour of the phenyl group is somewhat different from the methyl group, in that the former has more than one characteristic absorption. In general, the vibrations characteristic of the aromatic ring remain unaltered when attached to another element, and hence the presence of the ring can be easily established. For the phenyl ring the C-H stretching vibration occurs at 2940 cm ', and the C-H deformation vibration at 1470-1370. In the phosphorus compounds studied during this investigation, the deformation fre• quency Is invariably at 1435-1445 in the form of an intense sharp band, and Is accompanied by two other sharp bands of weaker intensity—one at 1490 and the other at 1590 cm '.

The prominent feature of these two absorptions is that their - 141 -

Plate No. 1.

Pig. No. 1. Phenyl trif luorome thyl iodopho sphine,,

Pig. No. 2. Phenyltrifluoromethylphosphinic Acid. Plato No. 2. _ 141 _

Fig. No. 3. Dimethyltrifluoromethylphosphine.

Fig. No. 4. Methylbistrifluoromethylphosphine.

Fig. No. 5. Phenylbistrifluoromethylphosphine.

i ! i - 142 -

intensity (and usually not their position) varies from molecule to molecule, and is found to depend in some way

on the other substituents on phosphorus. These two vibra•

tions consist of a "lateral dilation and contraction of the

ring 9 produced mainly by stretching and compressing of the

C-H bond"^"^l The absorption which is said to be very sen•

sitive to the substituent on the phenyl ring (phosphorus (136) in this case) is said to occur at 1045-1185 • However there are three bands appearing in this region: (1) 995" 1005, (2) 1030, (3) 1070 cm"; each of them due to a different mode. These are found to be constant both for the compounds (129) studied here and for those reported elsewherev i The other absorptions due to the phenyl ring also appear at.constant frequencies: e.g., those at 690, 770-740 are due to out of plane vibration and hence need not be discussed further. There are however some weak absorptions between 1050 and 1175 due to hydrogen bending vibrations.

These appear in practically all P-phenyl compounds with varying intensity. In trifluoromethyl compounds however they are probably hidden by the strong CF, stretching vlbra- 3 tions and are not observed. The superposition of the phenyl group frequencies on those of the trifluoromethyl group allows a correlation of the spectra of the phenyl-trifluoromethyl phosphines. - 143 -

The following table gives the absorption maxima of these phosphines:

*C H CP PI 6 5 3

Abs. Intensity Abs. Intensity Abs. Intensity Abs. Intens:

3060 W + 1690 W + 1335 ¥ 1025 M

2900 W 1675 ¥ 1310 ¥ 1000 M 2340 ¥ + 1660 ¥ 1270 ¥ 830 ¥ •

1880 W r 1585 W + 1210 M 745 S

1800 W- 1490 W+ + 1150 S+. 715 ¥

1725 w- 1740 M 1115 s+- 690 S 1710 ¥- 1385 ¥ 1070 M

(C H ) CP P 6 5 2 3

3060 w +• 1585 ¥ +- 1150 S + 845 ¥ 3000 V 1570 ¥ - 1105 S + 800 ¥

2910 w - 1485 W + +- 1070 M 745 S

2240 W = 1440 M 1027 W-H + 720 ¥

1965 ¥ 1385 ¥ 1000 ¥ + 695 S 1880 W 1325 ¥ 970 W

1810 ¥ 1310 ¥ 915 ¥ 1660 ¥ 1275 ¥ 875 W

C6H5(CF3)2P

3080 1870 ¥ 1730 1660 ¥

2920 ¥ 1835 ¥- 1715 ¥ 1645 ¥

2320 W + 1810 ¥- 1695 ¥ 1635 ¥

2220 W = 1770 ¥- 1680 ¥ 1615 ¥ 1980 tf ~ 1745 ¥- 1670 ¥ 1590 ¥ + - 144 -

e H (CP ) p (Continued) 6 5- 3-2 Abs. Intensity Abs. Intensity Abs. Intensity

1575 W- 1390 ¥ - 1030 tf+ 4-

1570 W= 1330 ¥+- 1000 M

1555 ¥= 1265 ¥' 875 W +

1540 ¥- 1190 S + 805 M

1507 ¥ 1170 s 750 S

1490 W + 1140 s + 745 s

1475 ¥- 1100 s H- 690 s

1445 M 1070 M 700 M (sho 675 ¥

The best compound to consider first is the iodophosphine C H (CP )PI, since further substitution either 6 5 3 with CF or phenyl gives more complex spectra. The spec- 3 trum of this compound is not markedly different from what would be expected of a combination of trifluoromethyl and phenyl group frequencies* There are two strong bands at

1150 and 1115 cm1 corresponding to the stretching fre• quencies of the CF group. The absorption at 1115 cm 1 may 3 be assigned to the symmetrical stretching and that at 1150 to the asymmetric mode, by analogy with CF,I. The stretch- 3 ing and deformation frequencies of the aromatic C-H are unaltered and so are those fo-r1 the out of plane vibrations, which occur at 745 and 690 cm The remaining maxima may - 145 -

be assigned to the various combination modes, except the P-C vibration which appears as a weak absorption at 715 om '.

A fact which is conspicuous in this spectra is the predomi• nance of the phenyl group frequencies. Thus all the absorp•

tions characteristic of a monosubstituted benzene ring are present here, but those of the trifluoromethyl group are not observable except, of course, the CP stretching* The 3 CF deformation vibration is missing, possibly overlapped 3 with the out of plane vibrations of the benzene ring. The C-F overtone which is quite marked in other trifluoromethyl phosphines appears as a.very weak absorption. The spectrum of diphenyltrifluoromethylphosphine similarly shows strong absorptions characteristic of the phenyl group. Thus,except the CF stretching vibrations 3 at 1105 (due to symmetric mode) and 1150 (due to asymmetric mode), the remaining maxima resemble those of triphenyl• phosphine. Most of the maxima have even the same shape as (41) that of triphenylphosphine • The CF overtone occurs as -I 3 a weak absorption at 2300 cm and the P-C stretching and CF^ deformation vibrations do not appear in the range studied. One marked feature of the spectrum of this com• pound, and also of the other phenyl-trifluoromethyl-phos• phines, is the absence of the P-C stretching vibration from the observed range. This will be discussed later. - 146

Phenylbistrifluoromethylphosphine may be expected to show most of the frequencies of the trifluoromethyl group. The spectrum consists of a series of weak maxima, some of which can be traced back to the CP group, as 3 seen in the case of CP I. Thus the C-F overtone appears -! 3 at 2320 cm , the CP^ stretching frequencies are of course present and appear at 1190, 1140 and 1100. The second of these maxima is diffuse and is actually a doublet. The deformation frequency of the CP group does not appear again, 3 and,since it has not been found in any of the phenylphos- be

phines considered so far, it mayAconcluded that It is ob• scured by other bands. The P-C stretching vibration, which for the phenylphosphines appears at 715* also cannot be detected In the spectrum. It has been suggested that the shifting of the P-C to higher frequency is similar to the shift of P-0 with electronegative substituents. Thus It is not observed in triphenylphosphine,also. The common feature of the phenyl-trifluoromethyl- phosphines may be described as the predominance of the aromatic ring vibrations. This may be compared with the spectrum of CH (CF ) P, in which the intensity of C-H 3 3 2 stretching is of a low intensity. The shapes of the bands -I in the 1470 to 1370 cm region is worth noting. In phenyltrifluoromethyliodophosphine and diphenyltrifluoromethylphosphine the intensity of the band at 1590 is greater than at 1490 cm ', but In phenylbistrifluoromethylphosphine they are comparable. A similar reversal takes place in the - 147 -

case of substitutions of more electronegative groups: e.g., in phenyldichlorophosphine G _H PCI and benzenephosphonic 6 5 2 acid C H PO(OH) . This is particularly true of pentavalent 6 5 .2 phosphorus compounds: e.g., (C H )P(0)C1, triphenyl 6 5. phosphate, etc.

The spectra of the phosphonium compounds has not been treated separately so far. The infra-red studies for these compounds appear to be quite interesting, since there is usually a marked shift from the parent phosphines. This would be expected from the change in -the structure of the ,(137) compounds. The phosphonium compounds have a tetragonal structure with a D symmetry. As observed in other struc- 4h ture changes, the tendency would be a shift towards shorter wave-length. In the case of PH I and PH , the fundamental 4 3 -I P-H frequencies are observed at 2372 and 2280 cm , and 2421 and 2327 cm ' respectively. The following table gives the spectra of some of the phosphonium compounds prepared during this investigation.

(CH ) PI * 3 4

Abs. Intensity Abs. Intensity 2970 M 1280 W 2920 W 1150 W- 2850 W 1045 w- 2050 w 970-940 S (diffuse) 1545 w 860 W . 1450 M 780 w 1375 M 770 M

* Nujol Mull **KBr Pellet Plate No. 5. - 147 -

Pig. No. 7. Methyldiphenyltrifluororaethylphos- phoniura iodide.

Pig. No. 8. Methyltriphenylphosphonium iodide.

Fig. No. g. Methyldiphenylphosphine oxide.

Fig. No. 10. Dimethylbistrifluoromethylphosphonium iodide. - 148 - (CH ) (CP ) PI 5 2 5 2 Abs. Intensity Abs. Intensity Abs. Intensity

3020 M 1350 M 2970 ¥ + 1300 M*- 980 s 2320 ¥ 1210 M 920 M 2220 ¥ 1180 St 890 Shou] 1500 ¥ 1150 M 850 ¥ 1450 M 765 M 745 S

;H (c H ) PI 3 6 5 3 Abs. Intensity Abs. Intensity Abs. Intensity

3020 ¥ 1685 W 1305 W 2980 ¥ 1640 ¥ 1180 ¥ + 2910 W-f- 1610 ¥ 1160 ¥ + -<- 2860 ¥ -f 1580 M 1110 S 2720 ¥- 1570 ¥-•- 1070 2325 ¥ 1555 ¥ 1025 ¥ 2300 ¥ 1535,1545 ¥- 995 M 2200 ¥ 1480 ¥ + ->- 920 M + 1830 W 1465 ¥ 915,905 M +• 1815 ¥ 1435 M +• 855 ¥ 1780 ¥ 1395 ¥ + + 785 M 1725 ¥ 1335 ¥+ 750 S 1705 ¥ 1325 W + 715 M 690 S CH,(C^H )^CP PI^*- 3 6 5 2 3 Abs. Intensity Abs. Intensity Abs. Intensity 3120 ¥ 1680 ¥ 1300 ¥ 3000 ¥ 1665 ¥ 1180) S 2920 M 1640 ¥ 1170) S 2860 ¥ + 1616 ¥ 1105 s 2320 ¥ 1585 ¥+-+- 1110 M + 2250 ¥ 1570 ¥- 1095 W-f- 2200 ¥ 1555 ¥ 1030 ¥ 2000 ¥ 1535,1530 ¥ 995 1835 ¥ 1505 W 920 M + 1825 ¥ 1485 ¥ + 915 M + 1805 ¥ 1470,1465 W 795 W+4- 1765 ¥ 1440 M 755 •M 1715 ¥ 1405 ¥ 745 M 1710 ¥ 1340 ¥+ 725 ¥-H 1690 ¥ 1325 ¥ + 685 M +

Hujol Mull **KBr Pellet - 149 -

It can be seen from the above table that the characteristic frequencies have shifted to shorter wave lengths. This is particularly apparent In the phenyl- phosphonium compounds. The C-H (aliphatic), C-H (aroma• tic) stretching frequency, the phenyl group out of plane vibrations, and also the trifluoromethyl stretching fre- -I quency are shifted 10-30 cm to shorter wavelength. One of the most characteristic features of the phosphonium compounds, or in general the quadruply connected aromatic phosphorus compounds, is that the P-C stretching fre- -I quency appears as a strong band at about 720 cm • The band at 725 cm' in CH (CH ) CP PI and at 715 cm"' in 3 6 5 2 3 CH -(C-H,.) PI are attributed to this absorption. A simi- 3 6 5 3 lar effect is noted in the case of triphenylphosphine oxide and methyldiphenylphosphine oxide, for which this absorption occurs at 720 and 710 respectively (observed during this investigation). It is known that the electronegativity of the substituents markedly shifts a particular characteristic absorp• tion. This has been illustrated for the phosphoryl group P^O. With three highly electronegative substituents, the P=)0 frequency lies at 1300 (for (CP ) PO it occurs at -I 53 1325 cm ). For two electronegative substituents, it occurs - 150 -

at 1260; and for one it occurs at 1230, e.g., in (C H ) P0C1. 6 5.2 For substituents such as phenyl and methyl groups, it occurs -I (129) at 1190 and 1176 cm respectively . For methyldiphenylphosphine oxide it occurs at 1175, and for silver phenyltrifluoromethylphosphinate it occurs at 1225 cm\ Since the acidity of substituted phosphorus acids depends on the electron-withdrawing effect of the substituents, It would appear that phenyltrifluoromethylphosphinic acid with one phenyl group is not a strong acid, compared with trifluoromethylphosphonic acid whose P = 0 occurs at 1300, Rather, its acidity would be comparable with the aryl or alkyl phosphinic acids. It may be mentioned that the P-C stretch• ing frequency appears at 715 cm1 although it is, absent in CJL_('CF ) P. 6 5 .3.2 The question of the appearance of additional frequencies with the .expansion of valence shell brings us to the consideration of the spectra of the complexes. This is indeed observed to be the case, for in the phenyl phos• phine complexes of platinum(Il) chloride and boron tri• fluoride a new band appears in the expected region. The following table shows the P-C (aromatic) absorption of the complexes. Pig. No. 11. Trimethylphosphine-boron trifluoride.

Pig. No. 14. Triphenylphosphine-boron trifluoride. - 151 -

C H (CP ) P PtCl 705 65 322 ;2 700

(C H ) CP P.BF 700 6 5 2 3 3

715

/I 715 C 6 H 5 CP_P.B3 P3

This absorption may therefore be taken as the characteristic of the quadruply connected phenyl-phosphorus compounds. This is borne out from a comparison of the spectra of the twenty-one phenyl phosphorus compounds (quadruply connected) reported by Daasch and Smith, twenty containing sharp and strong maxima, while the remaining one has not been com• pletely studied. The trivalent compounds reported have -I . weak or no absorption in this region (700 cm )• The other observations regarding the complexes are as follows: the boron trifluoride complexes of the phosphines have all the absorptions characteristic of the phosphines but do not have any corresponding to those of boron trifluoride. A strong and broad band appears in the region 1175-1200 cm '. That the strong absorption results from the change of symmetry due to complex formation and not to a reaction with any of the groups on phosphorus is suggested by the following facts: -152-

1. '-' The phosphine can be liberated from the complex on treatment with water. In the case of trifluoromethyl substituted phosphines fluoroform is evolved on such treatment. 2. The CP^ stretching frequency would be shifted to longer wave lengths as observed in the case of reaction

with trimethyltrifluoromethyltin which gives CP3BP5 and whose C-F stretching frequency is shifted to 962 from

110imn0 .n,-cm •1 (158)

3. The I.R. spectrum does not reveal any RVjO ab• sorption. It is therefore likely that the strong absorp• tion may be due to a change of symmetry of the boron trifluoride molecule. In the case of ketone-BP^ complexes also, similar bands have been noted (139) and have been interpreted as due to the coordinate bond B-*0. A com• parison of the spectrum of the phosphine complexes from the following table (which gives only the Important maxima) shows that most of the features are common.

(CH3)3P.BP3

3000w 2900w 1425W I310w,+V I300w- 1125s 1085s 1060s 1037s (1125-1037) 970m 785w+- 772w 705w 675w Strong and broad

(CH3)2CP3P.BF3 3100W+- 3000W4- 2300w- 1430w+ 1320m 1240W+-

1175s (1175-1025 strong and broad) 970m 925ra 885m

820W+ 780w 765w 750w 725w 705ra 675m - 153 -

3150W 3050w + 295OW 2300w 1975w 1900w

1800w 1590w 1530W- 1475* 1440w 1315w-t- 1220m 1175m + 1150s 1125s 1095s (broad)

1070m + 1030m 995m 900m + 870-835 (broad) 790w 745s 700m + 690s I ) P.BP 5 3 3 3250m 3150w +• 3050w 2400w 2325w 1950w

1875w 1800w 1700w 162 5w 1575w + 1475w +

1435m 132 5w 1300w 1235w 1180w + 1160w +

1110a 1075-1085s IO3O-IO5OS 1000m 910m-t- 885ra 770s (755w,750w) 740s 725w 715m 695s 680ra

The above table shows/_th'at the C-H aliphatic or aro• matic is shifted to lower wavelength. The P-C stretch- j ing frequency for the methyl phosphines remains approximately the same. The best resolution for the strong absorption at

- 1100 cm ' is that for the compound (CH )0CP P.BP , which 6523 3 gives three maxima, 1150, 1125 and 1095. The CF, frequencies 3 do not seem to have changed and an overlapping absorption seems to have come in. The spectrum of (C H ) P.BF shows an _l . 6 5 3 3 absorption at 1110 cm . A comparison with the methyl phos• phines shows that they also absorb strongly at 1125. There are other frequency shifts which occur in the boron trifluo• ride complexes. The weak absorption at 785 cm ', for instance, is common in all phosphine complexes, but appears neither in boron trifluoride nor in the phosphines themselves. This may be attributed to the P-*B bond. -5-54-

The spectra of the platinum(II) chloride complexes do not differ very much from those of the parent phosphines. The following table lists the absorption maxima of the complexes studied.

[(CH3)3P] vPtClr 2960w 2985w 2810w- I428w+ 1420w +

1315W+ 1298m 1283w-»- 975m 956m + 862 , 868w + 745w+ 731w 680,670w

[(CH3)2CP3P]2PtCl2

2995w 2915w-«- 2850w- 1445w- 1430w+

1405w+ 1315w+ 1293w-«-+ 1182s 1135,1120s

965m $22m + 866m 758w + 748W+ 720w +

[CH3(CF3)2VtCl2 3010w 2920w 2840w - 2320w- 14l2w + 1308w + 1287w 1202s 1170s 1130s 913m +• 898m 760,755w 740w

It is observed that for'(CHj) P and (CH3)2(CF3)P complexes no shift in the C-H stretching frequency occurs, but for CH_(CF,) P a shift of 30 cm"1 occurs towards 3 3 2 shorter wave-length. The CF3 stretching frequency is un•

altered. The CH3 rocking frequency shifts to shorter wave-length in the case of (CPL) P and (CH ) CF P by 3 3 3 2 3 J 16-30 and 10-16 respectively, but is unchanged for CH,(CF_) P. The P-C stretching frequency is found to be 3 3 2 shifted to shorter wavelength in all cases. For (CH,) P 3 3 it is shifted by 25, for(CH5) CF P by 40, and for 1 23

CH3(CF3)2P by 35 cm" . Fig. No. 15. Bis(diphenyltrifluoromethylphosphine)dichloroplatinum(II).

Fig. No. 16. Bis (phenylbis trifluoromethyl phosphine )dichloroplatinum(II).

Fig. No. 17. Bis(phenylbistrifluoromethylpbosphine)dichlorodibromoplatinum(IV). -155-

The following table gives the spectra of the phenyl-trifluororaethyl-phosphine complexes.

