Infrared Studies of Group Vib Metal Carbonyl Derivatives

Home , Molybdenum hexacarbonyl

INFRARED STUDIES OF GROUP VIB

METAL CARBONYL DERIVATIVES

APPROVED t

Graduate CommitteeJ irmci Maj6r Prenfessor

Committee Member

ciu.// Committee Member

mmittee Member

Director of the Department of Chemistry

Dean df the Graduate School Brown, Richard A.. Infrared Studies of Group VIB Metal Carbonvl Derivatives. Doctor of Philosophy (Chemistry), August, 1971, 80 pp., 17 tables, 17 figures, bibliography, 66 titles. The infrared spectra in the carbonyl stretching region and metal-carbon stretching region have been obtained for sixty-one derivatives of M(C0)g (M * Cr, Mo, or W). The CO and MC stretching frequencies have been used to help resolve the inconsistencies and discrepancies on bonding in octahedral metal carbonyls found in the literature. Thirty-seven monosubstituted complexes of the general formula

LM(C0)5 (L SS a monodentate ligand containing a N, P, As, Sb, Bi, 0, or S donor atom) were prepared by thermal, photolytic, or re- placement reactions in various organic solvents. Twenty-six disubstituted complexes of the general formula cls-(bid)M(CO)^ (bid = a bidentate ligand containing N, P, As, or S donor atoms) were also prepared.

Plots of the A^ and E mode carbonyl stretching frequencies and the k^ and CO force constants of ten (amine)W(C0)^ complexes vs. the pK of the amine were made. No correlations be-

tween the trans -CO parameters [t>(C0) A^ and k^] and the pK& could be identified. Consequently, it was concluded that the isotropic inductive effect, which transmits electronic charge through the central metal sigma system, has no observable effect on the CO stretching frequencies. Very good linear trends were obtained

from plots of the pK& of the ligand vs. the cis-CO parameters

(2) £*(C0) Ax , i>(C0) E, and 1^3• These trends can be explained by a "direct ligand to ligand donation" first proposed by Fenske

in 1970 for the Mn(CO)^X series. In this through space donation,

the ligand sigma orbital overlaps with the pi system of the equa-

torial MCO groups. An increase in the basicity of the ligand

produces a greater overlap and this is exhibited' by a lower CO

stretching frequency. The following order of importance as ligand

bonding properties affect the CO stretching frequencies is con-

cluded! pi bonding) through space bonding^ sigma bonding.

The use of CO stretching frequencies to predict the MC bond-

ing properties has been necessary in the past because of the lack

of MC stretching frequencies in the literature, In this investi-

gation, plots of the MC E mode stretching frequency were made

against the CO E mode stretching frequency, pK& of the ligand, and Pauling electronegativity of the ligand donor atom.

The plot of the CO vs. the MC stretching frequencies shows

two trends. First, a distinct decrease in CO stretching frequency is accompanied by a decrease in the MC stretching frequency when complexes containing different ligand donor atoms are compared. Second, within a series of complexes which contain pi-bonding ligands with the same donor atom, the expected inverse relationship is seen.

An accurate inverse relationship is found between the MC stretching frequency and the Pauling electronegativity of the donor atom. This trend supports the ligand to ligand donation concept. It has been found that the MC stretching frequency for complexes which contain ligands with aliphatic substituents can be determined within ±1.2 cm"1 by the following equation! V(MC) « -20,6 [electronegativity of the donor atom] + 431. From the evidence obtained in this investigation, the following order of importance for ligand bonding effects on the MC stretching frequency is obtained! through space donation) pi bonding) sigma bonding. It is concluded that variations in MC frequencies in octahedral metal carbonyl complexes brought about by differences in the ligand bonding properties are dependent on the above three factors, whereas CO frequencies are affected only by through space and pi-bonding effects. • MP INFRARED STUDIES OF GROUP VIB METAL CARBONYL DERIVATIVES

DISSERTATION

Presented to the Graduate Council of the North Texas State University in Partial Fulfillment of the Requirements

For the Degree of

DOCTOR OF PHILOSOPHY

Richard it. Brown, B, A,f M. S. T, A H Denton, Texas August, 1971 TABLE OF CONTENTS

Page LIST OF TABLES iv LIST OF ILLUSTRATIONS . vt LIST OF ABBREVIATIONS AND SYMBOLS . . . .viii Chapter I. INTRODUCTION 1 Bonding Theories The Problem II. EXPERIMENTAL PROCEDURES 17 Reagents and Supplementary Techniques Preparations Infrared Spectra Elemental Analyses III. INFRARED STUDIES OF MONOSUBSTITUTED DERIVATIVES . 27 Carbonyl Stretching Region Metal-Carbon Stretching Region Unmeasurable Factors IV. INFRARED STUDIES OF DISUBSTITUTED DERIVATIVES . . 61 V. SUMMARY. 69 General Conclusions Proposals for Future Work APPENDIX. BIBLIOGRAPHY ...... 77

iii LIST OF TABLES

Table Page

I, Force Constants for Molybdenum Carbonyls 8

Hi, CO Stretching Frequencies and Force Constants in LMo(CO)^ Molecules 9 III. Effect of Charge on y(CO) and i>(MC), in cm of Some Isoelectronic Metal Carbonyls. . . . 10

IV. Metal-carbon and Carbon-oxygen Stretching Frequencies for Some cis-^MoCCO)^ Molecules. , ...... 15

V. Analyses and Physical Data for Monosubstituted Metal Carbonyl Derivatives . . . . 24

VI. Analyses for Monosubstituted and Disubstituted Octahedral Metal Carbonyl Derivatives. ... 25

VII. Solvent Effects on LW(CO)^ Complexes, in cm"1 . . 28

VIII. Carbonyl Stretching Frequencies for Group VIB Monosubstituted Products ... 39 IX. Far Infrared Spectra of Monosubstituted Products of the Group VIB Metal Carbonyls 49

X. Band Ranges of Donor Atom Complexes . 51

XI. Effect on i>(CO) and i>(MC) for a Decreasing Ligand Bonding Effect...... 57 XII. Carbonjrl Stretching Frequencies For cis-disubstituted Group VIB Metal Carbonyl Deriva- tives in Carbon Disulfide Solutions 62

XIII. Far Infrared Frequencies for cis-disubstituted Group VIB Metal Carbonyl Derivatives in Methylene Chloride Solutions ... 63

XIV. MC Vibrations of cis-MoCCO)^!^ Complexes, .... 65

XV. Intense Metal-carbon Stretching Frequencies of cis-disubstituted Tungsten Carbonyls .... 67

iv LIST OF TABLES Continued

Table Page XVI. Metal-carbon Stretching Frequencies for trans-disubstituted Complexes. 68 XVII, Ligands for Future Complexes. 71 LIST OF ILLUSTRATIONS

Figure Page 1. Resonance Structures of Nickel Carbonyl. «... 2 2. Far Infrared Spectrum of the Diars Ligand, ... 30 3. Far Infrared Spectrum of (diars)W(CO)^ ..... 31 4. Far Infrared Spectrum of (diars)Mo(CO)^. .... 32 5. Far Infrared Spectrum of (diars )Cr(CX))^. .... 33 6. Infrared Spectrum of PhoFW(CO),- in the CO Region 34 7. Far Infrared Spectrum of Ph^PWCCO)^...... 35 8. Infrared Spectrum of (BuO)oFW(CO)c in the

CO Region .•...r...«...... 36 9. Far Infrared Spectrum of (BuO)gPW(CO),j . ... .37 10. Plot of the pK vs. the A^^ 9(CO) for amineW(C07^ complexes ...... 41 11. Plot of the pK vs. the v(C0) for amineW(C07ej complexes ...... 42 12. Plot of the pK vs. the E »(C0) for amineW(CO;^ complexes . 43

13. Plot of the pK vs. the kx CO Force Constant for amineW(CO)^ complexes 45

14. Plot of the pKQ vs. the k2 CO Force Constant for amineW(CO)^ complexes.. 46 15. Plot of the E Mode g(MC) vs. the E Mode v(CO) for Tungsten Pentacarbonyl Complexes. ... 52 16. Plot of the E Mode »>(MC) vs. the Mode Carbonyl Stretching Frequency for Tungsten Pentacarbonyl Complexes ...... 54

vi LIST OF ILLUSTRATIONS Continued

Figure Page 17. Plot of the E Mode tf(MC) v&. the Pauling Electronegativity for Tungsten Penta- carbonyl Complexes. 55

vii LIST OF ABBREVIATIONS AND SYMBOLS an ss aniline ba « benzylamine bid * bidentate ligand Bu » n-butyl cha = cyclohexylamine dea « diethylamine diars » o-phenylemebis(dimethylarsine) dien » diethylenetriamine diphos = bis(l,2-diphenylphosphino)ethane dmf ss diraethylf ormamide dpae » bis(1,2-diphenylarsino)ethane dth = 2,5-dithiahexane dto ss 2,2,7,7-tetramethyl-3,6 -dithiaoctane Et ss ethyl L » monodentate ligand Me ss methyl rarph ss morpholine prop ss n-propanol o-Clan ss o-chloroaniline p-anis ss p-anisidine p-Clan ss p-chloroaniline P-en ss ethylenediphosphine

viii LIST OF ABBREVIATIONS AND SYMBOLS Continued

Ph » phenyl phen as o-phenanthroline 4-pic ss 4-picoline pipd = piperidine ptpz » piperaztne

Pver • P(OCH2)3CCH3 py » pyridine thf = tetrahydrofuran tht « tetrahydrothiophene traen as tetramethylethylenediamine tmpa = tetramethylpropylenediamine X = CI, Br, I O - phosphorus complexes • a= amine complexes V •« acetonitrile complex V = oxygen complexes A as antimony complexes A as sulfur complexes • as arsenic complexes • « bismuth complexes

ix CHAPTER I

INTRODUCTION

Bonding Theories

Since this thesis is related to the controversial sub- ject of bonding in metal carbonyls, it is fitting to begin with a discussion of the various bonding theories that have been presented.

