The Chemistry of Group 6 and 7 Transition

THE CHEMISTRY OF GROUP 6 AND 7 TRANSITION

METAL ORGANOMETALLIC NITROSYL COMPLEXES

BRIAN WILLIAM STIRLING KOLTHAMMER

B.Sc. (Honours), University of British Columbia, 1975

A THESIS SUBMITTED IN PARTIAL. FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

THE FACULTY OF GRADUATE STUDIES

in the Department of

Chemistry

We accept this thesis as conforming to the

required standard

THE UNIVERSITY OF BRITISH COLUMBIA

February, 1979

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

The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5

Date H&AcL M Jill ABSTRACT

Nitrosyl chloride exhibits a number of different

reaction modes in its reactions with monomeric and dimeric

neutral carbonyl complexes of transition metals. From its

reaction with [CpCr(CO)3]2 under controlled conditions, the

organometallic compounds CpCr (CO) 2 (NO) , CpCr(NO)2Cl,

[CpCrCl2]2,, and [CpCr (NO) Cl]2 can be obtained. In contrast.,,

the analogous [CpM(CO)3]2 (M — Mo or W) compounds react with

C1N0 to produce CpM(CO)3Cl and CpM(NO)2Cl in comparable

yields. The (arene)M(CO)3 (M = Mo or W) compounds form the

C1 polymeric [M(NO)2Cl2]n species via labile M (CO) 2 (NO) 2 2

intermediates under identical experimental conditions. Poss

ible pathways leading to the formation of all products are

presented.

Trithiazyl trichloride, N^S^Cl^, introduces the

thionitrosyl group onto a metal centre during the reaction.

Na[CpCr (CO) ] + 3"3N3S3C13 • CpCr (CO) 2 (NS)

An x-ray crystallographic analysis of this complex shows

that the thionitrosyl group coordinates essentially linearly

to the chromium via the nitrogen atom. A second product

formed in this reaction, Cp2Cr2(CO)^S, possesses a novel

Cr-S-Cr linkage which is linear, short, and chemically inert

The cations, [ (RC^H^)Mn (CO)''2 (NO) ] * (R = H or Me) react with I in acetone at room temperature to produce (RC5H4)Mn(CO)(NO)I. These species have very labile CO ligand

which are readily displaced by Lewis bases to produce (RC^H4)

Mn(L) (NO) I [R = H, L = PPh3 or P(OPh)3; R = Me, L = PPh3,

- P(OPh)3, or P(C6H1:L)3]. The reactions of Br , Clo, and N02~

+ with [(RC^H^)Mn(CO)2(NO)] produce the unusual bimetallic

compounds (RC5H4)2 Mn2 (NO)3 X (R == H or Me; X = Cl, Br, or N02)

The compound [CpCr(NO)2]2 abstracts all of the

chlorine ligands from SnCl4, MC12 (M = Hg, Sn, or Pb), CpFe-

(CO)2Cl, and Mn(CO)5Cl in. refluxing thf to form CpCr(NO)2Cl. The other products are the metals (M), [CpFe(CO)»]„, and

Mn2(CO)^Q, respectively. The chromium dimer also abstracts halogen from vic-dihaloalkanes to produce the corresponding alkenes in good yields. - iv -

ACKNOWLEDGEMENTS

I wish to thank the faculty and technical

staff of the Chemistry department for their assistance and guidance throughout this study. In particular, I wish to thank Prof. N.L. Paddock who read this thesis and offered suggestions for improvements I am indebted to the people of Room 325 for providing a pleasant atmosphere for work

and especially I acknowledge Dr. J.T. Malito, D.T. Martin and B.W. Hames. The work of Jen Kolthammer, who typed

this thesis, is greatly appreciated.

Finally, I wish to express my gratitude to

Peter Legzdins whose perseverence and encouragement are the foundations of this work. - v -

TABLE OF CONTENTS

Page

ABSTRACT ii

ACKNOWLEDGEMENTS iiv

TABLE OF CONTENTS V

LIST OF TABLES vii

LIST OF FIGURES . . ix

ABBREVIATIONS AND COMMON NAMES x

CHAPTER I INTRODUCTION 1

CHAPTER II SOME REACTIONS OF NITROSYL CHLORIDE

WITH NEUTRAL CARBONYL COMPLEXES ... 7

Experimental 9

Results and Discussion 19 Reactions of Nitrosyl Chloride with

[CpM(CO) -J2 (M = Cr, Mo, or W) and

[CpMn(COr (NO) ]2 19

Reactions of Nitrosyl Chloride with Other Neutral Carbonyl Complexes .. 28

Reactions of Nitrosyl Chloride with

CpMn(CO)3 33

Reactions of Nitrosyl Chloride

Attributable to Cl2 and NO 34

CHAPTER III REACTIONS OF TRITHIAZYL TRICHLORIDE WITH TRANSITION METAL CARBONYL COMPOUNDS 36

Experimental 37

Results and Discussion 42

CHAPTER IV REACTIONS OF DICARBONYL(n5-CYCLO- PENTADIENYL)NITROSYLMANGANESE HEXA- FLUOROPHOSPHATE WITH HALIDE IONS .. 5 9

Experimental 61 - vi -

Page

Results and Discussion 73

CHAPTER V SOME ASPECTS OF THE CHEMISTRY OF BIS[ (n 5-CYCLOPENTADIENYL)DINITROSYL- CHROMIUM] 99

Experimental 99

Results and Discussion 105

Selective Removal of Halogen from Organic Halides 115

REFERENCES 119 - vii -

LIST OF TABLES

Table Page

I Low-Resolution Mass Spectral Data for

[CpCrCl2]2 and [CpCr(NO)Cl2]2 22

II Nitrosyl Stretching Frequencies of

the Complexes ML2(NO)2C12 31

III Reactions of N^S Cl^ with some Tran• sition Metal Compounds 39

5 IV Physical Properties of (n-C5H[-) Cr-

(CO)2(NX) Complexes 44

V Low-Resolution Mass Spectral Data for

(C5H5) Cr (CO) 2 (NX). Complexes 4 6

VI Low-Resolution Mass Spectral Data for

[(C5H5).Cr(CO)2]2S 53

VII Mass Spectral Data for (RC5H.)Mn(CO)- (NO) I Complexes 63

VIII Physical Properties of the Complexes

(RC5H5)Mn.(L) (NO) I 66

Mn IX Elemental Analyses for (RC^H.)2 2~

(NO)3 X Complexes 71

X Physical Properties of (RC5H4)2Mn2~

(NO)3 X Complexes 72

XI Mass Spectral Data for (RCj-H .) Mn(NO) -

(PPh3)I ..7 78

XII Mass Spectral Data for (RC-H.) Mn (NO) -

. [P(0Ph)o]I and (CcH_)Mn(N07TP (CCH, ,) , 3 3 [P(C6Hl )3]I ....S.H. 79

XIII Mass Spectral Data for (C,H7)Fe(CO)-

(PPh3)I v :.. 80 XIV 13C NMR Spectral Data of Some (MeCp)Mn Compounds 86

XV Mass Spectral Data for (C^H-)Re(CO)- (NO) I 89 - viii -

Table Page

XVI Mass Spectral Data for (RCVH.)„Mn„-

(NO)3I 92

XVII Mass Spectral Data for (RC-HJ9Mn0-

(NO)3Br 93

XVIII Mass Spectral Data for (RCr-H.) 9Mn~-

(NO)3 C1 94

XIX Mass Spectral Data for (C-H-)-Mn--

(NO)3R 95

XX *H NMR Spectral Data for (RCRH.)9Mn0-

(NO)3X 97

XXI Reactions of j^CpCr(NO)2 ]2 with some Halogen-Containing Compounds 101

XXII High-Resolution Mass Spectral.Data

for [(C5H5)Cr(NO)2]2 107 - ix -

LIST.OF FIGURES

Figure Page

+ 1 Structure of [.Ru(PPh3>2 (NO) 2C1] 3

2 Apparatus for Purifying Nitrosyl Chloride 11

3 Molecular structure of (n5 -Cj-H,.) Cr-

(CO)2(NS) 48

4 Molecular structure of [ (ri 5-CJ-HJ. ) Cr-

(CO)2]2S 55

5 The *H NMR Spectra of (MeCp) Mn (CO) , (MeCp) Mn (CO) _ (PPh^) , [.(MeCp) Mn (CO) -

(NO)(PPh3)]PFfi, and (MeCp)Mn(NO)-

(PPh3)I . 83 6 Infrared Spectral changes accompany•

ing the reactions of [CpCr(NO)0]0 ... 110 - x -

ABBREVIATIONS AND COMMON NAMES

The abbreviations used in this thesis are those recommended in the Handbook for Authors of Papers in American Chemical Society Publications (ACS 1978). o A Angstrom atm atmospheres Bu butyl calcd calculated cm 1 wave numbers in reciprocal centimeters Cp pentahapto-cyclopentadienyl d day(s) dec decomposes Et ethyl h hour(s) Hz Hertz, cycles per second IR infrared J magnetic resonance coupling constant m/z mass to charge ratio Me methyl MeCp pentahapto-methylcyclopentadienyl min minute (s) mm millimeters of mercury mmol millimole NMR nuclear magnetic resonance Ph phenyl thf tetrahydrofuran 6 NMR chemical shift n5 pentahapto v IR stretching frequency - 1

CHAPTER I

INTRODUCTION

A distinguishing trait of the d-block elements is their ability to form complexes with neutral molecules such as isocyanides, phosphines, amines, carbon monoxide, and ni• trogen monoxide. The most important of these ligands is car• bon monoxide, and volumes of information1 have been published not only on the preparation of transition metal carbonyls but also on the use of these complexes in organic synthesis and catalysis. The chemistry of transition metal nitrogen mono• xide compounds is less well developed. However, the extent of the chemistry that may be exhibited by these nitrosyl compounds and their derivatives is potentially as broad as that of the carbonyl complexes.

Although nitrogen monoxide and carbon monoxide are known to bond to transition metals in an analogous fashion, the NO ligand contains one more electron ins.a TT* orbital.

The presence of this extra electron also allows a nitrosyl group to behave in a fashion unobserved for a carbonyl ligand, ive. to form a bent M-N-0 bond. The two different bonding modes may be described as follows:

(1) Linear The nitrosonium ion, NO , is lsoelec- tronic with carbon monoxide and, thus, it has three bonding electron pairs between the atoms and a lone electron pair on - 2 -

both the nitrogen and oxygen.

Both atoms are sp hybridized and both are potential donors. However, the.nitrogen coordinates preferentially, thereby avoiding a large formal positive charge on the more electronegative element. The nitrosyl ion can be considered as a a-donor and the resulting M-NEO .is linear. Occupied metal dTT orbitals provide some degree of MTT-^-NOTT* overlap estab• lishing a synergistic bonding relationship. (Alternatively, the linear group may be considered as a bond between nitrogen monoxide.and a.metal.containing an empty a-orbital and a half- filled Tr-orbital which-interacts with the ir* electron of the

NO). When bonding in this way, the nitrosyl ligand is a for• mal three-electron donor.

(2) Bent A bent nitrosyl ligand is an analogue of an organic nitroso group or the NO group in C1N0. The M-N-0 linkage consists of a doubly bonded.NO group, a single a-bond between the nitrogen and the metal, and a lone pair of elec• trons on the nitrogen atom. The nitrogen atom in this case is sp2 hybridized and the resulting M-N-0 system is bent.

When bonding in this way, the nitrosyl ligand is a formal one-electron donor. The resolution to the bent/linear duality of the ligand . lies in whether the pair of electrons in ques• tion will be forced to reside in an atomic orbital on the nitrogen atom or whether there is a low-lying molecular or• bital available to it.

An ideal characterization of these two types of bonding is present in the molecular structure of the dinitro- - 3 -

+ 2 syl cation, [Ru(PPh3)2(NO)2C1] , shown in Figure l . The basal nitrosyl ligand forms a linear M-N-0 link and the short M-N bond distance is indicative of the multiple bond• ing described above. The axial ligand contains a longer

M-N distance and a distinctly bent M-N-0 group with an angle of 136°. Although the ideal bond angle for the bent system is 120°, differing amounts of interaction between the lone pair on the ligand and the metal orbitals produce M-N-0 groups with bond angles ranging from 120° to 180°2. The ability of the ligand to be a variable 1+3 electron donor to a metal centre will greatly affect the chemistry of such complexes. In fact, tautomerism between the two possible forms can convert a coordinatively saturated compound to a reactive unsaturated species without the customary require• ment of the dissociation of a ligand. It is therefore reasonable to expect that nitrosyl complexes should exhibit different chemical and catalytic properties from their iso- - 4 -

electronic carbonyl analogues.

One of the first reports of this unique chemistry

was the extraordinary specificity shown by Fe(CO)2(NO)2 to• wards olefin dimerization3. When butadiene was treated with

1% by weight of the iron nitrosyl, 4-vinylcyclohex-l-ene was

formed as the sole product. Even the presence of other reactants or additives like Et^Al, PPh^, and pyridine had no

influence on reactivity or specificity. The presence of the nitrosyl ligands was essential for this reaction since a variety.of iron carbonyl derivatives exhibited no catalytic

activity. More recently it has been shown1* that species like

Fe(NO)2(L)2 (L = donor solvent), which may well be interme• diates in the above dimerization, are also equally specific

for the formation of the CgH^2 product.

Historically, the first organometallic complexes containing nitrogen monoxide were formed by metal compounds requiring an odd number of electrons to satisfy the effective atomic number rule. Examples5'6 of these are:

CHC1,.

CO- (CO) 0 + 2N0 =»• 2Co (CO) 0 (NO) RT 3

CfiHfi

[CpCr (CO) -]7 + 2N0 » 2CpCr(CO)„(NO) RT

pentane

Cp9Ni + NO • CpNi (NO)

A number of other syntheses of transition metal nitrosyls involved unique routes7- In some cases8 the formation of nitrosyl complexes was totally.unexpected, e.g. - 5 -

Et?0 Mn(CO) H + MNTS —• Mn(CO).(NO) RT

(MNTS - N-methyl-N-nitroso-p-toluenesulphonamide)

+ dl1 a [CpMo(CO)3 (NH3) ] + NaN03 - 3 • HCl,, CpMo(NO)2Cl

More general preparative routes have been studied9 only in more recent years.

At the outset of this research, the objectives were threefold, namely

(1) the preparation of organometallic nitrosyl com• plexes ,

(2) the study of their characteristic chemistry particularly with respect to that exhibited by their isostructural and isoelectronic carbonyl analogues, and

(3) the eventual use of organometallic nitrosyl com• plexes as specific reactants or selective catalysts in organic synthesis. In this context, Chapter II describes the reac• tions of a number of neutral metal carbonyl complexes with nitrosyl chloride and the different reaction modes of this reagent. The properties of the chloronitrosyl products from these reactions are also discussed. Chapter IV describes the successful attempt to prepare CpMn(CO)(NO)I and discusses the basic features which dominate its chemistry. These findings are then readily compared with the chemistry of the

known analogues CpCr(NO)2I and CpFe(CO)2I. In the final

chapter, some chemistry of [CpCr(NO)2]2 is presented and contrasted with that of[CpMn(CO)(NO)], and the extensively - 6 -

studied [CpFe(CO)2]2. This chapter concludes with an account

of the discovery of the unique selectivity of [CpCr(NO)2]2 in the dehalogenation of organic halides. CHAPTER II

SOME REACTIONS OF NITROSYL CHLORIDE WITH NEUTRAL CARBONYL

COMPLEXES

There was no general preparative route to transition metal nitrosyl compounds before 1970. Also, many of the then existing methods produced the desired products in low yields

and/or with much expenditure of effort. .Recently, several more, generally useful procedures have been reported and these include:

(1) the photo-induced reaction of metal carbonyl complexes with nitrogen monoxide10,

Cr(CO)6 + NO ** Cr(NO)4 (1) hexanes

CpCr (CO) 0 (NO) + NO »* CpCr(N0)oCl (2)

CHC13

(2) the reaction of nitrogen monoxide with reactive

transition metal complexes11,

hexanes

Cp~Cr + 2NO • CpCr (NO) 9 (Cc-H ) (3) ^ RT

thf

CpCr (CO)((NO) (thf) +NO CpCr (NO) 9 (N0o) (4) RT and (3) the reaction.of nitrosyl chloride with transi• tion metal carbonyl complexes12. - 8 -

(Ph2P)2 N[W(CO)5 Br] +C1N0 » W (C0)-4 (NO) Br (5)

Fe(CO)2(NO)2 + C1NO Fe(NO)3Cl (6)

In this latter category, two types of reactions are illus• trated. The first is the reaction.of C1N0 with transition metal carbonyl anions,.a route recently studied as a general synthetic approach to metal nitrosyl complexes9. It was shown that the stoichiometric reaction of nitrosyl chloride with weakly nucleophilic anions provided a convenient means

of preparing neutral complexes such as CpM(CO)2(NO) (M = Cr,

Mo, or W), Mn(CO)4(NO), and Fe(CO)2(NO)2. The second type of reaction, between C1N0 and neutral carbonyl-containing compounds, readily affords neutral chloronitrosyl complexes in most instances. However, in some cases unexpected pro•

ducts result. As an example, when CpMo(CO)2(NO) is treated

with C1N0, a minor product is [CpMo(NO)Cl2]2 whose occurrence, it is believed12, reflects the fact that C1N0 exists in solu• tion as part of the equilibrium

2C1N0 ,, 2N0 + Cl2 (7)

In other words, solutions of nitrosyl chloride may exhibit reactions that can be attributed to any of the chemical entities present in the above equilibrium. Even when nitro• syl chloride reacts as such with neutral carbonyl complexes, a number of different reaction modes can be envisaged for it.