_(C6H5)2CPgPJ 2Ptci2

3075w 2940w + 2350w 1960w - 1900w - 1825w- 1725w 1660w 1600w + 1590w +- 1550w 1480w + 1430m 1390w + 1325w + 1280w + 125 5w 1170s 1130s 1105m + 1075m 1060m 1035w + 1020w +• 995w-t- 970w- 900w - 835w + 805w -t- 745m 715m 690m +

Pi PtCl J2 2

3075w 2985w- 2350w - 1960w- 1890w- 1800w- 1590w- 1475W4- 1430m 1370w 1315w + 1300w 123 5w 1150s 1120s 1095s 1065m 1030m 1020m 995m

970w 925w 840w 785w 740m + 705m 685s

It is observed that inthe last case there is a shift in the CF^ stretching frequency. For diphenyltrifluoromethylphosphine the shift is 25 cm"l towards shorter wave-length, and for phenylbistrifluoromethyl• phosphine the shift is 40 cra~l towards longer wave-length. -156-

The effect may possibly be due to interactions of the substituent groups. The other characteristic frequencies of the phenyl groups are found to remain unchanged. This is in contrast with tile methyl-phosphines where the CF^ frequencies are unaltered and the methyl vibrations suffer a change. The other interesting feature of these complexes is the appearance of the P-C (phenyl) absorption which has already been pointed out. -157-

Q a A | J | R |X

CONCLUSIONS

It is clear from the foregoing discussion that one effect alone does not explain all the properties of the phosphines under study. Among the various effects that have been called upon to explain the different properties, electronegativity, the Inductive effect, and the steric effect of the CF^ group have been considered as factors responsible for the many observations. Per• haps the most Important of these is the inductive effect of the electronegative trifluoromethyl group, which decreases the availability of the lone pair electrons on the phosphorus atom. In effect this increases the "electronegativity" of the complete phosphine molecule. -158-

Kagarise ^^'^has used an empirical equation for the calculation of the electronegativity of groups. His equation for a group A(x,y,z) containing three atoms (x,y,z) attached to a central atom A is of the type:

x(eff,= ^ + _i_(Xx+x^Xz)

Extension of this equation to the phosphines would give a rough estimate of the "electronegativity" of the phos• phines. Such values have been calculated for the phos• phines studied during this investigation, and are reported in the following table. In preparing this table, the electronegativity of the trifluoromethyl, phenyl, and (|0 2.7, and 2.3. Phosphine Electronegativity Phosphine Elec tronegatIvi ty

(CF5)3P 2.70 (CH3)3P 2.25

(CP5)CH3P 2 2.53 (C6H5)3P .40 2. (CP3)2C6H5P 60 PP3 3.05

CF3(CH3)2P 2.37 PCI3 2.55

CP3(C6H5)2P 2.50 PH3 2.10 This approximation shows that the phosphines with electronegative substituents such as the phenyl and trifluoromethyl groups will behave like the trihalides of phosphorus. This is Indeed found to be the case. Such electronegative groups will also affect the electron density on the central atom. A rough estimate of this factor can be obtained from the electronegativities of the - 159 - atom A and the substituent'X attached to A by assuming that the bonding electrons will be divided between A and X in the (141) ratio of their electronegativities • For a single bonond the number of electrons on A in A-X would be given by; ? *A+ %' and for A in A(x,y,z) by:

XA *X ^A^^Y XA*XZ The following table gives the number of bonding electrons n in the three covalent bonds on P in the various phosphines. Phosphine n Phosphine n

(CF ) P 2.33 (CH3)3P 2.86 3,3

(CF ) CH P 2.51 (C6H5)3P 2.62 3 2 3

(CF3)2C6H5P 2.43 PF3 2.06

GF3('CH )2P 2.69 PCI, 3 2.47

CF3(C6H5)2P 2.53 3.00 It will be seen from the above tables that general trend of reactivity is borne out. It may be general• ised that phosphines with an electronegativity higher than 2.50 would not normally be reactive towards Lewis acids. Deviations from this generalisation may be explained on the basis of the various effects enumerated earlier. The anomalous behaviour of phosphine PH, has been explained 3 as due to the difference In the degree of hybridization (142) of the phosphorus atom , and has been considered earlier in explaining the reactivity of the above-mentioned phos• phines with boron trifluoride. Similarly the unexpected -160- reactivity of the other phosphines towards Lewis acids can be explained on the basis of the pi-bonding charac• ter. The ability of PCI and PF to form compounds 3 3 PCl_.BBr_ and PP_.BH, is an example of this type. Hence 3 3 3 3 this generalisation concerning the relation between electronegativity and reactivity of the phosphines must be , used with Caution. Many of the properties of the trifluoromethyl-phosphines e.g. complex formation must be explained dn terms of steric effects together with the possibilities of pi-bond formation. It is clear then that the perfluoroalkyl groups and the trifluoromethyl group in particular, because of their unique combination of size and electronegativity, impart interesting and unusual properties to the molecules of which they form a part. It can be seen from the fore• going discussion and also from the calculated electronega• tivity that with the gradual introduction of the trifluoro• methyl group, the availability of the lone pair electrons is reduced and hence donor properties of phosphorus are diminished. Much further study, particularly of a quan• titative nature is needed to fully understand these char• acteristics. EXPERIMENTAL - 161 -

I EXPERIMENTAL METHODS

1. General Techniques Most of the compounds studied were volatile in nature and in many cases reacted with air and moisture. Consequently they were manipulated in a conventional vacuum system. The system was of Pyrex glass and consisted of a number of traps for fractional distillation, large bulbs for storage, cold finger, molecular weight bulb, manometer, and several inlet points. A "Duo Seal Hi Vac" pump was used in conjunction with a mercury diffu- -4- sion pump to give a vacuum of 10 mm, which was satisfac• tory for most purposeso A volatile compound was introduced into the system by freezing it in liquid nitrogen, pumping off the air within the tube or container holding the material, and then allowing the compound to slowly expand into the system. For fractionation, mixtures of volatile compon• ents were passed through a series of traps which were cooled to different temperatures. The cooling was effected by surrounding each trap with a slush bath, which was pre• pared by cooling an appropriate organic solvent to its freezing point with liquid nitrogen. For a satisfactory fractionation by this method, it is necessary that the volatile mixture passes at a pressure of 1 - 5 mm and -162- o that the boiling points are at least 20 apart. In most cases separation had to be repeated a number of times to obtain a pure product. Molecular weights of gases were obtained by Regnault's method. The gases were allowed to expand into a bulb of known volume (208 ml) and the pressure was noted from the manometer. The molecular weight was calculated from the mass, volume, pressure, and temp• erature by applying the gas law. Most of the reactions were carried out in Garius tubes which were constructed with a thick-walled capillary at one end. After evacuation of the tube, the reactants were condensed into It by freezing the end of the tube in liquid nitrogen, and the capillary was sealed. When the reaction was complete, the tip of the Carius tube was broken inside an evacuated length of rubber pressure tubing, and the volatile components fractionated into the vacuum system. Pinal purification was frequently effected by distilling the products in a still of approximately 5 ml capacity and 8™ column outside the vacuum system in an atmosphere of nitrogen. The appropriate fractions were purified for -J63- analytical purposes by vapour phase chromatography using a 10' column of "Ucon polar", a silicone type packing. A small amount (10 ml) of the distilled sample was in• jected for a test run on to the column which had been heated to the required temperature. The flow of the different components was recorded and the elution time of the main component was determined. A large amount (0.25 ml) of the sample was then injected and the main component(i); ; collected in a cooled collector. By control• ling the temperature of the column at about the boiling point of the desired product and maintaining a steady flow of helium, complete separation of the components was effected.

Melting points were recorded by direct obser• vation under a magnifying glass. Boiling points were determined by the inverted capillary method, and also by plot• ting the vapour pressure against the inverse of temper• ature (•VT) an(* extrapolation to a pressure of 760 mm, taking values close to the boiling point. The vapour pressure was obtained by using an isoteniscope and re• cording- the pressure from manometers. An effective control of temperature is therefore necessary. The constant tem• perature bath for the isoteniscope was of paraffin oil -164- heated with an electric immersion heater. The heat was o controlled toil by using a thermal regulator. Substances which were reactive towards air and moisture were prepared In the bulb of the isoteniscope. For the manipulation of involatile substances reactive towards air and moisture, a dry box was used. A steady stream of nitrogen swept through the box in which a fresh surface of phosphorus pentoxide was left exposed. 2. Analytical Methods 2a. Analyses for carbon, hydrogen, fluorine, and phosphorus were made by microchemical methods ( by Dr. Alfred Barnhardt). Determinations of the halogen contents of the platinum(Il) halide complexes and of the t t ammonium chloroplatinate. 2b. The trifluoromethyl group of the phosphorus compounds can be easily hydrolysed to give fluoroform quantitatively. This was frequently used as a method of , identification of the compounds as well as for analysis. -165-

20 ml of 10 -20$ aqueous sodium hydroxide were placed in a Pyrex tube and the dissolved air removed, by pumping in vacuum. The sample was then weighed and sealed in small evacuated tubes, which were sealed with the alkali solut• ion and broken inside the large tube. In most cases the o reaction tube was heated to 80 for 24 hours. The fluoro• form was then purified by fractionation and weighed in the molecular weight bulb. The infra-red spectrum and the molecular weight were considered sufficient for the iden• tification of fluoroform. Acidification of the remaining alkaline solution usually gave an acid or its salt which was Identified by its melting point and from its infra• red spectrum. 5. Infra-red Spectra The determination of infra-red spectra was a very convenient means of identification of the compounds and/or mixtures. The presence of a trifluoromethyl group for instance was indicated by the strong absorption in the 8 -9/o region. Since the spectra of the different com• pounds differ from one another in this finger print region, impurities ( e.g. fluoroform in trifluoroiodomethane ) could easily be identified. The spectra of the purified compounds were -166- recorded on a Perkin Elmer model 21 recording spectro• photometer, while for preliminary identification use was made of the "Infracord". Both are double beam instruments, fitted with rock salt optics. The spectra of the volatile compounds were taken by enclosing the sample at a known pressure in an evacuated 10 cm gas cell, and those of li• quids by pressing them between rock salt discs to give a capillary film. For solids, either a mull was prepared with nujol or hexachlorobutadiene, or a potassium bromide (124) pellet was used. The pellet technique was preferred, since only a small sample was needed. 4* Ultra-violet Spectra Absorption spectra in the visible and ultra• violet regions were recorded on a Cary model 14 spectro• photometer. The cells were of fused quartz and their absorption path lengths were either 1 or 10 mm. All sol• vents were of A.R. grade. For solutions which decomposed on standing, the recording was taken first with a more concentrated solution for a test run and the different absorption bands were resolved by taking dilute solutions. 5. Magnetic Susceptibility ^1 7 ^ These measurements were made on a Gouy magnetic balance which was sensitive to changes of ±0.00002 g. The -167- current through the electromagnet was. regulated within 0.001$. The susceptibilities were measured at room tem• perature.; only. Solid, samples were finely ground and packed to a height of 2.5 to 4 cm in tubes of 3*5 ram diameter and 15 cm in length. With careful packing, the packing error was reduced to less.than 3%* The apparatus was calibrated with benzene. 6. Dipole Moment These measurements were made with.a simple Slbarch dielectric constant meter. Standard solutions were prepared by dissolving the compounds in reagent grade solvents which were dried by the standard methods• The solvents used were chloroform, benzene, and carbon tetrachloride. Chloroform was dried over calcium chloride, benzene over phosphorus pentoxide, and carbon tetrachlor• ide over potassium sulphate. The dipole moment of the compound was calculated to an accuracy of ±0.5 D from the dielectric constant of the solution and the solvent. -168-

II PREPARATION OF THE PHOSPHINES

1 a. Preparation of Trifluoroiodomethane For the preparation of silver trifluoroacetate, silver oxide (lOOg) was treated with a 50% aqueous sol• ution of trifluoroacetic acid (100 g). After the unreacted silver oxide had been removed by filtration, the solution was concentrated in vacuo and the solid finally dried over phosphorus pentoxide. The yield was quanti• tative (180 g). 1 b« Silver trifluoroacetate (110 gj was intimately mixed with an excess of iodine (330 g). The mixture was placed in a round bottom flask, fitted with an air and water condenser and connected to a tower containing sodium hydroxide pellets. This was connected by means of rubber tubing to a trap, cooled in a dry ice-alcohol mixture, followed by two traps cooled in liquid nitrogen. The last trap was connected to a calcium chloride tube to protect the product from atmospheric moisture. The reaction was initiated by heating the mix• ture at the upper edge with a free flame, avoiding ex• cessive heating. The gases evolved during the reaction consisted of trifluoroiodomethane,and carbon dioxide. -169-

Sorae iodine also sublimed but this was condensed by the water and air condensers. Most of the COg was removed by -the sodium hydroxide tower. The vapours of trifluoro• iodomethane condensing into the traps still contained some carbon dioxide and iodine as impurities. The product was therefore fractionated in the vacuum system, the trifluoroiodomethane condensing in the trap cooled to -132 • This fraction was recycled through a long tube packed with sodium hydroxide, and after another fraction• ation, was sufficiently pure. The purity was tested by molecular weight measurements and by the infra-red spectrum. After purification, it was stored in the large bulb (painted black) attached to the vacuum system or sealed in Carius tubes.

Trifluoroiodomethane has now become commercially available, in most cases containing only a trace of fluoroform as an impurity. Later in the work, therefore, it was directly condensed from the cylinders and was fractionated only when a particularly pure sample was desired. 2, Preparation of Trimethylphosphine This compound was prepared by the Grignard Method. The reaction was carefully carried out in an -170- inert atmosphere by reacting methyl iodide and Magnesium turnings. The methylraagnesium iodide (1 Mole) so obtained was cooled vigorously by placing the reaction flask in a mixture of dry ice and alcohol, and a solution of phos• phorus trichloride ( 22.4 g, 0.16 mole ) in 50 ml ether was added cautiously with vigorous stirring. In these reactions it was observed that when the Grignard reagent was not cooled to these temperatures, an orange solid was deposited. If the stirring was not vigorous, it was found that local reaction set in with explosive violence. The addition of phosphorus trichloride was therefore slow and took about two and one half hours. The flask was then allowed to warm to room temperature, and waa heated directly to distill off the phosphine and ether. When necessary more ether was added to flush out the phosphine, and dis• tillation resumed, this time until no distillate was obtained.

The distillate was kept cool and a solution of silver iodide in a saturated aqueous solution of potassium iodide ( 5 nil ) was added. The mixture was shaken vig•

orously for two hours. sj_Ver iodide adduct of trimethylphosphine separated and was filtered out, washed first with potassium iodide solution then with water, -171- and finally dried over phosphorus pentoxide. (Total yield 32 g or 62%)

To regenerate the phosphine from the silver iodide adduct, the latter was genfLy warmed and the vapours allowed to pass through traps cooled with melting carbon tetrachloride,, dry ice-alcohol mixture, and liquid nitro- o gen. The pure phosphine collected in the -78 trap, 3 a. Preparation of Dimethyltrifluoromethylphosphine -

Trimethylphosphine (2 g, 0,0Z£> mole) and tri• fluoroiodomethane (4«1 g, 0.21 mole) were sealed in a Garius tube. That the reaction started much below room temperature was apparent from the rapid deposition of a white solid. This solid dissolved in liquid trifluoro• iodomethane and reappeared as the tube warmed up. The deposition of white solid continued but after one half hour the reaction slowed down considerably. The tube was left for 24 hours and was opened into the vacuum system for fractionation of the products. The phosphine o was condensed at -78 bath, trifluoroiodomethane by the o pentane bath (-132 ), and fluoroform passed on to the; liquid nitrogen trap. The quantities of the three products were 0.95 S (7.37 mmole), 0.75 g (3.8 mmole), and 0.073 g

(0.1 mmole) respectively. The white solid in the tube consisted of tetramethyl phosphonium iodide and a volatile -172- white solid which was found to sublime into the vacuum system.

3b. To obtain a larger quantity of the phosphine,

4 g (0.05mole) trimethylphosphine and 20 g (0.1 mole) trifluoroiodomethane were sealed. The rapid reaction at low temperature could be readily seen in this large scale experiment. In order to speed up the reaction, the tube was shaken for six hours, and after a total of 18 hours of reaction the reactants and products were separated. The yield was very poor. Prom a series of fractionations only 0.875 g (6.7 ram°le) of pure phosphine was obtained* The phosphine was separated from traces of CF^I by con• densing the mixture on to a large excess of silver iodide. The phosphine forms an unstable adduct and so CP I can be separated. The adduct decomposes above 5 &n(i gives pure phosphine. By repeating the process of forming the silver iodide adduct and decomposing it, pure phospnine could be obtained. However only 8.43 g(°-G>3 mole) of tri• fluoroiodomethane could be recovered. 3 c. The amount of trifluoroiodomethane consumed did not exactly correspond with the expected stoichiometry, and hence the volatile white solid was analysed for the trifluoromethyl groups. The solid (0.472 g) was treated with 20%, sodium hydroxide (5 ml) at room temperature.

After 60 hours, fractionation gave fluoroform (0.235 g? -173-

3.36 mmole) identified from its molecular weight. (Found

71.0, calculated 70.0) This corresponds with the loss of two trifluoromethyl groups from what might be dimethyl - bistrifluoromethylphosphonium iodide ( CF^, found49.8$;

calculated for (CH^)g(CF^)2PI, 42.3$) • Evaporation of the pale yellow hydrolysis solution gave a solid whose infra-red spectrum showed the absence of trifluoromethyl groups and corresponded with that of sodium salt of dimethylphosphlnic acid. o The original solid melted at 60 C and absorbed strongly in the 8 - 9/i- region of the infra-red , indicatin the presence of trifluoromethyl groups. On standing over a long period, fluoroform was evolved, leaving a red hygroscopic solid of unknown composition.

3 d. To further characterize this compound, two experiments were performed. 1. Tetramethylphosphonium iodide (O.I367 g) was sealed with trifluoroiodomethane

(0..5 g)» There was no immediate reaction although liquid trifluoroiodomethane seemed to dissolve the solid. On opening the tube after 72 hours, the trifluoroiodomethane was recovered quantitatively. 2. Dimethyltrifluoromethyl phosphine (0.1 g) was sealed with trifluoroiodomethane o (0.2 g). There was no reaction in the gas phase at 25 nor at lower temperatures. However, on the removal of all -174-

o volatile material at -78 , a white solid formed which could be sublimed to cooler parts of me tube and appeared to be similar to the white solid thought to be dimethylbistrifluoromethylphosphonium iodide. The separation of the reactants was difficult and no solid sublimed into the system. The infra-red spectrum of the volatile products showed the presence of fluoroform, probably due to dis• sociation of the above phosphonium iodide. 3 e. Since the reaction in the gas phase was slow, this reaction was performed in the liquid phase by treat• ing 0.1232 g of -the phosphine with 2.0 g of trifluoro• iodomethane. Fractionation after 120 hours left behind a small amount of the white solid which was spectroscopically identical with the original white solid. 4 a. Preparation of Tristrifluoromethylphosphine The method used was the same as reported earlier, i.e. by heating red or white phosphorus with trifluoro• iodomethane in sealed Pyrex tubes orin an autoclave. Varying proportions of phosphorus to iodide, and different conditions of temperature were studied. Typical results are shown in the following table. When white phosphorus was used,'it \tfas first reduced to powder form, by vigor• ous shaking of molten phosphorus under di stilled water. Successive treatments removed most of the impurities and -175- the last traces of water were removed in vacuo. However the yields of the required phosphine were still rather low, this being attributed to the presence of small amounts of phosphorus oxide. When red phosphorus and trifluoro• methyl iodide, in the ratio of 1:2 by weight, were heated, the yield of phosphine was again low although recycling of the iodides with more trifluoromethyl iodide increased the yield somewhat. The highest yields were obtained when small amounts of free iodine were present. All of the trifluoromethyl iodide was then utilised to give a higher ratio of the phosphine to iodides. Under these conditions there was also formed in small amounts an oily, yellow liquid of unknown composition which was immiscible with the iodides, and which was involatile at room tem• perature. The yields shown in the following table are (4) much higher than those reported originally* , and com- (9) pare favourably with those of Burg and Mahler* • Wt. of Phosphorus Wt. of CP3I Conditions Products Yield fo o

2 g. white 2 g 225 for 48 hr P(CF3)3 32

P(CF3)2I 13

PCP3I2 3

CP3I 30 CP^H 9 -176-

13 g white 8 g 216° P(CF3)3 40

P(CF3)2I 10

PCF3I2 2

CF3I 25

CF3H 8

13 g red 8 g P(CF3)5 26 after recycling of the iodides 39 0 5 g red 10 g 216 for 48 hr P(CF,), 47 •> 3 + 0.5 g I2 P(CF3)2I 15

P(GF3)I2 2

GF3I 0.3

CF3H 7o3 -t-unknown liquid In all these experiments the residue in the tube was a red solid which was identified as a mixture of phosphorus triiodide and phosphorus diiodide. 4 b. In order to elucidate the mechanism of these reactions, a reaction was performed in which there was no iodide present. .6.7 g silver trifluoroacetate, 0.5 g red phosphorus, and a trace of iodine were heated in a o Carius tube to 250 for 12 hours. The only volatile product obtained was trifluoroacetic anhydride (molecular weight observed 212, calculated 210). Since the compound does not contain any phosphorus, this experiment shows that -177- there is no reaction between silvei&trifluoroacetate and phosphorus. However in the presence of excess of iodine the phosphines have been obtained. Another experiment o carried out in an autoclave at 285 did not produce tristrifluoromethylphosphine or fluoroform, but gave phosphorus trifluoride and carbon tetrafluoride instead. 5 a» Preparation of Methylbistrifluoromethylphosphine Tristrifluoromethylphosphine (1.3 g, 5*46 mmole) was sealed with methyl iodide (0.83 g, 5»8 mmole) and o - o heated to 230 for 12 hours, and at 235 for a further 20 hours. The two reactants, which originally formed separate layers at room temperature, after reaction formed a homo• geneous solution. The completion of reaction could be seen by cooling the reaction tube in liquid nitrogen ..,('; and allowing it to slowly warm up. If the reaction was not complete, the solution would not remain homogeneous and would separate Into two layers on reaching room tem• perature. The separation of the products was very tedious and required, a series of fractionations to isolate the pure phosphine. The volatile products from the above reaction consisted of methylbistrifluoromethylphosphine (0.615 g, 3*34 mmole) corresponding to a. yield of 60$ based on the amount of tristrifluoromethylphosphine -178- eonsumed, trifluoroiodomethane 11%, and fluoroform !%•

There was also an involatile residue in the tube. This consisted of some insoluble carbonaceous matter which was not identified, but definitely did not contain a

CF^ group as shown by the infra-red spectrum. The residue also contained a white solid which was found to be tri- (2) methyltrifluoromethylphosphonium iodide .