In 1935 Brockway and Cross (1) published the unexpected result that the nickel-carbon bond length in Ni(CO)^ was ab- normally short in relation to the predicted bond length determined from the individual covalent radii. This was interpreted as evidence of multiple bonding between the metal and carbon atoms, and was explained by a series of Pauling valence bond resonance structures involving double bonds, as shown in Figure 1, This idea was further explained in

Pauling's monograph (2),

Since that time, it has become evident that metal carbonyls are a very special class of compounds. They may be thought of as formed from the carbon monoxide molecule and a zero-valent transition metal atom. First, the metals obey the effective atomic number rule by attaining an electronic configuration which is the same as the next rare gas.

Second, compounds which contain a central metal atom in a III C C I •U=V; :C=0- :6=C=Ni=C=6i I C B. 13! C.

C Osc-Ni — CSQ:

0: II II c C 11 II :0—c Ni= :C=0: :0=C* -MI' :C==0; I I! C C D. II E. 0 :0

Fig, 1--Resonance structures of nickel tetracarbonyl subnormal valency (in this case, usually zero) are often very unstable, because there can be very little electrosta- tic attraction between a zero-valent metal and a polar ligand. Finally, the metal acquires a negative formal charge for every attached carbon monoxide. The nickel in structure

A of Figure 1 has a formal charge of -4, which certainly would not be considered stable.

It was generally accepted, by the beginning of the

I960*s, that metal carbonyls were stabilized by the ability of the central metal atom to share this excess negative charge by using some of its filled non-bonding d orbitals and some vacant orbitals on the carbon monoxide ligand to form pi bonds (3-7), Other important references have also given a general review of metal carbonyls pertinent to this discussion (8,9).

A more accurate description of the bonding, in terns of molecular orbital theory, has been given by a number of authors (3-5). The bonding can most easily be explained for the Group VIB octahedral metal carbonylsi Cr(CO)g,

Mo(CO)g, and W(CO)^, The carbon monoxide molecule contains ten valence electrons. Six of these are found in two pi- bonding molecular orbitals and a sigma-bonding molecular orbital, as shown, where the second pi-bonding molecular orbital, iTxz, is perpendicular to the page. The other four electrons are in two directional non-bonding molecular C-> TT,i

ofcbitals on the carbon and oxygen. It is assumed that an

s and a p atomic orbital from both the carbon and oxygen z are used to form the sigma-bonding molecular orbital, the

two non-bonding molecular orbitals, and an antibonding mo-

lecular orbital which is vacant. The px and py atomic orbitals from each atom are used to give two pi-bonding mo-

lecular orbitals that are filled and two pi-antibonding

molecular orbitals (if*) that are vacant.

The basic premise (3) of the molecular orbital theory

is that "only orbitals which transform as the same repre-

sentation of the molecular point group can combine together

to give molecular orbitals." From this it is seen that the

s, Px» Py» P7» dz2» and dx2_y2 atomic orbitals of the metal 3 2 atom are used to form sp d hybrid orbitals which are of the

correct symmetry to form sigma bonds with the non-bonding 0>M<0 + —> G>MQQC ==Q: electron pair oil the carbon atom. The charge that is built up on the central metal atom by this dative bond is reduced by a back donation from the filled metal d orgitals (d „, xv •?&. y b

0 \> O G? d„_, and d _) into the pi-anti-bonding orbitals of carbon yz xvz monoxide. It is this electron balance or synergic effect, which removes the excess negative charge from the metal, that is used to explain the stability of the metal carbonyls,

It must be remembered that this back donation can be looked upon as a mechanism equivalent to that of Brockway and Cross in their explanation of Ni(CO)^ (l).

M-C=0. « » M=C=0: <-> (+>

The above bonding explanation was further extended and put on a more quantitative level in the now classic series of papers by Cotton and co-workers (10-13). A simple model was proposed for analyzing and assigning, according to Orgel (14), th© infrared-active carbonyl stretching frequencies in octahedral metal carbonyl derivatives (10), A number of assumptions were made. First, that there was no coupling between the CO vibrations and any other skeletal modes. This is a reasonable assumption since the nearest frequencies to the CO vibrations (1800-2100 cm"1) are the MCO deformations which are found below 700 cm"1. Second, no anharmonicity corrections were made to the observed fundamental vibrations. This was mainly due to expediency, since these minor corrections became very unwieldy and were not usually available. With these assumptions and other deductions, a mathematical model was developed that allowed the calculation of CO force constants from the observed frequencies. It should be pointed out here that this is the standard method used today by investigators in carbonyl chemistry to calculate force constants of octahedral metal carbonyl derivatives, and it is the method used in this thesis.

Perhaps the most important statement of Cotton's work was his symmetry factorability of sigma- and pi-bonding orbitals. From the symmetry requirements of octahedral complexes, the metal orbitals that may be used in bonding are of Eg, T^u, and T2g symmetry, whereas those on the

CO are of Tlg, T2g, Tlu, and T2u symmetry. The Tlu ligand orbitals can overlap with the p^, py, and p2 metal orbitals and its T2g orbital® can overlap with the dxy, dyg5, and &^z metal orbitals. If the metal is to have a full set of six

octahedral sigma bonds which span the representations A^+

Eg+Tlu, only the metal T2g orbitals are left for pi bonding.

For reasons of symmetry, the T2g orbitals will not mix with any of the other valence shell orbitals, and Cotton assumes,

to a first approximation, that the sigma and pi bonding in

octahedral complexes can be treated separately. It must be

noted here also, that other investigators have interpreted

this to mean that there will be no variation in sigma bond-

ing in these complexes. Cotton does not specifically men-

tion anything about sigma variations, although it is implic-

itly understood that the sigma bonding is constant. For

this reason, his works have been called the "pi-bonding

only" theory, which will be known as "Cotton's theory" in

this thesis. He goes on to explain that variations in the

CO stretching frequencies, or force constants, are caused

by variations in the pi-bonding system which are brought

about by differences in pi-accepting ability of the ligands.

For example, consider the substitution of CO by a weaker

pi-accepting ligand. This causes more pi charge to be dis-

tributed to the remaining CO groups, which produces an in-

crease in the MC bond order and a decrease in the CO' bond

order. This is exhibited by a higher MC frequency and a

lower CO frequency. 8

There is a considerable amount of experimental evidence to support this theory. Cotton (10-12) cites the decreasing

V>(CO) and force constants in a series of increasingly substituted derivatives of molybdenum hexacarbonyl, of which a representative sample is given in Table I, The force constants k^ and 1^ always refer to the CO trans and els to

TABLE X

FORCE CONSTANTS FOR MOLYBDENUM CARBONYLS

Complex Force constants, mdynes/~ 8

MO(C0)6 16,52

Mo(CO)5PPh,} 15,57 15.99

Mo(CO)^(PPho)i-trans 15.45

Mo ( CO ) ^ ( diphos ) - cis. 14.64 15.41

Mo(CO) jCPPh^^-cis 14.10 m mm mm

Mo ( CO ) 2 ( diphos ) 2-cis, 13.37

the ligand, respectively. Because these phosphorus ligands are weaker pi acceptors than CO, the electrons in the metal d orbitals concerned here must be shared to a greater extent by the remaining CO groups in the molecule. This increases the MC pi bond on the CO groups and decreases the

CO pi bond, which is exhibited by a lower j>(CO) and a lower

CO force constant. A similar lowering of v(CO) and its force constants is observed in a series of monosubstituted derivatives in which the pi-accepting ability of the ligand decreases.

Table II shows a series of molybdenum derivatives in which the ligand pi-accepting ability varies from slightly greater than that of CO to a ligand that was said to be a pi donor (8, 12).

TABLE II CO STRETCHING FREQUENCIES AND FORCE CONSTANTS IN LMo(CO)5 MOLECULES*

-1 V(CO), cm k, mdynes/& L A^ E A1 kl k2

PF3 2104 2012 1990 16.57 '16.53 CO 1990 (T- ) •»•»«•*»*» 16.52 PC13 2095 1999 1985 16.38 16.46 PCl2(OEt) 2091 1987 1975 16.15 16.33 P(OPh)3 2083 1975 1963 16.97 16.14 P(OMe)3 2080 1967 1950 15.62 16.02 SbPh3 2073 1954 1954 15.58 16.00 PPh3 2078 1951 1951 15.57 15.99 AsPh3 2074 1951 1951 15.56 15.95 PEtj 2070 1941 1948 15.40 15.88 py 2079 1890 1944 14.56 15.94 cha 2072 1895 1938 14.65 15.83 c dmf 2068 1847 1924 13.93 15.67 hydrocarbon solutions, ^Spectrum taken in CHCl^ solution, cSpeetrum taken in dmf solution. 10

Even though th© abov© ©vid©nc© was c^uxt© substantial, another type of series was often presented (4, 5) to further solidify Cotton's theory. Table III shows two isoelectronic

TABLE III -1 EFFECT OF CHARGE ON v»(CO> AND V(MC), IN cm OF SOME ISOELECTRONIC METAL CARBONYLS

+1 V(CO), Cr(CO)6 Mn(CO)6

V(CO) 1859 1981 2090 y(MC) 460 441 416

-2 -1 Fe(CO)4 Co(CO)4 Ni(C0)4

i>(CO) 1786 1886 2057 V(MC) 464 439 367 series of metal carbonyIs in which the central charge on the metal varies. As the charge on the central metal be- comes more negative, more electrons are available for MC pi bonding. This reduces the CO pi bond to produce a lower )>(CO), and increases the MC pi bond, raising the i>(MC).