Among these are:

(1) displacement of ligands capable of donating a total of four electrons to a metal centre in a coordinatively - 9 -

saturated complex,

(2) complete displacement of a hydrocarbon ligand regardless of the number,of electrons that it formally donates to the metal, and

(3) formal reaction as a nitrosonium salt with only

Not being coordinated to the metal centre. This chapterc;.e

describes new reactions between C1N0 and [CpM(CO)^]2 (M = Cr,

Mo, or W), [CpMn(CO)(NO)]2, (arene)M(CO)3 (M = Cr, Mo, or W),

(C^H,-) Fe (CO) 2 (NO) , and CpMn(CO)3, reactions which typify these reaction.modes.

Experimental

All chemicals used were of reagent grade or compar• able purity and were either purchased (from commercial suppli• ers) or prepared according to reported procedures. Their purity was ascertained from elemental analyses and/or melting point determinations. All melting points are uncorrected and were taken in capillaries under prepurified nitrogen . using a Gallenkamp Melting Point Apparatus. Nitrogen monox• ide (Matheson CP. grade, 99.0% min.) was further purified by passing it through a column of activated silica gel maintained at -78° C. Its purity was confirmed by mass spectral analysis. All solvents were dried according to standard procedures13 and thoroughly purged with prepurified nitrogen prior to use. All manipulations, unless otherwise stated, were performed on the bench using conventional tech• niques for the manipulation of air sensitive compounds14 or -10-

in a Vacuum Atmospheres Corporation Dri-Lab model HE-43-2 dry box filled with prepurified nitrogen.

Infrared spectra were recorded on Perkin Elmer 457 or 710A spectrophotometers and calibrated with the 16 01 cm 1 absorption band of a polystyrene film. Proton magnetic res• onance spectra were recorded on a Varian Associates T-60 spectrometer using tetramethylsilane as an internal standard.

Carbon-13 NMR spectra were recorded on a Varian Associates

CFT-20 spectrometer with reference to the solvent used. All

13C chemical shifts are reported in ppm downfield from Me^Si.

The low-resolution mass spectra were taken at 70 eV on an

Atlas CH4B spectrometer and the high-resolution mass spectral data were obtained on an Associated Electrical Industries

MS9 02 spectrometer with the assistance of Dr. G. Eigendorf and Mr. J.W. Nip. Elemental analyses were performed by Mr.

P. Borda and.x-ray structural determinations were carried out by.Dr. T.J. Greenhough.

Preparation of Nitrosyl Chloride

Nitrosyl chloride.was prepared in the following man• ner. A 100 mL three-necked flask was equipped with a nitro• gen inlet, a dropping funnel, and a drying tower (2 x 20 cm) packed from top to bottom with equal volumes of anhydrous

CaCl2, KC1, and NaN02. The top of the tower was fitted with a 5 mL graduated cold trap equipped with a stopcock on the trap inlet, as shown in Figure 2. The trap outlet was con• nected to a 100 mL two-necked flask equipped with a nitrogen FROM CINO GENERATOR

FIG 2 APPARATUS FOR PURIFYING NITROSYL CHLORIDE - 12 -

inlet secured with a silica gel drying tube. After flushing the entire apparatus with nitrogen, the reaction flask was charged with concentrated aqueous HCl (32 mL). An aqueous

solution (10)mL) of NaN02 (5.54 g) was added dropwise to the rapidly stirred acid solution.at room temperature. The gaseous C1NO which formed instantly was carried by a slow

stream of N2 into the cold trap held at -78° C. In this man• ner, 2.5 mL (50 mmol) of C1N0 were generated. This was dis•

tilled under vacuum into the 100.mL flask and 30 mL CH2C12 were added to'the cold C1NO to yield a deep•red solution. 'All subsequent reactions involving C1NO were performed by the

dropwise addition of the CH2C12 solution to the appropriate reaction mixture while monitoring the course of the reaction by infrared spectroscopy.

Reaction of Nitrosyl -Chloride with. [CpCr (CO) 0^2' To a s^rre<^-

15 solution of.[CpCr(CO)3]2 (2.0 g, 5.0 mmol) in dichloromethane (60 mL) was added.dropwise a solution of C1NO at room temperature. Gas evolution.occurred and the solution became yellow-green in colour.. The progress of the reaction was monitored by infrared spectroscopy, and the C1NO solution was added until the carbonyl absorptions due to the initial reactant had disappeared. The.solvent was removed from the solution in vacuo, leaving a green residue. This residue was extracted with hexanes to obtain an orange solution. The hexanes were removed from the extracts under reduced pressure, and the resulting orange solid was sublimed at 40° C - 13 -

(5 x 10 3 mm) onto a water-cooled prober The orange sub• limate (^0.70 g) was identified by its infrared spectrum as

CpCr(CO)2(NO)16• The hexane-insoluble residue was dissolved in dichloromethane (25 mL). The addition of hexanes (50 mL) to this solution precipitated a dark green solid which was collected by filtration. The filtrate was taken to dryness under reduced pressure, and the residue was redissolved in

CH2C12 (10 mL). The resulting solution was filtered through a short (2x5 cm) Florisil column. The solvent was removed from the filtrate in vacuo to obtain 0.80 g of a gold solid

15 identified by its IR spectrum as CpCr(NO)2C1 . The dark green solid collected previously was treated in the following manner. Volatile compounds were removed.at 60° C and 5 x

10 3 mm, and then the residue was dissolved in dichloromethane

(30 mL). This solution was filtered and addition of hexanes

(60 mL) precipitated ^0.30 g of a dark green solid identified

Tne by its mass spectrum as [CpCrCl2]2' final filtrate

contained a small amount ('vO.l g) of [CpCr (NO) Cl] 2 as ev• idenced by its IR spectrum. However, this latter complex could not be satisfactorily purified because its solubility properties were identical to those exhibited by [CpCrC^^-

The yields of all product complexes depend markedly on the amount of nitrosyl chloride added.

Reactions of [CpCr (NO) Cl] 2 and [CpCrC^Jo with NO. These re• actions were carried out in a.similar manner. For example,

17 [CpCr(N0)C1]9 (0.10 g, 0.29 mmol) was dissolved in dichloro- - 14 -

methane (40 mL) and a stream of prepurified nitrogen monoxide was bubbled through the solution. Immediately the green solution became green-brown, and.the.NO flow was.stopped after several minutes. The solution was then filtered through a short (3x2 cm) Florisil column and the solvent was removed from the filtrate in vacuo to obtain a quantita•

tive yield of CpCr(NO)2Cl. In the case of [CpCrCl2]2, a much

lower yield of CpCr (NO) 2Cl was obtained.

Reaction of CpCr(CO)2(NO) with Cl2or I2. A saturated CH2Cl2

solution of Cl2 was added dropwise at room temperature to a

16 stirred orange solution of CpCr(CO)2(NO) (0.60 g, 3.0 mmol) in dichloromethane (.30 mL) . Gas evolution occurred and a green solid precipitated.as the solution became yellow-green in colour. Just enough chlorine was added to react with all

of the CpCr(CO)2(NO) as monitored.by IR spectroscopy. The final reaction mixture was filtered and ..the solvent was re• moved from the filtrate in vacuo to obtain 0.26 g (41% yield based on Cr) of a green-golden solid identified by its

infrared spectrum as CpCr(NO)2Cl.

The reaction.of CpCr(CO)2(NO) with I2 was carried out similarly. However, an IR. absorption due to an inter• mediate nitrosyl complex was observed, during the reaction.

The intermediate slowly decomposes to the only isolable

nitrosyl species, CpCr(NO)2I.

Decomposition of [CpCr(NO)Cl]2. A solution.of [CpCr(NO)Cl]2

(0.37 g, 1.0 mmol) in benzene (40 mL) was stirred at room - 15 -

temperature for 20 h, during which time a blue-green precip• itate formed. . The mixture was filtered through 2 cm of Flor- isil producing a golden filtrate. The benzene was removed in vacuo and the residue dried for 1 h at 25° C (5 x 10 3mm).

The gold-brown solid was identified as CpCr(NO)2Cl (0.19 g,

45%) by.its characteristic spectral properties.

Reactions of [CpM(CO),]^ (M = Mo or W) with CINQ. To a

stirred dichloromethane solution (50 mL) of [CpMo(CO)3]2

(0.74 g, 2.0 mmol) at room temperature was added dropwise a dichloromethane solution of C1N0. The reaction mixture became green-brown immediately and gas was evolved. Again, just enough nitrosyl•chloride was added to react with all of the initial carbonyl dimer. The final solution was concen• trated at-reduced pressure .to ^15.mL and syringed onto a

2 x 20 cm Florisil column.. Elution of the column with CH2C12 developed two bands. The.first band, orange in colour, was collected and concentrated in vacuo to 10 mL. The addition of hexane (30 mL) to this solution resulted in the crystal• lization of analytically pure CpMo^Oj^Cl.

Anal, calcd.for•C8H5Mo03Cl: C, 34.25; H, 1.80.

1 Found: C, 33.89; H, 1.9 3. vco cm" (CH-2C'l2)".: 205 7, 19 76.

Elution of the second band from the column pro•

duced a green solution which contained CpMo(NO)2C1, iden• tified by its IR spectrum12'16. This product was crystal• lized from the eluate by the addition of hexanes. The yields of both organometallic products were typically 35% and were - 16 -

greatly dependent on the amount, of C1N0 added since both complexes reacted further with this reagent.

The reaction of [CpW(CO)3]2 with nitrosyl chloride

produced CpW(NO)2Cl and CpW (GO^Cl in an analogous manner.

Reaction of [CpMn (CO) (NO) ] 2 with CINQ. A dichloromethane solution (30 mL) containing 0.36 g (1.0 mmol) of [CpMn(CO)-

18 (NO)]2 was treated dropwise at room temperature with a solution.of C1NO in the same solvent. Gas evolution was observed and an off-white solid precipitated. Just enough

C1NO was added.to react with all of the starting material.

The mixture was concentrated to ^15 mL and filtered through

2 cm of Celite. Hexanes (10 mL) were added to the red-black filtrate and slow concentration of this solution in vacuo

produced microcrystalline Cp2Mn2(NO)3C1 (0.12 g, 30% yield)

(vide infra).

Reaction of (o-xylene) Mo (CO) with CINQ. The compound (o-

19 xylene)Mo(CO)3 (0.74 g, 2:6 mmol) was dissolved in di• chloromethane (4 0 mL) and the stirred solution was treated dropwise at room temperature with a solution of C1N0 in dichloromethane. Gas evolution was immediate, the yellow solution became orange-brown, and a green solid precipitated.

Just enough C1NO was added to react completely with the in• itial carbonyl complex. After addition of C1NO was completed, an infrared spectrum of the supernatant solution indicated the presence of a carbonylnitrosyl compound. However, con• tinued stirring of the reaction mixture for several minutes - 17 -

caused.more green solid to form. Hence, stirring was main• tained until the supernatant was colourless. The solvent was then removed in vacuo and the green residue dissolved in tetrahydrofuran to obtain a clear green solution. An infra• red spectrum of this solution revealed that solvated [Mo-

20 INO)2CI2]R was the only nitrosyl complex present.

Reaction of [Mo(NO)^Cl^]n with Ph-,P. The polymeric [Mo-

(NO)2Cl2]n produced in the previous reaction (0.59 g) was

stirred in a refluxing benzene solution (60 mL) of Ph3P

(2.0 g, 7.6 mmol). After 1 h the initial mixture had become a clear green solution, thereby indicating that adduct for• mation was complete. The solvent was removed in vacuo and the yellow-green residue was extracted with dichloromethane

(40 mL). Slow addition of hexanes (100 mL) precipitated

2 the well known yellow-green Mo(NO)2C12(PPh3)2 ° •

Reactions of (arene)W(CO)3 [arene = C6H£, CH.,C6H5, or

(CH^j^C^H^] with CINQ. The reactions of nitrosyl chloride

21 with (arene)W(CO)3 complexes were carried out in a manner identical to that described previously for the molybdenum analogue. However, the progress of these reactions was slight• ly different. For example, when just enough C1NO to consume

the tungsten reactant had been added, very little [W(N0)2~

Cl2]n had precipitated. An infrared spectrum of the reac• tion mixture revealed the presence of a carbonylnitrosyl complex which was not affected by the addition of an excess of nitrosyl chloride. This complex was isolated by - 18 -

filtering the final reaction mixture and taking the filtrate to dryness in vacuo. The resulting red-brown solid was soluble in tetrahydrofuran, dichloromethane, and benzene, and slightly soluble in hexane. Pure samples of this compound could not be obtained because.of its tendency to transform

20 slowly to [W(NO)2C12]n in solution.at room temperature. In fact, stirring a dichloromethane solution of this compound for

48 h precipitated [W(NO)2Cl2]n quantitatively. The red-

brown complex was tentatively formulated as W(CO)2(NO)2C12

1 by virtue of its infrared spectrum [vCQ cm (CH2C12) 2145,

-1 2070. vNQ cm (CH2C12) 1815, 1725].

Reaction of (Cp5) Fe (CO) 2 (NO) with CINQ. A pentane solution

22 (30 mL) of (C3H5)Fe(CO)2(NO) cooled to 0° C was treated with a solution of C1NO in dichloromethane. The red solu• tion immediately darkened and gas was evolved. When the reaction was complete, the solvents were removed in vacuo leaving a red-brown solid. Sublimation of this residue at

40° C (5 x 10 3 mm) onto a water-cooled probe produced

[Fe (IJOi)'^Cl] 2 as evidenced by its IR and mass spectra.

Reaction of CpMn(C0)3 with CINQ. To a stirred solution of

CpMn(CO)3 (0.41 g, 2.0 mmol) in dichloromethane (40 mL) at room temperature was added dropwise a solution of C1NO in

CH2CI2. After a few minutes, gas was evolved and the solu• tion became cloudy. The reaction was exothermic and a large amount of C1NO was consumed. When the initial complex had completely reacted (as indicated by IR spectroscopy), the - 19 -

reaction mixture was taken to dryness in vacuo. The resulting residue was extracted with ethanol (95%) and the extracts were treated with a saturated aqueous solution of NH^PF^, thereby precipitating a bright yellow solid. This solid

(0.38 g, 54% yield) was identified as [CpMn(CO)2(NO)]PFg by its characteristic infrared spectrum2 3.

Reaction of Mn^(CO)^Q with CINQ. A stirred dichloromethane

solution (100 mL) of Mn2(CO)^Q (1.0 g, 2.6 mmol) was treated at room temperature with an excess of C1NO. The yellow solu• tion became orange initially, but no gas was evolved. The reaction mixture was stirred for 3 h, during which time a yellow solid precipitated and some gas evolution occurred.

The solvent was then removed in vacuo, and the yellow residue was sublimed at 50° C (5 x 10 3 mm) onto a water-cooled probe

to obtain 0.23 g (38% yield) of Mn(CO)5Cl.

Anal, calcd for C505MnCl: C, 26.06. Found: C,

25 .99.

Results and Discussion

Reactions of Nitrosyl Chloride with [CpM(CO).J2 (M = Cr,

Mo, or W) and [CpMn(CO)(NO)]2.

The ability of nitrosyl chloride to react by various modes is clearly illustrated by its reaction with .[CpCr-

(CO)3]2. If an excess of C1NO is employed, CpCr(NO)2C1 is the major organometallic product obtained. However, if only sufficient C1NO to consume the original dimer is added, the - 20 -

principal organometallic products are CpCr(N0)2Cl and [CpCr-

Cl2]2' Although both of these compounds are well known, their production in this reaction is unique. The formation

of CpCr(N0)2Cl can be readily understood if one considers the initial species produced in this reaction. When only a

small amount of nitrosyl chloride is mixed with [CpCr (CO) ^]2 , the presence of a carbonylnitrosyl complex is indicated by the infrared spectrum of the reaction mixture. This complex

can be easily isolated and identified as CpCr(CO)2(NO). It has been previously established12'16 that this complex is

smoothly converted to CpCr(NO)2Cl by treatment with C1NO.

The formation of the dicarbonylnitrosyl intermediate thus resembles the cleavage of the starting carbonyl dimer by

21 nitrogen monoxide * which also produced CpCr (CO) 2 (NO) .

Therefore, the ultimate nitrosyl-containing product is probably formed by the following sequential reactions:

[CpCr(CO)3]2 + 2C1NO • 2CpCr (CO) 2 (NO) + 2CO + Cl2 (8)

CpCr (CO) 2 (NO) + C1NO • CpCr(NO)2Cl + 2CO (9)

The other product, [CpCrCl2]2, is rather unexpected.

It is not produced in the reactions of Cl2 with [CpCr(CO)3]2,

CpCr(CO)2(NO), or CpCr(NO)2Cl, nor is it formed in the re• actions of the latter two compounds with nitrosyl chloride.

It thus appears that a novel reaction mode of nitrosyl

chloride with [CpCr(CO)3]2 leads to this surprising product, i.e. - 21 -

C1N [CpCr(CO)3]2 °». [CpCrCl2]2 (10)

This reaction parallels that described previously2 5 for

the carbonyl dimer with CH2=CHCH2X (X = Br or I), i.e.

XCHCH=CH0

[CpCr(CO)3]2 [CpCrX2] (11) in which carbonyl- or allyl-confcaining intermediates were not observed.

The complex CpCr(NO)2Cl has been well character•

26 ized , and [CpCrCl2]2 has been previously prepared by sever• al other methods27. The latter compound has also been sug•

2 3 gested as an intermediate in the preparation of CpCr(N0)2Cl

from CrCl3, NaCj-H,. , and NO, although it was not isolated.