When equimolar quantities were used, all the methyl iodide was used up but some tristrifluoromethyl• phosphine was left unreacted. Tristrifluoromethylphos• phine (0.67 g, 2.81 mmole) and methyl iodide (0.39 g* o 2.75 mmole) were heated to 230 for 48 hours. There was less carbonisation but the two phosphines were diffi• cult to separate. 5 b. Methylbistrifluoromethylphosphine was also prepared by heating tristrifluoromethylphosphine (0.56g) o with methyl mercuric chloride (0.40 g) to 220 for 16 hours. The solid methyl mercuric chloride was found to carbonise slightly. The reaction was slow and the phosphi were found to be difficult',:»to separate. -179-

III PHENYL-TRIFLUOROMETHYL-PHOSPHINES

A 1. Preparation of Phenylbistrifluoromethylphosphine a* Preparation of Phenyldichlorophosphine This compound was prepared by the Friedel- Crafts reaction, originally reported by Michaelis. However, modifications of the method have been described by Buchner and Lockhart* ' and these were employed. 165 S phosphorus trichloride, 23.4 g benzene, and 53 g aluminium trichloride anhydrous were refluxed, at first slowly and then vigorously for one and one half hours or until the evolution of HC1 ceased. The heating was then stopped and 62 g phosphorus oxychloride were added drop by drop while the mixture was still hot. The AlCl'POCl, 3 J complex precipitated as awhite granular solid. The liquid layer was extracted with 6-8 portions each of 100 ml of petroleum ether. The residue was filtered and the filtrate along with the extract was subjected to vacuum distillation. The product distilling over between 107 - 0 112 was collected. The infra-red spectrum of the product corresponded with that reported* » b. Preparation of Phenylphosphine The method of Michaelis was attempted but found un• satisfactory. The phosphine was prepared by the reduction of -180- phenyldichlorophosphine with lithium aluminium hydride. 18.8 g phenyldichlorophosphine in 100 ml diethyl ether was added cautiously to a well stirred suspension of lithium aluminium hydride (3 g) in 100 ml ether. The reaction was vigorous and was carried out at 0 C. After the addition of phenyldichlorophosphine was complete, the mixture was refluxed for 30 minutes and 5 ml of dis• tilled water were added dropwise. This mixture was refluxed for an hour and then distilled directly. The o phenylphosphine distilled at 160 but was contaminated with water. It was therefore dissolved in ether, and after siphoning out the water, the ether solution was dried with calcium chloride. It was then distilled in a still of 2 5 ml capacity and 8" column. The resulting product was pure phenylphosphine. The infra-red spectrum of this compound has not been reported but the sharp band at 2300 cm"-'", characteristic of the P-H bond, easily identified the product. c. In another preparation, the reaction was carried out in n-butyl ether in order to slow down the reaction, the same quantities being used. The reaction was smooth but the separation by distillation was not very effective, possibly because of the close boiling points of the phosphine and ether. -181- d. Preparation of Tetraphenylcyclotetraphosphine This compound was prepared by the reaction of phenyldichlorophosphine and phenylphosphine.

H P) + 2C6H5PC12+ 2C6H5PH2 * (C6 5 4 ^Cl In a three necked flask, which had been flushed with nitrogen and which was fitted with a stirrer and con• denser, was placed a 50 ml ether solution of 18 g phenyl• dichlorophosphine, and while this solution was being stirred, a 50 ml ether solution of llg phenylphosphine was slowly added. The solution gradually turned yellow but a solid was not deposited immediately. After the addition was complete, the solution was refluxed for three hours during which time a white solid was deposited and the evolution of HG1 ceased. The ether solution was decanted off, and the remaining solid was washed with ether and then dried. The yield, of tetraphenylcyclo• tetraphosphine was S0%» The compound was characterized o by its melting point 148 - 150 and its infra-red spectrum.*1*) e. Interaction of Tetraphenylcyclotetraphosphine and Trifluoroiodomethane Tetraphenylcyclotetraphosphine (1.0 g) was sealed with trifluoroiodomethane (2.025 g) and left at room temperature for 24 hours. The solid phosphine is -182-

insoluble in trifluoroiodomethane, and floats on the

liquid CF_I. The tube containing the reactants was heated to 70 for 24 hours but no reaction occurred. o

It was then heated to 150 for 12 hours. On cooling,

the solid phosphine separated in the form of yellow

crystals. The trifluoroiodomethane also changed its

colour, becoming slightly reddish, indicating that some

slight reaction had occurred. The reaction was then o

conducted at 185 for 12 hours, when a dark red Involatile

liquid was obtained and 0.558 g trifluoroiodomethane was recovered. The dark red liquid was shaken with mer•

cury and the remaining liquid extracted with ether.

After removal of ether, 0.45 g of a liquid of low volatil•

ity was obtained and was identified as phenylbistrifluoro• methylphosphine. (Pound C, 39.35%; H, 2.10%; P, 45.40$;

P, 12.30$. Calculated for C_H_FJP, C,39.03$; H, 2.03$; o 5 o P, 46.36$; P, 12.60$)

In order to investigate the mechanism of the

reaction of trifluoroiodomethane and tetraphenylcyclote-

traphosphlne, and also to characterize the other reaction

products, the following experiments were performed.

£. Tetraphenylcyclotetraphosphine (1 g) and o

trifluoroiodomethane ( 2 g ) were heated at 165 for 20

hours. The mixture became dark red and no solid separated -183- on cooling. Distillation under vacuum gave phenylbis- triluoromethylphosphine (0.3 g), showing that the reaction can be carried out above the melting point of the phos• phine. gr. Tetraphenylcyclotetraphosphine (2 g) and trifluoroiodomethane. (5 g) were sealed in a pyrex tube and irradiated with ultra-violet light from a 200 watt U.V. lamp at a distance of 20 cm. The radiation was concentrated on the liquid CF^I and the rest of the tube was wrapped with aluminium foil so that the vapour phase was not irradiated. The reaction was slow, possibly because of the heterogeneous phases. The liquid phase became darker as the reaction proceeded, and after 15 days of irradiation, fractionation of the products gave phenylbistrifluoromethylphosphine (0.899g) and unreacted trifluoroiodomethane (2.192 g). The consumption of 2.803 g of the latter is about one gram in excess of what is required for the production of the above amount of phosphine. h. In order to account for the above loss of CF,I, the other products were analysed. The rest of the 5 products were the unreacted tetraphenylcyclotetraphosphine and a thick reddish syrup. The infra-red spectrum of this syrup indicated strong absorption in the 8 - 9/t region, -184- characteristic of CF, groups. Treatment of a small amount j of this substance with sodium hydroxide solution evolved fluoroform. 0.32 g of this reddish liquid gave 0.012 g or 3*7$ fluoroform, which was not a quantitative amount to correspond with the analysis of a possible compound. i. Tetraphenylcyclotetraphosphine (1.5 g) and trifluoroiodomethane were sealed in a Carius tube add o heated to 185 for 12 hours. The volatile compounds were fractionated through -78, -132 , and -196 baths. A small amount of phosphine distilled over and collected o in the -78 bath. Trifluoroiodomethane was collected in o the -132 bath, whereas fluoroform and hexaf luoroethane were condensed in the liquid nitrogen trap. The tri• fluoroiodomethane which was recovered weighed 5»5 g and the other volatile products were only 0.022 g. The latter were identified by their infra-red spectra. The remaining liquid was subjected to fractional distillation outside the vacuum system under a pressure of 20 mm. Two fractions were obtained, one boiling at o o 62 - 65 (4.9 g) and the other boiling at 112 - 116 (3.8 g). A thick liquid, which solidified on standing, remained in the distillation flask. j. Characterization of the Fractions The fraction boiling at 62 - 65° was identified -185- as phenylbistrifluoromethylphosphine from the Infra-red spectrum of the liquid. The phosphine was slightly coloured, possibly because of the presence of traces of iodine. It was therfore purified by shaking with mercury for 24 hours, followed by distillation in an atmosphere of nitrogen. Two fractions were obtained, o o one boiling at 84 - 86 and the other at 148 - 150 • The Infra-red spectrum of the first fraction indicated the presence of a P-H bond by the characteristic absorp• tion at 2300 cm"-'-. Since the quantity of this fraction was not very significant (ca. 0.1 g) it was not inves• tigated further. o The other fraction boiling at 148 - 150 was further purified by vapour phase chromatography. The o temperature of the furnace was maintained at 120 and the column used was "Ucon polar". The spectrum showed a wide gap between the small amount of impurity and the phosphine, showing that the latter after distillation was 98$ pure. The phosphine purified this way was used for further investigation. o k. The fraction boiling at 112 - 114 (at 20 ram) was identified as phenyltrifluoromethyliodophosphine. (Pound 1,41.2$ Calculated for C HP PI; I, 41.78$) The 7 5 3 -186- infra-red spectrum (fig. 1 ) showed two strong bands in the region associated with C-F stretching frequencies corresponding to one trifluoromethyl group. It was ob• served that on cooling, this fraction deposited needle- shaped crystals which were similar to and identified by their melting point as phosphorus triiodide. The presence of phosphorus triiodide was possibly due to the disproportionation of the idophosphine as shown later.

1. The fraction remaining in the still soli• dified on cooling into a resinous mass. Treatment with water gave a strongly acid solution but did not precipi• tate any solid. The solution was brown and contained free iodine and iodides. The original material was in• soluble in petroleum ether, but seemed partially soluble in acetone. The solid recovered from the acetone solution did not show any absorption for the C-F stretching fre• quency region, but did contain a phenyl group. Analysis showed it to be an iodide, possibly phenyldiiodophosphine. m. In another experiment, the liquid (15 g) remaining in the tube after distillation of the phosphine was sealed with trifluoroiodomethane (25 g) and mercury (80 g). The mixture was shaken for 48 hours. After fractionation of the volatile products, the mixture was extracted with ether. The evaporation of the solvent -187- left a thick pale yellow liquid (20 g). Prom analysis

it was shown not to contain any iodides, and from the

infra-red spectrum was found to contain trifluoromethyl

groups. 0.322 g of this substance was treated with a

20$ sodium hydroxide solution and this gave 0.0428 g or

13.28$ fluoroform.

2. Diphenyltrifluoromethylphosphine

a. Preparation of Diphenylchlorophosphine

The preparation of this compound was attempted

by the disproprtionation of phenyldichlorophosphine (37 )#

75 g of the latter were heated in three sealed tubes for five days. The decomposition reaction was slow and mostly

incomplete, for at the end of this period only 1 g of a fraction boiling over 300 was obtained. The rest of the products consisted of phosphorus trichloride and unreacted phenyldichlorophosphine•

b. The preparation was attempted by treating phenyldichlorophosphine with lithium phenyl. Lithium phenyl was obtained commercially as a 0.75 molar suspen•

sion in pentane. The suspension (70 ml, 0.052 mole) was placed in a three-necked flask which was flushed with nitrogen, and phenyldichlorophosphine (9 g,0.05 mole)was added dropwise. The reaction was vigorous and the flask had to be cooled in an Ice bath. At the end of the reaction -188- th e pentane solution was evaporated in vacuo, and this gave o a solid, melting at 85 , which was identified spectroscopically,to be triphenylphosphine. The reaction was carried 0 out at -78 , but the product still was triphenylphosphine. No diphenylchlorophosphine could be obtained. c. Diphenylchlorophosphine was prepared by the (40).

method of Steube, LeSuer, and Norman a To a well-stirred mixture of phosphorus pentasulphide (208 g, 0.47 mole) arid benzene (224 g» 3»18 mole), aluminium chloride (222 g, 1.66 mole) was gradually added at such a rate that the benzene did not boil. The mixture was refluxed for five hours, and after standing for three hours was poured onto crushed ice. The dark green liquid so obtained was separated, washed with more water, then dried with magnesium sulphate. The same volume of benzene was added to the above solution of diphenylphosphinodithioic acid, and while this solution was cooled in an ice bath and stirred, a rapid stream of chlorine was passed through it. Di• phenyl tri chl or ophospho ran e separated as an oil which soon solidified to give orange yellow crystals. 200 ml of petroleum ether was added to this mixture. After an hour the supernatent liquid was decanted and the solid residue was washed with more petroleum ether. Red phosphorus (15*5 g» 0.5 mole) was added to this mixture (solid and -189- 1 o

petroleum ether) and heated slowly on an oil bath to 1800 When the more volatile products, phosphorus trichloride and petroleum ether, distilled over, the residual mixture o was vacuum distilled and the fraction boiling at 178 at 20mm was collected. This gave 64 g or 63% yield of di• phenylchlorophosphine. d. Diphenylphosphine was prepared by adding an ethereal solution of diphenylchlorophosphine (22 g, 0.1 mole) to a suspension of lithium metal (0.3 g) in ether. The reaction was controlled by cooling the react• ion flask in an ice bath. After the addition was complete, the mixture was refluxed and treated with water. At the end of this reaction, the precipitated lithium chloride was filtered off and the ether solution was distilled. After the ether was distilled off, diphenylphosphine was distilled in vacuo. e. Preparation of Tetraphenyldiphosphine An ethereal solution of diphenylphosphine (9 g, 0.05 mole) Was added gradually to another ether solution of diphenylchlorophosphine (11 g, 0.05 mole). The result• ing mixture was refluxed for two hours when tetraphenyl• diphosphine separated as a white solid. The solid was washed with ether and dried, and then sealed with tri• fluoroiodomethane for further reaction. -190-

f. The preparation of this compound jCCgH^JgPJ^ was also attempted through the formation of the dlphenyl- diphosphinebisodium adduct. To a well-stirred mixture of freshly cut softium pieces (3 g) and tetrahydrofuron (100 ml), phenyldichlorophosphine (17»9 g* 0.1 mole) was added in a nitrogen atmosphere. The reaction was vigo• rous and the flask had to be cooled. The colour of the solution changed to yellow and finally became bright red. The unreacted sodium was separated and iodobenzene (20.4 g, 0.1 mole) was added gradually. Sodium iodide was seen to separate, but the solution on evaporation did not leave any residue corresponding to tetraphenyldiphosphine. The solid residue left after distillation did, however, in• dicate the presence of P-CgH^ bond by its infra-red spec• trum.

The preparation of tetraphenyldiphosphine by the above method was repeated by using powdered sodium in xylene, and also by using lithium. Positive results could not, however, be obtained.

g. Interaction of Tetraphenyldiphosphine and Trifluoroiodomethane Tetraphenyldiphosphine (1.2 g, 3.2 mmole) and an excess of trifluoroiodomethane (12.2 g, 62.2 mmole) o were heated in a Pyrex tube to 185 for 12 hours. After -191- fractie-nation of Hie products, trifluoroiodomethane (11.5 g> 58• 5 mmole) and a small amount of fluoroform (0.004 g) were obtained as the volatile products, and the residue in the tube was a thick red liquid. The loss of trifluoroiodomethane indicated that some reaction had occurred. The involatile red liquid was therefore treated with petroleum ether to extract the phosphine, much of the former being insoluble in this solvent. Infra-red spectrum of the remaining red liquid did not indicate the presence of a CP^ group, and analysis showed it to be an iodophosphine containing free iodine and probably was diphenyliodophosphine.

Evaporation of the petroleum ether extract in vacuum left an involatile liquid (0.4 g) whose infra• red spectrum had two strong bands in the C-F stretching frequency region, and also the characteristic frequenc• ies of the phenyl group. Treatment of this liquid with alcoholic potassium hydroxide gave fluoroform. Analysis of a pure sample (purified by vapour phase chromatography o using a silicone column it a; temperature of 230 with helium flowing at a pressure of 7 p.s.i.) showed it to be diphenyltrifluoromethylphosphine. (Found C, 60.86$; H, 4.25$; F, 22.69$; P, 11.79$. Calculated for C, ,H F,P; C, 13 10 o 61.41$; H, 3.94$; P, 22.45$; P, 12.21$) -192- h. To elucidate the reaction mechanism tetra• phenyldiphosphine (1.0 g, 2.7 mmole) and trifluoroiodo• methane (10 g, 51 mmole) were irradiated with ultra• violet light for seven days. The diphosphine [(OgH,-JgPJ 2 was insoluble in CF,I, but as the reaction proceeded, the colour of the liquid became darker. Fractionation of the volatile products gave trifluoroiodomethane (9*6 g) and extraction of the residue with petroleum ether left an insoluble red liquid whose infra-red spectrum corresponded with the one obtained on heating the two reactants. The petroleum ether extract gave diphenyltrifluoromethylphos• phine (0.15 g), identified from its infra-red spectrum (fig. 6 )„ Some of the unreacted diphosphine was also found with the involatile residue.,

I• Reaction of Triphenylphosphine with Trifluoroiodomethane Triphenylphosphine (2.5 g, 9«54 mmole) was heated with excess trifluoroiodomethane (14.0 g, 71«4 mmole) to 185 for four hours. The solid phosphine (CgHj-J^P is easily soluble in the liquid CF^I at room temperature and as the tube Is gradually heated, the solution becomes yellow, orange, and finally reddish brown. Fractionation of the volatile products gave trifluoroiodomethane (10.6 g, 75.7$), fluoroform (0.4628 g, 9»25%) and a small amount of trifluoromethylbenzene -193- (0.0434 g» 0.42$). A thick reddish brown mass was left in the reaction tube and was extracted with petroleum ether. Vacuum distillation of this extract gave diphenyltrifluoromethylphosphine (0.2 g), which was identified from its infra-red spectrum (fig. 6 ). The infra-red spectrum of the residual reddish brown liquid was iden• tical with that obtained from the reaction of tetraphenyl• diphosphine and trifluoroiodomethane. The reaction of triphenylphosphine and trifluoro iodomethane at lower temperatures, 70 and 110 for 24 hours each, gave back the CP I quantitatively, and at o J 214 gave a reddish brown resinous substance which could not be identified. However 12$ of the trifluoroiodometh• ane was consumed. j. Reaction of Diphenylchlorophosphine and Trifluoroiodomethane Diphenylchlorophosphine (5«6 g)or(25..5 mmole) and trifluoroiodomethane (12.5 g, 63.7 mmole) were heated o 205 for 12 hours. The reactants were miscible at room temperature and formed a pale yellow solution. After reaction, the solution which became reddish brown was fractionated in the vacuum system. A mixture of hexafluoroethane and fluoroform was obtained in trace amounts. The other volatile products were trifluorochloromethane -194- (1.24 g, 14*8$), unreacted trifluoroiodomethane (8.79 g» 10*3%)* and a small amount of trifluoromethylbenzene (0.0438 g). The involatile liquid was extracted with petroleum ether. The residual red liquid was identified as diphenyliodophosphine from its infra-red spectrum, and was similar in all respects to the red liquid in reactions HI'gig), HE 2(h), and HI 2(i). k. In another experiment employing the same conditions and the same amount of diphenylchlorophosphine but a larger excess of trifiluoroiodomethane (17*0 g) than in HI 2(j), 5.0 g of crude diphenyltrifluoromethyl• phosphine by extracting with petroleum ether and only a small amount of trifluorochloromethane (0.1 g) were ob• tained. Distillation of the crude phosphine under vacuum o gave a fraction (3»5 g) boiling at 112 - 130 , and an involatile residue which was identified as diphenylchloro• phosphine. o The fraction boiling at 112 - 130 was further pruified by vapour phase chromatography to give three fractions. The infra-red spectra of the three fractions showed them to be trifluoromethylbenzene, phenyltrifluoromethylchlorophosphine, and diphenyltrifluoromethylphosphine. 1. The involatile reddish brown liquid, identi•

fied spectroscopically as (C^-H[-)9PI, was shaken with tri- -195- fluoroiodomethane (23.7 g) and mercury (168.5 g) for 120 hours. At the end of this period, trifluoroiodomethane was recovered quantitatively (23.3 g) from the reaction mixture, showing that the expected reaction giving

(C6H5^2CP3P did not occur» -196-

B PROPERTIES AMD REACTIONS OF PHENHJ-TRIFLUOROMETRYL-PHOSPHINES

1« .Phenylbigtrifluoromethylphosphine a* Physical Properties Phenylbistrifluoromethylphosphine is a colour• less oily liquid whose odour is not as obnoxious as those of other phosphines. Its boiling point, determined by o the inverted capillary method, is 148 - 150 , and its vapour pressure was found to be as follows. T VT IO~3 P log P

26 0.33 44 17 I.2304 33 0.3268 20 1.3010 41 0.3185 25 1.3979 51 0.3086 35 1.5441 61 0.2994 46 1.6628 71 0.2907 63 1.7997 77 0.2857 77 1.8865 81 0.2825 90 1.9542 86 0.2726 110 2.0414 90 0.2755 123 2.0899 94 0.2725 139 2.1430 96 0.2710 150 2.1761 100 0.2681 165 2.2175 105 0.2646 204 2.3096 108 0.2625 223 2.3483 -197-