The above ideas and experimental evidence served to confirm Cotton's theory for use in descriptions of metal carbonyl bonding properties. Although other ideas were presented, such as relationships comparing bond strength, ab- solute bond order, force constants, and *>(CO), they were not 11

used so widely. Basolo arid Pearson (5) note that there is no direct or obvious relationship between bond strength and force constants of the CO bond. The force constant is related to the shape of the Morse potential well, and the bond strength is related to the depth of the potential well. This has been ignored by certain investigators in discussions concerning bond strength (15). In 1966 and 1967 Angelici (16, 17) published two papers explaining the variation oftf(CO) onl y in terms of sigma bonding, which was completely in opposition to Cotton's theory. In his second more important paper (17), he reports the )>(C0) of a series of monosubstituted tungsten carbonyl compounds with amine, pyridine, and phosphine ligands. The

complexes are considered to be in the C^y point group in which, according to group theory, the metal d and d xz yz orbitals can be used either for sigma or pi bonding. This gives a path for ligand sigma-bonding effects to be transferred into the pi system of these complexes. By plotting

K P a the ligand against the j>(CO) or force constants, trends are observed which can be explained in terms of ligand sigma bonding, Angelici even states "there is no question that W-L sigma bonding does affect W-C-0 pi bonding," and that differences between phosphine and amine i>(CO) need not be explained in terms of W-P pi bonding as has been done in the past." A critical discussion of Angelici's proposals will be given in Chapter III. 12

The above two diametrically opposed theories led to new proposals by other investigators that claimed sigma and pi bonding were responsible for the observed variations in CO frequencies. Brown and Darensbourg (18, 19), using group dipole moments derived from v(CO) intensity data, have proposed that both sigma and pi bonding are necessary to explain the bonding in metal carbonyls. An increase in negative charge on the metal should raise the metal pi- bonding orbitals in energy and allow a greater pi-electron

flow to the CO group. This increased d orbital energy allows an increased overlap with pi-bonding ligands which

changes the distribution neglibly and affects the y(CO)

only slightly. The increased negative charge on the metal, which was caused by inductive effects of the ligand, also reduces the metal acidity for the CO electron pair which in

turn reduces the MC sigma bond and lowers the »>(C0). This proposal, which implicitly assumes a greater sigma effect

in the trans position to the ligand, suggests that the major cause of i>(C0) variation is caused by sigma inductive effects.

The latest attempt to explain this bonding dilemma was proposed by Graham (20). His approach is based on the simple premise that ligand sigma-inductive effects are isotropic at the central metal and affect all CO force constants equally, and that ligand pi-bonding properties affect the trans CO force constant twice as much. This allowed a 13

mathematical calculation to be made, based on Cotton's fore© constants, which gave sigma- and pi-accepting parameters of ligands relative to a standardi the non-pi-bonding ligand, cyclohexylamine. By comparing all ligands relative to the standard, trends in sigma- and pi-accepting ability of ligands could be made. This method of separating sigma- and pi-bonding properties of ligands was adopted immediately by many investigators in metal carbonyl chemistry.

The Problem With three different proposals for the bonding in metal carbonyls, it was decided to look into the situation more thoroughly in order to see what other evidence was available to support or refute any of these ideas. It became obvious that a definite contradiction existed between the kinetic evidence of various metal carbonyls, and the concept of MC bond strengths as predicted by Cotton's theory, it had been common to predict metal-carbon bond strengths from the CO stretching frequencies (8, 12, 21) by using the standard valence bond description of bonding in the M-C-0 moiety,

M— > M=C=6: r~> <+> w Metal carbonyl derivatives of amine ligands (which are considered to be hard bases) have a lower i)(CO) than deriva~ tives of phosphine ligands (which are soft bases). This led to the prediction that the MC bond in the hard base complex 14 should have a higher bond order and therefore a stronger bond. But kinetic evidence (22-24) definitely showed that, for the dissociative step,

(bid)Mo(CO)4 » (bid)Mo(eo)3 the rate is much faster for the loss of a CO from the amine

complex. This was explained by assuming the transition state was stabilized rather than by a destabilization of the ground state.

Another case in which lKCO) incorrectly predicts the labilizing of CO is observed when comparing the dissociation of CO from Mn(CO)g+* and Mn(CO)^Cl. The CO force constants

(25) for Mn(CO)g+1 (k^ - 18.0 md/$) and Mn(C0)^Cl (k^ »

16.27 md/8, k-2 » 17,63 md/S) predict a weaker MC bond in + 1 Mn(C0)g , which suggests it would lose CO more readily than Mn(CO)^Cl, The evidence, in contrast, shows that Mn(C0)g+1 has no recognizable exchange with "CO after 15 hours at 30°C whereas M^CO^Cl has a rate constant of 3,0 x 10"^ sec"1 at 31.8°C (27).

Cotton and Richardson (13) have noted that the Cr-C bond lengths for (benzene)Cr(CO)3 and (dien)Cr(C0)3 are essentially equal, which leads to the assumption of similar

Cr-C bond strengths. Yet this is in disagreement with the

Cr-C bond strengths predicted from the CO frequencies. The higher CO frequencies for the benzene complex (1987 and 1917

) (28) in comparison to the diethylenetriamine complex 15

1884 and 1735 cm"1) (11) predict a considerable stronger

Cr-C bond In the benzene complex.

Some of the above evidence prompted Dobson and Houk

(29) to publish the MC stretching frequencies of some of the complexes used in their kinetic work. Table IV shows that the decreasing trend in (CO) cannot be used to predict an increasing trend in bond strength of (MC), because the (MC) changes in the opposite direction as expected from

Cotton's theory,

TABLE IV METAL-CARBON AND CARBON-OXYGEN STRETCHING FREQUENCIES FOR SOME cis-L2Mo(CO)4 MOLECULES

(MC), -1 (CO), -1 L2 cm cm tmen 410 398 374 364 2013 1890 1875 1837 phen 409 394 379 368 2025 1906 1875 1826 dth 405 395 375 2030 1919 1905 1869

p C Et3)2 428 413 404 392 2014 1915 1901 1890 diphos 430 418 402 387 2028 1932 1919 1906

Perhaps the most glaring omission in all of the above experimental evidence was the lack of any substantial data on MC stretching frequencies, even though this evidence should be more closely related to MC bonding properties than most other evidence. This was due to a number of difficulties. ' - - i - '

First, far-infrared spectrophotometers were not generally available until the 1960's. Second, the MC region also contains ligand vibrations and MCO deformation vibrations which may overlap MC bands or interfere with MC band assignments.

Third, it has been stated by many investigators that the MC frequencies may be extensively coupled with other skeletal vibrations of the molecule. And finally, the available spectra were usually obtained from Csl pellets or nujol mulls, which lead to the possibility of interfering crystal lattice effects in the spectrum.

The initial step in this study was to prepare and re- cord the far-infrared spectra of 37 monosubstituted octahedral metal carbonyl derivatives of chromium, molybdenum, and tungsten. By using a large number of compounds, and recording the infrared spectra of solutions of the compounds, most of the above problems could be overcome. These results prompted the investigation of a series of disubstituted complexes of the same family and a critical evaluation of the existing bonding theories. CHAPTER II

EXPERIMENTAL

Reagents and Supplementary Techniques

The metal carbonyls were purchased from Pressure Chemi- cal Co. and Climax Molybdenum Co., and were used without further purification. The ligands were obtained from various chemical supply houses in practical grade or better, and were used without further purification. Butoxydiphenyl- phosphine and dibutoxyphenylphosphine were graciously do- nated by Arapahoe Chemicals, Division of Syntex Corporation.

All reaction solutions were purged with nitrogen before starting and kept over nitrogen during the work-up procedures. Although the monosubstituted complexes containing ligands with phosphorus, arsenic, and antimony donor atoms are stable to air in solution, those with nitrogen, bismuth, and Group VIA ligands require rigorous exclusion of air to prevent decomposition.

Melting points were taken on samples in an open capil- lary and are uncorrected. They were run on a HOOVER Capil- lary Melting Point Apparatus, catalog # 6406-H, distributed by the Arthur H. Thomas Company.

The force constant and Graham parameter calculations were made using the computer program given in the Appendix.

T 7 18

All computing was performed at the North Texas State Univer- sity Computing Center on an IBM 360, model 50.

Preparations

Ph3EM(CO)5, (E = P, As, Sb; M = Cr, Mo.).--Although these complexes had been prepared earlier (30-32), the methods were altered to give better yields and cleaner products. The complexes were prepared in a two-necked 250 ml round bottom flask to which was connected a water condenser. The condenser outlet was connected to a 1000 ml gas collect- ing tube by a rubber hose and glass tubing. The flask was charged with 1.37 x 10"^ mole of M(CO)g, 1.13 x 10"^ mole of ligand, 100 ml of 2,2,5-trimethylhexane, and a teflon- coated magnetic spin bar. The flask was then purged with nitrogen for five minutes with stirring, then stoppered and heated to reflux by a heating mantle. The solution was re- fluxed until 1.13 x 10" mole of CO had been collected or until the rate of evolution was less than 20 ml per hour. The flask was cooled to -10°C overnight and the product was collected in a medium frit. It was then dried at 50°C and 0.1 mm for two hours to remove any excess metal hexacar- boriyl. The crude product was dissolved in acetone and pre- cipitated immediately by the addition of water, filtered and dried at 0.1 mm for one hour at 25°C. The resulting product was then recrystallized from hexane until pure. Yields ranged from 60-90 per cent. 19

Ph^EW(CO)s, (E « P, As, Sb).—The preparation of these complexes is Identical to that above except a 2:1 mixture of n-decane and 2,2,5-trimethylhexane was used instead of

pure 2,2,5-trimethylhexane. Yields ranged from 60-90 per cent.

Ph3BiM(CO)5, (M « Cr, Mo, W).--These complexes were prepared in a 500 ml photochemical reaction vessel similar to that supplied by Ace Glass Co., catalog # 6524-10, and irradiated with a Hanovia 450 watt quartz lamp, stock # 679A0360. PhgBi (5.35 x 10"3 mole) was added to 400 ml of benzene saturated with an excess of the metal hexacarbonyl. This solution was poured into the reaction vessel, purged with nitrogen for five minutes, and then irradiated with continued purging for 15 minutes. The solution was immediately transferred to a 1000 ml round bottom flask and the o benzene was removed on a rotary evaporator at 25 C using a vacuum pump. The flask was then put on a vacuum rack for 12 hours at 25°C and 0.1 mm to remove the excess hexacarbonyl. The product was then extracted with 150 ml of hexane and frit filtered into an ice cooled filter flask. The product was crystallized at -10°C for no more than eight hours, after which time it was collected on a frit and dried at 0.1 mm for one hour.. Any further attempts at recrystallization resulted in enough decomposition to prevent the product from crystallizing. These complexes are unstable in hexane 20

solution, even at -10°C if left for a day or longer, but the pure crystals are air stable at room temperature.