A similar complex has been reported28 to result from the re• action of chromocene with HCl(g). Most of these reports, however, are probably dealing with a solvated species such

25 as CpGrCl2•thf since the preparative reactions are carried out in tetrahydrofuran. Desolvation of this species affords

"CpCrCl2" as a blue-green amorphous powder which is not very soluble in common organic solvents. In contrast, the green

[CpCrCl2l2 that is isolated here is very soluble, even in dichloromethane. Although the previously reported observa• tions may pertain to various chloro complexes, the exact formulation of our compound is confirmed by its mass spectrum which is summarized in Table I. The spectrum exhibits the parent ion and the expected fragmentation pattern of dimeric

[CpCrCl9]„, namely the sequential loss of cyclopentadienyl - 22 -

Table I. Low-Resolution Mass Spectral Data for [CpCrCl2]

and [CpCr (N0)C1] 9

Rel Rel m/z abund Assignment3 m/z abund Assignment3

+ + 374 5 (C5H5)2Cr2Cl4 364 4 (C5H5)2Cr2Cl2(NO)2

+ + 339 43 (C5H5)2Cr2Cl3 334 33 (C5H5)2Cr2Cl2(NO)

+ + 304 5 (C5H5)2Cr2Cl2 304 34 (C5H5)2Cr2Cl2

+ + 274 7 C5H5Cr2Cl3 182 100 (C5H5)2Cr

+ + 187 7 C5H5CrCl2 15 2 29 C5H5CrCl

+ + 182 22 (C5H5)2Cr 117 31 C5H5Cr

+ + 152 100 C5H5CrCl 65 24 C5H5

+ + 117 10 CcHcCr 52 23 Cr 5 5

65 16 C|H5+

7 r 52 20 Cr+

The assignments involve the most abundant naturally 5 2 35 occurring isotopes, i.e. Cr and Cl, in each fragment. - 23 -

and chlorine ligands. The molecular structure of this com• pound probably contains either two or four chlorine bridges between the metal atoms. Since the completion of this work, two further reports of this compound have appeared. The

29 10 photolysis of CpCr(CO)3Me , [CpCr(CO)3]2, or [CpCr(CO)2]2

in halogenated solvents (commonly CHC13) leads to the forma•

tion of large amounts of [CpCrCl2]2/ In these reactions it appears the photodecarbonylation produces a radical intermedi• ate which abstracts chlorine from the solvent to produce,

eventually, the chloro-bridged species. When [CpCrCl2]2, dissolved in dichloromethane, is treated with nitrogen

monoxide, this dimeric structure is disrupted and CpCr(NO)2Cl is produced. The yields of this latter conversion are quite low, and this may account for the low yields obtained in the

23 original preparation of CpCr(NO)2C1 .

A third, albeit minor, product of the reaction of

[CpCr(CO)3]2 with C1N0 is [CpCr (NO) Cl] 2 . 'In view of the

known reaction of Cl2(g) with CpMo(CO)2(NO) to yield [CpMo-

30 (NO)Cl2]2 , it is not unreasonable to expect that the anal•

ogous reaction between CpCr(CO)2(NO) and Cl2(g) could produce

[CpCr(NO)Cl]2. However, we find that this reaction results in an unusual disproportionation which leads to the forma•

tion of CpCr(NO)2Cl in high yields (with respect to the nitrosyl.ligand). Furthermore, no reaction between CpCr-

(NO)2C1 and Cl2 or C1N0 occurs in solution, thereby excluding

these as pathways leading to the production of [CpCr(NO)Cl]2.

A fourth possibility might be the reaction of nitrosyl - 24 -

chloride with an intermediate carbonyl complex, but no absorptions attributable to carbonyl-containing species other than CpCr(CO)2(NO) are observed in the infrared spectrum of

the reaction mixture. Hence, the [CpCr(NO)Cl]2 is probably

formed directly from [CpCr(CO)3]2/by the reaction

[CpCr(CO)3]2 + 2C1N0 [CpCr (CO) (NO) Cl]2 + 4C0 (12) followed immediately by

[CpCr (CO) (NO) Cl]2 +• [CpCr (NO) Cl]2 + 2C0 (13) as chlorine.bridges are formed.in the final product. The displacement of two carbonyl ligands by each C1N0 added in reaction (12) represents a very common reaction mode of nitrosyl chloride and has numerous precedents. One example

which is very similar to this is the conversion of [Re(CO)4~

Cl]2 to [Re(CO)2(NO)Cl2]2 by the process depicted in equation (14)31. The spontaneous liberation of carbon

4 [Re(CO)4Cl]2 + 2C1N0 *> [Re (CO) 2 (NO) Cl2]2 " + C0 (14) monoxide invoked in reaction (13) appears to be a general property of a number of carbonylhalonitrosyl complexes, and some verified examples of such transformations are discussed in subsequent paragraphs.

The previously unknown dimeric complex, [CpCr(NO)Cl]2

17 has since been prepared by another method . When CpCr(NO)2Cl is treated with NaOEt in tetrahydrofuran at room temperature, - 25 -

a metathetical reaction occurs and CpCr(N0)20Et is formed as an unstable red oil. Upon exposure to high vacuum at room temperature, the ethoxide derivative spontaneously loses

nitrogen monoxide to yield [CpCr(NO)(OEt)]2. Treatment of a benzene solution of the ethoxo dimer with HCl(g) affords

[CpCr(NO)Cl]2 quantitatively. The chloro compound exhibits a mass spectrum (Table I) which is consistent with this dimeric formulation and it exhibits a single absorption in the IR spectrum at 16 78 cm 1 attributable to a terminal nitrosyl group. Its molecular structure is, presumably,

32 33 similar to those possessed by the complexes [CpCr(NO)L]2 '

(L = SMe, SPh, or NMe2) in which L groups bridge two CpCr(NO)

moieties. In solution in benzene [CpCr(NO)Cl]2 is slowly con•

verted (^72 h) to CpCr(NO)2Cl and a blue-green, non-nitrosyl containing species. This transformation can be inhib• ited by the addition of PPh^ and does not occur in donor solvents such as tetrahydrofuran. This is due to the forma•

31f tion of CpCr(NO) (PPh3)Cl with the former and the probable formation of CpCr(NO)Cl•thf in tetrahydrofuran. This forma•

tion of CpCr(NO)2Cl, therefore, probably reflects some form of intermetallic transfer of the nitrosyl ligand in the dimer

v AT 1 only. The analogous compound [CpCr(NO)I]2 ( NQ 168 0 cm )

is formed in the reaction of I2 with CpCr(CO)2(NO) but this

intermediate decomposes in hours to CpCr(NO)2I. (Again, if

PPh^ is present, this decomposition does not occur and

CpCr (NO) (PPh-.)I is formed) . This may also be the pathway - 26 -

by which Cl2(g) converts CpCr(CO)2(NO) to CpCr(NO)2Cl al•

though -no intermediate [CpCr(NO)Cl]2 is observed during this

reaction. The chloro dimer is also cleaved by nitrogen mon•

oxide, a quantitative conversion to CpCr(NO)2Cl being observed.

In contrast to [CpCr(CO)^]2, the analogous molyb•

denum and tungsten compounds [CpM(CO)3]2 (M.= Mo or W) react with an excess of nitrosyl chloride to produce intractable

brown-black solids. However, if the progress of the reaction

is monitored by infrared spectroscopy and the addition of

ClNO is stopped.at the appropriate time, the following reac•

tion can be effected:

[CpM(CO)3]2 + 2C1N0 • CpM(NO) 2C1. + CpM(CO)3Cl + 3C0 (15)

Unlike the chromium case, no.carbonylnitrosyl intermediate

which can account for the formation of the CpM(NO)2Cl com• plexes is observed during the course of this reaction. Thus,

although it has been established that the CpM(NO)2Cl com• plexes are conveniently produced by the reaction of ClNO with

12 CpM(CO)2(NO) , these latter compounds are not detectable at

any time during the course of reaction (15). This is not

surprising in view of the lack of reaction between [CpM-

2 (CO)3]2 (M = Mo or W) and NO at room temperature **. The

derivation of the chlorodinitrosyl complexes from the parent dimers is therefore somewhat enigmatic.

The CpM(CO)3C1 (M = Mo or W) products may result

from the cleavage of the carbonyl dimers by ClNO in a manner

12 similar to that described for [CpFe(CO)0]0 . However, - 27 -

since a second complex is also.formed in reaction (15), it

is more probable that both CpM(CO)3Cl and CpM(NO)2C1 are produced from the same dimeric molecule. Support for this• inference comes from the fact that the infrared absorptions due to the two product complexes increase in intensity at similar rates as reaction (15) progresses and that the pro• ducts are formed in comparable yields. Also, the reaction

between C1N0 and CpM(CO)3Cl does not produce CpM(NO)2Cl.

Hence, reaction (15) appears to follow a unique mechanistic

pathway which involves C1N0 and. the dimers [CpM(CO)3]2 (M =

Mo or W) . Since both CpM(NO)2 C1 and CpM(CO)3Cl react further with C1N0, their yields from reaction (15) are drastically reduced if an excess of nitrosyl chloride is used.

When the dimeric [CpMn(CO)(NO)]2 is treated with nitrosyl chloride, an unusual type of substitution product results. Considering the above studies, it would seem prob• able that the bimetallic system would be cleaved producing

species like CpMn(NO)2 and.CpMnXNO)(CO)Cl. Instead, C1N0 displaces the customary two carbonyl ligands even though it is removing one from each manganese centre, i.e.

[CpMn(CO) (N0)]2 + C1N0 • Cp(NO)2MnMn(NO) (Cl)Cp + 2C0 (16)

The product in this reaction is an air stable, diamagnetic, red-brown solid whose structure probably consists of one

CpMn(NO) group and one CpMnCl group joined by two NO bridges and a metal-metal bond. In order to satisfy the effective - 28 -

atomic number rule, the bridging nitrosyl ligands must act as

two electron donors to the CpMnCl unit and only single electron donors to the CpMn(NO) group. .This asymmetry of the bridging unit is demonstrated in the structures of the anal•

3s 36 ogous compounds Cp2Mn2(NO)3(N02) and Cp2Mn2(NO)3(C5H5) .

This complex has been prepared in another context and its full characterization is presented in Chapter IV.

Reactions of Nitrosyl Chloride with Other Neutral Carbonyl

Complexes.

Nitrosyl chloride reacts rapidly with (arene)M-

(CO)3 complexes (M = Mo or W) at room temperature to even•

tually produce the polymeric [M(NO) 2Cl2]n,, compounds . Al• though these complexes have been previously prepared by another route20, the fact that they are formed in this re• action reflects an unprecedented reaction mode of ClNO.

The displacement of olefinic ligands by nitrosyl chloride has been reported37, but the displacement of the arene ligand has not been previously reported. The reaction of (arene)-

Cr(CO)3 complexes with ClNO at room temperature produces - 29 -

species of the type [Cr(NO)2(Cl)2]n and [Cr(NO)Cl3ln which

were not readily separable. A recent report38 indicates

that ClNO reacts with these ( arene) Cr (CO) 3 compounds in

tetrahydrofuran or dichloromethane below -30° C to form in•

tense red solutions which contain, reactive complex fragments

of the type [CICr (CO) 2 (NO).] . These fragments decompose on

warming to room temperature.

The allyl ligand of (C3H5)Fe(CO)2(NO) is also dis•

placed by ClNO, the reaction leading ultimately to the pro•

duction of [Fe(NO)2Cl]2. During the course of the reaction,

the formation of Fe(NO)3Cl was observed and this latter com•

plex readily decomposes to give the dinitrosyl product9.'10.

17 In quite similar reactions, CpCo(CO)2 and CpRe(CO)3 react

with nitrosyl chloride at -78° C to produce [Co(NO)2C1]2 and

[Re(CO)2(NO)Cl2]2, respectively. The cyclopentadieny1 ligand

is apparently removed by ClNO in these conversions in a man•

ner completely analogous to the displacement of the arene

group described above.

During the reactions involving the (arene)W(CO)3

compounds, an intermediate carbonylnitrosyl complex is formed

and this persists in solution for several hours at room tern-,

C1 perature. This intermediate is formulated as W(CO)2(NO)2 2 on the basis of the infrared spectrum which it exhibits in dichloromethane solution, i.e. carbonyl-stretching absorptions

at 2145 and 2070 cm 1 and nitrosyl-stretching absorptions at

1815 and 1725 cm 1. Consistent with this formulation, these - 30 -

nitrosyl absorptions occur at higher frequencies than those

20 reported for the related complexes W(NO)2C12L2 (Table II),

an expected observation since the carbonyl ligand is a

better TT-acid. Dichloromethane solutions of W (CO) 2 (NO) 2Cl2

are red in colour, are air sensitive, and slowly deposit

[W(NO)2Cl2]n while being stirred at room temperature under

an inert atmosphere. Hence, although W ( CO) 2 (NO) 2C12 is

stable in solution for short periods.of time at ambient

temperature, the carbonyl ligands in the complex are quite

labile and are eventually replaced by chlorine bridges in

an associated complex as indicated in equation (17).

nW(CO)2 (NO) 2C12 • [W(NO)2Cl2]n + 2nCO (17)

During the reactions involving the (arene)Mo(CO)^ compounds,

the intermediate Mo (CO) 2 (NO) 2C12 species can be detected by

IR spectroscopy (Table II), but it is stable in solution for only a few minutes at room temperature. Like its tungsten

s ntaneousl analogue, Mo(CO)2(NO)2C12 P° y evolves gas and forms

[Mo(NO) 2Cl2-' n wn;"-ch can be characterized as its triphenylphosphine adduct2 0.

This lability of carbonyl ligands appears to be an intrinsic property of transition metal carbonyl nitrosyl ha-

lides and several other examples have been observed in our

17 laboratory. For instance , W(CO)4(NO)Cl readily evolves carbon monoxide when dissolved in tetrahydrofuran at room tem•

perature and transforms to [W(CO)9(NO)(thf)Cl]0, i.e. Table II. Nitrosyl Stretching Frequencies3 of the Complexes

ML2 (NO) 2C12

Compound vCQ(cm M vNQ(cm M

Mo (CO) 2 (NO) 2C12 2160, 2080 1840, 1750

b Mo(PPh3)2(NO)2C12 1790, 1670

b Mo(AsPh3)2 :(N0)-2C12 1765, 1645

W(CO) 2 (NO) 2C12 2145, 2070 1815, 1725

b W(PPh3)2(NO)2C12 1790, 1670

b W(AsPh3)2 (N0).2C12 1765, 1645

in dichloromethane solution

data taken from reference 20 - 32 -

thf 2W(C0) (N0)C1 [W(CO)2 (NO) (thf) Cl]2 + 4CO (18)

The molecular structure of this dimer in all likelihood con• tains two W(CO)2(NO)(thf) groups linked by chlorine bridges so that the valence electron configuration of the metal sat• isfies the inert gas formalism. Similarly, when CpWtCO^CNO)

is treated with I2 in dichloromethane, an intermediate carbonylnitrosyl species is formed which slowly decomposes (1 h) to [CpW(NO)I2]239• This reaction occurs as follows:

CpW(CO)-2(NO) + I2 • CpW(CO) (NO) I2 + CO (19)

CpW(CO) (NO) I • [CpW(NO)I2]2 + CO (20)

This latter reaction is completely reversible under an atmos• phere of carbon monoxide.

Another transformation which follows a similar pat• tern is the formation of [Co^O^Cl^ by the reaction of

17 Co(CO)3(NO) with nitrosyl chloride . Although an interme• diate species is not detected in this instance, this conver• sion likely occurs via the sequential reactions (21). and (2 2) ,

Co(CO)3(NO) + ClNO • Co(CO) (NO)2C1 + 2CO (21)

2Co(CO) (NO)2C1 #> [Co (NO) 2C1] 2 + 2CO (22) both of which, as shown above, have precedents. This pro• pensity of carbonylhalonitrosyl complexes to lose carbonyl ligands and form dimeric or polymeric compounds by the con• comitant formation of halide bridges can also be invoked to - 33 -

rationalize the products obtained from other reactions in•

volving nitrosyl chloride and a neutral carbonyl complex. For

example, [M(C0)4C12]2 (M = Mo or W) complexes are converted

0 by ClNO to [M(NO)Cl3]n and small amounts of [M(NO)2Cl2]"* .

The trichloro-polymer may well result from the reactions

[M(C0)4C12]2 + 2C1N0 » [M(CO)2 (N0)C13]2 + 4C0 (23)

n[M(CO)2 (N0)C13]2 • [M(NO) Clg] 2 . + .4nC0 (24) which involve the same modes of transformation described

above for Co(CO)3(NO) with ClNO. (The dinitrosyl complexes may well result from some intermetallic NO transfer as dis•

cussed previously).

Reactions of Nitrosyl Chloride with CpMn(CO)3.

Unlike its rhenium analogue, CpMn(CO)3 reacts slowly

at room temperature with ClNO and the cyclopentadienyl group

is not displaced from the metal during the reaction. In•

stead, ClNO appears to behave analogously to a nitrosonium

salt as the product obtained.is the well known cation

+lf1 [CpMn(CO)2 (NO) ] . The yields of this reaction, though,

are considerably less than those observed when NOPF^ itself

is used42. This cation does not react further even when

treated with an excess of ClNO for several hours, thereby

reflecting its inherent stability. A few other examples of

this type of behaviour of ClNO have been reported. For ex•

43 ample , both ClNO and BrNO react with Fe(CO)3(PPh3)2 in

+ - acetonitrile to give [Fe (CO) 9 (NO) (PPh-J ] X . - 34 -

Reactions of.Nitrosyl Chloride attributable to Cl^ and NO.