Th e vapor pressure follows the equation: log P(mm) = 7.5606- 1985 10 rjT-

The latent heat of vaporization calculated from the above -I - data is 9054 kcal mole and the Trouton's constant is 21.37. 1 (b). The phosphine is stable In air and is o unchanged on heating up to 200 . Phenylbistrifluoromethyl- o phosphine (1.058 g) was heated to 210 for 48 hours. The phosphine was recovered quantitatively (1.004 g), and only traces of fluoroform and silicon tetrafluoride could be identified spectroscopically. The phosphine (0.639 g) was o then heated to 300 for 48 hours. The tube walls were etched but the phosphine was not all pyrolyzed and most of it (0.48 g) was recovered unchanged. The other volatile materials were fluoroform, silicon tetrafluoride and some trifluoromethylbenzene. This shows that the phosphine is o only 25$ pyrolyzed when heated at 300 for 48 hours. 1(c). . Reactions6fPtienylbistrifluoromethy 1 - phosphine: The phosphine does not react with silver iodide, a solution of silver iodide in potassium iodide, or with car• bon disulphide. 1 (d). Hydrolysis with water: The phosphine (0.277 g, 1.12 cummole) was sealed with water' (1.28 g). The reaction tube was left at room temperature for 48 hours. The reactants formed two separate layers. On opening the tube, the phosphine was recovered quantitatively. Heating - 198 - the reaction tube to 80 for 24 hours gave only a trace of fluoroform, identified spectroscopically. The reactants o were then heated to llO for J2 hours. This gave a small amount of fluoroform (0.038 g, 0.92 mmole). A crystalline residue was left in the tube when the reactants were pumped off and was identified as phenylphosphonous acid, melting o "(44) at 69 (reported M.Pt. 70-71 ) 1(e) Hydrolysis with alkali: The phosphine (0.273 g, 1.11 mmole) was sealed with 5 ml of 20% alkali solution (sodium hydroxide). The reaction was slow at room temperature and evolution of fluoroform continued slowly. o The reaction was carried out at 80 for 24 hours. When the tube was opened, fluoroform was recovered almost quantita• tively (0.149 g, 2.13 mmole). This hydrolysis accounted for 96.4$ of the trifluoromethyl groups JCF^ found as fluoroform 54.8$; calculated for CgH^CF ^P, 56.1$.] The solid resi• due obtained on evaporation of the alkaline solution was found to contain the sodium salt of phenylphosphonous acid. o Acidifying this salt gave the acid, M.Pt. 69 • 1(f) Hydrolysis with acid; The phosphine (0.372 g, 1.51 mmole) was heated to 80° for 24 hours with 36 N hydrochloric acid (2 g). The reactants formed separate layers and did not seem to react. They were then heated to o 110 for 48 hours. Fractionation did not give any fluoroform. -199 -

o They were finally heated to 185 for 120 hours. This gave a trace amount of fluoroform (0.0022 g). The phosphine and acid still formed two layers and the former was recovered / quantitatively. REACTION Op;PHENYLBISTRIFLUOROMETHYLPHOSPHINE WITH HALOGENS: 1(g) Reaction with iodine: Phenylbistrifluoro• methylphosphine (0.4736 g, 1.93 mmole) was treated with iodine (0.508 g, 2.0 mmole). At room temperature, the mix• ture formed a brown liquid but did not seem to react. No o reaction occurred when the mixture was heated first to 80 , o o o then 110 and to 150 • After heating at 185 for 48 hours, the products were a small amount of fluoroform (0.028 g, 0.4 mmole), trifluoroiodomethane (0.382 g, 1.96 mmole), phosphorus triiodide and some unreacted phosphine. The amount of trifluoroiodomethane was only 50$ of the expected quantity. In a second experiment using excess iodine (1.163 g, 4.58 mmole), the phosphine (0.3899 g, 1.58 mmole) o was heated to 185 for 48 hours to give trifluoroiodomethane (0.481 g, 2.47 mmole) and fluoroform (0.032 g, O.46 mmole). A small amount of benzene (0.055 g) and traces of unreacted phosphine were also present among the reaction products. The conversion into fluoroform and trifluoroiodomethane accounted for 91*5% of the trifluoromethyl groups. The for• mation of fluoroform and benzene might be due to the small traces of moisvture on iodine which is not removed even on ex- - 200 - tensive drying* 1(h) Reaction with bromine; The phosphine (0.695 g» 283 mmole) was reacted with bromine (0.450 g, 2.83 mmole). The reaction was vigorous and an orange- yellow solid was immediately deposited. The reaction could, however, be controlled by carrying out the reaction in car• bon tetrachloride solution. The completion of the reaction was marked by the coloration of the solution and by the precipitation of the phosphorane. Washing with small amounts of carbon tetrachloride to remove excess bromine and then pumping off the solvent gave pure phenylbistrifluoromethyldibromophosphorane (Found Br 38>93#, calcu• lated for CQHCF-PBr , Br 39.41$).

o 0 o d. l(i) The phosphorane reacted very readily with water with the loss of one equivalent of CF and formation 3 of a white solid. The dibromophosphorane (O.324 g, 0.798 mmole) was sealed with water (1.0 g) and left at room temperature overnight. Fluoroform (0.060 g, 0.85 mmole) was evolved corresponding to the loss of one CF per mole. 3 (Found CF,, 18.4$. Calculated for C H F PBr ; CF , 34.5$). 2 8 5 6 2 3 A white solid was obtained when the liquid was pumped off. It was recrystallized from water and dried over phosphorus pentoxide. The solid was identified spectroscopically as phenyltrifluoromethylphosphinic acid CJl (CF )P(0)0H. The o 6 5 3. acid melted at 84-86 . The silver salt of this acid was - 201 - obtained by treating the aqueous solution of the acid with silver oxide, filtering off any excess of the oxide and evaporating the solid in vacuo* The resulting solid was dried over phosphorus pentoxide. The silver salt C H (CP )P(0)0Ag (Found Ag, 33.81%; calculated for C H F P0 Ag; Ag, 34.06$) 7 5 3 2 was a crystalline solid melting at 294-96 and was very sen• sitive to light. The silver salt was easily prepared, however, by treating the mixture of the phosphorane C H_(CF ) PBr and ^ 6 5 3 2 2 water with silver oxide. The precipitated silver bromide was filtered out along with the excess silver oxide, and the evaporation of the solution gave a product identical with that obtained from the reaction with the acid. l(j) Reaction with trifluoroiodomethane: Phenyl• bis trif luoromethylphosphine (O.4I5 g, 1.69 mmole) was treated with trifluoroiodomethane (1.151 g, 5»91 mmole). The reac• tants were miscible at room temperature. They were heated o to 230 for 10 hours. Fractionation of the products gave fluoroform (0.1902 g, 2.72 mmole) trifluoroiodomethane (0.8848 g, 4.54 mmole) and unreacted phosphine C H (CF ) P 6 5 3 2 (0.1743 g» 0.708 mmole). Trifluoromethylbenzene was identi• fied among the products spectroscopically but the same method did not indicate the presence of tristrifluoromethylphosphine. The reaction tube was covered with charred material and con• tained some phosphorus triiodide. - 202 -

l(k) Reaction with methyl iodide: Phenylbistri• fluoromethylphosphine (0,627 g, 2,55 mmole) and methyl iodide o (1.031 g, 7»26 mmole) were heated to 230 • The reactants were miscible at room temperature but did not seem to react. After heating for 10 hours, trifluoroiodomethane (0.087 g» 0.446 mmole) and fluoroform (0.0589 g, 0.84 mmole) and a mix• ture of methyl iodide and trifluoroiodomethane (0.180 g>) were obtained as the volatile products. The residual liquid was a black carbonized product consisting of a mixture of methyl iodide and phenylbistrifluoromethylphosphine. The expected products (CH )C H (CF )P or [(CH )C H (CF ) plVwere not 3 6 5 3 L 3. 6 5 3 2 J identified among the products. . 2. Phenyltrifluoromethyllodophosphine 2 (a) Physical properties: Phenyltrifluoro- methyliodophosphine is a reddish-brown liquid (perhaps due o to traces of free iodine) which boils at 112-114 at 20 mm pressure. It fumes in air and reacts with moisture. It dissolves in water and the solution so obtained is highly acidic. It also reacts with organic solvents; e.g., acetone from which it cannot be recovered unchanged. 2 (b) It is unstable at high temperatures and undergoes disproportionation. The iodophosphine (2.003 g) o was heated in a sealed tube at 220 for 12 hours. The volatile products were small amounts of fluoroform (0.02 g), trifluoroiodomethane (0.06 g) and traces of benzene. The involatile products were phenylbistrifluoromethylphosphine, - 203 - some unreacted iodophosphine C H (CP )PI and phosphorus 6 5 3 triiodide. 2(c) Hydrolysis with alkali: Phenyltrifluoro• methyliodophosphine (0.334 g, 1.1 mmole) was reacted with 5 ml of 20$ sodium hydroxide solution. There was immediate reaction at room temperature and fluoroform was evolved. However, this evolution was not quantitative. The reaction was therefore carried out at 100 for 15 hours, when 0.0694 g (0.99 mmole) fluoroform was evolved. (CF, found 3 as CF H, 20.75$; calculated for C H F PI, 23.03$.) The 3 7 5 3 hydrolysis was only 90$ complete. The residue after evapo• ration of water contained a hygroscopic sodium salt whose infra-red spectrum corresponded with that of sodium phenylphosphonate. 2(d) Hydrolysis with water: Phenyltrifluoro• methyliodophosphine (0.334 g) was treated with 0.125 g water and left in a sealed tube overnight. On pumping off the liquid, a white solid was obtained. The M.Pt. of this o solid was 84-86 and in all respects was similar to the compound obtained from the aqueous hydrolysis of the phos• phorane C H (CF ) PBr in l(.i). Its silver salt was also 6 5 3 2 2 prepared by reacting the iodophosphosphine with water, treating the aqueous solution with silver oxide and filter• ing out the silver iodide and excess silver oxide. The solution was concentrated in vacuo and the needle-shaped i. - 204 - crystalline solid dried over phosphorus pentoxide. The silver salt was identified analytically (Pound Ag, 33*80$, calcu• lated for CCE (CP )P(0)0Ag, 34.06$), by its melting point o 6 5 3. of 294-96 and also by its infra-red spectrum (fig. Z). The aqueous hydrolysis also gave a small amount of a liquid whose infra-red spectrum showed the presence of P-H, P-C^Ht- and P-CP bonds showing the probable formation ob 3 of phenyltrifluoromethylphosphine C H (CP )PH. 6 5 3 2(e) Reaction with trifluoroiodomethane: The iodophosphine (2«347 g, 7.72 mmole) was heated with trifluoro- o iodomethane (2.299 g, 11.8 mmole) to 200 for 12 hours. The reactants formed a homogeneous solution at room temperature but after reaction crystals of phosphorus triiodide could easily be recognised. Fractionation gave trifluoroiodo• methane quantitatively (96.1$) (2.210 g, 11.33 mmole), and traces of fluoroform. Among the other products which, pre• sumably resulted from disproportionation of the iodophosphine were phenylbistrifluoromethylphosphine (0.617 g, 2.51 mmole), some benzene, phosphorus triiodide and unreacted iodophosphine. 2(f) Reaction with trifluoroiodomethane and mercury: Phenyltrifluoromethyliodophosphine (2.8g, 9»21 mmole) was sealed with an excess of trifluoroiodomethane(10 g, 51•3 mmole) and mercury (54 g) in a Pyrex tube and shaken for 24 hours. Fractionation after the reaction gave trifluoroio• domethane (8.9 g» 45«6 mmole) and phenylbistrifluoromethyl- - 205 - phosphine (1.5 g, 6.1 mmole). Extraction of the solid product with ether gave a thick liquid which was found to be identi• cal with the one obtained in IK l(m) (Reaction with residual liq.+ CP I + Hg). 3 3. Diphenyltrifluoromethylphosphine

3(a) Physical properties: Diphenyltrifluoro• methylphosphine is a colourless oily liquid. Like phenyl• bis trif luoromethylphosphine, its odour is not obnoxious. 0 If boils at 255-57 . Its vapor pressure was found to be 1 follows:

T I/T x io3 P log P

327 0.3058 16 1.2041 347 0.2882 19 1.2788 368 0.2718 23 1.3617 381 0.2625 27 1.4314 392 0.2551 31 1.4914 404 0.2475 38 1.5798 415 0.2410 44 1.6435 425 0.2352 53 1.7243 435 0.2299 64 1.8062 441 0.2267 78 1.8921 446 0.2242 87 1.9395 455 0.2198 104 2.0170 461 0.2169 140 2.1461 466 0.2146 162 2.2095 471 0.2123 184 2.2648 476 0.2101 210 2.3222 480 0.2083 233 2.3674 485 0.2062 265 2.4232 490 ^ 0.2041 301 2.4786 495 0.2020 339 2.5302 The above data gives the following equation for vapor. ;pres sure: Log P(mm) a . 7.781 - 2598 T - 206 -

-l whence the latent heat of vaporization is 11850 cals mole and the Trouton's constant is 22.93* 3(b) Diphenyltrifluoromethylphosphine is quite a stable in air. In a sealed tube it could be heated to 200 without any significant change. When it was heated to 300 for 24 hours, only mild carbonisation took place and 85$ phosphine was recovered. The volatile products were silicon tetrafluoride, fluoroform and benzene. REACTIONS OF DIPHEimiTRIFLUOROMETHYLPHOSPHINE: 3(c) Reaction with water: The phosphine is immiscible and does not react with water even at high tem• peratures. The phosphine (0.223 g) was sealed with water (1.2 g) and heated to 120 for 48 hours. Fractionation did not give any fluoroform and the phosphine was recovered quantitatively. 3(d) Reaction with hydrochloric acid; Diphenyl- trifluoromethylphosphine (0.344 g) was sealed with 36 N hydro- o chloric acid (2.4 g) and heated to 150 • At the end of the reaction period, the phosphine was still immiscible with the acid and was recovered unchanged. 3(e) Reaction with aqueous alkali; The phos• phine (0.242 g) was sealed with 5 ml of 20$ sodium hydrox• ide solution. There was no reaction at room temperature. The o reactants were heated to 80 for 24 hours but at the end of this period the phosphine still remained as an immiscible - 207 - liquid. The reaction tube was then heated to 100 for 24 hours. No reaction seemed to have occurred and only a trace of fluoroform was recovered. 3(f) Reaction with alcoholic potassium hydroxide: The hydrolysis was attempted by sealing the - phosphine (0.2137 g, 0.84 mmole) with alcoholic potassium hydroxide (5 ml of 20$ solution). The reaction was very o slow at room temperature and hence was conducted at 70 for 96 hours. Fractionation gave fluoroform (0.046 g, 0.657 mmole). (CF found 21.5$; calculated for (CH ) CF P, 3 6 5.2 3 27.16$.) The hydrolysis was only 78$ complete. The residual solution was evaporated to dryness and after dissolving in water was acidified with hydro• chloric acid. This gave a white precipitate which was washed with water and dried over phosphorus pentoxide. The o melting point of 193 and the infra-red spectrum of this substance showed it to be diphenylphosphinic acid

(26) (CCH_)_P(O)OH. o 5 c. REACTION WITH HALOGENS: 3(g) Reaction with iodine: A carbon tetra• chloride solution of diphenyltrifluoromethylphosphine (0.1788 g, 0.70 mmole) was added tp an iodine (0.18 g, 0.71 mmole) solution in the same solvent. After standing for an hour, a brown-black oil separated. The supernatant liquid was decanted and the oil washed, and finally the last traces of the solvent were removed in vacuo. The - 208 - thick oily liquid was identified as diphenyltrifluoromethyldiiodophosphorane (Pound 1^, 49*32$; calculated for

(C H )0CF PI , 50.0$). 0 5^32 3(h) Diphenyltrifluoromethyldiiodophosphorane (0.123 g, 0.24 mmole) was sealed with 2.5 ml of 20$ aqueous sodium hydroxide solution. Fluoroform was immediately evolved and to complete the reaction the reaction tube was o heated to 80 . After 24 hours, 0.0155 g (0.22 mmole) fluoroform was obtained representing 91*7$ hydrolysis. 3(i) Diphenyltrifluoromethyldiiodophosphorane is stable towards water. The phosphorane (0.254 g, 0.5 mmol o was heated with water to 80 for 24 hours. Fractionation after this period did not produce any fluoroform. 3(j) Diphenyltrifluoromethylphosphine (0.1782 g, 0.70 mmole) and excess of iodine (0.50 f, 1.97 mmole) o were heated to 200 for 24 hours. Fractionation of the products gave only traces of fluoroform and no trifluoro• iodomethane was obtained, showing the stability of the phos• phorane at this temperature. 3(k) Reaction with bromine; To a carbon tetrachloride solution of the phosphine (0.1658 g, 0.65 mmole) was added a solution of bromine (0.105 g, 0.66 mmole) in the same solvent. An orange-coloured oil separated to• wards the end of the reaction. The product (0.2694 g, O.65 mmole) was washed, and after removal of excess solvent in vacuo was identified as diphenyltrifluoromethyldibromo- - 209 - phosphorane (Pound Br, 38.07$; calculated for (C^H^CF^PBr^ 38.64$). 3(1) Diphenyltrifluoromethyldibromophosphorane (0.2723 g, 0.66 mmole) was treated with aqueous sodium hy• droxide (5 ml of 20$ solution). There was immediate reaction and fluoroform (0.0436 g, 0.62 mmole) was evolved, represent• ing 96.1$ hydrolysis. The resulting solution was acidified with hydrochloric acid, which gave a white precipitate of 0 (26) diphenylphosphinic acid (M.Pt. 194 )• The dibroraophosphorane was treated with excess 36 N hydrochloric acid and heated to 80 but no reaction occurred. There was also no reaction when the phosphorane o was heated with water to 80 • 3(m) Reaction with trifluoroiodomethane: Diphenyltrifluoromethylphosphine (0.2178 g, 0.86 mmole) was sealed with trifluoroiodomethane (0.8557 g, 4.36 mmole). The two reactants were immiscible at low temperatures and there was no reaction at room temperature. The mixture was o heated to 100 for 24 hours. The solution remained color• less and the trifluoroiodomethane was recovered quantitatively. o The reaction was then conducted at 200 for 24 hours. The solution was colored slightly brown and a small amount of thick black liquid appeared to be separating. Fractionation of the reactants gave 95«4$ trifluoroiodomethane (0.8179 g, 4.173 mmole) and traces of fluoroform (identified spectro- blacscopically)k liqui.d diThde noinfra-ret indicatd spectrue the presencm of thee ofsmal a lC F amount of - 210 - group and a qualitative analysis showed it to be a phenyl- iodo-phosphine, most probably diphenyliodophosphine. 3(n) Reaction with methyl iodide: Diphenyl- trifluoromethylphosphine (0.2337 g, 0.92 mmole) was treate with methyl iodide (0.2693 g» 1.89 mmole). The reactants were miscible at room temperature. They were heated o gradually to 100 for 12 hours. An orange colored oil slowly separated. The oil was cooled in liquid nitrogen and allowed to warm up slowly. This gave a solid product. Excess methyl iodide (0.1391 g> 0.977 mmole) was removed from the solid and the latter dissolved in ethyl alcohol. On treatment with a large excess of ether, a yellow powder was obtained. This was identified as methyldiphenyltrifluoromethylphosphonium iodide (Pound: C, 42.4$; H, 3.3$; P, 14.2$; P, 7.6$. Calculated for C H P PI: C,42.6$; 14 13 3 H, 3.3$; P, 14.3$; P, 7.9$.) 3(o) The phosphonium compound melted at 123- o 26 and was quite stable in air. With water it reacted slowly to give fluoroform quantitatively. The phosphonium iodide (0.127 g, 0.32 mmole) was treated with an excess of water (3.5 g) to give 99.1$ fluoroform (0.0223 g, 0.318 mmole) (CF found 17.56$; calculated for CH (C H ) CP P I 3 3 6 5,2 3 17.68$). The water solution was highly acidic. On eva• poration of water, an oil was obtained. The latter was purified by treating its benzene solution with silver oxid - 211 -

Evaporation of the benzene solution gave a solid melting at o 111-112 and was identified as methyldiphenylphosphine oxide. The identity of the latter compound was confirmed (36) by preparing it by standard methods and comparing the

infra-red spectra0 - 212 -

IV COMPLEXES OF THE PHOSPHINES

1. Borontrlfluorlde Complexes Boron trifluoride was obtained commercially, and was purified by fractionation in the vacuum system. The reaction with the phosphines was carried out by condensing the two in an evacuated tube. Since the complexes were re• active towards moisture, study of the properties of the complexes was carried out in the glove box, through which a steady stream of dry nitrogen was passing. 1(a) Trimethylphosphine: The phosphine (0.1995 g» 2.62 mmoles) was reacted with a slight excess of boron trifluoride (0.1927 g, 2.79 mmoles) in a sealed a tube. The reaction occurred 78 and a white solid was obtained. After 48 hours, excess boron trifluoride (0.0031 g, 0.05 mmole) was removed giving a ratio of phosphine:to boron trifluoride of 1:1.05. Trimethylphosphinerborontrifluoride is a white o crystalline solid melting at 126-130 with decomposition. The compound decomposed slowly in moist air. It decomposed on treatment with water, giving trimethylphosphine. Other polar solvents; e.g., acetone and alcohol, reacted In the same manner. It Is only slightly soluble in chloroform and insoluble in carbon tetrachloride and carbon disulphide. - 213 -

The saturation pressure of the compound was ob• served to be as follows:

T I/T x 105 P log P

30S - 0.3247 3 0.4771 333 0.3003 4 0.6021 348 0.2873 11 1.0414 363 0.2755 17 1.2304 368 0.2718 21 1.3222 373 0.2681 26 1.4150 378 0.2646 30 1.4771 383 0.2611 39 1.5911 388 0.2578 49 1.6902 393 0.2545 59 1.7709 398 0.2512 72 1.8573 403 0.2481 91 1.9590 408 0.2450 111 2.0453 413 0.2421 142 2.1523 418 0.2392 174 2.2405 423 0.2365 217 2.3365 428 0.2336 288 2.4594 The plot o'f log P against l/T showed a break near the melting point. The saturation pressure of the solid is given by the equation log Pmm = 8.460 - 2627 10 rp o in the range 35-100 whence the heat of sublimation is -1 11.98 kcal mole • 1(b) Dimethyltrifluoromethylphosphine: Diraethyltrifluoromethylphosphine (0.2952 g, 2.27 mmole) was sealed with boron trifluoride (0.1617 g* 2.37 mmole). As the phosphine melted, a thick liquid was found to separate. The reaction was complete when the tube reached room tempera• ture. The amount of boron trifluoride recovered (0.0028 g - 214 - corresponding to a reaction with 0.1589 g or 2.33 mmole) gave a ratio of 1:1.03. The product was purified by treat• ment with carbon tetrachloride. The compound was obtained as a colourless oily o liquid which solidified ^ 25 into a glass and the latter o softened at approximately~S • The complex is easily de• composed by air and moisture. Water liberated the phosphine o and heating in moist air at 150 gave traces of fluoroform. The complex showed the same behaviour toward polar and non- polar solvents as the trimethylphosphine analogue. The saturation pressure of the compound was as T l/T x 105 P log P . follows: 22 6 0.4425 8 0.9081 229 0.4367 12 1.0792 233 0.4292 14 1.1461 235 0.4255 17 1.2304 238 0.4202 22 1.3424 241 0.4149 28 1.4472 243 0.4115 33 1.5185 245.5 0.4074 41 1.6128 247.5 0.4041 49 1.6902 250 0.4000 59 1.7709 252 0.3968 69 1.8388 254 0.3937 74 1.8692 256 0.3906 98 1.9912 257.5 0.3883 114 2.0569 259 0.3861 130 2.II39 260.5 0.3839 149 2.1732 262.5 0.3810 178 2.2 504 264.5 0.3781 215 2.3324 266 0.3759 245 ' 2.3892 267.5 0.3738 282 2.4502 269.5 0.3710 331 2.5198 271.5 0.3683 353 2.5478 - 215 -

The saturation pressure follows the equation log.. P(mm) = 10.354 - , 2146 whence the heat of vaporization is 9*68 kcal mole • 1(c) MethyIbistrifluoromethylphosphine (0.2690 g, I.46 mmole) was sealed with boron trifluoride (0.0938 g, 1.38 mmole). There was no perceptible reaction but on cooling o below -78 , the mixture of the reactants solidified. On warming up, a very volatile gas (identified as BP_) 3 volatilised. The reaction tube was kept at room tempera• ture for 120 hours but no complex separated. The tube was o cooled to -78 and the volatiles were separated. Boron trifluoride was recovered quantitatively showing that no reaction had occurred. 1(d) Tristrifluoromethylphosphine (0.3106 g, I.30 mmole) was sealed with boron trifluoride (0.1934 g» o 2.84 mmole) and kept at -112 . The two compounds were miscible at this temperature, but when warmed to room tempera• ture did not give any complex. The volatiles were separated by keeping the reaction tube at -112 and fractionating in the vacuum system. Boron trifluoride was recovered quanti• tatively, showing that no reaction occurred. 1(e) Phenylbistrifluoromethylphosphine: The phos• phine (0.3562 g, 1.587 mmole) was sealed with boron tri• fluoride (0.1331 g, 1.96 mmole). The reaction did not seem to occur at room temperature, whereupon the tube was cooled o to —78 • A solid was deposited but fractionation as des- - 216 - cribed above, gave back boron trifluoride quantitatively, and the spectrum of the residual products did not show any of the characteristic absorptions corresponding to the phosphine- boron trifluoride complex. 1(f) Diphenyltrifluoromethylphosphine (0.254 g, 1 mmole) was reacted with excess of boron trifluoride (0.136 g, 2 mmole). At first no reaction appeared to take place. The tube was then cooled to -78 and warmed up slowly. A thick oil deposited. This was isolated by pumping off the excess of boron trifluoride (0.063 g» 0.93 mmole), which showed that the complex formed with the ratio of 1:1.07 of phosphine: boron trifluoride. The compound was purified by treating it with carbon tetrachloride in which it was in• soluble. Diphenyltrifluoromethylphosphine-boron trifluoride is a colourless oily liquid, which is very reactive towards moisture. Treatment with water, alcohol and acetone decom• poses the compound and gives the phosphine. Similar to other phosphine complexes, it is insoluble in non-polar solvents. The complex is quite stable in dry air at room o temperature but dissociates completely above 100 . The saturation pressure of the compound was found to be as fol• lows : - 217 -

T I/T x 1b3 P Log P

312 0.3205 6 0.7782 323 0.3096 12 1.0792 328 0.3049 15 1.1761 338 0.2959 27 1.4314 343 0.2915 32 1.5051 349 0.2865 39 1.5911 354 . 0.2825 46 1.6628 360 0.2777 55 1.7404 364 0.2747 62 1.7924 368 0.2717 70 1.8451 372 0.2688 80 1.9031 377 0.2653 94 1.9731 381 0.2625 111 2.0453 The saturation pressure follows the equation: log P(ram) = 6.609 - 1753

whence the heat of vaporization is 8.O4 kcal mole . •1(g) Triphenylphosphine: Boron trifluoride was passed in a solution of triphenylphosphine (0.3682 g, 1.405 mmole) in petroleum ether. A white solid was im• mediately precipitated. The solid was purified by washing with petroleum ether and finally pumping off the latter in vacuum. This gave triphenylphosphine-boron trifluoride (O.464O g, 1.405 mmole) and was confirmed by analysis.

(Found C, 63.5$; H, 5.02$. Calculated for (CrH ) P.BF : 6 5 3 3 C, 64.6$; H, 4.7$.) Triphenylphosphine-boron trifluoride is o a white solid melting at 120-130 . It is stable in air but polar solvents decompose it. Like the other phosphine com• plexes this is also insoluble in non-polar solvents. - 218 -

The saturation pressure of the compound was found to be as follows: T i/T x 103 P log P

353 0.2833 10 1.0000 376 0.2660 17 1.2304 386 0.2591 21 1.3222 400 0.2500 26 1.4150 406 O.2463 28 1.4472 411 0.2433 30 1.4771 419 0.2387 33 1.5185 424 0.2360 35 1.5441 430 0.2326 38 1.5798 437 0.2290 42 1.6232 441 0.2268 45 1.6532 446 0.2242 64 1.8062 The saturation pressure equation calculated from the above data is ; P(mm) = 3.840 - 972 10 "IF" whence the heat of sublimation is 4*43 kcal mole . 2. PLATINUM(II) CHLORIDE COMPLEXES Platinum(II) chloride was prepared by heating o chloroplatinic acid (obtained commercially) to 325 in an (117) atmosphere of nitrogen . The complexes were prepared by reacting the phosphine directly with the solid platinum(II) chloride in which case the reaction was slow, or by react• ing In the presence of a solvent. The reaction in the latter case was also slow but had the advantage of giving a homogeneous crystalline product. The complex was also prepared by treating an aqueous solution of potassium - 219 - chloroplatinite, prepared by the standard method (later ob• tained commercially) with an alcoholic or acetone solution of the phosphine. The identities of the compounds were determined from the ratio of reactants as well as from standard methods of analysis. 2(a) Bis(trimethylphosphine)dichloroplatinum(II): Trimethylphosphine (0.220 g, 2.89 mmole) was sealed with platinum(Il) chloride (0.2556 g, 0.96 mmole). Complex for• mation was favoured when the phosphine was in the liquid phase. The reaction, however, did not go to completion and unreacted phosphine (0.1272 g, 1.67 mmole) was recovered after seven days. The mixture of the complex and platinum(II) chloride was extracted with methyl alcohol to give white crystals of the complex. The reaction occurred more rapidly in a benzene .suspension but still the yield was low. Trimethylphosphine, (0.195 g* 2.5:6,' mmole) shaken for 2 4 hours with platinum(II) chloride (0.3345 g, 1.26 mmole) in 2.5 ml benzene, gave only 0.10 g of the complex, representing a 20$ yield. . Better yields of the complex were obtained by shaking an aqueous solution of potassium chloroplatinite (1.20 g, 2.89 mmole) with the phosphine (0.43 g» 5.66 mmole). The mixture was heated on a steam bath for 30 minutes and the white complex was filtered and washed with water, alcohol - 220 - and ether. Recrystallization from methanol gave a yield of

0.51 g» or 41$ of bistrimethylphosphine-dichloroplatinum(II). (Pound Pt, 45.5$; CI, 17.0$. Calculated for [(CH <) P1 PtCl i L 3,3 2 ,2 Pt 44.7$; CI 16.1$) The complex dissolves readily in chloroform, is sparingly soluble in ethanol and almost insoluble in ether, 1 benzene and carbon tetrachloride. In polar solvents, par• ticularly water, heating causes decomposition and free phos• phine is evolved.

The complex melted at 324-326 (with decomp.) and the dissociation pressure was found to be as follows i _3 T P log P i/T x 10 341 0.2933 4 0.602 357 0.2801 7 0.8451 377 0.2653 14 1.1461 387 0.2584 19 * 1.2788 400 0.2500 26 1.4150 408 0.2451 30 1.4771 413 0.2421 33 1.5185 428 0.2336 40 1.6021 433 0.2309 45 1.6532 438 0.2283 50 1.6990 443 0.2257 57 1.7559 448 0.2232 64 1.8062 453 0.2208 72 1.8573 458 0.2183 80 1.9031 463 0.2160 91 1.9590 468 0.2137 103 2.0128 473 0.2114 116 2.0645 478 O.2092 134 2.1271 483 0.2070 165 2.2175 488 0.2049 200 2.3010 493 0.2028 238 2.3766

o The dissociation is more rapid above 200 • The o dissociation pressure in the range of 155-190 is given - 221 - by the equation: log P(mra) = 6.510 - 2108 10 rj-i -1 whence the heat of dissociation is 9.59 kcals mole . 2(b) Bis(dimethyltrifluoromethylphosphine)dichloroplatinum(II): Dimethyltrifluoromethylphosphine (0.412 g, 3*17 mmole) was reacted with platinum(II) chloride (O.425 g, 1.59 mmole). After 48 hours at room temperature no phos• phine was recovered and a,pale yellow solid was obtained which was purified by recrystallization from methanol to give white, needle-shaped crystals of bis(dimethyltrifluoro• me thylphosphine) dichloroplatinum( II ) . (Pound Pt 37«2$; dl .13.-256. Calculated for (CH ) CP P PtCl : Pt 37.1$; 2 2 3.2 3 CI 13.5$). The complex melted at 188-190 with decomposition. The dissociation pressure was found to be as follows: T I/T x 105 P Log P 365 O.274O 21 1.3222 371 0.2695 26 1.4150 379 0.2639 34 1.5315 384 0.2605 42 1,6232 391 0.2558 54 1.7324 394 0.2538 59 I.7709 397 O.2519 67 1.8261 400 0.2500 75 1.8751 407 0.2457 87 1.9395 413 0.2421 97 1.9868 425 0.2353 110 2.0414 439 0.2278 119 2.0755 449 0.2227 125 2.0969 468 0.2137 163 2.2122 473 0.2114 196 2.2923 478 0.2092 229 2.3598 483 0.2070 311 2.4928 - 222 -

The dissociation pressure in the range of 90-130 is given by the equation Log P(ram) = 7.969 - 2438 10 ip -1 whence the heat of dissociation is 11.31 kcals mole . As the compound is heated gradually it becomes black due to decomposition. The white crystals darken completely^, 150 • Decomposition is more rapid after the o complex has melted. The dissociation above 150 is irre• versible, which was found by allowing the phosphine (iden• tified as such spectroscopically) to be in contact with the solid. There was no reaction and the phosphine did not con• dense. When heated in air the phosphine,evolved due to decomposition, caught fire* Bis(dimethyltrifluoromethylphosphine)dichloroplatinum(II) is quite stable in air and is not affected by moisture. It is soluble in alcohol and chloroform, but not in carbon tetrachloride and ether. It is not soluble in cold water, but reacts slowly with hot water to evolve fluoroform. The complex (0.094 g, 0.18 mmole) was added to 1 ml of water and heated to boiling for two hours. Frac• tionation of the products gave only 65$ fluoroform (0.016 g, 0.23 mmole). The reaction in a sealed tube at 100 for 24 hours was much slower and gave only 45$ fluoroform. In both cases a black residue was deposited. - 223 -

The complex gave fluoroform on treatment with alkali. The compound (0.0958 g, 0.182 mmole) was heated o to 80 with a 25$ aqueous sodium hydroxide, and a 90$ yield of fluoroform (0.0230 g, 0.328 mmole) was obtained. The complex (0.102 g) was sealed with trifluoro• iodomethane (1.00 g) in a small Carius tube. It was kept o at -78 for 72 hours and at room temperature for seven days. Fractionation at the end of this period gave tri• fluoroiodomethane (0.988 g) quantitatively, showing that no reaction occurred. The complex (0.120 g) was treated with methyl iodide (1.1.g) in which it dissolved but evaporation of methyl iodide gave almost unchanged reactants and a. trace of fluoroform." 2(c) BlsX'methylbis trif luoromethyl phosphine )dichloroplatinum(II); Methylbistrifluoromethylphosphine

(O.729O g, 3.956 mmole) was sealed with platinum(II) chlor• ide (0.522 g, 1;.'96 mmole) at room temperature. After 24 hours 0.3148 g (1.71 mmole) phosphine had reacted. The reaction product was extracted with carbon tetrachloride and on evaporation of the solvent a yellow crystalline solid (O.45O6 g, 0.71 mmole) was obtained. This was iden• tified as bis(methylbistrifluoromethylphosphine)dichloroplatinum(Il)o (Found Pt 29.9$; 61 11.2$. Calculated for - 224 -

CH (CP ) P PtCl : Pt 30.7$; CI 11.2$). In other attempts 3. 3-2 2 2 to prepare the compound by keeping the reactants at lower temperatures and for longer periods, unreacted phosphine was always recovered. Bis(methylbistrifluororaethylphosphine)dichloro- o platinum(II) melted at 85-87 and the dissociation pressure was recorded.as follows: T l/T x 105 P log P 333 0.3003 9 0..9542 344 0.2907 16 1.2041 354 0.2825 22 1.3424 366 0.2732 27 1.4314 377 0.2653 34 1.5315 386 0.2591 41 1.6128 399 0.2506 55 1.7324 410 0.2439 74 1.8692 418 0.2392 98 1.9912 432 O.2315 143 2.1553 435 0.2299 175 2.2430 438 0.2283 209 2.3201 442 0.2262 254 2.4048 445 0.2247 295 2.4698 447 0.2237 345 2.5378 449 0.2227 386 2.5866

The dissociation pressure in the range of 80-140 may be expressed by the equation: log P(mm) = 4.885 - 1258 10 TJT' whence the heat of dissociation Is 5*76 kcals mole'1'. The o complex decomposes irreversibly above 150 since the dis• sociated phosphine (identified spectroscopically) does not - 225 - condense on cooling to form the complex again. The complex is soluble in carbon tetrachloride, ether, acetone and alcohol, but is insoluble in cold water. It is slightly soluble in boiling water but no decomposition occurs. Treatment with aqueous sodium hydroxide (0.105 g» 0.166 mmole complex with 2.5 ml of 20$ alkali solution) at o 80 for 24 hours gave 50$ fluoroform (0.023 g, 0.328 mmole). The reaction was slow at room temperature and the solution became yellow after the reaction. The compound dissolved in trifluoroiodomethane and methyl iodide to give a yellow solution, but the reactants were recovered quantitatively with traces of fluoroform in each case. 2(d) Reaction of Tristrifluoromethylphosphine with Platinum(II) Chloride: Tristrifluoromethylphosphine (0.175 g> 0.866 mmole) was sealed with platinum(II) chloride (0.132 g, 0.496 mmole) in a small tube and left at room temperature for 120 hours. No reaction seemed to occur; hence the tube was o warmed to 80 for 12 hours. At the end of this period the phosphine was recovered quantitatively, showing that no re• action had occurred. Another attempt was made by passing the phosphine in a stream of nitrogen over platinum(II) chloride heated to o 200 , but no reaction appeared to have occurred. - 226 -

Tristrifluoromethylphosphine (0.243 g, 1.02 mmole) was sealed with a suspension of platinum(II) chloride (0.12 g, 0.45 mmole) in methyl alcohol (1 ml). Methanol developed a golden yellow colour, and if more concentrated solutions were taken the colour was darker. The tube was left at room temperature for 96 hours. During this time it was observed that a few colourless crystals were deposited on the tube wall. Fractionation of the products gave fluoroform (0.0207 g, 0.295 mmole) and a mixture of methanol and tris• trifluoromethylphosphine which was difficult to separate. However, a yellow resinous product was obtained on pumping off the alcohol. The crystals which had appeared in the tube could not be isolated after evaporating the alcohol. Further treatment with alcohol gave a small amount of a pale yellow solid contaminated with platinum chloride. This yellow solid was hydrolysed with aqueous sodium hy- • I- droxide and 13$ fluoroform was obtained. The alkaline residue still contained a trifluoromethyl group as observed from the infra-red spectrum. • The above experiment was repeated, using butanol instead of methanol in order to facilitate separation. The products were 75$ of the unreacted phosphine, 5$ fluoroform and a small amount of yellow resinous material as obtained above. The infra-red spectrum of this substance showed - 227 -

strong absorptions in the 8-9/fregion corresponding to the C-P stretching frequency. There were three broad bands in this region for this substance, whereas the phosphine shows four sharp ones.

2(e) Bi3(phenylbis trifluoromethylphosphine)dichloroplatinum(II)s Phenylbi s trif1uoromethylpho s phine (0.7925 g, 3.22 mmole) was heated with platinum(II) chloride o (0.5079 g» 1.16 mmole) to 100 for seven days. The reaction was slow at room temperature and a grey product was obtained under these conditions. Heating accelerated the process and greenish-yellow crystals lere deposited. At the end of the reaction period excess phosphine (0.206 g, 0.84 mmole) was recovered and the greenish solid was recrystallized from acetone. This was identified as bis(phenylbistrifluoromethylphosphine)dichloroplatinum(II). (Pound C, 25.6$;

c H F P PtC1 8 H, 1.36$; P, 29.44$. Calculated for 1g 10 12 2 2 C, 25.4$; H, 1.37$; P, 30.1$.) Treatment of a solution of phenylbistrifluoro- .methylphosphine in acetone with an aqueous solution of potassium chloroplatinite gave a small amount of a solid o a > 300 besides the one melting at 134-36 • It was insoluble in non-polar solvents and was possibly the cis isomer. Since it was not obtained in any large proportion it was not investigated. The main component, melted at o 134-136 , was soluble in most organic solvents, and was not affected by boiling water. It was also soluble in tri- - 223 - fluoroiodomethane and methyl iodide, giving a yellow solution but no reaction was observed to take place. The complex (0.129 g, 0.17 mmole) was treated with aqueous sodium hydroxide (2.5 ml of 20$ solution). Re• action commenced immediately the reactants came in contact, and to complete the reaction, the mixture was heated to 80 for 12 hours. This gave 93*5$ fluoroform (0.0439 g, 0.627 mmole). Bis(phenylbistrifluoromethylphosphine)dichloroplatinum(Il) (0.271 g, 0.357 mmole) was dissolved in carbon tetrachloride, and a small excess of a dilute solution of bromine in the same solvent added to it. On standing, an orange coloured precipitate was obtained. The solvent and excess bromine were pumped off, and a product corresponding to the addition of two equivalents of bromine (0.328 g, o 0i.357, mmole) was obtained as an orange solid melting at 73 • I Thermal decomposition of this substance gave pure phosphine, suggesting that the reaction with bromine had produced bis(phenylbistrifluoromethylphosphine)dichlorodibromoplatinum(IV)• 1 This compound was characterised by hydrolysing it with aqueous alkali. 0.128 g (0.139 mmole) of the substance o on heating with alkaline solution to 80 gave 0.037 g» (0.556 mmole) or 96.2% fluoroform. The infra-red spectrum of the compound (fig.17 ) - 229 - showed that only monosubstituted phenyl group was present, and there was, a shift in the C-P absorption as compared with the phosphine. A similar compound was obtained by treating a solution of bis(phenylbistrifluoromethylphosphine)dichloroplatinum(II) (O.I44 g, 0.19 mmole) in carbon tetrachloride with an iodine solution in the same solvent. A brown solid was obtained (0.192 g, 0.19 mmole). The gain in weight of the solid corresponded with the formation of bis(phenylbistrifluoromethylphosphine)dichlorodiiodoplatinum(IV)• To establish the structure of bis(phenylbistrifluoromethylphosphine)dichloroplatinum(II), it was treated with ethylenediamine. A large excess of ethylenediamine and a mixture of water and the complex C H (CP ) P PtCl 6 5 3.2 2 2 were heated with shaking to effect partial solution. After cooling this solution, a concentrated aqueous solution of potassium chloroplatinite was added. The precipitate so obtained was found,spectroscopically, not to contain any phenylbis trif luoromethylphosphine, s turning that the struc• ture was not cis. 2(f) Bis(diphenyltrifluoromethylphosphine)dichloroplatinum(II): Diphenyltrifluoromethylphosphine (O.254 g» 1 mmole) in acetone was added to an aqueous solu• tion of potassium chloroplatinite (0.21 g, O.5O6 mmole) and the mixture was heated for 50 minutes. A reddish-orange - 230 -

liquid separated as the acetone volatilised. This liquid became a resinous mass when cooled. Its acetone solution was treated with animal charcoal and after filtration the yellow solution so obtained was treated with a large excess of water. A pale yellow solid was obtained and was iden• tified as bis(diphenyltrifluoromethylphosphine)dichloroplatinum(II). The complex was analysed for fluoroform by treating it with bromine. (Pound CF^, 16.9$. Calculated

for (CgH^CF P 2PtCl2: CFy 17.8$.) The compound so obtained was treated with ether. A small amount was found to be insoluble in this solvent. o The main component melted at 63-65 and was identified as the trans isomer (see later). The small fraction melted at 230 and probably was the cis isomer. The main component was soluble in most organic solvents but insoluble in water. It was not affected by boiling water nor by cold aqueous alkali. Alcoholic potas• sium hydroxide evolved fluoroform slowly at room temperature. The complex (0.216 g, 0.279 mmole) was heated to 80 with potassium hydroxide for 36 flours. The reaction was , . >x quite "slow even at this temperature since only 85$ fluoro• form (0.0327 g, 0.478 mmole) was evolved. The complex was soluble in trifluoroiodomethane and methyl iodide, but they effected no change on it. - 231

Reaction of bis(diphenyltrifluoromethylphosphine dichloroplatinum(Il) (0.128 g, 0.165 mmole) with a carbon tetrachloride solution of bromine gave a yellow precipitat Evaporation of solvent and excess bromine gave a yellow solid (0.154 g» 0.165 mmole)—which corresponded to the addition of two moles of bromine and possibly was bis(di• phenyl trif luoromethylphosphine)dichlorodibromoplatinum(ISO The substance is soluble in water and other polar solvents Hydrolysis of this.compound (0.144 S» 0.154 mmole) with alkali gave fluoroform (0.021 g, 0.33 mmole) immediately.