Preparation of liquid complexes«--Liquid complexes are more difficult to purify than solid products since the high boiling solvent used in the preparation tends to remain dissolved in the product. For this reason, the method of Stroh- meier and Miiller (33) was used to prepare LW(CO)^, (L « butoxydiphenylphosphine, dibutoxyphenylphosphine, tributyl phosphite, tributylphosphine, triphenyl phosphite, and tri- butylstibine), W(C0)g (1.37 x 10" mole) was dissolved in reagent grade tetrahydrofuran and the solution was poured into the photochemical reaction vessel and irradiated for 25 minutes using the same procedure described in the prepa-

ration of the Ph3BiM(CO)5 complexes. The ligand (1,30 x

-2

10 mole) was also added to the 1000 ml round bottom flask and the tetrahydrofuran was then removed using a rotary evaporator, the last remaining traces being removed at 90°C. The green or blue oily residue was then chromatographed on a 1" x 3M silica column with heptane to give a clear yellow solution. The heptane was removed on the rotary evaporator and the yellow product was sealed in a glass ampoule under vacuum. AmW(CO),-, (Am «= piperidine, cyclohexylamine, pipera- zine. benzylamlne, morpholine. diethylamine. 4-picollne. 21

pyridine, p-anisidlne. p-chloroanlline. o-chloroaniline. and acetonitrile') .--Although many monosubstituted amine complexes have been prepared (11, 17, 34), it was found that a variation of Angelici and Malone's method (17) gave cleaner products containing no disubstituted impurities. W(CO)g (1,37 x 10 mole) and 1.30 x 10" mole of the ligand were dissolved in 400 ml of benzene and irradiated for 15-20 minutes by the method described above for the preparation of PhgBiM(CO),.. The solution was then transferred to a 1000 ml round bottom flask and the benzene was removed using a vacuum rotary evaporator. The yellow residue was then dried for 12 hours at 0.1 mm and 25°C to remove any excess hexacarbonyl and ligand. The products were found to be spectro- scopically pure in the carbonyl region, and they were used without further purification. Yields ranged from 50-80 per cent.

LW(CO)5, (L » tetrahydrofuran, n-propanol, tetrahydrothiophene. thiophenol).--These complexes are highly unstable in solution and could not be isolated. They were made by the method described above for the preparation of amine derivatives with the following exceptions. One hundred ml of the ligand. was mixed with 300 ml of 2,2,4-trimethylpentane and the solution irradiated for 30 minutes. The infrared spectra of the carbonyl and metal-carbon stretching regions of the reaction solution were recorded immediately 22

after the termination of the irradiation. No crystalliza- tion was attempted.

BidM(CO)^, (Bid « phen (35), tmen (36), diphos (37),

dpae (37), diars (37), P-en (38), dto (39), dth (40), and

tmpa (41); M = Cr, Mo, W).--These complexes were prepared

in a manner wholly analogous to the methods given in the

references cited. The products were usually purified by

recrystallization from acetone-water mixtures. The -d(CO)

agreed with the values given in the literature.

trans-(PPhj^MfCQ)^. (M « Cr, Mo, W).--These complexes were prepared and purified in a manner wholly analogous to the method given in the literature (30), except that a Ii2 mixture of 2,2,5-trimethylhexane and n-decane, rather than diglyme, was used as a reaction medium.

Infrared Spectra

All infrared spectra were recorded on a Perkin-Elmer model 621 grating spectrophotometer which was purged with dry air, and were calibrated using the water vapor bands

(42, 43) at 1869.36 and 303.0 cm"1. A wavelength scale expansion of 5X was used, with a spectral slit width of

2.4-1.7 cm"1 (2100-1800 cm""1) or 2.1-3.2 cm"1 (600-300 cm"1).

Spectra were recorded using 2,2,4-trimethylpentane solutions in 0.1 mm NaCl cells for the 2100-1700 cm"1 region, and di- chloromethane solutions in 0.2 mm or 0.5 mm Csl cells for 23 the 650-300 cm"1 region. Band positions were determined by finding the midpoint at half intensity on isolated bands, or at 70-90 per cent intensity on those with overlapping bands. All positions should be accurate to better than tl cm"1, except where noted. Since many of the ligands have moderately intense ab- sorption bands in the 300-600 cm"1 region, it was necessary to distinguish beteeen these bands and those of the metal- carbon stretch. This was done by comparing the spectra of chromium, molybdenum, and tungsten derivatives of each ligand. In all cases the ligand bands remained constant within ±2 cm"1 whereas the MC bands varied by considerably more. This is most evident when comparing a chromium derivative with the molybdenum or tungsten derivative, since the most intense CrC stretching band is at least 50 cm"1 higher than the corresponding MoC or WC stretching band.

Elemental Analyses The carbon, hydrogen and nitrogen analyses of a representative selection of the compounds made for this study were run by the North Texas State University Analytical Service on an F&M Scientific Carbon-Hydrogen-Nitrogen Ana- lyzer, Model 185 or by the Midwest Microlab Inc., Indiana- polis, Indiana. All samples were run a minimum of two times, and the average of the runs was used for the results listed in Tables V and VI. 24

CO CO CO CO CO 1-4 CO r~4 CO r~i r»i CO CO r-4 cd r~4 cd r-4 cd cd r-4 r-i CO cd 4J cd 4J «d 4J 4J • cd cd r-4 P CO 4J CO 4J CO CO 4J P cd CO >» <0 >* CO CO >* CO >> CO X 4-> >> u r-4 >> u r-t >> X u Q o 05 M o cd o CD o O P Q 60 o •P 5e a £ • & CO 3s CO & G i o O CD o >* CD o o 0) cd o O »H r-4 u r-4 4-> H . F—J p U u r-4 4J r-S *r4 r-4 o r-4 Q R-4 •r-4 Q x± r-4 O* CD 0) JG 0) CD •s I I 0 *r4 £& se & >» & & £ & u >, o O O o 0) H CD r-4 CD R*^ r-4 CD o CD . s & r-i a ' CO r-4 o r-4 r-4 o r-4 r-4 i—I o r-4 G cd 0) G cd 0) cd G CD 0) cd w CD cd >* a H a P* CO OH >> 05 a a CO >% 13 H a hH H CD CO TJ O vO m r- CM m r-4 O o a P3 in V0 CD 0 0) CD o CO CO CO 00 m vO O vO CO O M a CM CO CO in 0 W t*4 06 u3 *d VO G CM in vO CO st o in o\ o < Q o 00 ON in rH m m 1—4 w G 3 CO• m • a CD O PQ 60 £* CO CO CM CO CM CM CM CM CM CM CM CM O S O H - m o CO o NO o CO o CO w •OfQ * \D in in in 4 k (0 CO

CO CO CO CO CO CO CO co xi CO XI jd CO xi x: CO JC XI co a* *£ JB •Q PL, x: a< a* £2 cu JC cn •H •rl 0* CO CM X* cu *o a< cu <5 C CO CO CO XI PQ •H G in in fr* in m *• 8 8 v-/ 8 o u O w H o o U O a o se: 3: O s Q s o 2 25

TABLE VI ANALYSES FOR MONOSUBSTITUTED AND DISUBSTITUTED OCTAHEDRAL METAL CARBONYL DERIVATIVES

% Carbon % Hydrogen % Nitrogen Compound Calc'd Found Calc'd Found Calc'd Found

Cr(CO)^dto 45.40 45.58 5.95 6.20

Cr(C0)4dth 33.57 33.55 3.50 3.39

Mo(C0)4dth 29.09 28.70 3.03 2.92

W(CO)4dth 22.97 22.60 2.39 2.26

Cr(C0)4diphos 64.05 64.42 4.45 4.38

Mo(C0)4diphos 59.40 61.29 4.13 3.98

W(CO)4diphos 51.87 52.99 3.60 3.37

Cr(C0)4dpae 55.38 55.64 3.85 3.64

Mo(C0)4dpae 51.87 51.50 3.60 3.47

W(CO)4dpae 46.03 46.06 3.20 3.07

Mo(CO)4(PPh3)2 65.57 66.82 4.10 4.05

W(CO)4(PPh3)2' 58.53 58.90 3.66 3.63

Cr(C0)4tmen 42.85 42.10 5.71 5.76 9.99 9.93

Mo(CO)4tmen 37.03 36.83 4.94 4.94 8.64 8.41

W(C0)4tmen 29.12 28.84 3.88 3.88 6.80 6.59 Cr(CO)^cha 45.36 45.15 4.47 4.52 4.81 4.62 Mo(CO)^cha 39.40 38.37 3.88 3.95 4.18 4.21

W(CO)5cha 31.21 30.66 3.08 3.00 3.31 3.03

W(CO)5py 29.78 29.09 1.24 1.21 3.48 3.35

W(CO)5an 31.65 31.19 1.68 . 1.61- 3.37 3.20

The North Texas State University Analytical Service was unable to obtain reproducible results on most of the nitrogen donor complexes, even though many of them had already been characterized in the literature. In these cases, the purity 26 of the compounds was checked by comparing their infrared bands in the carbonyl region with those of the known complexes. CHAPTER III

INFRARED STUDIES OF MONOSUBSTITUTED DERIVATIVES

This study was initiated by a search for a suitable solvent. The only criteria necessary were that it be trans- parent to infrared radiation in the 300-700 cm"^ region and

that the compounds be sufficiently soluble in it to get a

satisfactory intensity of the metal-carbon stretching bands.

The nonpolar solvent, iso-octane, was the first choice,

since it is well known that polar solvents affect the band

position and band width of CO bands (44). For this investi-

gation, the cis-disubstituted complexes are not soluble

enough in hydrocarbons, so the second choice, methylene

chloride, was chosen.

A preliminary study of the differences produced in band

position and width at half intensity was made by varying the

phase of the sample. Standard techniques of nujol mulls and

Csl pellets were compared with iso-octane and methylene

chloride solutions of some simple metal carbonyl compounds

to determine the practicability of methylene chloride.

Table VII shows the results of this work for four compounds.

There is still a considerable difference in the band widths

of the MC bands when changing from iso-octane to methylene

chloride solutions, as there is in the CO region. But the

27 28

MC band positions are nearly constant, varying only slightly with a change in solvent.