As mentioned briefly in the introduction to this

chapter, the reactions of C1N0 in certain instances may be more readily viewed as reactions of either chlorine or ni•

trogen monoxide. The more common of these reactions involves

the Cl2 part of the equilibrium (7). The following reac•

tions show characteristics of only this species in the reac-

tant solution, elgl

M2(CO)1Q + 2C1N0 •> 2M(C0)5C1 + 2N0 (25)

(M = Mn or Re)

[CpFe(CO)2]2 + 2C1N0 2CpFe(CO)2Cl + 2N0 (26)

[CpCr(NO)2l2 + 2C1N0 • 2CpCr(NO)2Cl + 2N0 (27)

and no nitrosyl-containing species are observed at all in

reactions (25) and (26). It thus appears that none of these

species react with nitrosyl chloride itself. Also, it is

lt h 5 1 1 known that Mn2(CO)1() \ [CpFe (CO) 2]2 , and [CpCr (NO) 2]2

all require more forcing conditions to react with nitrogen

monoxide. So it seems probable that it is simply the Cl2 part of the reactant solution which effects the above trans•

formations. During the following reaction,

CpM(CO)2(NO) + C1N0 • CpM(NO)2Cl + 2C0 (28)

(M = Cr, Mo, or W) minor but significant amounts of a by-product are formed. In - 35 -

the molybdenum.case, it has been identified as.[CpMo(NO)-

CI2] 2 anc* this same product has been observed for the reac•

30 tion of CpMo (CO) 2 (NO) andCl2(g) . However, for. CpW (CO) 2~

(NO), since the reaction is normally carried out at -78° C,

only a very small amount of a red by-product is formed. The

IR spectrum of this solid is consistent with its formulation

as [CpW(NO) CI2] 2 i-n comparison with that of the recently

39 prepared [CpW(NO)I212 • During the reaction of CpCr(CO)2-

(NO) with C1N0, the blue-green by-product is most likely

some [CpCrClx]n species similar to those described earlier.

More important, though, is the fact that C1N0 itself reacts

readily with the CpM(CO)2(NO)-complexes to give the desired products in excellent yields.

There are no examples as yet showing the reaction of only the nitrogen monoxide part of the equilibrium except

for the reaction discussed earlier involving [CpCr(CO)^]^•

The problem which arises here, of course, is the fact that the product of this reaction, CpCr(CO)^ (NO), reacts further with C1N0. Therefore, unlike the previous reactions invol• ving C^, the product observed.for the reaction

[CpCr(CO)3]2 + 2N0 • 2CpCr(CO)2(NO) + 2C0 (29) is not the final product in the reaction of this dimer with nitrosyl chloride. CHAPTER III

REACTIONS.OF TRITHIAZYL TRICHLORIDE WITH TRANSITION METAL

CARBONYL COMPOUNDS

A natural extension of the study of the prepara•

tion and properties of transition metal nitrosyl complexes

is the investigation of transition metal thionitrosyl (NS)

complexes. A comparison of the physical properties of these

familial compounds should lead to a better understanding of both the nitrosyl and thionitrosyl ligand. At the present

time there is a striking paucity of thionitrosyl complexes

and the few such coordination compounds that are known**6

result from the reaction of elemental sulphur, propylene

sulphide, or disulphur dichloride with coordinated hitrido

ligands in the precursors, e.g.

Mo(N) (S2CNR2) • + Sg Mo(NS) (S2CNR2)3 (30)

[Re(NBr2) (PR3)3]2 + S2Cl2 • [Re(NS) (Cl) (Br) (PR3>3] (31)

In reactions resembling the procedures used to synthesize various organometallic nitrosyl complexes, namely the treat• ment of.organometallic carbonyl compounds with nitrosyl chloride (Chapter II), this chapter describes attempts to directly introduce the thionitrosyl functionality using tri-

thiazyl trichloride, N^S^C!-,. - 37 -

Experimental

All experimental procedures described here were per•

formed under the same general conditions outlined in Chapter

II. Trithiazyl trichloride was prepared by the literature methodh7 and recrystallized from carbon tetrachloride.

Reaction of Na [CpCr (CO) ^] with Cl^^N^. To a stirred tetra• hydrof uran solution (60 mL) containing 2.24 g (10.0 mmol) of

16 Na[CpCr(CO)3] cooled to -78° C was added dropwise a thf

solution of Cl^S^N^ (0.82 g, 3.35 mmol). Gas evolution oc• curred, a precipitate formed, and the reaction mixture developed a red-brown colouration. After the addition of the

Cl^S^N^ was complete (30 min), the mixture was allowed to warm

slowly to room temperature. The tetrahydrofuran was removed

in vacuo leaving a green-brown residue. This solid was

suspended in toluene (30 mL) and transferred to the top of a

3 x 10 cm Florisil column. Elution of the column with tol• uene produced two bands (red and green in colour) which were collected together and taken to dryness under reduced pres•

sure. Sublimation at 30° C (5x10 3 mm) onto a dry-ice cooled probe produced 0.9 2 g (4.2 mmol, 21% yield) of red

crystalline CpCr(CO)2(NS).

Anal, calcd for C_,HcCr0oNS: C, 38.36; H, 2.30;

N, 6.39. Found: C, 38.64; H, 2.20; N, 6.37. Mp 68-69° C.

The residue from the sublimation was extracted with dichloromethane and the resulting olive green solution was treated with hexanes and slowly concentrated in vacuo. In - 38 -

this manner, crystals of [CpCr(CO)2]2S (0.65 g, 34% yield based on Cr) were produced.

Anal, calcd for C14H1QCr204S: C, 44.45; H, 2.67;

S, 8.48. Found: C, 44.47; H, 2.64; S, 8.19. Mp (in air)

112-113° C dec.

Reactions of Cl.,S^N3 with other Transition Metal Carbonyl

Complexes. The reactions of Cl^S^N^ with other complexes were performed similarly and the experimental details are

summarized in Table III.

•Reaction of CpCr (CO)2 ;('NS) with nitrosyl chloride. A di•

chloromethane solution .(60 mL); containing 0.88 g (4.0 mmol)

CpCr(CO)2(NS) was treated dropwise at room temperature with

a solution of ClNO in the same solvent. Gas evolution oc•

curred and a green-brown solid precipitated. Just enough

ClNO was added to react with all the thionitrosyl complex

(monitored by infrared spectroscopy). The mixture was then concentrated to 15 mL and transferred to a 3 x 8 cm Florisil

column. Elution of the column with dichloromethane produced

three components:

(1) a fast moving yellow-orange band containing

^0.05 g of material,

(2) a golden-brown band.containing CpCr(NO)2Cl. The

total amount isolated was 0.23 g (27%),

(3) a blue-green band which could not be eluted from

the column with CH0C10. Table III. Reactions of N3S3C13 with some Transition Metal Compounds

Amt. of

Transition metal cmpd. N3S3C13 Solvent Temp. Products(yields) Isolation and (mmol) (mL) (mmol) Identification

Na[CpW(CO)3] (5.0) 1.7 thf(150) -78° [CpW(CO)3]2(20%) Chromatography on Florisil; infrared CpW(CO)3 ci(io%) cl spectrum

Na[CpMo(CO) ] (6.2) 2.4 thf (120) -7( [CpMo(CO) ]2(25%) Chromatography on Florisil; infrared CpMo(CO) Cl(15%) spectrum3

Na[Mn(CO)J (5.6) 2.0 thf(100) 2 0° Mn2(CO)1Q(25%) Sublimation at 40° (5 x 10_3 mm); infrared spectrum3

CpCr(CO)2 (NO) (3.0) 1.0 thf(lOO) 20° CpCr(NO)2C1(35%) Chromatography on Florisil; infrared spectrum3

3 CpMo (CO) (NO) (5.0) 1.6 CH2C12 (100) 20° [CpMo(NO)Cl] Infrared spectrum (<5%)

By comparison with the infrared spectrum of the authentic compound. - 40 -

Reaction of Nitrosyl Chloride with [CpCr(CO)^]and

[CpCr(CO)2^2' A dichloromethane solution of G1NO was added

dropwise to a stirred, room temperature solution of [CpCr-

s (CO)2]2 (0.38 g, 1.0 mmol) in the same solvent (40 mL).

Gas evolution occurred, the solution turned bright green,

and a fine yellow solid precipitated. When all the sulphur

complex had reacted, the mixture was reduced in volume to 10 mL and transferred to the top of a 2 x 5.. cm Florisil column.

Washing the column with CE^C^ produced a golden - solution•which was taken to dryness in vacuo. The residue was identified

as CpCr(NO)2Cl (0.26 g, 60% yield). The reaction of

[CpCr(CO)2]2 with C1NO proceeded similarly producing CpCr-

(NO)2C1 in 42% yield.

Reaction of CpCr(CO)2(NS) with PPh.,. Two different experiments

were performed in an attempt to produce CpCr(CO)(PPh^)(NS).

In the first, a toluene solution (30 mL) containing CpCr-

(CO)2(NS) (0.22 g, 1.0 mmol) was treated with PPh3 (0.52 g,

2.0 mmol) and the mixture held at reflux for 70 h. At the

end of this time, an IR spectrum of the solution indicated

that.no reaction had occurred. The toluene was removed in

vacuo and the remaining residue sublimed onto a dry-ice

3 cooled probe (30° C, 5 x 10~ mm) to recover-.CpCr (CO) 2 (NS)

almost quantitatively.

The second experiment involved photolysis of a

hexanes solution (200 mL) containing CpCr(CO)2(NS) (0.22 g,

1.0 mmol) using a 140 W medium pressure mercury lamp. After - 41 -

6 h, complete destruction of the organometallic thionitrosyl complex had occurred and no new complexes containing the NS ligand were detected.

Reaction of CpCr(CO)2(NS) with NOPF£. The reaction between

CpCr (CO) 2 (NS) and NOPFg was carried out in Cr^C^/Ct^CN at

T78° C in a similar fashion to that reported55 for the reac•

tion of CpM(CO)2(NO) (M = Mo or W) with NOPFg. The resulting blue-green product was very reactive and could not be purified.

It was tentatively identified as-=>-[CpCrr(eo,), (NO) :(NS) ] PFr based on its IRb spectrum: (2122, itLJ90 , and 1243 cm"1).

Reaction.of [CpCr(CO)(NO)(NS)]PF£ with Iodide Ion. A stirred acetone solution (40 mL) containing Nal (0.30 g, 2.0 mmol) was treated with the solid thionitrosyl salt (0.50 g) and the resulting green solution slowly turned green-brown. Gas evolution was observed and a green solid precipitated. The mixture was stirred for 2 h and then the acetone was removed in vacuo. The blue-green residue was extracted with CE^C^ and the extracts filtered through 2 cm of Florisil producing

9 a golden-brown filtrate which was found to contain CpCr(NO)2I

(0.14 g, ^25% yield).

Reaction of [CpCrCCO^K with Nitrogen Monoxide. Prepurified nitrogen monoxide was bubbled slowly through a toluene solu• tion (25 mL) containing 0.45 g (1.30 mmol) of [CpCr(CO)212 8 for 12 h. During this period, the green solution developed an orange colouration. The resulting solution was concen- - 42 -

trated to ^10 mL in vacuo and then transferred to the top of a 3 x 5 cmoFlorisil column made up in dichloromethane. Elu• tion of the column with dichloromethane developed an orange band that was collected and taken to dryness under reduced pressure. . Sublimation of the residue at room temperature

(5 x 10.3 mm) onto a dry-ice cooled probe afforded 0.23 g

12 16 (1.1 mmol; 43% yield) of CpCr(CO)2(NO) ' .

The Florisil column.was then eluted with tetrahydrofuran to produce a dark green band which also was collected and taken to dryness.in vacuo. Crystallization of the resulting solid from Ct^C^-hexanes yielded green crystals of

11 CpCr(NO)2(N02) (0.20 g, 35% yield) which was identified by its characteristic physical properties.

Results and Discussion

The reaction of trithiazyl trichloride, with Na-

[CpCr(CO)3] produces CpCr(CO)2(NS), the first organometallic

thionitrosyl complex, in 21% yield.

thf Na [CpCr (CO)+ %N S Cl CpCr (CO) , (NS) + NaCl + CO J 3 3 3 _7go c £

(32)

The success of this reaction reflects the fact that in donor

solvents , trithia;zyl- trichloride^ probably exists . as • a solva-

ted monomer, i.e. NSCKthf)^ . (This is based on the observa•

tion that in solvents such.as thf or CH^CN, N^S^Cl.^ forms

green solutions which exhibit a vNg in their IR spectrum at

1220 cm-1 where as in CC1. solution or as a Nujol mull this - 43 -

same absorption occurs at ^1000 cm 1). A comparison of the physical properties of the new thionitrosyl product (I) with those exhibited by its nitrosyl analogue (II) allows, for the first time, a direct contrast of,the bonding properties of

the NO and NS ligand.

Dicarbonyl(n5-cyclopentadienyl) thionitrosylchromium.; ,i is a dark red-violet, diamagnetic solid which dissolves in common organic solvents to give blood-red solutions that even• tually deposit some decomposition products when exposed to air for several hours. The pure solid is reasonably stable in air but is best stored under dinitrogen. Its infrared spectrum in hexanes (Table IV) exhibits the expected three strong bands attributable to terminal CO and NS groups. The

1 6 vNS band occurs in the frequency range found * for other

thionitrosyl complexes. The v n bands of I appear at slight- - 44 -

5 Table IV.. Physical Properties of (n-C^H,_) Cr (CO) 0(NX)

Complexes

X 0

colour red-violet orange-red mp, °C 68.0 - 69.0 69i5 - 70.5

2033 s, 1962 s 2028 s, 1955 s vCQ, cm (in.hexane) 1 Cm 1180 s. 1713 s v NX' (in hexane)

1 E NMR, 6 ppm 5.08 5.03

(in CDC13)

1 3 C NMR, 6 ppm 92. 75 (CCH[.) 90.76 (C5H5)

(in CDC13) 239.43 (CO) 237.63 (CO) - 45 -

ly higher frequencies that those of II, thereby suggesting that the NS ligand is more effective at removing electron density from the central metal than is the NO ligand. The

Cr-N bond in I also appears to be somewhat stronger than the

Cr-N bond in II, as evidenced by the mass spectral data dis• played in Table V. While both complexes exhibit fragmentation patterns corresponding to the sequential loss of ligands and the common base peak can be assigned to the Cj-H,_Cr+ ion, the

C^H,-CrNS+ ion is markedly more abundant in the mass spectrum of I than is the C^H,-CrNO+ ion in the spectrum of II.

The NMR spectral data of compounds I and II (Table

IV) provide an interesting contrast. The *H NMR spectrum of

I consists of a single sharp peak which occurs at a slightly lower field than the corresponding absorption due to the cyclopentadienyl protons of II. Similarly, the13 C NMR chem• ical shifts of the cyclopentadienyl and carbonyl carbons are further downfield from Me^Si for complex I. A comparable downfield shift for 5 (13 C^H^) has previously been observed1*9

when a CO group in CpMn(CO)3 (isoelectronic with II) has

been replaced by a CS group to give CpMn(CO)2(CS) (isoelec• tronic with I). However such a substitution also results in an upfield shift of 6 (13C0) which is exactly opposite to the effect that is observed in going from II to I. Down- field shifts of 13C0 resonances are normally associated with the replacement of a carbonyl ligand by a donor ligand on the carbonyl complex [e.g. CpMo(CO)„(NO) exhibits 6 (13C0) Table V. Low-Resolution Mass Spectral Data for (Cj-H^Cr-

(CO)0(NX) Complexes

X = S X = 0

Rel 3 Rel m/ z Assignment m/z abund abund

+ 219 36 C5H5Cr(CO)2(NX) 26 203

+ 191 8 C5H5Cr(CO)(NX) 21 175

+ 163 74 CcHcCr(NX) 13 147

+ 117 100 C5H5Cr 100 117

52 63 Cr+ 37 52

The assignments involve the most abundant naturally occur• ring isotopes in each fragment. - 47 -

at 226.72 while CpMo(CO)(NO)(PPh^) exhibits 6 (13C0) at

244.86]50 and the observed downfield shift in the above in• stance ^may.ybe due to a large increase in donor strength of the NS ligand vs. the NO ligand with only a small increase in.

Lewis acid strength. It is obvious that more work is re• quired to interpret the different electron-donating and electron-accepting abilities of the two ligands.

The molecular structure of CpCr(CO)2(NS) is shown in Figure 3, with important bond lengths and bond angles being summarized there. Generally, the molecular geometry is similar to that exhibited by other "piano stool" molecules

51 52 [e.g. CpMn(CO)3 and CpCr(CO)2(NO) ]. The Cr-C-0 linkages are inherently linear, and the Cr-C(Cp), Cr-C(O), and C-0 bond lengths are comparable to those found in other cyclopentadienylchromium carbonyls27 • The most chemically inter• esting feature of the structure is the fact that the thio• nitrosyl ligand coordinates essentially linearly to the metal o via the nitrogen atom. The Cr-N bond length of .1.694 A falls in the range of values reported2 7 for Cr-N bonds formed by linear, terminal nitrosyl ligands. Hence in a formal sense, the thionitrosyl group (an overall three- electron donor) can be considered. to be bonded as NS+, a mode of coordination that is directly analogous to metal- thiocarbonyl bonding and involves the synergistic coupling of a and TT bonding components. Consistent with this view of back-donation from Cr TT orbitals to NS TT* orbitals is the - 48 -

5 Figure 3. Molecular structure of (n -C5H5)Cr(CO)2(NS). o Selected average bond lengths (A) and angles (°): Cr-N, 1.694; Cr-C(O), 1.883; C-0, 1.131; N-S, 1.551; Cr-N-S, 176.8; Cr-C-O, 178.1; C(0)-Cr-C(0), 92.4; C(0)-Cr-N, 94.8. - 49 -

fact that the N-S distance of 1.551 A ..in the complex is

longer than the NS equilibrium bond length of 1.440 A deter• mined spectroscopically in the vapour state.53. Considering

the above spectroscopic comparison of CpCr(CO)2(NS) and

CpCr(CO)2(NO), it would be expected that the Cr-N(S) bond

length would be shorter than the Cr-N(O) bond length in the

respective molecules. Regrettably, an effective comparison of these distances is precluded.by crystallographic disorder

among the CO and NO groups in the solid state structure of

2 CpCr(CO)2(NO)! .

The presence of the thionitrosyl ligand is expected

to have only a minor effect on the chemical reactivity of

CpCr(CO)2(NS) compared to that of the nitrosyl derivative.