(Pound CP^ 14.5$. Calculated for UCgHLj^F^P PtCl Brn 2 2 2 14.7$). Bis(diphenyltrifluoromethylphosphine)dichloroplatinum(II) (0.142 g, 0.183 mmole) was treated with a solution of Iodine in carbon tetrachloride to give an addi tion product (0.188 g, 0.183 mmole). A dark brown solid was precipitated and the gain in weight corresponded with the formation of bis(diphenyltrifluoromethylphosphine)- dichlorodiiodoplatinum(IV). The elucidation of the structure of the main component from the preparation of the complex was carried out by treating with ethylenediamine. No precipitate con• taining the phosphine and ethylenediamine was obtained (as found spectroscopically), showing that bis(diphenyltrifluoromethylphosphine)dichloroplatinum(Il) was probably a trans isomer. - 232 -

DETERMINATION OF DIPOLE MOMENTS

Accurate determination of the dipole moment was not possible in most cases because (1) of low solubility in solvents of low dielectric constant and (2) of their tendency (in the case of trimethylphosphine and dimethyltrifluoromethylphosphine complexes) to decompose slowly in the presence of moisture. The calculation of this con- (146) stant was therefore done by using Jensen's formula - for such cases. The dipole moments of the compounds were found to be as listed in the following table. Molar concentration soln. P i^(D) m ^ (CH ) P PtCl measured in chloroform: benzene (1:1) solu- L 3.3 J2 2 tion (£ mix = 3.380) 0.000466 3.426 3320 13.1 ±0.5 0.000977 3.441 3780 (CH ) CP P PtCl measured in chloroform solution 3 2 3 2 2 (£CHC1 = 4'947) 0.00108 4.982 1667 0.00189 5.007 1806 9.2 ±0.5

(CH (CP ) P PtCl measured in carbon tetrachloride solution 3, 3-2 2 2 (£cci = 2-261> 4 0.00297 2.261 0.00525 2.261 0.0 r(C H ) CP P PtCl measured in chloroform solution 6 5 2 3 2 2 2 (6CHC1 = 4-955) 3 0.00132 4.955 0.00391 4.955 0.0 - 233 -

Molar concentration soln. P M>CD) m

(C H (CF ) P n PtCl measured in chloroform solution 6 5 3.2 J2 ^CHClj = 4-955) 0.00142 4.955 0.00495 4.955 0.0

3* Complexes of the Nickel Salts The complexes were prepared by reacting anhydrous nickel salts (except nickel nitrate, which was used as the hexahydrate) with phosphines in 1:2 ratio in sealed evacu• ated tubes,and were purified by recrystallization from butanol. Use of the glove box was necessary since all the compounds were sensitive towards moisture. Unless other• wise stated, carbon tetrachloride solution was used in measurements of absorption spectra. A. TRIMETHYLPHOSPHINE COMPLEXES (a) Bis(trimethylphosphine)dichloronickel(II): Nickel chloride (0.2233 g, 1.72 mmole) was reacted with trimethylphosphine (0.3485 g, 4*58 mmole). The reaction started at room temperature with the development of a purple colour. The reaction was complete in one-half hour arid the product at this stage was black violet. When the reaction tube was cooled in liquid nitrogen the product assumed a pink colour (only in the presence of excess phosphine). After removing the excess phosphine (0.098 g, 1.28 mmole) - 234 - the solid was recrystallized from butanol to give crimson red crystals. This was identified as his(trimethylphos• phine )dichloronickel( II ) . (Pound Ni 20.05$, CI 25.14$. Calculated for f(CH ) P NiCl : Ni 20.56$, CI 25.27$.). L 3.3 J 2 2 The complex was sensitive to moisture. Water gave a pink solution which decomposed easily with the for• mation of a transient blue colour and with evolution of phosphine. Acids easily faded the colour but a dilute alka• line solution returned it. It is easily soluble in polar solvents but only slightly so in non-polar solvents. The colour in the various solvents is different. In non-polar solvents,like carbon tetrachloride and benzene,it is pink. It is violet in chloroform, orange in diethyl ether and petroleum ether, and deep blue in acetone. The colour of these solutions faded gradually,giving the nickel salt and the phosphine, 3(h) Bis(trimethylphosphine)dibromonickel(II): Nickel bromide (0.732 g, 3»36 mmole) was reacted with tri• methylphosphine (0.5141 g, 6.76 mmole). Reaction started at room temperature with the formation of dark violet solid. However, the reaction did not go to completion after 24 hours and most of the phosphine (0.343 g) was recovered. The solid and unreacted phosphine- were then refluxed for 30 minutes,when crimson red crystals were obtained. This was - 235 - identified as bis(trimethylphosphine)dibromonickel(II)•

(Pound Ni 16.01%, Br 42.7$. Calculated for (CH ) P NiBr : D 3 2 2 Ni 15.68$, Br 43.24$.) The compound was slowly decomposed by moisture. It was soluble in polar solvents with easy decomposition. The solutions in practically all solvents were usually pink. 3(c) Bis(trimethylphosphine)di iodonickel(II): Nickel iodide (1.1193 g> 3*65 mmole) was sealed with tri• methylphosphine (0.545 g> 7.17 mmole). The reaction was slow and after 48 hours a small amount of phosphine (0.0694 g) was still left, a dark brown solid also being formed. The pure product (dark brown) was obtained from hot butanol and was identified as bis(trimethylphosphine)diiodonickel(II).

(Pound Ni 11.85$, I0 54-30$. Calculated for f(GH_) p| NiCl : [ 3 3 2 2

Ni 12.50$, i2 54.72$.) The compound is. not affected by moisture. It dis• solves in warm water, giving a pink solution.which is de• colorized on acidification. The color is returned when the solution is neutralised again with dilute alkali. The solu• tions in most solvents are pink. 3(d) Bis(trimethylphosphine)dithiocyanatonickel(II)t Nickel thiocyanate (0.4223 g, 2.43 mmole) was treated with trimethylphosphine (O.484I g, 6«37 mmole). The reaction tube was opened after seven days and unreacted phosphine (0.2987 g, 3.93 mmole) was recovered. This gave a ratio of 1:1 for the - 236 -

reactants. The product at this stage was blue-black. On re• fluxing with butanol and an excess of phosphine the crystals obtained were orange yellow and were identified as bis(trimethylphosphine)dithiocyanatonickel(II). (Pound Ni 11,27%,

(SCN)" 34.45$. Calculated for (CH ) P Ni(SCN) 3 3 2 2 Ni 17.79$, (SCN)~ 34.60$.)

The compound was not affected by moisture; in fact it was only slightly soluble in cold water. It dis• solved in warm water with decomposition. It was only spar• ingly soluble in ether, but was fairly soluble in benzene and carbon tetrachloride.

3(e) Bis(trimethylphosphine)dinitratonickel(II);

Trimethylphosphine (0,1992 g, 2.62 mmole) was sealed with nickel nitrate hexahydrate (0.381 g, 1.31 mmole). The re• action occurred at room temperature with the formation of a dark red sticky substance. Only traces of phosphine mixed with water were recovered. Attempts were made to obtain a crystalline product,; by (1) heating the hexahydrate to o 120 to drive off as much of the water as possible, and

(2) by refluxing the mixture of nickel nitrate hexahydrate and phosphine with acetic acid, butanol, and tetrahydro- furan, but without any satisfactory results. For analyti•

cal and magnetic measurements, nickel nitrate hexahydrate was heated to 120 and condensed with an excess - 237 -

of phosphine and butanol. After a homogeneous solution was obtained by warming, the butanol was pumped off. Next it was treated with a larger excess of phosphine (to serve as solvent). The complex so obtained was taken up in butanol, and was identified as bis(trimethylphosphine)dinitratonickel(Il). (Pound Ni 17.33$. Calculated for [(CH ) Pi Ni (NO ) : I 3.3 J2 3.2 Ni 17.37$). The compound was very sensitive towards moisture and was easily decomposed by water.

B. -DIMETHYLTRIFLUOROMETHYLPHOSPHINE COMPLEXES The reaction with dimethyltrifluoromethylphosphine had to be carried out in anhydrous conditions. The hydrated nickel salts on being warmed with solvents gave off fluoro• form. Recrystallization was also not possible for this reason. Direct reactions were therefore carried out in all cases. 3(f) Bis(dimethyltrifluo rome thylpho s phi n e)di chlo- ronickel(II): Nickel chloride (0.2336 g, 1.81 mmole) was allowed to react with dimethyltrifluoromethylphosphine (0.5850 g, 4«5 mmole) for seven days. When freshly sealed the complex was scarlet red and turned blue oh cooling (only in excess phosphine), but when left for a long period it became green. The recovery of excess phosphine (0.1949 g> - 238 -

1.50 mmole) showed that the reaction had occurred in the ratio of 1:2 (of nickel chloride to phosphine) and the pro• duct was identified as bis(dimethyltrifluoromethylphos• phine )dichloronickel( II) . (Found Ni 14.72$, CI 13.15$. Calculated for ["(CH ) CF Pi NiCl : Hi 14*91$, CI 13.25$..) L 3 2 3 J 2 2 This compound is soluble in polar solvents but decomposes easily. The absorption spectrum was measured from a freshly prepared methanol solution. 3(g) Bis(dimethyltrifluoromethylphosphine)dibromonickel(Il): Nickel bromide (0.1920 g, 0.88 mmole) was sealed with dimethyltrifluoromethylphosphine (0.2306 g, 1.77 mmole). The reaction was slow but was complete in 15 days giving a dull black solid and only traces of phos• phine. This was identified as bis(dimethyltrifluoro• methylphosphine )dibromonickel( II) . (Found Ni 11.84$, Br 34.10$. Calculated for (CH ) CF Pi NiBr : Ni 12.14$, . . 3 2 3 J2 2 Br 33.47$.) The compound decomposed easily in moist air but was quite stable in a dry atmosphere. It was decomposed easily by most polar solvents in which it was soluble. 3(h) Bis(dimethyltrifluoromethylphosphine)diiodonickel(II): Dimethyltrifluoromethylphosphine (0.2439 g, 1.87 mmole) was reacted with nickel iodide (0.311 g, 1 mmole). The reaction was slow and the resulting product - 239 - ttfas a dark brown solid which was identified as bis(dimethyl• trif luoromethyl)diiodonickel(II). (Pound Ni 9.74$,

Ig 43.80$. Calculated for (CH ) CF P Nil : Ni 10.14$, 3.2 3 2 2 1,44.40$.) The compound was practically insoluble in cold water and on warming with it, gave off the phosphine. The complex dissolved in benzene and carbon tetrachloride, but was soluble with immediate decomposition in most other sol• vents. 3(i) Bis(dimethyltrifluoromethylphosphine)dithiocyanato-nickel(II): Diraethylbistrifluoromethylphosphine (0.340 g, 2.61 mmole) was treated itfith nickel thiocyanate (0.2281 g, 1.31 mmole). Only traces of unreacted phosphine were recovered and a yellow solid was obtained. This could be purified by refluxing with butanol,and was identified as bis(dimethyltrifluoromethylphosphine)dithiocyanatonickel(II). (Pounds Ni 13.42$; (SON)" 26.25$. Calculated for

(CH3)2CP3P 2Ni(SCN) : Ni 13.36$; (SON)"" 26.73$.) This compound was stable in moist air and was soluble in warm water with slow decomposition. It was soluble in most organic solvents but the polar ones decom- poseiit more easily. - 240 -

3 (j) Bis(dimethyltrifluoromethylphosphine)dinitratonickel(II): Various experiments (as for trimethyl• phosphine) were conducted to isolate a stable crystalline complex with nickel nitrate, but the best results were ob• tained by first heating the salt (0.222 g, 0.76 mmole) to 120 and then condensing a large excess of phosphine (0.52 g, 4.0 mmole) in a small tube (so that the phosphine is in a liquid phase). Slight warming was sufficient to make the product homogeneous. The dark red sticky sub• stance was taken up in butanol and was identified as bis(dimethyltrifluoromethylphosphine)dinitratonickel(II). .(Pound Ni,13.22$. Calculated for l~(CH ) CF P~| Ni (NO ) : L 3 2 3J2 5 2 Ni,13.12%)

C. REACTION WITH OTHER PHOSPHINES The nickel salts were treated with methylbistrifluoromethylphosphine, phenylbis trifluoromethylphosphine and tristrifluoromethylphosphine but no compound formation was observed. The treatment was attempted both with and without solvents. When performed in the presence of sol• vents, the recovered phosphines were contaminated with fluoroform. Preliminary experiments with diphenyltrifluoromethylphosphine showed that the complexes were form• ing, but these have not been studied in detail. - 241 -

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M. A. A. BEG AND H. C. CLARK

ABSTRACT

The formation of co-ordination compounds of (CH3)3P, (CH3)2PCF3, CH3P(CF3)2, and

P(CF3)3> with boron trifluoride and platinum (II) chloride has been studied. The properties

of the new compounds (CH3)2PCF3.BF3, [(CH3)2PCF3]2PtCl2, [CH?P(CF3)2]2PtCl2 are described, and it is hence concluded that the stabilities of the boron trifluoride compounds decrease in the order

(CH,),P.BF, > (CH3)2PCF3.BF3 > (CH3P(CF3)2BF3 > P(CF3)3.BF3), while for the platinum (II) complexes the order of stability is

[(CH3)3P]2PtCl2 < [(CH3)2PCF3]2PtCI2 > [CH3P(CF3)2]2PtCI2 > ([P(CF3)3]2PtCl2). These two orders are related to the electronegativity of the trifluoromethyl group and its influence on the bonding properties of the phosphorus atoms.

INTRODUCTION While a range of organometallic and organometalloidal trifluoromethyl compounds has been prepared, little quantitative information is so far available for the trifluoromethyl group. Since its electronegativity will differ widely from that of a normal alkyl or aryl group, these organometalloidal compounds may be expected to show unusual properties. A study has therefore been made of the effect of the trifluoromethyl group on the donor properties of substituted phosphines. Two types of addition products may be formed: (a) those containing-only a

phosphorus and a transition metal, e.g. (R3P)2PtCl2. The effect of the electronegative trifluoromethyl group on the formation of a- and x-bonds will vary and may be investi• gated by examining the properties of these two classes of compounds.

EXPERIMENTAL Preparation of the Phosphines Trimethylphosphine was prepared by the method of Mann and Wells (1). This reaction normally gives low yields, but it was found that, with strong cooling of the reaction vessel in an acetone - solid CO2 mixture, yields of 60% could be regularly obtained. The phosphine was isolated as the silver iodide complex, which, when warmed in vacuo, readily evolved the phosphi'ne. The reaction of trimethylphosphine with trifluoroiodomethane, as described by Haszeldine and West (2), was used to prepare dimethyl trifluoromethylphosphine, but yields higher than 33% based on CF3I could not be obtained. The reaction appeared to commence below —78° and was virtually complete after the mixture had stood at room temperature for about 30 minutes. Apart from the desired product and an involatile residue of tetramethylphosphonium iodide, a volatile white solid identified as dimethyl bis(trifluoromethyl)phosphonium iodide, m.p. 60°, was also found. The latter compound (0.472 g) reacted with excess aqueous sodium hydroxide at room temperature to give fluoroform (0.235 g) corresponding to the loss of two CF3 groups. Purification of the "^Manuscript received August 20, 1959. Contribution from the Chemistry Department, University of British Columbia, Vancouver 8, B.C. 'Presented at the International Conference on Co-ordination Chemistry, London, April 1959.

Can. J. Chem. Vol. 38 (1960) 119 120 CANADIAN JOURNAL OF CHEMISTRY. VOL. 38, 1960 dimethyl trifluoromethylphosphine was best achieved by thermal decomposition of its silver iodide complex as described by Haszeldine and West. Methyl bis(trifluoromethyl)phosphine was prepared by reacting tris-trifluoromethylphosphine with methyl iodide as described by Haszeldine and West (3).. The-preparation of t-ris(trifluoromethyl)phosphine from phosphorus and trifluoroiodo• methane followed the methods of earlier workers (4). Commercial boron trifluoride was used after purification by vacuum distillation. Platinum (II) chloride was prepared by heating chloroplatinic acid to 325° in an atmos• phere of nitrogen. The complexes described below were prepared by reacting the phos• phines with boron trifluoride or platinum (II) chloride in sealed, evacuated tubes. The identities of the boron trifluoride derivatives were determined from the ratios of the reactants and those of the platinum (II) chloride complexes by standard methods of analysis. Saturation pressures were measured with an isoteniscope, the boron trifluoride compounds being prepared directly in its bulb in order to avoid decomposition with moisture.

Compounds with Boron Trifluoride (a) Trimethylphosphine.—The phosphine (0.1995 g, 2.60 mmoles) reacted immediately with boron-trifluoride (0.1927 g, 2.79 mmoles) to give a white solid. The recovery of excess trifluoride (0.0031 g) gave a ratio phosphine:boron trifluoride of 1:1. The com• pound (CH3)3P.BF3 has been reported previously (5) but few of its properties have been described. It is decomposed slowly in moist air, and rapidly in water, acetone, and ethanol. It is only slightly soluble in chloroform and insoluble in carbon tetrachloride and carbon disulphide. The melting point is 126-130° (decomp.) and the saturation pressure is given by the equation logio p (mm) = 8.460 — (2627/ T) in the range 25o-100°, whence the heat of sublimation is 11.98 kcal mole-1. (b) Dimethyl trifluoromethylphosphine.—The phosphine (0.2952 g, 2.27 mmole) reacted with boron trifluoride (0.1589 g, 2.27 mmole) to give a white solid which melted below room temperature to a viscous liquid. The compound showed the same behavior towards moist air and polar solvents as its trimethylphosphine analogue. The melting or freezing point could not be precisely determined since supercooling to a glass occurred. Softening of the glass took place at approximately —9° C. The vapor pressure of the compound is given by the equation logio p (mm) = 10.354— (2146/T) whence the heat of vaporization is 9.68 kcal mole-1. (c) Methyl bis(trifluoromethyl)phosphine.—In this case, no reaction occurred after 120 hours at room temperature between the phosphine (0.2690 g) and boron trifluoride (0.0938 g). Cooling to —78° still allowed the boron trifluoride to be recovered and there was no sign of complex formation. Similarly, the treatment of tristrifluoromethyl• phosphine (0.3106 g) with boron trifluoride (0.1934 g) failed to reveal the formation of any complex.