TABLE VII -1 SOLVENT EFFECTS ON LW(CO)5 COMPLEXES, IN cm

L • CO Ph3P PhujSb C6HnNH2

CO Region

Iso-octane 1984 (9)* 1943(14) 1948(11) 1931 (9) Methylene chloride 1976(22) 1938(28) 1943(22) 1926(24) 1 1 « 1 * * 1 1 I 'C t Nujol 1981(**) •».._•( >'oV ) # \r. r v

MC Region

Iso-octane 374(11) 384 (9) 385 (9) 372(10) Methylene chloride 372(21) 382(15) 386(13) 371(24) Nujol 374(23) 383(12) 385 (9) 369(19)

Csl pellet --- 383(13) 384(15) 367(19)

Band widths at half intensity shown in parentheses 'Appearance of at least two more bands, with band width at half intensity greater than 60 cm**1.

After a spectrum had been recorded, accurate band positions were determined. The analogous compounds of chromium, molybdenum, and tungsten were compared in order to identify those bands attributable to MC, MCO, and ligand vibrations. This was done by assigning those bands which did not vary more than ±2 cm ^ as ligand vibrations. A second method was also used by comparing the spectrum of the chromium complex with those of the molybdenum and tungsten complexes. The 29

Cr-C vibrations are usually 50-100 cm"* higher than those of tungsten and molybdenum, which are very similar and usually within 5-10 cm"1 of each other. This is best de- monstrated by comparing the far infrared spectra of the ligand diars and its chromium, molybdenum, and tungsten complexes, shown in Figures 2-5, The two bands at 355 and 366 cm"1 in the complexes can be associated with the slightly split strong band at 346 cm"''" in the spectrum of the pure ligand.

One of the greatest aids for identifying the MC vibrations is that they are of the same symmetry as the CO vibrations. There are three infrared active vibrations in the monosubstituted complexes (2A^ + E) of which the E mode has the greatest intensity (14). Figures 6-9 show four typical spectra in the CO and MC regions. Even though the kl and E bands are accidentally degenerate in the CO region

for the Ph3P complex, they are well separated in the MC region (450, 418, and 383 cm 1). The weakness of the MC vi-

brations of A1 symmetry make some of these assignments questionable! this problem cannot be resolved with certainty until Raman data become available,

Carbonyl Stretching Region A preliminary survey of the results of the MC region demanded a re-evaluation of the available theories discussed in the Introduction. This led to a thorough examination of 30

600 500 400 300 cm- i Fig. 2--Far infrared spectrum of the diars ligand 31

600 500 400 300 cm- i

Fig. 3--Far infrared spectrum of (diars)W(C0)4 32

600 500 400 300 cm -I Fig. 4--Far infrared spectrum of (diars)Ho(CO)^ 33

600 500 400 300 cm- i

Fig. 5--Far infrared spectrum of (diars)Cr(C0)y 34

2100 2000 1900 cm -i Fig. 6--Infrared spectrum of Ph3PW(CO>5 in the CO region 35

600 500 400 300 cm -l

Fig, 7—Far infrared spectrum of Ph3PW(CO>5 36

o o G> G O •H 60 £ -P c

m /•N o o

0££ CO o ° o OJ

O 00 O 60 OJ •H &M 37

O o to

m o o 8 si" 04 CO i

O* - %

2 4J U

GO •r4 E*t 38

the CO frequency data shown in Table VIII in light of those theories. The data were first tested for the sigma-only theory proposed by Angelici and Malone (17). A careful examination of the paper shows two basic errors in the presentation. First, in three of the five phosphine complexes listed, values have been estimated to be 5.5 cm"1 higher than those of the E mode values. There is no theoretical justi- fication for this method of estimation. These overlapping (1)

V A1 ' and E bands are said to be symmetrical with no shoulders, although his spectra of the aniline complexes have clearly resolved bands with separations of the A^1) and E bands listed as 4.5, 4.5, and 6.0 cm"1. Comparisons of the and E bands of Ph^FWCCO)^ and Ph^BiWCCO)^ complexes in the present investigation show a definite shoulder on the PhgBi complex for an A^1^ position which is only 5.5 m "I

cm" above the E band position. The Ph3P complex has a symmetrical band in agreement with that observed by Angelici. The E mode bands of both the Ph^P and Ph^Bi complexes have band widths (13 and 14 cm"1 respectively) at half intensity similar to those of Angelici*s complexes. From this evidence, it seems unlikely that Angelici's A^1^ band positions for the three phosphine complexes are acceptable, and any trends based on these values should be viewed with skepticism. 39

TABLE VIII

CARBONYL STRETCHING FREQUENCIES FOR GROUP VIB MONOSUBSTITUTED PRODUCTS

(2) Cl) E A Complex A1 1

Cr(CO)5PPh3 2066m I945vs 1945vs Cr(CO)cjAsPhg 2068m 1946.5vs 1946.5vs

Cr(CO)5SbPh3 2065m 1948vs 1948vs

Cr(CO)5BiPh3 2068m 1951.5vs 1947m,sh Cr(CO)gCha 2068w 1935,5vs 1917ms

Mo(CO)5PPh3 2075m 1950.5vs 1948m,sh

Mo(CO)5AsPh3 2077m 1954.5vs 1948m,sh

Mo(CO)5SbPh3 2075m 1956vs 1952m,sh

Mo(CO)5BiPh3 2078m 1960vs 1960vs Mo(CO)^cha 2074w 1941vs 1921ms

W(CO)5PPh3 2075m 1944vs 1944vs

W(CO)5[PPh2(BuO)] 2074,5mw 1944s 1954.5m

W(CO)5[PPh(BuO)2] 2077mw 1947s 1957m

W(CO)5[P(BuO)3] 2079w 1946.5vs 1960,5mw

W(CO)5[P(PhO)3] 2084mw 1958.5s 1966m,sh

W(CO)5PBU3 2 068.5w 1935.5vs 1943m

W(CO)5AsPh3 2076m 1945vs 1945vs

W(CO)5SbPh3 2077m 1950vs 1950vs

W(CO)5SbBu3 2068mw 194Ovs 1940vs

W(CO)5BtPh3 2077mw 195lvs 1946m,sh

W(CO)5tht 2075mw 1941.5vs 1930.5ms

W(CO)5(PhSH) 208Ow 1948vs 1935,5m

W(CO)5ptpd 2072.5w I930vs 1919m WCCO^cha 2072w I930vs 1919.5m 40

TABLE VIII

»(CO) Complex (2) A1 E

W(CO)5pipz 2072.5w 193lvs 192Omw W(C0)gba 2072w 1932s 1920m,sh W(C0)5mrph 2073.5vw 1931,5vs 1922,5mw,sh W(CO)^dea 2073w 1930vs 1919m W(CO)5(4-pic) 2073w 1933.5vs 1919.5m W(CO)5py 2073w 1934vs 1921m W(C0)^an 2 074vw 1936vs 192Omw W(CO)5(p-anis) 2075w 1934.5vs 1919.5m W(C0)5(p-Clan) 2075w 1935.5vs 1923m W(CO)5(o-Clan) 2075w 1937vs 192Omw W(C0)5(MeCN) 2078w 1944.5vs 1927m W(C0)5thf 2078,5w 1936s 1914m W(C0)2(n-prop) 2075w 1930s 1941m,sh

Second, it can also be seen from Angelici's graphs,

that lines representing trends of kx and the CO stretching frequencies for nitrogen complexes may have been drawn fortuitously. This is particularly noticeable in his graph

of pKa vs. kx, where the variation of k1 is only 0.11 mdynes/S (see Appendix).

It is worthwhile to compare graphs of the present data, which have no approximations, with those of Angelici's.

Figures 10-12 show plots of the pKa (45) of the nitrogen ligand vs., the CO stretching frequency. No trends are 41

2072 2073 2074 2075 i/(C0), Aj^ mode, cm"*1

Fig. 10--Plot of the pK& ys, the A^^ carbonyl stretching frequency for amineW(C0>5 complexes. 42

pKa

1919 1920 1921 1922 1923 1 v (C0)t A/'Vmode, cm" (i) Fig, 11--Plot of the pK& vs. the ' carbonyl stretching frequency for amineW(CO)^ complexes. 43

pKa

1930 1932 1934 1936 1938 v (CO), E mode, cm"'

Fig, l2--Plot of the pKa v^. the E carbonyl stretching frequency for amineW(CO)5 complexes. 44

observed for the A^ vibrations with the pK^ of the ligand. A very good trend is observed with the E mode vibration, in agreement with a similar trend observed by Angelici, Figure

13 shows a plot of the trans-k^ force constant vs. the pKfl of the ligand for the nitrogen complexes. The corresponding plot of amine complexes by Angelici shows a questionable trend, as mentioned above. The plot of the cis-kn force constants is shown in Figure 14, and is in general agreement with that of Angelici's. Since the arguments presented in Angelici*s paper were established on the above disputed trends, no further comparison of the present work was done with his proposals. It is also worth noting that Stewart and Treichel (46) have applied the concept of Graham parameters to Angelici*s data. They conclude that the variation caused by ligand properties strongly suggests the transmittal of a significant amount of this by pi bonding. They also have stated that this data can be well correlated with previous studies.

The lone trend observed with the E mode stretching frequency of the equatorial CO groups in the nitrogen complexes cannot be explained by any of the present sigma-or pi-bonding theories. All of these theories predict a similar trend in the trans-CO stretching frequency, since the sigma inductive effect is isotropic. Consequently, any ligand bonding variation that affects the cis-CO frequency by passing 45

Q Q ©

6 8

pKa

Fig. 13--Plot of the pK& vs. the kx carbonyl

stretching force constant for amineW(CO>5 complexes. 46

- - 15.82 Q

15.80 © o © 15.78 O K, © 15.76

• 15.74 ©

Q %w 15.72 - - i - i > i « » — 6 8 10 12

PK0

Fig, 14--Plot of pKa vs. the ^ carbonyl stretching

force constant for amineW(C0>5 complexes, 47

information through the central metal atom should also affect the trans-CO group. With this in mind, it appears that a proposal by Fenske and DeKock (47) can explain this observation. They have, suggested that changes in force constants and molecular orbital occupancies of the cis-CQ

groups in the Mn(CO>5X series can be explained by a "direct ligand to ligahd donation," This occurs by a direct overlap of the ligand sigma donor orbital with the pi* orbital on CO.

This proposal is also adaptable to the complexes in this investigation. The greater the pKa, or basicity, of the ligand, the more overlap that occurs with the equatorial CO groups. This lowers the CO frequency, as is observed.