Since the infrared absorptions for the carbonyl ligands are

of only slightly higher energy, there should not be a sig•

nificant increase in the lability. Indeed, this is found

to be true as the thionitrosyl.complex does not react with

PPh3 even at reflux in toluene. After several days, no

reaction has occurred and the CpCr(CO)2(NS) can be recovered

unaltered. This is comparable to the nitrosyl complex where

conditions of 160° in neat triphenylphosphine are required

to produce CpCr(CO)(PPh^)(NO)54. This latter phosphine

complex can also be prepared photochemically but photolysis

pp of CpCr(CO)2(NS) in the presence of h3 leads to the removal

of the carbonyl and thionitrosyl ligands from the starting

material. Apparently, a more selective photodecarbonylation - 50 -

method is required which will probably depend on an analysis of the electronic structure of the molecule. It may then be

possible to selectively irradiate.a solution of CpCr(CO)2(NS)

to achieve this result.

Further substitution reactions of the thionitrosyl

complex also give unusual results. The displacement of the

two!* carbonyl ligands with nitrosyl chloride to give CpCr(NO)-

(NS)Cl does not occur under the same conditions that trans•

form CpCr(CO)2(NO) to the dinitrosyl analogue. Instead, the

reaction of C1NO with CpCr(CO)2(NS) also produces CpCr(NO)2Cl

as the only isolable nitrosyl-containing product. There

are no new thionitrosyl complexes detected during the reaction.

Careful monitoring of the reaction by infrared spectroscopy

does suggest, though, the formation of an intermediate. It

is possible that CpCr(CO)2(NO) is formed since a small

shoulder appears on the low energy side of the 1711 cm 1

band of the product. However, both carbonyl absorptions of

this intermediate would be masked by those due to the

starting dicarbonylthionitrosyl compound. Also, CpCrtCO^-

(NO) reacts much faster with nitrosyl chloride than does

CpCr(CO)2(NS), thereby making it extremely difficult to

isolate any of the former if it is indeed formed during the

reaction of the thionitrosyl complex with C1N0. The pro•

duction of CpCr(CO)2(NO) by this reaction would not be

unusual in the light of the discussion of the reactivity of

C1NO.in the previous chapter. One possibility is the reac•

tion of the nitrogen monoxide part of the C1NO solution - 51 -

equilibrium (equation 7) with CpCr(CO)2(NS) to produce the

dicarbonylnitrosyl species. However no reaction occurs be•

tween NO and a solution of CpCr(CO)2(NS) at room temperature.

Thus CpCr (CO) 2 (NO) must be formed .by some other reaction

pathway. The reaction of ClNO with CpCr(CO)2(NS) also pro•

duces small amounts of a yellow and an orange-yellow solid.

Because of the limited quantities of these products, exact

identification could not be made.

At present, no other fully characterized substitu•

tion product containing an intact Cr-NS group has been pre•

pared. However, one reaction which appears to produce a new

thionitrosyl species is

"•" • CH?C19/CH CN

CpCr (CO) 0 (NS) + NOPF, - - —> [CpCr(CO)(NO)(NS)]PF, A b -78° C + CO (33)

This reaction parallels exactly that of CpM(CO)2(NO) (M =

Cr, Mo, or W) with this same nitrosonium salt55. The pro•

duct of reaction (33) is a water-sensitive, green-black pow•

der which is insoluble in all but those solvents with which

it reacts.. It was assigned the composition [CpCr(CO)(NO)-

(NS)]PFg on the basis of its infrared spectrum (Nujol mull)

1 which exhibits bands assignable to a vCQ at 2122 cm , a

-1 1 vNQ at 1790 cm , and a vNg at 1243 cm" and by analogy to

other reactions of nitrosonium salts with complexes like

CpCr(CO)2(NS). The carbonyl and nitrosyl stretching fre•

quencies are in the range previously observed for carbonyl-

nitrosyl cations55'56. Also, the thionitrosyl stretching - 52 -

frequency is at higher energy in this cation than in the

neutral CpCr(CO)2(NS). This is consistent with a decrease in electron density at the metal centre which manifests itself in less back donation from the metal to the IT* or• bitals of the NS ligand. Several attempts to prepare more stable substituted products of the type [CpCr(NO)(NS)(L)]-

PF6 [L = PPh3, P(OPh)3, or P(n-Bu)3] were unsuccessful. Also, nucleophilic attack of the iodide ion on the cation led to displacement of both the carbonyl and thionitrosyl ligand

producing [CpCr(NO)I]2 instead of the desired CpCr(NO)(NS)I.

The final product isolated from the reaction of [CpCr(CO)(NO)-

(NS)]PF, with KI was CpCr(N0)oI which was probably formed by O Z

the disproportionation of [CpCr(NO)I]2 discussed in Chapter

II.

The second product of the reaction of Na[CpCr(CO)3]

with N3S3C13 is Cp2Cr2(CO)4S. This sulphur complex is an air stable, diamagnetic solid.which is freely soluble in common organic solvents except paraffin hydrocarbons and sublimes without attendant decomposition at 80° C (5 x 10 3 mm) in a dynamic vacuum. Its low resolution mass spectrum

(Table VI) confirms its bimetallic nature and exhibits a

fragmentation pattern which indicates that the Cr2S grouping is quite resistant to cleavage. It exhibits infrared ab• sorptions due to carbonyl ligands at 2000, 1960, 1932, and

1924.cm 1 in hexanes and resonances in its 1H NMR at 6

4.87 (s) and in its 1 3C NMR at 5 245.9 (s, CO) and 6 89 .0 - 53 -

Table VI. Low-Resolution Mass Spectral Data for

[(C5H5)Cr(CO) 2]2S

Rel 3 m/z Assignment abund

+ 378 20 (C5H5)2Cr2(CO)4S

+ 322 14 (C5H5)2Cr2(CO)2S

+ 294 25 (C5H5)2Cr2(CO)S

+ 266 100 (C5H5)2Cr2S

+ 201 18 (C5H5)Cr2S

+ 182 96 (C5H5)2Cr

+ 136 28 Cr2S

2+ 133 18 (C5H5)2Cr2S

+ 117 30 (C5H5)Cr

52 75 Cr+

The assignments involve the most abundant naturally occur•

ring isotopes in each fragment. - 54 -

(s, C5H5) in CDC13. The NMR results show that the carbonyl

(and cyclopentadienyl) ligands are.magnetically equivalent on the time scale of the experiment-at room temperature. The

IR data suggest that a variable temperature NMR study of this complex would indicate that a low energy process such as rotation around the Cr-S bond - allows this averaging. Similar physical properties have been observed5 7 for the complexes

Cp2Mo2(CO)4(RCECR) (R = H, Et, or Ph) which have been shown

to contain a discrete [CpMo(CO)2]2 unit bridged by the acetylene ligand. Studies57 have provided evidence for rearrangement processes which average the environment of the

CO ligands at room temperature sufficiently fast to result in only, one 1 3C NMR resonance due to these ligands while the

IR spectrum still exhibits-four bands.

The molecular structure of [CpCr(CO)232S is shown in Figure .4. . The peripheral dimensions of the molecule are comparable to those found in other cyclopentadienylchromium carbonyls27. The most striking aspect of the structure is the central, essentially linear Cr-S-Cr linkage. The

o average Cr-S bond length of 2.075 A is markedly shorter than any such distance yet reported, and it implies, .the exis• tence of multiple bonding between the three atoms. This inference draws support from two previous structural deter- o

minations. A bond length of 2.510 A in (CO)5Cr(SPMe^) has been reported58 and assigned to a Cr-S single bond. The o observation59 of a Cr-S distance of 2.351 A in 5 Figure 4. Molecular structure of [-.(fi —C5H5) Cr (CO) 2]2 S. Selected average bond lengths (A) and angles (°): Cr-S, 2.075; Cr-C(O),

1.858; Cr-C(cp), 2.198; C-O, 1.143; Cr-S-Cr, 174.34; S-Cr-C(O),

94.7; S-Cr-Cp (centroid), 129.0; C(0)-Cr-C(0), 89.8. - 56 -

(CO) j-CrSFeCc^ (CO) g has been interpreted in terms of synergic a and IT bonding between the two atoms. To account for the extreme shortness of the Cr-S bond and the diamagnetism of

Cp2Cr2(CO)4S and to provide each chromium with the favoured 18-electron configuration, the bonding in the central unit is best represented as CrESECr in which chromium orbitals (principally 3d) overlap with appropriate sulfur orbitals.

There has been one previous report6 0 of a shorter metal-

sulfur bond; that in the complex ion {[(Ph2PCH2)3CCH3]2~

2+ Ni2S} which contains a linear Ni-S-Ni group with a Ni-S

o bond distance of 2.034 A/ It is interesting to note that in- this cation (and an analogous CO species) the L^M moieties are in initial 15-electron configurations and therefore a MES5M bonding rationale also accounts for the documented physical properties of these complexes.

The reactivity of the complex [CpCr(CO)2]2S and

the Cr2S unit can be readily compared to the reactivity of

the chromium-chromium -triple bond in [CpCr (CO) 2] 2 . Both of these compounds are reasonably stable towards air both in the solid state and in solution. Both react with C1NO to

produce the expected CpCr(NO)2C1. The strength of the Cr-

S-Cr linkage is demonstrated by the inertness of Cp2Cr2(CO)4S to several other reagents. A toluene solution of the sulfur complex maintained under 104 atm pressure of carbon monoxide showed no change after 18 h and the starting material could be recovered unaltered. However, under identical conditions, - 57 -

the dicarbonyl dimer incorporates two molecules of carbon monoxide to become [CpCr(CO)3]261• In their reactions with

nitrogen monoxide, [CpCr(CO)2]2S again shows no reactivity while the non-sulfur containing species is converted to a

mixture of CpCr(CO)2(NO) (43%) and CpCr(NO)2(N02) (35%) at room temperature.

Attempts at preparing other transition metal thio• nitrosyl complexes were not as successful as the previous example. Reactions of tetrahydrofuran solutions of N^S^Cl^ with the anions shown in Table III lead mostly to oxidation products, i.e.

LnM~ + N3S3C13 (LnM) 2 + "-S=N-"

In the case of [CpM(CO)3] (M = Mo or W), a second product

of the reaction is CpM(CO)3C1 which probably indicates that

at least two types of reactions are occurring. The products

from the reactions of trithiazyl trichloride with CpM(CO)2(NO)

(M = Cr or Mo) are totally inexplicable on the basis of the presently available information on the reactivities of

N3S3C13.

The success of this method in preparing the first organometallic thionitrosyl complex is quite surprising in

view.of the complexity of the reactant, (NSCl)3. The failure of the reaction with neutral compounds to produce the species

CpM(NO)(NS)Cl is not unexpected since the conditions used

to prepare the analogous CpM(NO)9C1 complexes are much less - 58 -

62 involved. - It is known that (NSC1)3 can be thermally de- polymerized to produce the monomeric thiazyl chloride. The

use of this simpler reactant may well lead to desired

conversions in a similar manner to the use of nitrosyl

chloride to prepare chloronitrosy1 compounds. - 59 -

CHAPTER IV

REACTIONS OF DICARBONYL(n5-CYCLOPENTADIENYL)NITROSYLMANGANESE

HEXAFLUOROPHOSPHATE WITH HALIDE IONS

Since a reinvestigation of the title cation was

carried out in 196418, a great deal of interest has arisen

in its reactions with a wide variety of nucleophiles. In

that same report, the reaction of [CpMn(CO)2(NO)]PF^ with

the tetrahydridoborate anion in a two phase water-benzene

system was found to produce [CpMn(CO)(N0)]2. This compound

probably resulted from the following sequence of reactions,

+ - [CpMn(CO)2 (N0) ] + H CpMn(CO) (NO) H-+-VC0. (34)

2CpMn(C0)(NO)H > [CpMn(CO)(NO)]2 + H2 (35)

The dimerization step (equation 35) is a common reaction of

thermally unstable metal carbonyl hydrides. More importantly,

the first of these reactions represents hydride attack on the

metal centre (with displacement of a CO ligand) and is a

common mode of nucleophilic attack on the manganese cation.

Other examples of nucleophiles which show this type of be•

63 _ 61 haviour include SC(CH3)3~ , S2CSC (CH3) 3 , and S^NR^ *

(R = Me or Et) and their mode of reaction is summarized in

equation (36). Loss of the second carbonyl ligand in this - 60 -

[CpMn(CO) 2 (NO) ] + S^NP^ CpMn(NO) (S^NF^) + 2CO (36) example is indicative of the lability of this ligand in

species like CpMn(CO)(NO)(S2CNR2) which may well be the initial product of nucleophilic attack.

A second site for this type of reaction to occur is shown in the next equation. Here, the methoxide ion attacks

+ [CpMn(CO)2(NO)] + MeO~ * CpMn(CO) (NO) [C(O) (OMe)] (37) the carbonyl ligand producing the carbomethoxy derivative,5.

Other nucleophiles have also been observedj'to react at the ligands rather than the metal centre. Various alkyl and aryl amines react with the cation at room temperature to yield the amido derivatives CpMn(CO)(NO)[C(0)NHR]66. Methyl-

lithium and phehyllithiumereact with [CpMn (CO) 2 (NO) ] PFg to give the ring addition products (5-exo-R-C^H,-)Mn(CO)^(NO) as well as the carbonyl addition products CpMn(CO)(NO)[C(0)R]

(R = Me or Ph) 6 7.

In an effort to extend the comparative chemistry of the carbonyl and nitrosyl ligands, it was hoped that the above results indicated that the reaction of halide ions with the [CpMn(CO)2(NO)]+ cation would produce the complexes

CpMn(CO)(NO)X (X = Cl, Br, or I). Then the chemistry of these species could be contrasted directly with that of the known isoelectronic CpCr (NO) 2% and CpFetCO^X complexes.

There was one brief report on this reaction which appeared during the course of this work6 8. The attack of the I ion - 61 -

on the thiocarbonyl derivative, [CpMn(CO)(CS)(NO)] was found to produce CpMn(CS)(NO)I as an air stable solid. Fur• thermore it was stated that the reaction of the dicarbonyl cation with I "resulted in the formation of carbonyl- and nitrosyl-free decomposition products of an unknown nature."

This chapter presents evidence that CpMn(CO)(NO)I and its methycyclopentadienyl congener can indeed be synthesized by this type of reaction. These complexes are also formed by

direct iodination of the dimers, [(RC5H4)Mn(CO)(NO)]2 (R =

H or Me). The reactions of the cation with Cl , Br , and

N02 are also discussed.

Experimental

All experimental procedures described were performed under the general conditions detailed in Chapter II.

Preparation of (RC^) Mn(CO) (NO)I (R = H or Me). Method A.

Solid KI (2.20 g, 13.3 mmol) was added to a stirred yellow

18 solution of [CpMn(CO)2(NO)]PF6 (4.50 g, 12.8 mmol) in acetone (100 mL) at room temperature. A reaction occurred immediately as evidenced by a change in colour to gray- brown, evolution of a gas, and formation of an off-white precipitate. The reaction mixture was stirred for 5 min during which time gas evolution ceased. The solvent was removed under reduced pressure, the resulting gray residue

was extracted with 3 x 25 mL portions of CH2C12, and the extracts were taken to dryness in vacuo to obtain a green- brown solid. This solid was formulated as slightly impure - 62 -

CpMn(CO)(NO)I by virtue of its IR spectrum in CH2C12 (which exhibited strong absorptions at 2030 and 1776 cm"1), its

1 E NMR spectrum in CDC13 (which showed a strong, sharp peak

at 6 5.30), and its ambient temperature mass spectrum, which

is summarized in Table VII. /Analytically pure samples of

this compound could not be obtained because it decomposed

both in solution and in.the solid, state. For instance, a

stirred.dichloromethane solution (20 mL) containing ^0.2 g

of CpMn(CO)(NO)I slowly deposited a green solid which was

insoluble in all common organic solvents; after 72 h complete

decomposition had occurred. As a solid, the complex decom• posed similarly but over a longer period of time (^8 days).

An acetone solution of [(MeCp)Mn(CO)2(NO)]PFg

reacted with KI to afford impure (MeCp)Mn(CO)(NO)I in an

identical manner as demonstrated by the infrared spectrum of

the product in CH2C12 which showed strong absorptions at

2050 and 1772 cm 1. Furthermore, the elemental composition

of this product was confirmed by a molecular weight deter•

mination using an A.E.I. MS 5 0 high-resolution mass spectro• meter (Calcd: 318.8902. Found: 318.8908).

This method of preparing the (RCr-H,^) Mn(CO) (NO) I

complexes could also be effected in tetrahydrofuran, as both

conversions went to completion within,10 min. However, IR monitoring of the final reaction mixtures indicated that both of the desired products decomposed more rapidly in this

solvent. This decomposition was complete after 6 h. - 63 -

Table VII. Mass Spectral Data for (RC5H4)Mn(CO)(NO)I

Complexes

R = H R = Me

Rel , Assignment m/z ' abund abund

+ 305 57 (RC5H4)Mn(CO) (NO) I 31 319

+ 277 69 (RCCH.)Mn(NO)I o 4 58 291

+ 275 12 (RC5H4)Mn(CO) I 8 289

+ 247 80 (RCCH.)MnI 100 261

+ 186 0 H(RC5H4)2 Mn 33 214

+ 185 0 (RC5H4)2Mn 29 213

+ 192 45 RC5H4I 29 206

182 60 Mnl+ 63 182

+ 130 34 (RC5H4)2 38 15 8

+ 120 100 (RC5H4)Mn 71 134

65 (150) RC5H4t (158) 79

55 29 Mn+ 50 55 - 64 -

18 Method B. To a stirred solution of [CpMn(CO)(NO)]2 (0.36 g,

1.0 mmol) in dichloromethane (50 mL) at room temperature was

added solid I2 (0.26 g, 1.0 mmol). The original red-violet solution rapidly turned green-brown and a dark green solid precipitated. After 3 min the reaction mixture was filtered and the filtrate taken to dryness .in.vacuo to obtain ^0.5 g of a green-brown solid which exhibited the spectroscopic characteristics of CpMn(CO)(NO)I (vide supra).