Compounds with Platinum (II) Chloride

(a) Trimethylphosphine.—The complex [(CH3)3P]2PtCl2 has been prepared previously (6) but it was here prepared for comparison with its trifluoromethyl analogues. Direct reaction between the phosphine and platinum (II) chloride in the absence of a solvent was very slow. In a benzene suspension, reaction was more rapid although the yield was still low. Thus trimethylphosphine (0.195 g) shaken for 24 hours with platinum (II) chloride (0.3345 g) in benzene gave only 0.10 g of the complex, a 20% yield. Higher yields could be obtained by using the method described by Jensen (7) for the preparation of the BEG AND CLARK: TRIFLUOROMETHYL GROUP 121 corresponding triethylphosphine complex. This involved shaking an aqueous solution of potassium chloroplatinite (1.20 g) with the phosphine (0.43 g). The mixture was heated on a steam bath for 30 minutes, and the white complex was filtered, and washed with water, alcohol, and ether. Recrystallization from methanol gave a yield of 0.51 g, a 4.1% yield of bis(trimethylphosphine)dichloroplatinum (II). Found: Pt, 45.5; CI, 17.0. Calc. for

[(CH3)3P]2PtCl2: Pt, 44.7; CI, 16.1%. The melting point is 324-326° and the dissociation pressure in the range 155-190° is given by the equation logio p (mm) = 6.510—(2108/T), whence the heat of dissociation is 9.59 kcal mole-1. The complex dissolves readily in chloroform, is sparingly soluble in ethanol, and almost insoluble in ether, benzene, and carbon tetrachloride. In water, particularly when heated, decomposition occurs and the free phosphine is evolved. {b) Dimethyl trifluoromethylphosphine.—The reaction of the phosphine (0.412 g, 3.17 mmoles) with platinum (II) chloride (0.425 g, 1.59 mmoles) at room temperature for 48 hours in a sealed tube gave a pale yellow product, which was recrystallized from methanol to give white, needle-shaped crystals of bis(dimethyl (trifluoromethyl) -

phosphine)dichloroplatinum (II). Found: Pt, 37.2; CI, 13.2. Calc. for [(CH3)2PCF3]2PtCl2: Pt, 37.1; CI, 13.5%. The complex melted at 188-190° with decomposition and the dissocia• tion pressure over the range 90-130° is given by the equation logio p (mm) = 7.969 — (2438/T) whence the heat of dissociation is 11.31 kcal mole-1. It is soluble in alcohol, chloroform, and carbon disulphide and insoluble in ether, benzene, and carbon tetra• chloride. It is not soluble in cold water, but reacts slowly with hot water to evolve fluoroform. Almost complete conversion (90%) to fluoroform is obtained on heating to :80° with 25% aqueous sodium hydroxide. (c) Methyl bis{trifluoromethyl)phosphine.—This phosphine and platinum (II) chloride in a 2:1 ratio reacted only slowly and unreacted phosphine was always recovered from the re• action tubes. Extraction of the solid reaction product with carbon tetrachloride or methanol and evaporation of the extract gave yellow crystals of bis(methyl bis(trifluoromethyl)-

phosphine)dichloroplatinum (II). Found: Pt, 29.9; CI, 11.2. Calc. for [CH3P(CF3)2]2-

PtCl2: Pt, 30.7; CI, 11.2%. The melting point is 85-87° and the dissociation pressure in the range 80-140° may be expressed as logio/' (mm) = 4.885 — (1258/T) whence the heat of dissociation is 5.76 kcal mole-1. The complex is soluble in carbon tetrachloride, ether, acetone, and alcohol, but is insoluble in water. Hydrolysis (50% approx.) to fluoroform occurs with 25% aqueous sodium hydroxide at 80°. (d) Tris(trifluoromethyl)phosphine.—The following experiments were performed in attempts to prepare a platinum (II) complex. In all cases the reactants were completely recovered and no sign of complex formation was observed, (i) Direct reaction of the phosphine (0.175 g) and platinum (II) chloride (0.132 g) at room temperature, (ii) The passage of the phosphine in a stream of nitrogen over platinum (II) chloride heated to 200°. {Hi) Reaction of the phosphine and platinum (II) chloride in methanol. Several experiments were performed under this last set of conditions and in all cases the methanol acquired a yellow color and a few colorless crystals appeared to be formed. All attempts to isolate a product were unsuccessful, apparently because of decomposition. Dipole Moments Because of the low solubility of the platinum complexes and also their tendency, in certain cases, to decompose slowly in the presence of moisture, accurate dipole moments were not calculated. The dielectric constants were measured with a simple Ebarch dielectric constant meter and dipole moments were calculated using Jensen's formula (8) for dilute solutions. The accuracy of the dipole moments is ±0.5 D. 122 CANADIAN JOURNAL OF CHEMISTRY. VOL. 38, 1960

TABLE

Molar concentration caoin Pm n (D)

[(CH3)3P]2PtCl2 measured in chloroform:benzene (1:1) solution (emiX = 3.380) 0.000466 3.426 - 3320 0.000977 3.441 3780 13.1 ±0.5

[(CH3)2PCF3]2PtCl2 measured in chloroform solution (ecHcia = 4.947) 0.00985 4.982 1667 0.00189 . 5.007 1806 9.2±0.5

[CH3P(CF3)2]2PtCl2 measured in carbon tetrachloride solution (eccu = 2.261) 0.00297 2.261 0.00525 2.261 0

DISCUSSION The addition compounds formed by phosphines with boron trifluoride result from dative c-bond formation from phosphorus to boron. Smaller secondary effects such as back co-ordination may also be involved but these are of only minor importance. Evidence

from other series of BF3 derivatives (9), comparable to that described here, reveals that a decrease in the electron-donating power of the co-ordinating base produces a correspond• ing decrease in the stability of the molecular addition compound. As a qualitative measure "of stability, we have here employed relative volatilities. The vapor pressure equations

quoted above show thedower volatility and greater stability of (CH3)3P.BF3 as compared with (CHs)2PCF3.BF3. The trifluoromethyl group thus markedly reduces the donor properties of the phosphorus atom. This is in accordance with a higher electronegativity and a smaller inductive effect for the trifluoromethyl in contrast to the methyl group.

Since the adduct (CF3)3P.BH3 does not exist (10) and since borine adducts are generally more stable than their boron trifluoride analogues, it is not surprising that methyl bis(trifluoromethyl)phosphine- and tris(trifluoromethyl)phosphine-boron tri• fluoride adducts could notbe isolated.

The possibility that steric interaction by the much larger CF3 group is responsible for the observed decrease in stability jnust also be considered, although the extent of such interaction is difficult to determine accurately. The steric requirements will certainly be greatest for tris(trifluoromethyl)phosphine for which Bowen (11) has shown the CPC

angles to be 100° and the CF3 groups all to lie on the same side of the phosphorus atom.

Also since there is some rearrangement of the planar BF3 molecule towards a tetrahedral configuration on formation of the co-ordinate bond, it would appear that steric interaction

between the CF3 groups and F atoms must be comparatively small. For the other phos•

phines with fewer CF3 groups, steric interactions will be of even less significance. The

observed decrease in stability of the BF3 adducts is therefore not due to. steric effects.

The infrared spectra of (CH3)3P.BF3 and (CH3)2PCF3.BF3 could not be completely resolved so that full interpretation is not possible. However, in both cases the B—F

-1 -1 stretching frequencies at 1450 and 1505 cm in BF3 were shifted to the 1175-1200 cm .

This is similar to the shifts observed for ketone-BF3 complexes by Susz et al. (12). There is

-1 also a considerable shifting of bands in the 650-750 cm region. Since both the BF3 bending and P—C (aliphatic) stretching frequencies occur in this region and since no other similar spectra are available for comparison, assignments have not been made. In phosphine - platinum (II) co-ordination compounds, in addition to the formation of dative c-bonds from phosphorus to platinum, strong ^7r-(f7r-bonding.is also possible and appears to be of considerable importance in determining,relative stabilities. As an extreme BEG AND CLARK: TRIFLUOROMETHYL GROUP 123

case, consider bis(trifluorophosphine)dichloroplatinum (II) (F3P)2PtCl2 (1/3) .-.Here the highly electronegative fluorine atoms reduce the electron donor properties of phosphorus, but at the same time cause considerable 7r-bonding which appears to involve the unshared rf-electron pairs of platinum and the vacant 3d orbitals of the phosphorus atoms. The extent of this electron drift from platinum back to phosphorus is shown by the small dipole moment of 4.4 D. This indicates a cM-configuration and must be compared with values of 11-12 D for the cis-isomers of bis(trialkylphosphine)dichloroplatinum (II) complexes. Similarly, the substitution of trifluoromethyl for methyl groups may tend to give increased ir-bonding between platinum and phosphorus although not to the same extent as phosphorus trifluoride. The configurations of the complexes described earlier can be deduced from their colors, solubilities in polar and non-polar solvents, and their dipole moments. Bis(trimethylphosphine)dichloroplatinum (II) and bis(dimethyl trifluoromethylphosphine)dichlorop!ati- num (II) are obtained as the cis-isomers since they are white solids and have large dipole moments. Bis(methyl bis(trifluoromethyl)phosphine)dichloroplatinum (II) is isolated in the trans-iorm which is yellow-orange and has a zero dipole moment. It must be empha• sized that these are the major components of reaction products prepared and recrystallized under the same conditions. In all three cases there were indications that the other isomer was also formed but only to the extent of less than about 5%. Since it is known that the isomer obtained under a given set of conditions may depend to some extent on relative solubilities, it would clearly be necessary to study in detail the cis-trans equilibria in order to determine unambiguously the relative stabilities of the isomers of the various com• plexes. However, since all our complexes could be prepared under identical conditions in the absence of solvents, the fact that different isomers are obtained with dimethyl trifluoromethylphosphine and methyl bis(trifluoromethyl)phosphine is significant and is discussed later. The relative stabilities of these new phosphine complexes may be examined in several ways. Chemically, the trimethylphosphine complex appears the least stable since decom• position always occurs to a small extent during recrystallization from methanol, and to a much larger extent on reaction with warm water. Also, the solid compound always smells strongly of the free phosphine. In contrast the other two complexes were odorless solids which could be recrystallized without decomposition and which reacted only slowly with hot water. An accurate index of thermal stability is seen in the heats of dissociation calculated from the observed dissociation pressures, the values being 6.7 kcal mole-1 for

-1 -1 «s-[(CH3)3P]2PtCl2, 11.3 kcal mole for c«-[(CH3)2PCF3]2PtCl2, and 5.8 kcal mole for

/raras-[CH3P(CF3)2]2PtCl2. The process of dissociation probably involves the loss of a phosphine molecule and the formation of a dimeric bridged complex,

2(phosphine)2PtCl2 —» 2phosphine + (phosphine)2Pt2Cl4 but it could alternatively result in the simultaneous loss of both phosphine molecules to give free platinum (II) chloride. Although the actual course of dissociation is unknown, the above values are considered a reasonable guide to relative stabilities of the platinum complexes and they show the order to be

(CH,),P < (CH3)2PCF3 > CH3P(CF3)2[ > P(CF,),].

Points of particular interest are: (a) the increase and then decrease in stability in the series as CF3 is substituted for CH3; (6) the non-existence, under the conditions so far studied, of a Pt(II) complex of tris(trifluoromethyl)phosphine; and (c) the fact that, under 124 CANADIAN JOURNAL OF CHEMISTRY. VOL. 38, 1900

the same conditions, dimethyl (trifluoromethyl)phosphine gives the cw-isomer, while methyl bis(trifluoromethyl)phosphine produces the trans-isomer. In platinum (II) com• plexes the greatest degree of x-bonding is obtained when the two x-bonding ligands are cis to one another (14). Substitution of the first methyl group by the more electronegative

CF3 group thus appears to give greater stability to the complex by causing a greater increase in x-bonding than is offset by the reduction in strength of the cr-bond. This can also be seen by a comparison of the dipole moment of 13.1 D for [(CH3)3P]2PtCl2 with that of 9.2 D for [(CH3)2PCF3]2PtCl2. For the complex of methyl bis(trifluoromethyl) phosphine there might be expected to occur one of only two possibilities: (a) introduction of the second CF3 group on each phosphine might produce even greater stability; or (b) the reduction in strength of the tr-bond may more than offset any increase in x-bonding so as to give a less stable complex. In either case, one might expect that the cw-isomer would be obtained. The occurrence of the trans-isomer is therefore unexpected, and can satisfactorily be explained, together with the non-existence of a tristrifluoromethyl• phosphine complex, in terms of steric hindrance. When models are drawn using the usual values of atomic radii, it can be shown that 2 trimethyl(or indeed any alkyl)phosphine molecules can be placed cis to one another about a platinum atom, but not 2 tristrifluoro• methylphosphine molecules. The observed effects are certainly not just due to the decreased donor properties of the phosphines since the cw-isomer of bis(trifluorophosphine)- dichloroplatinum (II) is known and is more stable than its

ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Research Council, and one of us (M. A. A. B.) expresses thanks for a scholarship received from C. S. I. R. (Pakistan) under the auspices of the Colombo Plan.

REFERENCES 1. MANN, F. G. and WELLS, A. F. J. Chem. Soc. 702 (1938). 2. HASZELDINE, R. N. and WEST, B. O. J. Chem. Soc. 3631 (1956). 3. HASZELDINE, R. N. and WEST, B. O. J. Chem. Soc. 3880 (1957). 4. BENNETT, F. W., EMELEUS, H. J., and HASZELDINE, R. N. J. Chem. Soc. 1565 (1953); BURG, A. B. and MAHLER, W. J. Am. Chem. Soc. 79, 247 (1957). 5. GRAHAM, W. A. G. and STONE, F. G. A. J. Inorg. & Nuclear Chem. 3, 164 (1956). 6. CAHOURS, A. Ann. 156, 302 (1870). 7. JENSEN, K. A. Z. anorg. Chem. 229, 225 (1936). 8. JENSEN, K. A. and NYGAARD, B. Acta Chem. Scand. 3, 479 (1949). 9. STONE, F. G. A. Chem. Rev. 58, 101 (1958). 10. BURG, A. B. and BRENDEL, G. J. Am. Chem. Soc. 80, 3198 (1958). 11. BOWEN, H. J. M. Trans. Faraday Soc. 50, 463 (1954). 12. CHALANDON, P. and Susz, B. P. Helv. Chim. Acta, 41, 697 (1958). 13. CHATT, J. and WILLIAMS, A. A. J. Chem. Soc. 3061 (1951): 14. CHATT, J. and WILKINS, R. G. J. Chem. Soc. 273 (1952). 15. EMELEUS, H. J. and SMITH, J. D. J. Chem. Soc. 527 (1958). 16. WILKINSON, G. J. Am. Chem. Soc. 73, 5501 (1951). CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART II. NICKEL (II) COMPLEXES OF TRIFLUOROMETHYL PHOSPHINES

M. A. A. BEG AND H. C. CLARK

Reprinted from CANADIAN JOURNAL OF CHEMISTRY 39, 595 (1961) CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART II. NICKEL (II) COMPLEXES OF TRIFLUOROMETHYL PHOSPHINES*

M. A. A. BEG AND H. C. CLARK

The ability of tri-alkyl and -aryl phosphines to form co-ordination compounds with transition metal salts is well established. However, this ability is considerably modified when the phosphine contains the highly electronegative trifluoromethyl group. This has been shown in the reactions of methyl-trifluoromethyl-phosphines with boron trifluoride and platinum (II) chloride (1), where the results have been interpreted in terms of the effect of the electron-withdrawing power of the trifluoromethyl group on the donor properties of the phosphines, and of the large steric requirements of the trifluoromethyl group. These two factors of the perturbing power or ligand field strength of the phosphines, and their steric requirements are just those that have been considered important in producing tetrahedral nickel (II) complexes (2). The first example of an apparently tetrahedral complex was (PEt3)2Ni(N03)2 (3), although the lack of a full structure determination left room for alternative configurations. For the triphenylphosphine

- - complexes (PPh3)2NiX2 where X = N03~, CI , Br~, I , detailed studies (4) leave no doubt that they possess tetrahedral structures. Other examples of tetrahedral nickel (II) complexes are now known (5). It therefore seemed of interest to examine the nickel (II) complexes of (CH3)3P, (CH3)2PCF3, CH3P(CF3)2, and P(CF3)3 wherever stable com• pounds could be isolated. Only the first two of these phosphines gave stable complexes and there were no indications of reaction between nickel (II) salts and either methyl - bistrifluoromethylphosphine or tristrifluoromethylphosphine. The complexes of diniethyl- trifluoromethylphosphine were considerably less stable than those of trimethylphosphine. The properties of the newly prepared compounds are shown in the table.

Magnetic moment Compound (B.M.) Color Absorption maxima

(Me3P)2Ni(N03)2 3.17 Dark red 4850(m), 3950(s), 3325(s) (Me3P)2NiCl2 Diamagnetic Crimson 5320(s), 3880(m), 3650(m), 2650(s) (Me3P)2NiBr2 Crimson 5400(m), 3800(m), 2700(s), 2425(w)

(Me3P)2NiI2 Dark brown 5175(m), 3875(w), 2850(vs), 2600(s)

(Me3P)2Ni(SCN)2 Orange-yellow 4600(sh), 3550(vs), 2975(s), 2600(s)

(Me2PCF3)2Ni(N03)2 2.93 Dark red 5550(w), 4850(s), 4150(s), 3270(s)

(Me2PCF3)2NiCl2 Diamagnetic Pink 4800(w), 4050(m), 3450(s), 2550(s)

(Me2PCF3)2NiBr2 Black 4875(s), 3950(s), 2625(s), 2400(s)

(Me2PCF„)2NiI2 Dark brown 3750(m), 3550(m), 3140(m), 2280(s)

(Me2PCF3)2Ni(SCN)2 Yellow 4600(m), 3675(vs), 2550(s)

The trimethylphospine complexes have not been reported previously and it is not surprising that the nitrate is paramagnetic and like its triethylphosphine analogue may be considered to be tetrahedral. The halogen and thiocyanate complexes are diamagnetic in accordance with the greater ligand strengths of these anions. The complexes of dimethyltrifluoromethyl phosphine are very similar to the trimethylphosphine compounds, only the nitrate is paramagnetic and possibly tetrahedral. *From part of a thesis submitted by M.A.A.B. in partial fulfillment of the requirements for the Ph.D. degree.

Can. J. Chem. Vol. 39 (19G1) 595 59G CANADIAN JOURNAL OF CHEMISTRY. VOL. 39, 1961

The intensity of the colors of the solid compounds and of the observed absorption bands suggest that charge-transfer transitions are involved. The fact that a nickel (II) complex of tristrifluoromethyl phosphine could not be obtained is consistent with its inability to give a platinum (II) compound (1). The smaller size of the nickel atom compared with platinum may explain why the latter but not the former can give a complex with methylbistrifluoromethyl phosphine..

EXPERIMENTAL v The methyl-trifluoromethyl-phosphines were prepared as described previously (1). All nickel salts were prepared in the anhydrous state, except the nitrate which was used as the hexahydrate. The trimethylphosphine complexes were prepared by direct reaction of the phosphines with the nickel salts in 2:1 ratio in sealed evacuated tubes, and were purified by refluxing with butanol for about 30 minutes when crystals of the complexes separated. In the case of nickel nitrate, the product could not be crystallized satisfactorily and solutions of the complex were used where necessary. For the dimethyltrifluoromethylphosphine complexes, crystallization was not possible owing to their instability. The preparations in these cases were therefore performed in the presence of excess phosphine which acted as a solvent and gave reasonably pure products. The analyses of the compounds are given in the table.

% Ni % X Calc. for Calc. for

Compound Found NiX2(PR3)2 Found NiX2(PR3)2 — —. (PMe3)2Ni(N03)2 17.33 17.37 20.05 20.56 25.14 25.27 (PMe3)2NiCl2 43.24 (PMe3)2NiBr2 16.01 15.68 42.70 54.72 (PMe3)2NiI2 11.85 12.50 54.30

(PMe3)2Ni(SCN)2 17.27 17.79 34.45 34.60 13.22 13.12 (Me2PCF3)2Ni(N03)2 — — 14.72 14.91 ' 18.15 18.25 (Me2PCF3)2NiCl2 33.47 (Me2PCF3)2NiBr2 H.84 12.14 34.10

(Me2PCF3)2NiI2 9.76 10.14 43.80 44.40 13.42 26.73 (Me2PCF3)2Ni(SCN)2 13.36 26.25

All the complexes except the iodides and thiocyanates decomposed in the presence of moisture. Although stable in dry solvents, wet polar solvents caused decomposition. Magnetic measurements were made on a Gouy magnetic balance, using powdered samples except for the nitrates for which solutions were used. Spectra were determined in carbon tetrachloride or methanol solutions using a Cary model 14 spectrophotometer.

ACKNOWLEDGMENTS The financial support of the National Research Council is gratefully acknowledged as is the award of a Colombo Plan scholarship to M.A.A.B.

1. M. A. A. BEG and H. C. CLARK. Can. J. Chem. 38, 119 (I960). 2. L. M. VENANZI. J. Inorg. & Nuclear Chem. 8, 137 (1958). 3. K. A. JENSEN. Z. anorg. u. allgem. Chem. 229, 225 (1936). 4. L. M. VENANZI and H. M. POWELL. Proc. Chem. Soc. 6 (1956). 5. N. S. GILL and R. S. NYIIOLM. J. Chem. Soc. 3997 (1959). RECEIVED DECEMBER 5, 1960. CHEMISTRY DEPARTMENT, UNIVERSITY OF BRITISH COLUMBIA, VANCOUVER, B.C. CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE AND RELATED COMPOUNDS

M. A. A. BEG AND H. C. CLARK

Reprinted from CANADIAN JOURNAL OF CHEMISTRY 39, 564 (1961) CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE AND RELATED COMPOUNDS

M. A. A. BEG AND H. C. CLARK CHEMISTRY OF THE TRIFLUOROMETHYL GROUP PART III. PHENYLBISTRIFLUOROMETHYLPHOSPHINE AND RELATED COMPOUNDS1

M. A. A. BEG AND H. C. CLARK

ABSTRACT The reaction of trifluoroiodomethane with tetraphenylcyclotetraphosphine leads to the formation, of phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine. The mechanism of the reaction is discussed and the physical and chemical properties of these compounds are reported. Bromine reacts with phenylbistrifluoromethylphosphine to form phenylbistrifluoromethyldibromophosphorane which is hydrolyzed to phenyltrifluorb-

methylphosphinic acid, C6H5(CF3)P(0)0H.