Although this effect could be applicable to all ligands, those which have pi-bonding ability will tend to obscure this trend. In addition, there has yet to be a significant 48

number of phosphines, the most common of the pi-bonding ligand s, to be recorded which have had their pK 'S reported. a

Without the pKfl's of a large number of them, no correlation can be attempted. Since "direct ligand to ligand donation" was not considered in the method of separating sigma- and pi-accepting abilities proposed by Graham (20), his parameters should be re-evaluated.

Metal-Carbon Stretching Region

With the exception of Bigorgne's excellent work on

monosubstituted derivatives (48), very few metal-carbon

stretching frequencies have been published (49). Most of

these have reported complexes containing ligands of the pi-

bonding donor atoms, P, As, Sb, and Bi. Two other papers

have published spectra of complexes containing amine li-

gands, but no distinction was made between MC and MCO vibra-

tions (50, 51). Bigorgne's work established the general

range and positions of the MC bands in monosubstituted mo-

lybdenum complexes. It was found (52-54) that this range

could also be applied to the tungsten analogs.

The infrared spectra in the 300-700 cm"1 region of

thirty-seven monosubstituted complexes prepared for this

investigation are listed in Table IX. The spectra of the

chromium and molybdenum complexes were used only as an aid

in the assignment of the bands in the tungsten spectra, and all further discussions will be based only on the spectra 49

TABLE IX FAR INFRARED SPECTRA OF MONOSUBSTITUTED PRODUCTS OF THE GROUP VIB METAL CARBONYLS

V(MC)' Complex E Other bands A1 Ai

Cr(CO)5PPh3 mm mm mm 54 3w 466m 520s 5l2m 497mw 42 Ow

Cr(CO)5AsPh3 mm mm 546mw 466s 476vs 4l9w 324m

Cr(CO)5SbPh3 — 545mw 465s 457ms

Cr(CO)5BiPh3 mm mm mm 545mw 456vs 448ms

Cr(CO)jCha mm mm mm 556m 444.5s 586w 413m 383vw

Ho(CO)5PPh3 446w 387sh 378s 5l9vs 512m 493m 417m

Mo(CO)5AsPh3 436vw 395m 378.5s 527vw 475s 327m

Mo(CO)5SbPh3 436vw 398s 379.5s 454ms 418vw 390m Mo(CO)5BiPh3 377s 448ms Mo(CO)^cha 376sh 364s 538mw 45 Ow W(CO)5PPh3 418mw 383s 510m 495m

W(CO)5[PPh2(BuO)] 428mw 4l0w 384s 506w 49 Ow — W(CO)5[PPh(BuO)2] 420mw 385.5s m m m

W(CO)5[P(BuO)3] 435wsh 42lmw 385.5s ...

W(CO)5[P(PhO)3] 432sh 415m 381.5s 6l5mw 499m 478mw W(CO)5PBu3 430mw 4l4w 387s ... W(CO)5AsPh3 429vw 4l0w 384s 475ms 327m W(CO)5SbPh3 431vw 411m 386.5s 453m W(CO)5SbBu3 434vw 4l3w 388s 5l2vw 454vw W(CO)5BiPh3 406w 383s 447ms 50

TABLE IX Continued

JKMC)* Complex E Other bands Ai aI

W(C0)5tht 42 7w 408w 378.5vs ne

W(CO)5(PhSH) 4l7w 395w 374vs ne W(C0)^pipd 429w 403w 371vs ... W(C0)^cha 429w 406w 370s 475w,br W(CO>5pip® 429w 404w . 37ls 620m

,W(CO)5ba 430vw 405vw 37lvs ... W(CO)^mrph 430vw 405mw 37lvs W(CO)^dea 429vw 403vw 373vs W(C0)^(4-pic) 428vw 407w 369,5vs 492ms 62 7w

W(C0)5py 428vw 403vw 368.5vs 468w,br

W(C0)5an 428vw 402vw 37lvs 5l9mw W(CO)^(p-anis) 42 7w 399mw 369vs 528mw 478w

W(CO)5(p-Clan) 425vw 381sh 37lvs 5l5m 497mw

W(C0)5(o-Clan) 44 Ow 403w 37lvs 6l4w 590sh

W(CO)5(MeCN) 428vw 388m 37lvs 620w

W(C0)5thf 403mw 364vs ne W(CO)^(n-prop) 402w 363vs ne

'"'Abbreviations usedt v, very? w, weakj m, mediumj s, strong; sh, shoulder* br, broad; ne, not examined. of the tungsten complexes. It is at once obvious from Table IX that the ligand donor atom is the major determinant of the MC band position. The two MC stretching vibrations of ^2. symmetry are weak and sometimes absent. ' For this reason * only the intense band of E symmetry will be considered.

Table X shows the general range for monosubstituted tungsten 51

complexes which contain various donor atom ligands. The general trend should be helpful for determining which ligand

TABLE X

BAND RANGES OF DONOR ATOM COMPLEXES

Ligand donor atom Range, in cm**''"

P, As, Sb, Bi 381.5 - 388 S 374 - 378.5

N 368.5 - 373

0 363 - 364

donor atom is attached to the metal carbonyl moiety when it contains more than one donor atom,

A comparison of the MC and CO vibrations of E symmetry

in Figure 15 shows a general trend in which the MC band de-

creases as the CO band decreases. This is in direct-vari-

ance with Cotton's theory which predicts an inverse rela-

tionship between the MC and CO frequencies. A closer ex-

amination of Figure 15 does show this inverse trend among

the pi-accepting ligands containing phosphorus, arsenic, antimony, and bismuth. It is also observed for the two sulfur containing ligands which are also capable of pi bonding. This trend is not observed for the nitrogen or oxygen containing ligands. It is also evident from the 52

390 r

'e 380- o

3701-

362- 1930 1940 1950 f(C0), E mode, ctn""8. Fig. 15--Plot of the E mode *>(MC) vs. the E mode >>(C0) for tungsten pentacarbonyl complexes. 53 closeness of MC band positions in the pyridine, aniline, and substituted pyridine complexes with those of the aliphatic amine complexes that very little, if any, metal- ligand pi bonding is taking place, as concluded by Cotton (11). A similar trend is observed for the correlation between CO vibrations and the E mode MC vibrations shown in Figure XVI. This was unexpected since there was no correlation between the trans-CO frequency and the pK& of the nitrogen donor ligands.

It appears that a change in the pi-accepting ability, caused by the substitutents attached to a specific donor atom, produces the predicted inverse relationship between

CO and MC stretching frequencies. Some other ligand effect which is more dominant than variations in its pi-accepting ability must be producing this change. This effect is di- rectly related to the specific donor atom, .which influences the position of the MC band more than any other ligand property. It is related to the electronegativity of the donor atom, as shown in Figure XVII, Although only six complexes were made containing oxygen, arsenic, antimony, and bismuth, it is evident that the MC stretching frequency range can be predicted quite accurately by the Pauling electronegativity of the donor atom. This has also been observed by Ugo, Ceninni, and Bonati (55) for a series of 54

390 •M A ° A O O - • o •o £ o ° 380

- V V

360 « —i i 1 1 1 L_ 1910 1930 I960 1970 v (CO), A|°mode, cm"1

Fig. 16--Plot of the E mode (MC) \/s, the mode carbonyl stretching frequency for tungsten pentacarbonyl complexes. 55

Bio ©

2.0 2.4 2.8 3.2 3.6 Pauling Electronegativity Fig, 17--Plot of the E mode v>(MC) vs. the Pauling electronegativity for tungsten pentacarbonyl complexes. 56

complexes ofJthe general form Mn(CO)^X, where X = CI, Br,

I, H, Me, Ph, and tolyl,

When the MC frequency of the series of tungsten com-

plexes formed with donor atoms attached only to alkyl sub-

stituents is plotted against Pauling electronegativity, a

very accurate equation can be obtained. The equation

})(MC) ss -20.6 [_Pauling electronegativity] + 431

was obtained from the plot of the monosubstituted tungsten

complexes which contained Bu^Sb, Bu^P, tht, cha, and thf.

It gives values accurate to tl,2 cm""1 for these complexes,

and should predict the y(MC) for any other complex formed

with a donor atom which has alkyl substituents attached to

it. The larger variations of other complexes containing

ligand donor atoms with pi-bonding substituents cannot be

determined in any accurate empirical form until a greater

number of complexes have been examined.

The question now arisest is the trend in MC vibrations, which is given by the above empirical equation, due to di-

rect ligand to ligand donation as explained earlier, or is

it due to an inductive effect? This can be answered by con-

sidering the MC and CO stretching frequencies, and the three factors that affect the bonding in metal carbonyls» (a) the pi-bonding variations and (b) the sigma through metal inductive effect as explained in Chapter I, and (c) Fenske's 57 through space effect described in the first part of this chapter. The following assumption is madej since there is no

trend in the trans-i>(CO) with the pK& of nitrogen ligands, it is assumed the sigma through metal inductive effect has no influence on carbonyl frequencies. Carbonyl frequencies are therefore related only to the pi and through space effects. Metal-carbon frequencies will be dependent on all t^iree factors. Table XI shows how the CO and MC stretching frequencies are affected when these ligand bonding effects are decreased.