6 9 The reaction between [ (MeCp)?Mn(CO) (NO) ]'2 ' and I2 proceeded analogously. Benzene could also be employed as a solvent for both transformations.

Preparation of CpMn(NO)(PPhg) I. A solution of CpMn(CO)(NO)I was prepared according to Method A using 1.05 g (3.0 mmol)

of [CpMn(CO)2(NO)]PFg and 0.50 g (3.3 mmol) of Nal in acetone.

The reaction mixture was filtered to remove the NaPF^ by• product, and the stirred green-brown filtrate was treated

with 0.80 g (3.0 mmol) of solid PPh3. Vigorous gas evolu• tion occurred immediately and the solution developed a brown colouration. After 5 min a brown, crystalline solid began to precipitate and crystallization was complete after 15 min. The solid was collected, washed with hexanes (2 x

10 mL), and dried in vacuo to obtain 0.93 g (58% yield) of

pure CpMn(NO) (PPh3)I.

Anal, calcd for C23H2QMnNOPI: C, 51.23; H, 3.74;

N, 2.60. Found: C, 51.33; H, 3.50; N, 2.65. vNQ (CH2C12)

1720 cm-1. 1H NMR (CDClg) 6 7.38 (15H,. m),, 4.72 (5H, s) . - 65 -

Mp 15 6° C dec.

Preparation of (MeCp)Mn(NO)(PPh,)I. A stirred dichloro• methane solution (50 mL) of (MeCpMn(CO) (NO) I prepared by-

Method B from 0.77 g (2.0 mmol) of [(MeCp)Mn(CO)(NO)]2 and

0.51 g (2.0 mmol) of I2 was treated with 0.90 g (3.5 mmol)

of solid PPh^ at room temperature. The solution became brown

and vigorous gas evolution occurred. After 15 min, hexanes

(20 mL) were added and the final reaction mixture was fil•

tered. Slow concentration of the filtrate under reduced

pressure afforded 1.64 g (74% yield) of (MeCp)Mn(PPh3)(NO)I

as a brown, microcrystalline solid.

Anal, calcd for C24H29MnNOPI: C, 52.10; H, 4.01;

N, 2.53. Found: C, 51.77; H, 3.81; N, 2.63. VNQ (CH2C12)

1720 cm-1. XH NMR (CDClg) 6 7.33 (15H, m), 4.93 (2H, b),

4.40 (IH, b) , 3.84 (IE), b) , 1.90 (3H, s) . Mp 132-133° C.

Reaction of (RC^H^)Mn(CO)(NO)I with Other Phosphines and

Phosphites. The reactions of the carbonyl.-nitrosyl iodides with other phosphorus-containing ligands were carried out as

described above. The physical properties of the products are

described in Table VIII.

Reaction of (RC^H^)Mn(CO)(NO)I with Other Lewis Bases. Solu•

tions of (RCj-H^) Mn(CO) (NO) I in dichloromethane when treated

with a slight excess of such Lewis bases as C^H^N, (CH^^SO,

HN(C6H13)2, (CH3)2NC(0)H, or C^H^N, slowly (^6 h) produce

variable yields (10 - 25%) of the complexes (RC^H^)2Mn2(NO)3I Table VIII. Physical Properties of the Complexes (RC5H5)Mn(L)(NO)I fR = H, L = P(OC6H5)3;

p R = Me, L = P(OC6H5)3 or (C6H1]L)3]

1 Mp Analysis: Calcd (Found) IR(vNQ) E NMR( RCnHj.) H N

-1 (CCHC)MnP(OC,Hc) _(NO) I 126° dec 47.04 3.43 2.39 1748 cm 4.48 (5H, s) DO D b j (46.90) (3.26) (2.36)

-1 (CgH7)MnP(OC6H5)3 (NO) I 84-85° 47.94 3.69 2. 33 1740 cm 4.70 (2H, b), (47.86) (3.51) (2.41) 4.33 (IH, b), 3.66 (IH, b), 1.60 (3H, s)

1 (CgH7)MnP(C6H11)3(NO)I 121-122° 50.54 7.06 2.45 1707 cm 5.47 (IH, b), (50.36) (7.09) (2.45) 5.17 (IH, b), 4.92 (IH, b), 3.85 (IH, b), c

ci b c in CH2C12 solution 6, in CDC13 solution covered by resonances due to L - 67 -

(R = H or Me). The products could be purified by removal of

the solvent in vacuo and recrystallization of the residue from

CH2Cl2/hexanes.

Anal, calcd for C10H10Mn2N3C>3I: C, 26.29; H, 2.21;

N, 9.19. Found: C, 26.46; H, 2.47; N, 9.23. .vNQ (CH2Cl2)

1748, 1526 cm"1. Mp 182° C dec.

Anal, calcd for C12H14Mn2N303I: C, 29772; H, 2.91;

N, 8.66. Found: C, 30.31; H, 3.33; N, 8.44. vNQ (CH2C12)

1734, 1520 cm"1. Mp 146-147° C.

A1H A Reaction of CpMn (CO) (NO) I with Na[ (g^OC^O) 2 2^ • stir•

red benzene solution (30 mL) containing CpMn(CO)(NO)I

(^2 mmol) was treated dropwise at room temperature with a

benzene solution of sodium dihydridobis(2-methoxyethoxy)-

aluminate. The green-brown reaction mixture slowly turned r

red-violet and a solid precipitated. The reaction was monitored by IR spectroscopy and the addition of the re•

ducing, agent stopped when all of the starting material had

reacted.- At this point the mixture was concentrated in vacuo

to 10 mL and then transferred by syringe to the top of a

2 x 5 cm column of alumina (Woelm neutral grade 1). Elution of the column with benzene produced a red-violet band which was collected and taken to dryness under reduced pressure.

18 The residue was identified as [CpMn(CO)(NO)]2 on the basis

of its IR, NMR, and mass spectra. (Yield ^52%) .

Reaction of (MeCp)Mn(CO)(NO)I with Zn/Hg. To a stirred zinc - 68 -

amalgam (2%) was added a tetrahydrofuran solution (30 mL) containing (MeCp)Mn(CO)(NO)I (^1 mmol). A gray solid slowly desposited as the supernatant turned red-brown. After 3 h the reaction was complete. The supernatant was removed by syringe,.filtered, and the resulting solution taken to dry• ness in.vacuo. The red-brown residue was purified as des•

6 9 cribed in the previous section and [ (MeCp) Mn (CO) (NO)]2 . was isolated in moderate yield (0.13 g, ^65%).

Preparation of [CpCr(CO)(NO)JPF6• The.complex, CpCr(CO)2(NO)

(0.61 g, 3.0 mmol) was dissolved in a mixture of CH2Cl2

(15 mL) and CH^CN (5 mL) and the orange solution was cooled to -78° C. Solid NOPFg (0.54 g, 3.1 mmol) was added and the mixture was stirred for 2 h. During this time the solution turned green and a similarly coloured solid formed. The ad•

dition of cold Ft20 (25 mL) precipitated more solid and the

product was collected on a fritte, washed with Et20, and dried

in vacuo. The product, [CpCr(CO)(NO)2]PF^, was identified by its characteristic physical properties. Yield = 0.97 g

(93%) .

Reaction of [CpCr(CO)(NO)2]PF^ with KI. To an acetone solu•

tion (30 mL) containing 0.35 g (1.0 mmol) [CpCr(CO)(NO)2]PFg was added 0.20 g (1.2 mmol) of solid KI. The mixture was stirred at room temperature for 2 h during which time it turned yellow-brown and a gray precipitate formed. The ace• tone was removed in vacuo and the residue was extracted with - 69 -

CE^C]^. The extracts were filtered through a 2 x 3 cm column

of Florisil and the filtrate was taken to dryness under

reduced pressure to produce CpCr (NO) 2I (0.21 g, 77% yield)

which was identified by its characteristic physical properties9.

Preparation of (MeCp)Fe(CO) (PPh3)I. A benzene solution (100

mL) containing 2.82 g (8.9 mmol) of (MeCp) Fe (CO) 2I (prepared

1 by the reaction of [ (MeCp) Fe (CO) 2 ]2 with I^ ) and 2.36 g

pp (9.0 mmol) of h3 was stirred at reflux for 18 h. The

solution was filtered hot and the solvent was removed in VV,G

vacuo. The residue was recrystallized from CH2cl2/hexanes

to obtain a nearly quantitative yield of (MeCp)Fe(CO)(PPh3)I.

Anal, calcd for C25H22OFeIP: C, 54.38; H, 4.02.

1 1 Found: C, 54.15; H, 4.01. vco (CH2Cl2) 1945 cm" . H NMR

(CDC13)•6 7.33 (15H, m), 4.78 (IH, b), 4.33 (1H, b), 3.80

(1H, b), 3.63 (IH, b), 2.12 (3H, s). Mp 146° C.

Preparation of CpRe (CO) (NO) I. A CH3CN solution of CpRe(CO)3

was treated with a slight excess of solid NOPF^ to produce

[CpRe(CO)2(NO)]PF6 completely analogously to the formation of

the manganese cation recently reported1*2. The rhenium cation was then reduced with NaBH^ in thf according to the pub•

lished procedure70. The product of this reaction, CpRe(CO)-

(NO)Me (0.22 g, 0.7 mmol), was dissolved in dichloromethane

(25 mL) and the solution was treated dropwise at room temper•

ature with a dichloromethane solution containing I2 (0.19 g).

The solution darkened and no gas evolution was observed. The - 70 -

solution was stirred.for 1 h and was then concentrated to

10 mL and filtered. Hexanes (10 mL) were added to the fil• trate and the solution concentrated to 3 mL as 0.23 g (75% yield) of crystalline CpRe(CO)(NO)I separated. The product was collected by filtration and dried in vacuo.

Anal, calcd for C6H5ReN02I: C, 16.52; H, 1.66;

N, 3.21. Found: C, 15.78; H, 1.12; N, 3.07. vC0(CH2Cl2)

1 1 1992 cm" . vNQ (CH2C12) 1733 cm" . *H NMR (CDC13) 6 5.78

(5H, s). Mp 135° C dec.

Reaction .of [CpMn (CO) 2 (NO) ] PF£ with NaBr. To a stirred ace•

tone solution (100 mL).containing [CpMn(CO)2 (NO) ]PFg (2.5 g,

7.1 mmol) was added solid NaBr (0.80 g, 7.8 mmol) . The or• ange solution gradually darkened and gas evolution was observed. The mixture was stirred for 1 h and then the sol• vent was removed in vacuo. The gray residue was care fully

extracted with 3 x 30 mL portions of CH2C12 and the residue washed a final time with 40 mL of this solvent. The com•

bined CH2C12 solutions were concentrated to 40 mL and hexanes (40 mL) were added. Slow removal of the solvent under reduced pressure produced 0.43 g (44% yield based on

the NO ligand) of Cp2Mn2(NO)3Br.

The reactions of the [ (RCr-H .) Mn(CO) ~ (NO) ] PF, (R = D 4 2 o

H or Me) complexes with NaBr, NaCl, and NaN02 were carried out similarly. The physical properties and analyses of the products are recorded in Tables IX and X. - 71 -

Table IX. Elemental Analyses for (RC5H4)2Mn2(NO)3X Complexes

Calcd Found

C H N C H N

R = H

Br 29.30 2.46 10.25 29.53 2.72 10.02

N02 31.94 2.68 14 .90 31.75 2.60 14 .79

C5H5 45 .59 3.83 10.63 44. 87 3.79 10. 71

CH3 38.28 3.80 12.18 38.39 3. 83 12.18

CH3

Br 32.90 3.22 9.59 33.20 3.24 9.41

N02 35 .66 3. 49 13.86 35.30 3.49 13.54 - 72 -

Table X. Physical Properties of (RC5H4) 2Mn2(NO) 3X Complexes

a -1 Colour Mp 2C12) cm

R = H

X = Br red-black 15 0° dec 1745 , 1527

Cl red-black b 1746, 1529

N02 red-brown 134° dec 1757, 1544

C H red-violet 153° dec 1730, 1510 5 5

CH3 dark red 163° dec 1723, 1501

R = CH3

X = Br red-black 144° dec 1734, 1522

Cl red-black b 1737, 1522

N02 red-brown 135° dec 1745, 1539

"All complexes explode violently on decomposition.

Analytically pure samples could not be obtained but data

obtained on impure samples: R = H, 145° dec; R = CH3,

141° dec. - 73 -

Reactions of Cp^Mn^(NO)^Br with NaC5H5 or LiMe. The reac• tions were carried out similarly except that the methyl- lithium reaction was done at -78° C. A 0.15 M solution of

NaC^Hj- in tetrahydrof uran was added dropwise to a stirred

room temperature solution of Cp2Mn2(NO)3Br (0.41 g, 1.0 mmol). The reaction occurred immediately as evidenced by a colour change to dark red and the formation of a fine precipitate. The progress of the reaction was monitored by

IR and the addition of the NaC<-H,- stopped when the bands due to the starting material had disappeared. The thf was removed under reduced pressure and the gray residue was extracted with 4 x 20 mL portions of dichloromethane. The resulting solution was concentrated in vacuo to 30 mL and hexanes (35 mL) were added. The total volume was reduced to

15 mL during which time essentially complete crystallization occurred. The red-violet crystals were collected, washed with hexanes, and dried in vacuo. Yield = 0.30 g (76%).

The physical properties and analytical data for the

complexes Cp0Mn«(NO)_R (R = Me or CrHr) are summarized in 2 2 3 bo Tables IX and X.

Results and.Discussion

Contrary to the claims of other investigators18'68, the previously unknown complex, CpMn(CO)(NO)I, and its methylcyclopentadieny1 analogue can be easily prepared by either of the reactions

[ (RC5H4)Mn(CO) (NO) ] 2 + I • 2(RC5H4)Mn(CO) (NO)I (38) - 74 -

[ (RC5H4)Mn(CO)2 (N0) ] + I * (RC^) Mn (CO) (NO) I + CO (39) both of which proceed-rapidly-to completion at room tempera^ ture. This is not surprising since these reactions are anal•

ogous to the formation of the isoelectronic CpFe(CO)2I or

18 1 1 CpCr (NO) 2I either by the direct iodination of the dimers ' * or from iodide attack on their respective cations, i.e.

+71 + [CpFe(CO)3] and [CpCr(CO)(NO)2] . The (RC5H4)Mn(CO)(NO)I complexes are air-sensitive, green-brown solids that dis• solve freely in common organic solvents except paraffin hydrocarbons. They decompose slowly both in solution and in the solid state even when maintained under an atmosphere of prepurified nitrogen. This behaviour is consistent with that postulated in Chapter II in which the thermal instability of transition metal carbonyl nitrosyl halides often leads to the formation of polymeric halogen-bridged species. The IR spectra of the (RC^H^)Mn(CO)(NO)I compounds exhibit the cus• tomary absorptions due to terminal carbonyl and nitrosyl ligands, and their 1H NMR spectra display resonances char•

acteristic of a pentahapto RC^H4 ligand. The presence of the parent ions and fragments showing the sequential loss of ligands from the metal centre in their mass spectra (Table

VII) are consistent with the above formulation.

In order to characterize these complexes further,

several typical transformations of (RC5H4)Mn(CO)(NO)X species were carried out. Zinc amalgam was used in a Wurtz coupling.reaction (equation 4 0) to produce the known dimers, - 75 -

thf 2(RC5H4)Mn(CO) (NO) I + Zn/Hg » [ (RC5H4) Mn ( CO) (NO) ] 2 (40).

[(RC5H4)Mn(CO)(NO)]2. A similar reaction has been reported

72 which yields [CpCr (NO) 2J 2 from CpCr (NO) 2C1 . The iodo species can also be reduced using a hydrido-reagent

(Na[(CH3OC2H40)2A1H2]), thereby again producing the dimeric

[(RC5H4)Mn(CO)(NO)]2 probably-via a sequence of reactions similar to equations 34 and 35 involving the intermediacy

of (RC5H4)Mn(CO)(NO)H. (The formation of such hydrides from reactions of this reducing agent with organometallic nitro• syl halides is the subject of a recent paper73). The forma-b tion of a product containing both carbonyl and nitrosyl ligands confirms the formulation of the starting material as a carbonyl nitrosyl complex. Furthermore, regardless of the

method by which solutions of (RC^H4)Mn(CO)(NO)I are generated, they readily evolve carbon monoxide when treated with triphenylphosphine, i.e.

(RC5H4)Mn(CO) (NO) I + PPh-3 • (RC^)Mn(PPh3) (NO) I + CO (41)

and the new crystalline complexes, (RCj-H,-)Mn(PPh3)(NO)I, can be isolated in good yields. This rapid displacement of

a carbonyl ligand is also observed for W(CO)4(NO)I which

forms the monosubstituted derivative mer-W(CO)3 (NO) (PPhp) I

p 74 when treated with P h3 at room temperature . The prepara•

tion of several other derivatives of the type (RC^H4)Mn-

(L)(NO)I [R = H, L = P(OPh)3; R = Me, L = P(OPh)3 or

P(CgH^^)3] can be carried out by analogous reactions and - 76 -

along with the above chemical and spectroscopic evidence supports the hypothesis that the complexes (RC^H^) Mn (CO)(NO)I do in fact exist and.are stable at room temperature for a reasonable period of time.

The chemistry of these complexes is dominated by the lability of the carbonyl group and the thermal instability of the compounds themseives. Because of this, preliminary attempts.at preparing alkyl or aryl derivatives by meta•

thesis failed. In contrast, the isoelectronic CpFe (CO) 2I

and CpCr(NO)2I are stable almost indefinitely (under N2) and

compounds of the type CpM(L2XR (M = Fe, L = CO; M = Cr, L =

NO) can be readily prepared26'72. Also, substitutionaof a CO or NO ligand in the latter compounds requires the presence of an excess of PPh^ in refluxing benzene for 18 h.