INTRODUCTION In previous papers in this series, the donor properties of methyl-trifluorom ethyl - phosphines were studied by the investigation of their ability to form complexes with boron trifluoride and platinum (II) chloride (1), and with a series of nickel (II) salts (2). Since much is known of the corresponding complexes of aryl phosphines, it seemed worth• while to study the donor properties of aryl-trifluoromethyl-phosphines. Unlike the methyl-trifluoromethyl-phosphines which have been known for some time (3, 4, 5), the phenyl-trifluoromethyl-phosphines had not been previously reported, although their arsine analogues had been prepared (6). We now report the preparation of phenylbistrifluoromethylphosphine.

DISCUSSION AND RESULTS Phenylbistrifluoromethylphosphine has been prepared by the reaction of trifluoroiodo• methane with tetraphenylcyclotetraphosphine, the properties of which have been reported by other workers (7, 8, 9). The reaction was performed at 185°, above the melting point of the tetraphosphine, and the other reaction products, besides phenylbistrifluoromethylphosphine, are phenyltrifluoromethyliodophosphine, which is a very involatile reddish brown liquid, and small amounts of fluoroform and hexafluoroethane. The mechanism of this reaction, involving the interaction of a perfluoroiodoalkane with a four-membered phosphorus ring is of some interest. A free-radical mechanism involving fission of phosphorus-phosphorus bonds by the attack of CF3 radicals seems probable. This is supported by the fact that the reaction will occur thermally or on ultra• violet irradiation of the tetraphosphine with trifluoroiodomethane. Since the simultaneous breaking of four P—P bonds is unlikely, the following reaction scheme may be suggested.

CeH& I

C6H5P—PC6H5 -CF3 C6H6P—P—CF3 CF3I C6H5P-

• || + • » I * I + C8H5P(CF3)2 + C6H6PI2

C6H5P—PC6H5 -I C6H5P—P—I C6H5P-

CF.Ij C6H6

| + 2C6H6(CF3)PI CeHgP •

2C6H6(CF3)PI C6H6P(CF3)2 + C6H6PI2. 'Manuscript received December 5, 1960. Contribution from the Department of Chemistry, University of British Columbia, Vancouver, B.C. From part of the thesis presented by M.A.A.B. in partial fulfillment of the requirements for the Ph.D. degree. Can. J. Chem. Vol. 39 (1961) 564 BEG AND CLARK: TRIFLUOROMETHYL GROUP 565

This scheme is supported by the observation that the reaction products contain phenylbistrifluoromethylphosphine and phenyltrifluoromethyliodophosphine in an ap• proximately 2:1 ratio, and also by the results of a separate experiment which indicated extensive disproportionation of the iodophosphine at 200° as indicated above. Phenylbistrifluoromethylphosphine is a colorless liquid boiling at 148-150°; it is stable at 200° and prolonged heating to 300° causes only partial decomposition. It is not hydrolyzed by acids, but reacts very slowly with water at 100° and much more rapidly with aqueous sodium hydroxide at 80°. The hydrolysis products are fluoroform and either phenylphosphonous acid C6H5PO2H27, or its sodium salt. Phenylbistrifluoromethylphosphine does not react with iodine at room temperature, but at 185° the trifluoromethyl groups are cleaved as trifluoroiodomethane. There is no evidence of the formation of the diiodophosphorane, C6H6(CF3)2Pl2. However, the phosphine reacted vigorously with bromine at room temperature to form phenylbistrifluoromethyldibromophosphorane. This is in agreement with the usual decrease in stability for dichloro-, dibromo-, and diiodo-phosphoranes. Phenylbistrifluoromethyl- dibromophosphorane is readily hydrolyzed by water losing only one of the two tri• fluoromethyl groups per molecule as fluoroform and producing phenyltrifluoromethyl-

phosphinic acid, C6H6(CF3)P(0)OH. Phenyltrifluoromethyliodophosphine is a reactive liquid which is readily hydrolyzed. Whereas alkaline hydrolysis produced fluoroform and the sodium phenylphosphonate, treatment with water gives phenyltrifluoromethylphosphine and phenyltrifluoromethylphosphinic acid, C6H5(CF3)P(0)OH. The production of phenyltrifluoromethylphosphinic acid from the aqueous hydrolysis of phenylbistrifluoromethyldibromophosphorane provides an interesting link between the trifluoromethyl- and aryl-phosphorus compounds. Whereas hydrolysis of triaryl- dichlorophosphoranes yields phosphine oxides (10), hydrolysis of tristrifluoromethyldichlorophosphorane (11) gives bistrifluoromethylphosphinic acid and one equivalent of fluoroform.

H20

(CF3)3PC12 > [(CF3)3P(OH)2] - (CF3)2P(0)OH + CF3H The hydrolysis of phenylbistrifluoromethyldibromophosphorane shows that the inter•

mediate compound C6HB(CF3)2P(OH)2 is unstable.

H20

C6H6(CF3)2PBr2 > [C6H5(CF3)2P(OH)2] C6H5(CF3)P(0)OH + CF3H The trifluoromethyl groups behave in the same way as in the hydrolysis of tristrifluoromethyldichlorophosphorane and the phenyl group shows its customary resistance to hydrolytic attack. The formation of phenyltrifluoromethylphosphinic acid from the hydrolysis of phenyltrifluoromethyliodophosphine is consistent with the general reactions of halophosphines (12). The spontaneous oxidation-reduction of the apparently unstable hydrolysis product leads to the production of phenyltrifluoromethylphosphine and phenyltrifluoromethylphosphinic acid.

H20

2C6H5(CF3)P1 -> [2C6Hs(CF3)POH] -> C6H6(CF3)PH + C6H6(CF,)P(0)OH The infrared spectra of these phenyl-trifluoromethylphosphorus compounds show the expected features. Absorption associated with the strong carbon-fluorine- stretching vibrations occurred in the 1100-1200 cm-1 region. However, it is of interest to notice 566 CANADIAN JOURNAL OF CHEMISTRY. VOL. 39, 1901

that the spectrum of silver phenyltrifluoromethylphosphinate, C6H5(CF3)P(0)OAg, showed absorption at 1225 cm-1 corresponding to the P:0 vibration. This absorption occurs in the same region for the aryl and alkyl phosphinic acids R.2P(0)OH, which are weak acids. For the strong acid, trifluoromethylphosphonic acid, this vibration is shifted to the higher frequency of 1300 cm-1 (13, 14). This might suggest that phenyltrifluoromethylphosphinic acid is a fairly weak acid.

EXPERIMENTAL The preparations of the starting materials were carried out in a nitrogen atmosphere. Reactions with trifluoroiodomethane were carried out in sealed evacuated Pyrex tubes and the products and reactants were manipulated by standard vacuum techniques, out of contact with air and moisture.

Preparation of Tetraphenylcyclotetraphosphine Phenyldichlorophosphine was obtained by the method of Buchner and Lockhart (15). The preparation of phenylphosphine by the Michaelis method (16, 17) is very cumbersome and gives a low yield. A much easier method (9, 18) is by reduction of phenyldichloro• phosphine with lithium aluminum hydride. Phenyldichlorophosphine (18.8 g) dissolved in 100 ml diethyl ether was added cautiously to a well-stirred suspension of lithium aluminum hydride (3 g) in 100 ml ether. The reaction was vigorous and cooling was necessary. After the addition of phenyldichlorophosphine had been completed, the mixture was refluxed for 30 minutes and 5 ml of water were added dropwise. After being refluxed for an hour, the mixture was distilled and the resulting phenylphosphine, distilling at 160°, was dried over calcium chloride (yield 55%). The preparation of tetraphenylcyclotetraphosphine by the Michaelis' method (19) is not convenient and the compound was prepared by adding phenylphosphine (11 g) in 50 ml ether to a well-stirred solution of phenyldichlorophosphine (18 g) in 50 ml ether. The solution gradually turned yellow but solid was not immediately deposited. After the addition was complete, the solution was refluxed for 3 hours during which time a white solid was deposited. The ether solution was decanted and the remaining solid was washed and dried. The yield of tetraphenylcyclotetraphosphine (m.p. 149-50°) was 90%.

Reaction of Tetraphenylcyclotetraphosphine with Trifluoroiodomethane Tetraphenylcyclotetraphosphine (1.0 g) was sealed with trifluoroiodomethane (2.025 g) and left at room temperature for 24 hours. The solid phosphine was insoluble in tri• fluoroiodomethane. No reaction occurred at 70° C over 24 hours, nor at 150° C for 12 hours, but on heating at 185° C for 12 hours a dark-red involatile liquid was obtained and 0.558 g of unreacted trifluoroiodomethane was recovered. The dark-red liquid was shaken with mercury and the remaining liquid extracted with ether. After removal of the ether, a liquid (0.45 g) of low volatility was obtained and identified as phenylbistrifluoromethylphosphine (Found: C, 39.35%; H, 2.10%; F, 45.40%; P, 12.30%. Calculated

for C8H6F6P: C, 39.03%; H, 2.03%; F, 46.36%; P, 12.60%). Phenylbistrifluoromethylphosphine is a colorless oily liquid whose odor is not as obnoxious as those of other phosphines. It boils at 148-150° and its vapor pressure is given by the equation log ^ = 7.5606 — (1985/T), whence the latent heat of vaporiza• tion is 9054 cal mole-1 and the Trouton's constant is 21.37. It is stable in air and does not react with water up to 100° C. It does not react with silver iodide, a solution of silver iodide in potassium iodide, or with carbon disulphide. BEG AND CLARK: TRIFLUOROMETHYL GROUP 567

Two separate experiments were performed to investigate the mechanism of the above reaction and to characterize the other reaction products. (1) Tetraphenylcyclotetraphosphine (2 g) was sealed with trifluoroiodomethane (5 g) in a Pyrex tube and was irradiated with ultraviolet radiation from a 200-watt U.V. lamp. The reaction was slow (possibly because of the heterogeneous phases), but after 15 days phenylbistrifluoromethylphosphine (0.899 g) and unreacted trifluoroiodomethane (2.192 g) were obtained. The rest of the product was a thick reddish syrup which showed strong absorption in the I.R. between 8-9 ju, characteristic of C—F stretching frequencies. This was not identified. (2) Tetraphenylcyclotetraphosphine (7.5 g) was sealed with 18 g trifluoroiodomethane and heated at 185° C for 12 hours. A volatile mixture of hexafluoroethane and fluoro• form (0.022 g), and 5.5 g of unreacted trifluoroiodomethane were recovered. The remaining liquid was subjected to fractional distillation under 20 mm pressure. Two fractions were obtained, one boiling at 62-65° (4.9 g) and the other boiling at 112-116° (3.8 g). A thick liquid which solidified on standing remained in the distillation flask. This showed strong absorption in the I.R., corresponding to the C—F stretching frequencies. Another experiment to identify this completely involatile liquid showed that it contained some iodides, including phosphorus triiodide. When treated with a large excess of trifluoroiodo• methane and mercury, some pure phenylbistrifluoromethyl phosphine was obtained, but the main product was a very viscous pale-yellow liquid, presumably polymeric. The liquid distilling at 62-65° was identified as phenylbistrifluoromethylphosphine and the fraction distilling at 112-114° was identified as phenyltrifluoromethyliodophos-

phine. (Found: I, 41.2%. Calculated for C7H6F3PI: I, 41.78%.)

Reactions of Phenylbistrifluoromethylphosphine (a) Hydrolysis Phenylbistrifluoromethylphosphine (0.277 g) was sealed with water (1.28 g). There was no reaction at room temperature and the reactants formed two separate layers. After heating at 80° for 24 hours, only a trace of fluoroform was obtained, while after 36 hours at 110°, 0.038 g fluoroform was evolved. Traces of benzene were also identified spectroscopically. There remained a white crystalline solid which melted at 69° and was identified as phenylphosphonous acid. Phenylbistrifluoromethylphosphine (0.273 g) was sealed with 5 ml of 20% aqueous sodium hydroxide solution. The reaction was slow at room temperature with the evolution of fluoroform. The tube was heated to 80° for 24 hours. The production of 0.149 g fluoro• form (mol. wt. obtained 70.0, calculated 70.0) showed that the hydrolysis was 96.4%

complete (CF3 obtained as CF3H: 54.8%; calculated for C6H6P(CF3): 56.1%). The solid obtained on evaporation of the solution was identified spectroscopically as the sodium salt of phenylphosphonous acid. Phenylbistrifluoromethylphosphine (0.372 g) and 36 N hydrochloric acid (2 g) were sealed. There was no reaction at room temperature and the reactants formed separate layers. There was no reaction at 80° for 24 hours and at 110° for 48 hours. The tube was finally heated to 185° for 120 hours. At the end of this period the amount of fluoroform evolved was only 0.0022 g and the phosphine was recovered almost quantitatively. (b) Reaction with Halogens (1) Iodine.—Phenylbistrifluoromethylphosphine (0.389 g) and iodine (1.163 g) did not react at room temperature, nor after heating at 150° for 24 hours. The mixture was finally heated to 185° for 48 hours. The products obtained, were fluoroform (0.032 g), 568 CANADIAN JOURNAL OF CHEMISTRY. VOL. 39, 1961 trifluoroiodomethane (0.481 g), (mol. wt. 194, calculated 196), benzene (0.055 g), and traces of unreacted phosphine. The conversion into fluoroform and trifluoroiodomethane accounted for 91.5% of the trifluoromethyl group. The formation of fluoroform and benzene may be due to the presence of small traces of moisture on the iodine which is not removed even on extensive drying. The. solid- left in the tube, after pumping off the volatiles, contained phosphorus triiodide and no phenyltrifluoromethyliodophosphine. (2) Bromine.—Phenylbistrifluoromethylphosphine (0.6965 g) and bromine (0.450 g) were combined. The ensuing vigorous reaction was controlled by performing the experi• ment in carbon tetrachloride solution and pumping off the volatiles after the reaction was complete. This was marked by the persistence of the bromine color. The reaction gave an orange-yellow solid which was very reactive towards moisture and was identified as phenylbistrifluoromethyldibromophosphorane (Found: Br, 38.93%. Calculated for

C8H6F6PBr2: Br, 39.41%). On reacting the dibromophosphorane with water, one equiva• lent of CF3 was lost and a white solid was left. The dibromophosphorane (0.324 g) was sealed with water (1.0 g) and left at room temperature overnight. Fluoroform (0.060 g) was evolved corresponding to a loss of one equivalent of CF3 per mole (Found: CF3,

18.4%. Calculated for C8H5F6PBr2:CF3, 34.5%). A white solid was obtained by pumping off the liquids, recrystallizing the residue from water, and finally drying over phosphorus pentoxide. The solid was identified spectroscopically as phenyltrifluoromethylphosphinic acid, C6H5(CF3)P(0)OH. The acid melted at 84-86°. The silver salt of the acid was obtained as needle-shaped crystals by treating the aqueous solution of the acid with silver oxide. The same salt could also be obtained from the reaction mixture of phenylbistrifluoromethyldibromophosphorane and water which had stood overnight and had lost one equivalent of CF3. The silver salt C6HB(CF3)P(0)OAg (Found: Ag, 33.81%.

Calculated for C7HeF3P02Ag: Ag, 34.06%) melted at 294-96° and was very sensitive to light.

(c) Pyrolysis of the Phosphine Phenylbistrifluoromethylphosphine (1.058 g) was heated to 210° for 48 hours; 1.004 g of the phosphine and traces of fluoroform and silicon tetrafluoride (identified spectro• scopically) were obtained. Phosphine (0.639 g) was heated to 300° for 48 hours. The tube walls were etched but the phosphine was not all pyrolyzed: 0.48 g was recovered unchanged. The other volatile materials were fluoroform, silicon tetrafluoride, and some benzene trifluoride.

Reactions of Phenyltrifluoromethyliodophosphine Phenyltrifluoromethyliodophosphine is a reddish-brown liquid which boils at 112-114° at 20 mm. It fumes in air and reacts slowly with water. The solution obtained by absorp• tion of water is highly acidic. It disproportionates on heating. (a) Hydrolysis Phenyltrifluoromethyliodophosphine (0.334 g) was treated with 5 ml of 20% sodium hydroxide. There was immediate reaction at room temperature. The tube was heated to 100° for 15 hours. Fluoroform (0.0694 g) (mol. wt. found 69.8, calculated 70.0) was evolved (CF3 found, 20.75%; calculated for C7H6F3PI, 23.03%). The hydrolysis was only 90% complete. The residue contained a hygroscopic sodium salt whose I.R. spectrum corresponded with that of sodium phenylphosphonate. Phenyltrifluoromethyliodophosphine (0.334 g) was treated with 0.125 g water and left in a sealed tube overnight. When water and other liquids were removed, a white solid was left. The melting point was 84-86° and in all respects the compound was similar to BEG AND CLARK: TRIFLUOROMETHYL GROUP 569 that obtained from the hydrolysis of phenylbistrifluoromethyldibromophosphorane. The silver salt was also prepared by reacting more of the iodophosphine with water and pre• cipitating the iodide as silver iodide. The solution was concentrated in vacuo and the solid dried over P206. The silver salt was identified analytically (Found: Ag, 33.80%. Calculated: Ag, 34.06%) by its melting point of 294-96°, and also spectroscopically. The above treatment of the iodophosphine also gave a small amount of a liquid whose

I.R. spectrum showed the presence of P—H, P—CeHs, and P—CF3 bonds. The hydrolysis with water therefore appears to give some phenyltrifluoromethylphosphine. (b) Reaction with Trifluoroiodomethane The iodophosphine (2.347 g) was heated with trifluoroiodomethane (2.299 g) at 200° for 12 hours. Trifluoroiodomethane (2.210 g, 96.1%) was recovered and the main products of reaction, presumably from the disproportionation of the iodophosphine, were phenylbistrifluoromethylphosphine (0.617 g), phosphorus triiodide, and benzene. Some of the unreacted iodophosphine was also identified among the products. (c) Reactions with Trifluoroiodomethane and Mercury The iodophosphine (2.8 g) and trifluoroiodomethane (10 g), with 54 g mercury, were sealed in a tube and shaken for 24 hours. Trifluoroiodomethane (8.9 g) was recovered and phenylbistrifluoromethylphosphine (1.5 g) was obtained. The loss of 1.1 g of trifluoroiodo- Hg methane indicated that the reaction C6H6PCF3I + CF3I ——> C6Ff5(CF3)2P had occurred. Besides the phosphine, some polymers were also obtained as mentioned earlier. Pyrolysis of phenyltrifluoromethylphosphine iodide: The iodophosphine (2.003 g) was heated in a sealed tube to 220° for 12 hours. Fluoroform (0.02 g) and trifluoroiodomethane (0.06 g) were obtained as the volatile products and there remained phenylbistrifluoromethylphosphine, benzene, phosphorus triiodide, and some unreacted phenyltrifluoromethyl iodophosphine. The I.R. spectra were taken on a Perkin-Elmer model 21 double-beam instrument with rock salt optics. Liquid films were used for liquids and KBr pellets for solids. The following absorption bands were noted for the compounds mentioned.

Phenylbistrifluoromethylphosphine 3080 (w) 2920 (w) 2320 (w) 1980 (w) 1870 (w) 1835 (w) 1810 (w) 1770 (w) 1745 (w) 1730 (w) 1670 (w) 1645 (w) 1590 (w) 1490 (w) 1445 (m) 1330 (w) 1265 (w) 1190 (s) 1140 (s) 1100 (s) 1070 (m) 1030 (w) 1000 (m) 875 (w) 805 (w) 750 (m) 745 (m) 690 (m) Phenyltrimioromethyliodophosphine 3060 (w) 2900 (w) 2340 (w) 1880 (w) 1800 (w) 1725 (w) 1710 (w) 1690 (w) 1675 (w) 1660 (w) 1585 (w) 1490 (w) 1440 (m) 1385 (w) 1335 (w) 1310 (w) 1270 (w) 1210 (m) 1150 (s) 1115 (s) 1070 (m) 1025 (m) 1000 (m) 830 (w) 745 (s) 715 (w) 690 (m) Silver phenyltrifluoromethyl phosphinate 3080 (w) 2900 (w) 2300 (w) 1860 (w) 1815 (w) 1725 (w) 1710 (w) 1690 (w) 1756 (w) 1640 (w) 1630 (w) 1590 (w) 1555 (w) 1485 (w) 1440 (m) 1335 (w) 1225 (s) 1200 (m) 1140 (s) 1110 (s) 1045 (m) 1015 (m) 995 (m) 970 (m) 870 (w) 760 (w) 740 (m) 715 (m) 695 (m) 570 CANADIAN JOURNAL OF CHEMISTRY. VOL. 39, 1901

ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Research Council, and one of us (M.A.A.B) expresses thanks for a scholarship received from C.S.I.R. (Pakistan) under the auspices of the Colombo Plan.

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