TABLE XI EFFECT ON j>(CO) AND T>(MC) FOR A DECREASING LIGAND BONDING EFFECT '

Ligand bonding mode j>(CO) (MC)

sigma bonding (through metal inductive effect) no effect increase pi bonding decrease increase Fenske's through space bonding (overlaps with the MC pi orbital) increase decrease

The amount of through space bonding will be determined by the extent of overlap between the ligand sigma orbital and the MC pi orbital. This is dependent on the diffuse- ness of the ligand sigma orbital, which is determined by 58 the electronegativity and effective nuclear charge on the ligand donor atom. The decrease in i>(CO) when going from a phosphorus donor atom to a nitrogen donor atom is caused by decreases in the ligand pi bonding and through space bonding. The lowers(CO) found for the nitrogen complexes demonstrates that ligand pi variations predominate over through space effects when considering the differences between pi- and non-pi-bonding ligands. Complexes containing oxygen donor atoms would be expected to have slightly higher CO frequencies due to a decrease in the through space effect. The two oxygen complexes studied have frequencies comparable to those of nitrogen complexes except for the bands which are 5- 10 cm lower, Since the spectra of these complexes were recorded in solutions containing 20-25 per cent of the ligand, it is expected that solvent effects would cause at least this much decrease in the CO frequencies. Since solvent effects produce only minor variations in MC frequencies, a comparison of complexes containing pi- bonding, nitrogen, and oxygen donor ligands can be under- taken. The change from a phosphorus donor atom to a nitrogen donor atom is attended by a decrease in ligand pi and through space bonding effects, and an increase in the ligand sigma bond. The decrease.in ligand pi bonding causes an 59

Increase in MC bonding, which is not enough to offset the decrease brought about by the other two factors. The nitrogen complexes have MC frequencies approximately 15 cm"'*' lower than those of the phosphorus complexes. Neither oxygen nor nitrogen donor atoms have pi-bonding ability and, therefore, their MC stretching frequencies will depend only on the variation of the sigma through metal inductive effect and the through space effect. Ligands containing oxygen donor atoms are weaker bases than those of nitrogen. Consequently, they donate less charge to the metal, increasing its sigma acidity for the CO groups and strengthening the MC sigma bonds. In contrast, the greater electronegativity of the oxygen atom reduces the diffuaeneea of its bonding orbital which decreases the through space effect and weakens the MC bond. The through space effect is dominant and the MC frequencies of the oxygen complexes (363-364 cm"*) are lower than those of the nitrogen complexes (369-373 cm"'"').

Another important correlation is observed between the MC stretching frequencies of this series of complexes and the kinetic data for the unimolecular dissociation of a CO group. Angelici and Graham (22) have shown that complexes with nitrogen donor ligands lose a CO more readily than those with phosphorus donor ligands. This investigation has shown that complexes with a lower i>(MC) lose CO more 60

easily. This evidence is strong support for a destabilized

ground state proposed by Dobson (29), rather than a stabi-

lized transition state proposed by Angelici (56).

Unmeasurable Factors

Lord and Miller (57) have stated four requirements for

strong coupling of vibrations in a molecule* "close prox-

imity of the vibrating atoms, strong forces between the

vibrating groups, approximate equality of the group fre-

quencies, and identical symmetry of the group vibrations."

Only the MC and MCO E mode frequencies are able to couple

according to these requirements. Since the trends in this

investigation are based to a large extent on the E mode

metal-carbon stretching vibration, it would be proper to

compare the observed trends in the MC region with those of

the MCO E mode vibrations. Group theory predicts six MCO vibrations (A^ + + 3E) of which four (A^ + 3E) are active in the infrared. These four bands are not always observed, and those that are observed cannot be assigned without the aid of Raman data. At present this data is available only for the M(C0)6 series (58), and until it be- comes available for the monosubstituted products, no conclusions can be made with regard to the coupling effects and MC band positions. CHAPTER IV

INFRARED STUDIES OF DISUBSTITUTED DERIVATIVES

Twenty-six els-disubstituted complexes and four trans- disubstituted complexes were also studied. Tables XII and XIII list the CO and MC stretching frequencies of the cis- disubstituted complexes. In contrast to the monoaubstituted complexes* the cla- disubstituted complexes have complicated spectra which are very difficult to interpret. They have four infrared al-

lowed vibrations (2A1 + Bx + B2) for the MC stretching vibrations, and in general, they are not all seen in the spectra. This is most frustrating for the chromium complexes , in which the MC region is of higher energy and overlaps the MCO region. Normally one or two strong MC bands are observed which can be used for comparison with other complexes, but no assignments can be made without Raman data. The spectra of the diars complexes in the MC region, which are the easiest to interpret and contain the most number of bands, are shown in Figures 3-5.

A number of references have appeared in the literature (49) listing band positions in the 300-700 cm~* region for cis-disubstituted complexes. All of the investigators used solid phase sampling techniques (nujol mulls Or Csl pellets)

61 62

TABLE XII CARBONYL STRETCHING FREQUENCIES FOR cis-DISUBSTITUTED GROUP VIB METAL CARBONYL DERIVATIVES IN CARBON DISULFIDE SOLUTIONS

-1 Complex P(CO), cm

Cr(CO)4phen 2007m 1901s 1893m,sh 1844m Mo(CO)4phen 20llmw 1903s 1889m 1846m W(C0)4phen 2003m 1892 s 1886sh 1840m Cr(CO)^tmen 2007w 1879sh 1868vs 1839ms

Mo(CO)^tmen 2014w • .... 188Qvs 1843m W(CO)4tmen 2007w 1872sh 1864vs 1838ms Cr(CO)4diphos 2011ms 1918ms 1903vs 1887ms Mo(CO)^diphos 2023ms 1925s 19l2vs 1894s W(CO)4diphos 2019ms 1918s 1903vs 1888s Cr(C0)4(P-en) 2019m 1932m 1907m Mo(CO)4(P-en) 2030m 1937m 1915s W(C0)4(P-en) 2026m 1930m 1907vs •c Cr(CO)4dpae 2011ms 1918ms 1902vs 1885s Mo(CO)4dpae 2024ms , 1925s 19l2vs 1894s W(CO)4dpae 20l9ms 1918s 1903vs 1887s Cr(CO)4diars 2007ms 1914ms 1994s 1885sh Mo(CO)4diars 2 02 0m 1922m 1907s 1894ms W(CO)4diars 2015m 1914m 1896s 1887sh Cr(CO)4dto 2016mw ---- 1893s 1867ms Mo(C0) dto 4 2024mw , •»«*«««* 1905s 1872ms W(CO)4dto 20l8mw 1897sh 1892 s 1868ms Cr(CO)4dth 20l7mw 1911ms 1894vs 1874s Mo(CO)4dth 2024mw 1911sh 1903vs 1878s W(CO) dth 4 2019mw 1906ms 189lvs 1874s Mo(CO)4tmpa 20l5mw 1881s «»"«* m m 1837ms W(CO) tnipa 4 20008mw 1873sh 1866s 1832m 63

CO * CO CD CO 6 c?o > > vO J 6 00 m ON e (0 in > & > • 6 oor^ o£ CM in r-tcn CO £ H in 00 CM oooo mCO oo vo 6 CO g co CO u CO >o g g oo g m sg e <»• on >CM > S s \o HN 0\f^ ON ON 6 VO (M ON VOO CO CM J xt- B WE GO <30 M & 1 2 * * row CO E co $ O co CM £* m co o CM in |B e a > e Hin Hv0

CO CO > co & k > CO A ON o m cn ^ cn Jf CM co co M o in h CO N N N H NO m r4 M CO CO CO ON CO ,x co co co co co m 3 r** # ^ S co co v0o5 a • o in <5 ON %O

£ 6 ® m g 6 00 m co r** 5 ^ CM ON 00 00 tn VO fN, 00 N n H m m •

CO CO /->, C o co 0) 6 c O in C H a ^ i . !|8.SS§8 8o . w •a- & H 3 ^ o w O • S 3s o o as ac O 3E ac 64

r-l in vO m a a B in CO a a ON ON ON vO r^ o o o «k «» vO 00 CO CO CO 03 g *> tn 00 00 cd CO CO CO CO m •» uo tn •Q CO CO CO J3t <0 CO «h «* «k * > > > J* > > «» m M 6 6 M a a ON CM r-4 CO f^ CO !£ a 0) vO <5 ON ON CO ON 00 in 00 ON 00 CO oo X! vO V0 in tn vO in in in in in O 00 ON 4J CO V0 > > > > > a & a CM fM 00 vo vO co ON vO *—l

>>>>> > 4J H £ ininfMcooo CM O I in

BCO B w ro i> s o r»«. »>. 4a N& m8 B I ** CO 00 to N OH oo sf tn oo ch on o

(0 d) CD U to $ m Q> o o jC 5o$, cfl *rl €0 a ex a) u o ju U X5 6 a XT *H TJ *0 a 13 X? U •a •a 4J •P 6 x xj st *d *d

TABLE XIV

MC VIBRATIONS OF cis-Mo(CO)4L2 COMPLEXES

1 L2 J>(MC), cm phase ref Monodentate liaands

(PH3)2 438w 2 480 451 412 390 nujol 61

Bidentate liaands diphos 430ms 418sh 402w 387m Csl 29 diphos 425s 403m 387s 365m nujol 62 diphos 427s 406mw 389ms 370w CH-Xl- * tL Z phen 409w 394sh 379sh 368vs Csl 29 phen mm m 399w 384sh 372vs nujol 63 phen m m mt m m m 394w 370vs CH2C12 •k

*This work 66

The results are fairly consistent for two of the lower bands, but the others are not in agreement. The amine complexes show similar discrepancies. It is quite possible that these discrepancies are caused by sampling techniques, Dobson and Houk (29) used Csl pellets} Chalmers, Lewis, and Whyman (62) used nujol mullsi and in this work the complexes were recorded as methylene chloride solutions. It has already been stated in Chapter III that band positions are not shifted signifi- cantly in the MC region* but the band width does increase considerably when run in methylene chloride solutions.

This increase may be enough to obscure any shoulders that have been reported by the other investigators. It should also be kept in mind that solid phase sampling techniques may lead to splitting of bands, due to the crystal site symmetry.

Without specific assignments for the observable MC bands of these compounds, no accurate correlations can be made other than a cursory comparison with the trends observed in the monosubstituted complexes. Using the lowest most intense band observed for each complex, the same general trend in MC frequencies is observed. Table XV shows this trend. The lower, strong band is about 5-10 cm"1 higher than the E mode bands in the monosubstituted complexes. There also seems to be less distinction between the 67

nitrogen and sulfur donor atom complexes, the band of the tmen complex being higher than that of the dto complex.