It therefore appears that it is not simply the presence of a nitrosyl ligand but the presence of a mixture of the two ligands (CO and NO) which.confers this odd thermal instab• ility on CpMn(CO)(NO)I.

The compounds (RC^H^)Mn(NO)(L)I [R = CH3 or H; L =

pp p H are P(OPh)3, h3, or (0g n)3] green to brown air-stable solids which are soluble in dichloromethane and chloroform, but less soluble in benzene, tetrahydrofuran, or acetone.

Their IR spectra display single nitrosy1-stretching absorp• tions in the range 1707 - 1748 cm"1 which are 30 - 70 cm"1 lower than those exhibited by the (RC^H^)Mn(CO)(NO)I com• plexes. The decrease in frequency as L varies in the order - 77 -

p c H has CO > P(OPh)3 > PPh3 > ( 6 11)3 been previously observed

in other systems and is consistent with the replacement of a

carbonyl ligand by a better electron donating phosphine li•

gand and the reported variation in a-donor, •re-acceptor abil•

ities of the different phosphines75. The mass spectra of the

two triphenylphosphine complexes (Table XI) reveal fragmen•

+ pp + tation patterns attributable to (RC^H^)Mn(NO)I and h3

ions. Parent ion peaks are not detectable even at such low

excitation potentials as 20 eV. A.similar pattern is obser•

ved for the other (RC5H4)Mn(L)(NO)I complexes (Table XII).

In contrast, the mass spectrum of the iron analogue, (MeCp)-

Fe(PPh3)(CO)I, (Table XIII) exhibits several fragments which maintain the metal-phosphine link (including the parent ion).

The difference in behaviour of these two isoelectronic com• plexes is surprising. It is expected, since NO is thought to

be a better Tr-aeid, that the nitrosyl ligand should better

stabilize an electron donating group attached to the metal.

Therefore, one would expect the manganese derivative to be

more stable. This is not observed. Also, the tricyclo-

hexylphosphine derivatives, which should be the most stable,

are observed to be quite unstable. Both complexes tend to

decompose slowly in a solution not containing an excess of

P(CgH^^)3 and.this proclivity to form free phosphine and aa

species like [CpMn(NO)I] has made the isolation of pure

CpMnIP(CgH11)3](NO)I extremely difficult. Obviously, the

presence of a strongly electron-donating phosphine is not - 78 -

Table XI. Mass Spectral Data for (RC5H4) Mn (NO) (PPh3) I*

R = H R = Me

Rel Rel m/z Assignments m/z abund abund

+ 277 3 (RC5H4)Mn(NO)I 9 291

+ 262 100 P(C6H5)3 100 262

+ 247 8 (RC5H4)MnI 0 261

+ 185 (RC5H4)2Mn 14 213 22 + 185 P(C5H5)2 5 185

182 6 Mnl + 9 182

+ 120 26 (RC5H4) Mn 14 134

+ 65 8 RC5H4 9 79

55 10 Mn+ 9 55

p c H and ^ass spectral data includes only P(CgH5)3 , ( ,g 5)2 ' fragments containing Mn. All spectra also included the

characteristic fragmentation patterns of P(C,H[-)-.. - 79 -

Table XII. Mass Spectral Data for (RC^H ) Mn (NO) [P (OPh) ,] Ia

R = H R = Me

Rel Rel m/z Assignment m/z abund abund

+ 310 100 P(OC6H5)3 100 310

+ 277 8 (RC5H4)Mn(NO) I 3 291

+ 247 13 (RC5H4)MnI 6 261

+ 185 0 (RC5H4)2Mn 5 213

182 5 Mnl+ 6 182

+ 120 17 (RC5H4)Mn 11 134

+ 65 34 RC5H4 26 79

55 7 Mn+ 7 55

a Mass Spectral Data for (C6H7) Mn(NO) [P (CgH1]L)3 ] I

+ + (C6H7)Mn(NO) I , 291 (18); PtCgH.^)^, 280 (80); (CgH7)MnI ,

+ + + 261 (42); (C6H7)2Mn , 213 (21); Mnl , 182 (37); (C6H?)Mn ,

134 (26); C,H*, 79 (88); Mn+, 55 (100). b /

+ p C H ^ass . spectral data include only L [L = P(OPh)3 or ( 6 li)3l and fragments containing Mn. All spectra also included the characteristic fragmentation patterns of L. - 80 -

Table XIII. Mass Spectral Data for (CH-) Fe (CO) (PPh_) Ia

.Rel m/ z Assignment "abund

+ 552 1 (C6H7) Fe [P(C6H5) 3] (CO)I

524 8 (C6H7)Fe[P(C6H5)

+ 445 1 Fe[P(C6H5)3]I

397 2 (C6H?)Fe [P(C6H5) + 3 =

+ 290 2 (C6H?)Fe(CO)I

+ 262 100 P(C6H5)3

+ 214 40 (C6H7)2Fe

183 36 Fel +

79 11 C H + 6 7 56 10 Fe+

a p + Mass spectral data includes only (CgH,-)3 and fragments containing Fe. All spectra also included the characteristic

fragmentation patterns, of P(C(-HC.)7. - 81 -

stabilized, by the nitrosyl ligand and it thus seems that

NO may not be as strong a ir-acid as is commonly believed. It is also reasonable.to conclude: that.the,a-donor.effects of the nitrosyl ligand are far more important than its electron accepting abilities in these complexes.

The *H NMR spectrum of CpMn(PPh3) (NO) I consists of a multiplet centered at. 6 7.32 and a singlet at 5 4. 72 of relative intensity 3:1, and these resonances can be assigned to the phenyl and cyclopentadienyl protons respectively.

The spectrum of the triphenylphosphite derivative is similar and can be assigned analogously. The 1H NMR spectra of the methylcyclopentadienyl derivatives also show resonances corresponding to the phosphinesligands as well as a singlet at ^ 6.2 assignable to the methyl group attached to the ring.

However, unlike the parent.carbonyl, (MeCp)Mn(CO)3, the four protons on the methylcyclopentadienyl ring are not magnet• ically equivalent. Instead, three resonances (four in the

case of the P(C,Hnn)_ derivative) are observed which are due 6 11 3 to the a, a', 3* 3' spin system. These resonances are assig• nable to the protons on the diastereotopic sides of the meth• ylcyclopentadienyl group and this magnetic non-equivalence confirms the presence of the asymmetric metal centre. It was previously reported76 that the carbonyl and nitrosyl groups

in the complex CpMo(CO)(NO)(PPhMe2) were sufficiently diff• erent to induce the magnetic non-equivalence of the two methyl groups even though these two ligands are similar in - 82 -

both structure and charge distribution. However, the induced inequivalence in this compound is extremely small compared to that observed in the manganese cases presented above. It is therefore of interest to compare the *H NMR spectra of the

series of related compounds (MeCp)Mn(CO)3, (MeCp) Mn (CO) 2~

(PPh3) , [ (MeCp)Mn(CO) (NO) (PPh3)]PFg, and (MeCp) Mn(PPh3) (NO) I. The spectra are reproduced in Figure 5. The spectrum of the parent carbonyl (5a) exhibits the expected resonances at 6 4.51 (4H, s) and 1.89 (3H, s) and the spectrum of the tri- phenylphosphihe derivative (5b) shows the inequivalent protons at the a and 3 positions. Interestingly, although the a and 6 proton resonances appear better resolved in the spectrum of the cation (5c), there still does not appear to be any observed magnetic inequivalence between the two sides of the methylcyclopentadienyl ring. This compound differs from the molybdenum complex cited previously in that its carbonyl and nitrosyl ligands are not sufficiently different - 83 -

Figure 5. The 1H NMR Spectra of

(a) (MeCp)Mn(CO)3,

(b) (MeCp) Mn(CO)2 (PPh3) ,

(d) (MeCp)Mn(NO) (PPh3) I

- 85 -

in this compound to induce the.magnetic inequivalence in the ring. The final spectrum in the figure is that of the com• plex (MeCp) Mn (PPh^) (NO) I and it exhibits the resonances pre• viously described. The direct assignment of these resonances is not possible at this time.

In order.to find a more sensitive probe of the asym• metry at the metal centre or, at least, the magnetic inequiv• alence on the ring, a study of the 13C NMR of these complexes was undertaken. The data obtained are summarized in Table

XIV. The assignments of the carbonyl and triphenylphosphine ligands are based on previously reported results77 and the expected chemical shifts of.these two ligands. The indirect coupling constants J( 3 ip.j^-i 3^) °f rb24 Hz between the 1 3C0

31 and PPh3 nuclei are common for a cis-ligand arrangement.

J for tne The direct.coupling constants (3ip_i3C) triphenylphosphine ligands are.reported.as well as the assignment of

the indirect coupling constants, J^3ip_i3C j and ^(3ip_i3c ^ based on previously reported data. The lack of interaction between the phosphorus and C-4 is not uncommon. The assign•

ment of the resonance for the .methyl carbon of the MeCj-H4 ligand is unambiguous as is that of the carbon adjacent to the methyl group. In the case of the other four ring car• bons, the anticipated results are indeed observed. Although

the spectra for (MeCp)Mn(CO)3 and (MeCp)Mn(CO) (PPh3) ex• hibit only two resonances for these carbon atoms, the cat-

ionic complex [(MeC5H4)Mn(CO)(NO)(PPh3)]PFg has four distinct Table XIV. 13C NMR Spectral Data of Some (MeCp)Mn Compounds

Compound 6 CO 6 PPh3 6 C(Cp) 6 C(CH3)

(MeCp)Mn(CO) 225 .,1 0 102. ,4 2 13.,3 0 82.,2 1 81.,7 2

PPh 232. .82 C 138. ,21 (JP. 40., 0 Hz) 98.,7 6 " 13..6 0 (MeCp)Mn(CO)2 3 l -c

24.4 Hz C 132. ,77 13., 2 Hz) 82.,9 1 JP-C 2 (JP. -C

127. ,90 J 8., 6 Hz) 81.,7 2 C3 < P--c

C 129. ,22 4

P (MeCp)Mn(CO) (NO) (PPh3)PFg 213. .91 C 131.,3 8 (J . 59 .2 Hz) 115.,2 3 11,.9 9 l -c

24.0 C 132. ,87 J 20.. 4 Hz) 98..1 1 JP-C 2 ( P--c

C 129.,9 1 J 11.. 4 Hz) 95..4 9 3 ( P--c

C 132. ,86 93..8 7 4 93,.3 6

(MeCp)Mn(NO) (PPhg) I C 134. .71 J 30,. 2 Hz) 106, .51 12,.8 2 l < P--c

C 133..2 9 J 9,. 8 Hz) 97,.0 2 2 ( P--c

C 127..9 6 J 9,. 4 Hz) 95,.6 1 3 ( P--c

C 129, .89 91..4 3 4 86.47 - 87 -

resonances in its spectrum. Of course, this effect is amp• lified for the neutral complex (MeCp)Mn(NO)(PPh^)I, where the four ligands differ to a larger extent in size and elec• tronic properties and therefore induce greater magnetic non-equivalence. However, this does confirm that 13C NMR spectroscopy is a more.sensitive probe of the asymmetry in these complexes.

Similar derivatives of manganese containing four different ligands have been prepared previously and separated into optical isomers. When the triphenylphosphine cation,

[CpMn(CO)(PPh3)(NO)]PFg, is treated with sodium L-menth-

oxide, diastereomers of the type CpMn(PPh3)(NO)[C(0)0- menthyl] result!8. By differential crystallization, essentially optically pure isomers are obtained. These dia• stereomers can then be acidified and the resulting solution treated with NH^PFg to produce the optically active (+) and

+ (-) [CpMn(CO) (PPh3) (NO)] cations. These cations are con- figurationally stable both in the solid-state and in solution.

Interestingly, the menthoxide derivatives slowly racemize in solution (via a phosphine dissociation pathway) and after several hours optical activity due to the metal centre is no longer observed.

The success of the present study in preparing the

new complexes (RC5H4)Mn(L)(NO)I [L = PPh3, P(0Ph)3, and

P(CgH^)3] initiated attempts to prepare (i) these same com• plexes by a different route, and (ii) the analogous rhenium - 88 -

complexes by the same or different routes. The first of these endeavours failed when it was observed that the cation

+ [(MeCp)Mn(CO)(PPh3)(N0)] did not react with any NaX (X = Cl,

Br, or I) in refluxing acetone. After five days, a majority of the starting material had decomposed. Attempts to pre• pare CpRe(CO) (NO)I by a method .analogous to the formation of the manganese derivative (equation 39) failed. The start•

ing cationic complex [CpRe (CO) 2 (NO) ] PFg. could be recovered unaltered after several days refluxing in an acetone solu• tion containing an excess of Nal. However, since this com• pound is of considerable interest for comparison, another preparative route was examined.

A common reaction of transition metal alkyl bonds

involves the cleavage of this linkage by I2 to give the alkyl iodide and the metal iodide. Since the compound CpRe (CO) -

(NO)Me had been previously reported70 in the literature, the reaction

CH2Cl2 CpRe (CO) (NO) Me + I CpRe (CO) (NO) I + Mel (42) was attempted and was found to produce the desired product in good yields. The IR, 'HJMR and mass spectral data (Table

XV) are consistent with the above formulation. The complex is air stable in the solid state and in solution and, in contrast to the manganese analogue, the carbonyl ligand is inert to substitution. CpRe(CO)(NO)I does not react with triphenylphosphine even when held .at reflux in a toluene solution containing an excess of this reagent. The unusual - 89 -

Table XV. Mass Spectral Data of (CVHj.) Re (CO). (NO) I

;Rel 3 m/z Assignment abund

+ 437 79 (C5H5)Re(CO)(NO)I

+ 409 86 (CCH[-) Re (NO) I b b

+ 379 100 (C5H5)Rel

+ 35 3 29 (C3H3) Rel

314 6 Rel+

2+ 218.5 6 (C5H5)Re(CO)(NO)I

2 + 204.5 8 (C5H5) Re (NO) I

2+ 189 .5 10 (C5H5)Rel

187 6 Re+

Assignments are based on the 87Re isotope. - 90 -

stability of this complex represents the only known example of a mixed carbonyl nitrosyl halide of a transition metal with an inert carbonyl ligand.

In the course of studying the chemical reactivity of the (RCj-H^) Mn (CO) (NO) I (R = H or Me) complexes, attempts to prepare derivatives containing N-donor ligands resulted in the observation of a unique disproportionation reaction

(RC5H4)Mn(CO) (NO) I + C^N • (RC5H4)2 Mn2 (NO) 3I (43)

which produced the species (RC,-H4)2 Mn2 (NO) ^I as the only isolable nitrosyl complexes. Although no reaction pathway is readily apparent, two observations should be noted.

Firstly, the reactions are relatively slow (^6 h) and care• ful monitoring of these conversions by IR spectroscopy does not show any evidence for the formation of an intermediate

(RCj-H4) Mn(L) (NO) I species. Secondly, a small amount of

NO(g) is present in the atmosphere above the reaction mix• ture and its presence may indicate that nitrosyl ligand transfer occurs via free.nitrogen monoxide. Also, during

the preparation of (RC^H4)Mn(CO)(NO)I in thf.or acetone, small amounts of these bimetallic complexes are formed indicating that O-donor ligands also facilitate these con• versions. Consistent with this inference is the fact that dimethylsulphoxide is as effective as.pyridine or pyrrol•

idine in producing the complexes (RC5H4)2Mn2(NO)^I from the parent carbonyl nitrosyl iodides. - 91 -

+ The reactions of the cations, [(RC^H^)Mn(CO)2(NO)] ,

with the nucleophiles Br , Cl , or N02 also produce com•

pounds of the formula (RC5H4)2Mn2(NO)3X (X = Br, Cl, or

N02). All of the bimetallic complexes are red-brown to red- black, relatively air stable compounds that are soluble in polar organic solvents, sparingly soluble in benzene, and in• soluble in hexanes. Their solutions display IR absorptions

(Table X) at ^1745 and /^1525 cm"1 attributable to terminal and bridging nitrosyl ligands respectively.. The mass spectra

(Table XVI) of the iodo-derivatives exhibit peaks due to the parent, P+, and the ions [P-NO]+, [P-2N0]+, and [P-3N0]+, as well as those arising from cleavage of the bimetallic

+ + species, i.e. [(RC5H4)Mn(NO)2] and [(RC5H4)Mnl] . The mass spectra of all of the derivatives are presented in Tables

XVII to XIX and they exhibit fragmentation patterns similar to the iodo complexes. It is interesting to note that un•

der certain conditions ions due to the species (RC,-H4)3~

Mn2(NO)3 may be observed in the mass spectra of these derivatives. Ion-molecule reactions, of the type shown in equation (44), have previously been observed in the mass spectra

+ (RC5H4)2Mn2(NO)3Br + (RC5H4) • (RC^)3 Mn2 (NO)3 +

Br+ (44)

of other nitrosyl compounds79.