TABLE XV INTENSE METAL-CARBON STRETCHING FREQUENCIES OF cis-DISUBSTITUTED TUNGSTEN CARBONYLS

Complex vKMC), cm"1

Nitrogen ComDlexes

W(C0)4tmpa 375

W(CO)4phen 375

W(C0)4tmen 380

Sulfur Complexes

W(CO)4dto 378

W(CO)4dth . •;[, • .385 ' • • '

r" 1 Phosphorus ComDlexes

W(CO)4(P-en) ; 395

W(CO)4diphos 396

Arsenic Complexes )

W(CO)4dpae 395

W(C0)4diars 400

Until these bands have been accurately assigned through the use of Raman data, no further relationships will be considered. The MC frequencies for six different trans-disubstituted complexes have been reported in the literature. Those bands 68 and the ones of the present investigation are shown in Table XVI. The MC band is easily identified, since the intense E mode is the only infrared active vibration for these

TABLE XVI METAL-CARBON STRETCHING FREQUENCIES FOR trans-DISUBSTITUTED COMPLEXES

Complex Cr Mo W ref,

M(CO)4(PPh3)2 477m 394s 396s 62 M(CO)4(PPh3)2 .... 400s ... 61 M(CO)4(PPh3)2 383m 392m 396m *

M(CO)4(Pver)2 477m mm m mm mm mm mm 51

M(CO)4[P(OMe)'3]2 mm m m 397s mmm 48

M(CO)4(PEt3)2 m mm m 405s mm m mm 48

M(CO)4(PBU3)2 --*• — 406vs *

*This work complexes. A comparison with the E mode band for the monosubstituted complexes shows the disubstituted product bands to be 15-25 cm"* higher. CHAPTER V

SUMMARY

General Conclusions Thirty-seven monosubstituted complexes of the type

LM(CO)5 (where M « Cr, Mo, Wj L • monodentate ligand containing a N, P, As, Sb, Bi, 0, or S donor atom), twenty-six cis-disubstituted complexes of the type (bid)M(CO)^ (where M s Cr, Mo, Wj bid = bidentate ligand containing N, P, S, or As donor atoms), and four trans-disubstituted complexes of the type I^MteO)^ (where L « PhgP, Bu^Pj M = Cr, Mo, or W), have been prepared. Their infrared spectra have been recorded in the 1700-2100 cnT^ and 300-700 cnT^ regions. Correlations between i>(CO), i)(MC), pK of the ligand, force constants, and Pauling electronegativity have been made. These results have been critically evaluated and compared with existing theories.

It has been found that MC stretching frequencies do not necessarily have an inverse relationship with CO stretching frequencies, in agreement with suggestions made by Dobson (29). For complexes with ligands containing alky1 substituents bonded to the donor atom, the MC E mode frequency can be related to the electronegativity of the donor atom by the equation! i?(MC) » -20,6 [[electronegativity] + 431,

69 70

It is also evident that the bonding characteristics in metal carbonyls must be re-evaluated in light of this evidence, The sigma only theory of Angelici and Halone has been placed on extremely shaky ground, and should not be used to predict any bonding properties of metal carbonyl compounds. The pi-only theory of Cotton and Kraihanzel may still be used to explain bonding changes brought about by variations in the pi-accepting ability of a series of ligands in which the donor atom is not changed, but should not be used alone to explain changes brought about by different donor atoms. By studying complexes containing such a broad range of ligands, it is now certain that the E mode MC stretching frequencies of monosubstituted complexes containing non-pi-bonding ligands are most strongly affected by a through space, direct ligand to ligand donation, and to a lesser extent by ligand sigma inductive effects. In contrast, the CO stretching frequencies are predominantly affected by changes in the pi-accepting ability of the ligand, and to a lesser extent by its through space bonding.

Proposals for Future Work The correlations from this investigation were hindered greatly by the inability to observe all the MC vibrations, and the inability to accurately assign the observed bands, especially for the cis-disubstituted complexes. It is an- ticipated that these problem's could be easily solved if 71

polarized Raman data were available. Therefore, the first and foremost need is to obtain Raman data for these complexes. Accurate identification of the A^ bands, which are more intense in the Raman spectra, would allow correlations with the pK , v(CO), and i>(MC) E modes. These results Cl should help distinguish whether ligand sigma bonding effects or direct ligand to ligand donation plays a dominant role in these complexes. Second, the trend observed between the i)(MC) and electronegativity should be more complete. It is recommended this be done by recording the spectra of complexes containing the ligands given in Table XVII.

TABLE XVII LIGANDS FOR FUTURE COMPLEXES

Donor atom Ligands

P PF3, PH3, P(OEt)xCl3-x

As AsHg, AsCl^, AsR^, As(0R)3

Sb SbCl3, Sb(OR)3

Bi BiR3

0 PhOH, R2CO, (RO)3PO, R3PO, Ft^O

S R2S, RSH, Ph2S

Se PhSeH, R2Se, RSeH, Ph2Se X EtCl, EtBr, PhCl, PhBr 72

At first glance one might think complexes with some of these ligands couldn't be made, but with a few added precautions and equipment* very satisfying results should be obtained. Since many of these complexes are presumably unstable at room temperature, special preparative techniques and infrared equipment will be needed. It is recommended they be made by the standard ultraviolet method used for the preparation of the oxygen complexes made in this investigation. The apparatus should be immersed in either an ice bath or some other cold bath, from which the liquid is circulated to cool the reactor cold finger. A low temperature infrared cell would also be needed.

Third, complexes containing the ligands EHxClg_x,

R 0R anc where a N EMX 3-X* E£Ix( )3_x» * ^x^S-x ( » As, and Sbj R s Et or Bu) would be readily adaptable to NMR studies. Those ligands which contain P have the greatest potential, since NMR signals can be observed for *H, "^P, ^C, and isotopes. The NMR results could then be correlated with infrared and Raman data.

Last, since the MC E mode of the MeCN tungsten complex is considerably higher than those of other nitrogen complexes, other nitrile complexes should be studied. The investigation could test the proposals presented in Chapter III in addition t:o determining any trends in pi-accepting ability. The preparation of complexes of the following riitriles should 73

be attemptedi HCN, C1CN, BrCN, ICN, MeCN, MeOCN, PhCN,

PhOCN, and H2NCN, The mass spectra of the above suggested complexes could also be examined. Kiser (64, 65) has laid the foundation for recording and interpreting mass spectra of metal car- bony 1 compounds, and his methods could yield a large series of papers on the mass spectra of these compounds. With the aid of metastable peaks, the decomposition pathways could be determined, and further evidence on competing reactions could be obtained. APPENDIX

COMPUTER PROGRAM USED TO CALCULATE FORCE CONSTANTS AND GRAHAM PARAMETERS

The following program (66) was used to calculate the force constants and Graham parameters of the monosubstituted metal carbonjrl complexes.

A test of twenty-seven sets of frequencies was made by varying the >>(C0) of the cyclohexylamine tungsten complex by -1, 0, or +1 cm"*1. Since the band positions in this work are accurate to tl cm 1 and errors should be the same for each band in a spectrum, those cases where all three modes were +1 or -1 cm"1 from the standard should show the greatest chance for error. In both cases, the errors in k^ and k2 are between 0,0159 and 0,0168 mdynes/S, In a few spectra of monosubstituted complexes, the upper Ax mode was very weak and may have been in error while the other two bands were accurate. Under these cir- cumstances , variations of "t\ cm 1 in the upper A^ band produced errors in k^ of less than 0,0014 mdynes/$r and errors in k2 of less than 0.0063 mdynes/8. Other variations in the series were less than 0.022 mdynes/8.

Since the variations of and k2 in the amine complexes examined in this work have an overall range of 0,057 and

74 75

0,204 mdynes/8 respectively, it is concluded that the trends are well outside the range of experimental error.

C PROGRAM USED TO CALCULATE FORCE CONSTANTS AND C GRAHAM PARAMETERS FOR MONOSUBSTITUTED OCTAHEDRAL C CARBONYLS. PUNCH FIXED POINT FREQUENCIES (IN C WAVENUMBERS), A1, A1PRIME, AND E IN UNITS OF C TEN COLUMNS. PUNCH NAME OF COMPOUND STARTING IN C COLUMN 31, MAXIMUM OF 28 COLUMNS. THE FIRST OF C EACH GROUP OF COMPOUNDS MUST BE THE CYCLOHEXYL C AMINE DERIVATIVE. A BLANK CARD MUST BE USED TO C SEPARATE EACH GROUP. THE LAST CARD IN THE DATA C DECK MUST HAVE A NEGATIVE WAVENUMBER IN THE C FIRST TEN COLUMNS. C DIMENSION CMPD(7) FUDGE=100000. 9 N=0 WRITE(6,10) 10 FORMAT(1H1,2X,2HA1,7X,3HA1/,7X,1HE,10X,2HK1,10X, 2HK2,1OX,2HKI,8X,15HSIGMA,9X,2HPI,9X,8HCOMPOUND,/) 1 READ(5,2)FREQ1,FREQ2,FREQE,CMPD 2 FORMAT(3F10.1,7A4) IF(FREQ1)7,9,3 3 XLAMls:. 05889*FREQ1*FREQ1 XLAM2=. 05889*FREQ2*FREQ2 XLAME=.05889*FREQE*FREQE A=.68572"(3."XLAM1+3,*XLAM2+14,«XLAME) T ERM=SWRT(A-A-4.7023*K4 „V0CLAM1*XLAM2+8.*XLAM1* XLAME+ 8.*XLAM2*XLAME1+2 0»*XLAME*XLAME)) RK2ls(A+TERM)/2 .0 RK22=(A-TERM)/2.0 RK11=6,8573*(XLAMl+XLAM2+2,*XLAME)-3.*RK2l RK12=6.8573"(XLAMl+XLAM2+2.*XLAME)-3.*RK22 RKA=(RK21-6.8573*XLAME)/2.0 RKB=(RK22-6.8573*XLAME)/2.0 IF(RKll)l2,11,11 11 RK1=RK11/FUDGE RK2=RK2l/FUDGE RKI=RKA/FUDGE GO TO 13 12 RKlsRKl2/FUDGE RK2=RK22/FUDGE RKI=RKB/FUDGE 13 IF(N)14,14,15 14 SKlssRKl SK2tsRK2 15 DELlsRKl-SKl 76

DEL2»RK2-SK2 SIGMA-2. *DEL2 -DELI PI=DEL2-SIGMA WRITE(6,4)FREQ1,FREQ2,FREQE,RK1,RK2,RKI,SIGMA,PI,CMPD 4 FORMAT(lHO,F6.1,3XfF6.1,3X,F6.1,3X,F8.4,4XfF8.4,4X, F8,4,4XtF8.4f14X,F8.4#4X»7A4) NsN+1 GO TO 1 7 STOP END BIBLIOGRAPHY

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