These complexes apparently belong to the general class

of compounds (RC^H4)2Mn2(NO)3X of which the members with - 92 -

Table XVI. Mass Spectral Data for (RC5H4)2Mn2(NO)3I

(R = H or Me)

R = He R = Me

Rel Rel , m/z Assignment , , m/z abund abund '

+ 457 6 (RC5H4) 2Mn2(NO)3I 17 485

+ 427 17 (RC5H4) 2Mn2(NO)2I 43 455

+ 397 8 (RC5H4) 2Mn2(NO) I 14 425

+ 367 29 (RC5H4) 2Mn2I 71 395

+ 24 7 4 (RC5H4) Mnl 7 261

+ 237 3 Mn2I 9 237

+ 191 3 (RC5H4) Mn20 0 205

+ 185 22 (RC5H4) 2Mn 25 213

+ 180 40 (RC5H4) Mn(NO)2 69 194

182 6 Mnl+ 12 182 i (RC + 15 0 15 5H4] Mn(NO) 22 164

+ 120 100 (RC5H4) Mn 100 134

+ 65 34 RC5H4 57 79

55 40 Mn+ 50 55 - 93 -

Table XVII. Mass Spectral Data for (RC5H4) 2Mn2(NO) 3Br

(R = H or Me)

R = H R = Me

Rel Rel m/ z Assignment3 m/ z abund abund

+ 409 1 (RC^H4) 2Mn2 (NO) 3Br 5 437

Br+ 379 3 (RC5H4)2Mn2(NO)2 15 407

+ 349 2 (RC5H4) 2Mn2(NO)Br 6 377

+ 330 3 (RC5H4)2Mn2(NO)3 0 35 8

+ 319 8 (RC5H4)2Mn2Br 45 347

+ 300 3 (RC5H4)2Mn2(NO)2 0 328

+ 270 3 (RC5H4)2Mn2(NO) 0 298

+ 199 1 (RC5H4)MnBr 0 214

+ 191 11 (RC5H4)Mn20 0 205

+ 185 40 (RC5H4)2Mn 25 213

+ 180 20 (RC5H4)Mn(NO) 2 55 19 4

+ 15 0 8 (RC5H4)Mn(NO) 14 164

134 3 MnBr+ 0 134

+ 120 110 0 (RC5H4)Mn 100 134

+ 65 60 RG5H4 86 79

55 53 Mn+ 30 55

aAssignments are based on the 79Br isotope. - 94 -

Table XVIII. Mass Spectral Data for (RC5H4) 2Mn2(NO) 3ci

(R = H or Me)

R = H R = Me

Rel 3 Rel m/z Assignment m/z abund abund

+ 365 5 (RC5H4)2Mn2(NO)3C1 6 393

+ 335 3 (RC5H4)2Mn2(NO)2C1 16 363

+ 330 7 (RC5H4)2Mn2(NO)3 7 358

+ 305 4 (RC5H4)2Mn2(NO)Cl 10 333

+ 300 . 10 (RC5H4)2Mn2(NO)2 328

+ 275 10 (RC5H4)2Mn2Cl 61 303

+ 270 9 (RC5H4) 2Mn2(NO) 3 298

+ 191 41 (RC5H4)Mn20 0 205

+ 185 35 (RC5H4) 2Mn 40 213

+ 180 28 (RC5H4)Mn(NO) 2 50 194

+ 150 15 (RC5H4) Mn (NO) 18 164

+ 120 48 (RC5H4)Mn 100 134

+ 65 100 RC5H4 90 79

55 41 Mn+ 44 55

Assignments are based on the 35C1 isotope. - 95 -

Table XIX. Mass Spectral Data for (Cj-H,-) 2Mn2(NO)3R

(R = CH. or C,HJ 3 b b

R = C5H5 R = CH3

Rel Rel m/z Assignment m/z abund abund

+ 395 1 (C5H5)2Mn2(NO) 3R 26 345

+ 365 2 (C5H5)2Mn2(NO)2R 11 315

+ 335 1 (C5H5)2Mn2(NO) R 11 2 85

+ 330 6 (C5H5)2Mn2(NO)3 3 330

+ 305 2 (C5H5)2Mn2R 82 255

+ 300 8 (C5H5)2Mn2(NO)2 6 300

+ 270 8 (C5H5)2Mn2(NO) 14 270

+ 191 37 (C5H5)Mn20 55 191

+ 185 75 (C5H5)2Mn 45 185

+ 180 7 (CcHc)Mn(NO) ~ 36 180 b b 2.

+ 150 6 (CcH[-)Mn(NO) 12 15 0 b b

+ 120 100 (CCHC)Mn 100 120 b b

66 67 C H + 11 66 5 6

+ 65 50 C5H5 6 65

55 38 Mn+ 45 55 - 96 -

26 35 79 R = H and X = C5H5 , N02 , and CgH5 have been previously

characterized. In fact, the C^H^ derivative can be readily

prepared by treating any of the species Cp2Mn2(NO)3X (X =

Cl, Br, I, or N02) with NaC5H,-. Also, other alkyl or aryl

derivatives may be obtained by using the appropriate lithium

reagent, e.g.

thf

Cp2Mn2 (NO) 3Br + MeLi Cp2Mn2 (NO) 3Me + LiBr (45)

— 78 °C

The *H NMR spectral data of the bimetallic com•

plexes are compiled in Table XX. The spectrum of Cp2Mn2-

(NO) 3I in CDC13 consists of one pair of resonances of equal

intensity at 6 5.53 and 5.34 and a second pair of different,

yet equal, intensity at <5 5.30 and 5.20. These two pairs

of signals are probably due to the cis and trans isomers

79 respectively . The *H NMR spectrum of Cp2Mn2(NO)3(C5H5)

also exhibits resonances due to cis and trans isomers.

Furthermore, the ratio of cis to trans isomers appears to be

very dependent on the solvent in which the spectrum is re•

corded and the data obtained at room temperature in acetone-

dg indicates that a complex intramolecular rearrangement pro•

cess occurs in solution. (This process may well involve

interconversion of the a- and TT-bonded cyclopentadienyl - 97 -

1 a Table XX. H NMR Spectral Data for (RCVH .)0 Mn0 (NO) ->X O 4 z 2 6

(R = H, X = Cl, Br, I , N02, CH3, or C5H5; R = Me, X = Cl,

Br, I, or N0o)

R = H

Cl 5 .50 (5H, s) / 5 .3 0 (5H, s)

Br 5 .53 (5H, S) / 5. 33 (5H, s)

I 5 .53 (5H, s) 7 5 .3 4 (5H, s)

5 .30 (5H, s) / 5 .2 0 (5H, s)

N02 5 .43 (5H, s) / 5 .3 2 (5H, s)

CH3 5 .17 (5H, s) / 5 .1 0 (5H, s) , - 0.60 (3H , s)

C5H5 5 .33 (5H, s) 1 5 .2 7 (5H, s) , 4 . 43 (5H, s) ,

5 .47 (5H, s) t 5 .4 0 (5H, s) , 4 .50 (5H, s)

Cl 5 .07 (6H, b) 1 4 .7 7 (2H, b) ,

1 .77 (3H, s) r 1. 53 (3H, s)

Br 5 .23 (6H, b) t 4. 83 (2H, b) ,

1 .98 (3H, s) i 1. 77 (3H, s)

I 5 . 47 (2H, b) i 5 .3 3 (4H, b) , 4 .90 (2H, b) ,

2 . 10 (3H, s) i 1. 87 (3H, s)

N02 5 . 30 (2H, b). i 5. 10 (4H, b) , 4 .90 (2H, b) ,

2 .03 (3H, s) r 1. 77 (3H, s)

a6, in CDC1-. solution - 98 -

rings). Studies to elucidate the mechanism of this process

are currently in progress. The 1H NMR spectra of the Cp^Mn.,-

(NO)3X (X = Br, Cl, N02, or Me) derivatives exhibit only two

resonances in the Tr-cyclopentadienyl proton region and there•

fore probably exist mainly, or exclusively, as trans isomers.

The spectrum of the methyl derivative also displays a single

resonance at 6 -0.6 assignable to the methyl group.

The spectra of the methylcyclopentadienyl derivatives

are somewhat more complicated. First of all, the iodo-

derivative does not appear to exist as a mixture of cis and

trans isomers (but rather exclusively trans) in this case.

Also, although one of the methylcyclopentadienyl ligand's protons on each complex appears as two resonances in the

ratio of 4:3 [identical to the case of (MeCp)Mn(CO)^], the

second such set of protons appears as three resonances in

the ratio of 2:2:3 as in the case of (MeCp)Mn(CO)2(PPh3).

It seems likely that the first MeCp ligand is attached to

the manganese centre bonded to the terminal nitrosyl ligand while the second ligand of this type is probably bound to

the metal atom attached to the X-group.

CH3 - 99 -

CHAPTER V

SOME ASPECTS OF THE CHEMISTRY OF BIS[(n5-CYCLOPENTADIENYL)-

DINITROSYLCHROMIUM]

The compound bis[(n5-cyclopentadienyl)dinitrosyl-

was 18 chromium],.[CpCr(NO)2]2' first obtained in 1964 by the sodium tetrahydridoborate reduction of CpCr(NO)2CI in an aqueous medium. Unfortunately, only relatively small quan• tities of the red-violet compound were available due to the

5% yield of the original preparation, and an extensive study of its characteristic reactions could not be made. It has

9 72 can be been recently shown ' that [CpCr(NO)2]2 very conven• iently synthesized in higher yields (55 - 75%) by reducing

CpCr(NO)2Cl with either zinc amalgam in tetrahydrofuran or sodium amalgam in benzene. In this manner, a sufficient

amount.of the dimer has become available to enable an inves•

tigation of its physical and chemical properties more fully than was previously possible. This chapter presents the results of these investigations and contrasts the chemistry of [CpCr(NO)2]2 with that exhibited by its isoelectronic

carbonyl analogue, [CpFe (CO) 2]2 •

Experimental

All experimental procedures described here were performed under the same general conditions detailed in - 100 -

Chapter II.

Reaction.: of [CpCr(NO) o with HCl(aq). To a stirred solu•

tion of [CpCr(NO)2]2 (0.17 g, 0.50 mmol) in ethanol (25 mL)

and dichloromethane (5 mL) was added 12 M HCl (1 mL, 12 mmol)

at room temperature. The reaction mixture retained its original red-violet colour until air was bubbled through it

for about 10 min, whereupon it became green-brown. At the\ end of this time the final mixture was taken to dryness in vacuo and the residue was extracted with dichloromethane

(30 mL). The extract was filtered and an IR spectrum of

J2 the filtrate.'showed it to contain CpCr (NO) 2C1 . The or•

ganometallic product (0.11 g, 52%) was obtained by removing

the solvent from the filtrate in vacuo.

Reaction of [CpCr(NO)2]2 with I,,. To a stirred dichlorometh•

ane solution (40 mL) of [CpCr(N0)2]2 (0.35 g, 1.0 mmol) at

room temperature was added I2 (0.28 g, 1.1 mmol). The

reaction mixture immediately changed colour from red-violet

to yellow-brown. It was stirred for 1 h, at which time, an

9 8 IR spectrum revealed CpCr(NO)2 I 'to as the only organometal•

lic product. The product could be isolated virtually quantitatively by taking the final solution to dryness in

vacuo.

The reactions of [CpCr(NO)2]2 with other inorganic

halogen-containing compounds were performed similarly, and

they are summarized in Table XXI. Table XXI. Reactions of [CpCr(NO)2]2 with some Halogen-Containing Compounds

Reactant Dimer Solvent Reaction Products Method of (mmol) (mmol) (mL) Conditions (yield) Isolation

C1N0 0.23 CH2C12 Immediate CpCr(NO)2C1 Removal of solvent (35) at 25° (>95%) in vacuo

SnCl4 1.5 thf Reflux 17 h CpCr(NO)2C1 Chromatography on (0.90) (50) (69%) Florisil with

CH2C12 as eluant

Chromatography on HgCl2 1.0 thf Reflux 24 h CpCr(NO)2Cl (1.0) (60) (>95%) Florisil

SnCl2 1.0 thf Reflux 24 h CpCr (NO) 2C1 Chromatography on (1.0) (60) (>95%) Florisil

PbCl2 1.0 thf Reflux 24 h CpCr(NO)2C1 Chromatography on (1.0) (60) (>95%) Florisil

prepared as described in Chapter II - 102 -

Reaction of [CpCr(NO)2 ]2 with CpFe(CO)2Cl. A mixture of

k 1 [CpCr(NO)2]2 (0.18 g, 0.50 mmol) and CpFe (CO) 2Cl (0.21 g,

1.0 mmol) in thf (40 mL) was heated under reflux for 4.5 h, during which time the reaction mixture developed a yellowish

tinge to its violet colouration. An IR spectrum.of the final reaction mixture at room temperature.indicated that it con•

tained some of the original reactant [CpCr(NO)2]2 as well as

the products CpCr(NO)2Cl and [CpFe(CO)2]2. In order to con•

firm the presence of this latter product, the final reaction mixture was chromatographed on.alumina with dichloromethane

as eluant. The first red-violet band to separate was

collected and the solvent removed from the eluate under

reduced pressure. The residue was identified as [CpFe(CO)2]2

by comparison of its IR (CH2C12) and NMR (C^Dg) spectra with spectra of an authentic sample of the compound.

Reaction of [CpCr(NO)2]2 with Mn(CO)5Cl. To a solution of

[CpCr(NO)2]2 (0.18 g, 0.50 mmol) in thf (40 mL) was added

8 0 Mn(CO)5Cl (0 . 23 g, 1.0 mmol). The resulting red-violet

solution was stirred at reflux for 70 h whereupon it became yellow-brown. The solution was allowed to cool to room

temperature when an IR spectrum indicated the formation of

Mn2(CO)10 as well as the expected CpCr(NO)2Cl. The products were isolated in the following manner. The thf was removed

in vacuo and the residue extracted with 10 mL of dichloro•

methane. The resulting solution was transferred to a 2 x 8

cm Florisil column and elution of the column with dichloro- - 103 -

methane produced - two bands. The first band, yellow in colour,

was collected.and found to contain Mn2(CO)^Q. The second

slow-moving band was golden-brown in colour and the IR

spectrum of the eluted solution showed it to contain CpCr-

(NO)2C1.

Pyrolysis of [CpCr (NO) 2]2 » A stirred red-violet solution of

[CpCr(NO)2]2.(0.75 g, 2.1 mmol) in toluene (100 mL) was

heated under gentle reflux for 24.h. During this time the

solution darkened and a black solid precipitated. The sol•

vent was removed from the final cooled reaction mixture in

vacuo, and the residue redissolved in .dichloromethane. The

dichloromethane solution was then syringed onto a 2 x 10 cm

Florisil column and a green band was eluted with this same

solvent. The eluate was taken to dryness in vacuo and the

residue was recrystallized from.CH2Cl2/hexanes to obtain

dark green crystals (0.11 g, 15%) of Cp2Cr2(NO)3(NH2).

Anal, calcd for C10H12Cr2N4O3: C, 35.30; H, 3.55;

N, 16.50. Found: C, 3 4.70; H, 3.60; N, 16.20.

An intense brown band was next eluted from the

Florisil column with thf as solvent, and the eluate was taken

to dryness in vacuo. The residue crystallized from CH2C12/

hexanes as a red-brown microcrystalline solid (0.30 g)

(Found:.C, 45.20; H, 4.00; N, 10.80))which displayed a

parent peak in its mass spectrum at m/z 531.899.

Pyrolysis of [(MeCp)Mn(CO)(NO)]0. A red-violet solution of - 104 -

69 [ (MeCp) Mn(CO) (NO) ]2 (0 .97 g, 2.5 mmol) in thf (50 mL) was heated.under reflux with stirring for 20 h. At the end of this time the reaction mixture had, deposited some black-brown insoluble material and.the supernatant liquid had a dark- green tinge . - An IR spectrum of the supernatant at room temperature did. not exhibit the ..carbonyl and nitrosyl ab• sorptions of the starting compound. The final reaction mix• ture was taken to dryness in vacuo. Dichloromethane (15 mL) was added to the residue, and the mixture (a green-black solution and rust-coloured solid) was transferred to the top of a 2 x 13 cm.Florisil column for subsequent chromatography.

Elution of the column withCH2Cl2 resulted.in the development of.two distinct bands. The first pale orange band, which

carried quickly down the column, was collected and compara•

tive IR spectroscopy of this fraction indicated that it

contained a very small amount of (MeCp)Mn(CO)3. The second

fraction to be eluted from the column was a very broad green- black band which required ^300 mL of solvent for complete elution. . This eluate was concentrated in vacuo to a volume

of 25 mL, and sufficient hexane was then added to induce the

crystallization of (MeCp)3Mn3(NO)4 (0.09 g, 10%).

c H Mn N : c Anal, calcd for 18 2i 3 4°4 ' 415.4 0; H, 4.05;

N, 10.70. Found: C, 41.40; H, 4.00; N, 10.90.

Reaction of [CpCr(NO)2]2 with 5,6-dibromocholestery1 bromide.

A thf solution (40 mL) containing [GpCr(NO)2]2 (0.35 g,

1.0 mmol) and 5,6-dibromocholesteryl bromide (0.61 g, 1.0 - 105 -

mmol) was stirred at reflux for 6 h. At the end of this time,

an infrared spectrum of the reaction solution indicated

complete conversion of the starting nitrosyl dimer to CpCr-

Br Tne (NO) 2 * solvent was removed under reduced pressure and

the remaining green-brown residue was dissolved in benzene.

Filtration of this solution through a 2 x 5 cm column of alum•

ina removed the organometallic product and the filtrate was

taken to dryness under reduced pressure to isolate pure

cholesteryl bromide in 89% yield.

All halogen abstraction reactions were performed

similarly using a variety of vic-dihaloalkanes (including

1,2-dibromocyclohexane, 1,2,5,6-tetrabromocyclooctane,

1,2-dipheny1-1,2-dibromoethane, and 5,6-dibromocholesterol)

and the organic products were isolated in an identical man•

ner.

Results.and Discussion

The compound [CpCr(NO)2]2 bears a remarkable resem•

blance to its isoelectronic carbonyl analogue [CpFe(CO)2]2•

Both compounds are red-purple solids which are insoluble in

water, sparingly soluble in non-polar organic solvents, and

soluble in polar organic solvents to give solutions which

oxidize gradually in air. In the solid state both dimers

exhibit trans ligand-bridged structures81, but the iron com•

pound can also be isolated in a cis bridged form under cer•

tain conditions?2. Both molecules also undergo rapid intra•

molecular rearrangement at room temperature83, existing in - 106 -

solution as an equilibrating mixture of all possible isomeric

structures.

L-CO, NO

The two compounds exhibit striking similarities in

some of their physical properties. The 70 eV mass spectral

data of both dimers are shown in Table XXII. In contrast to

81 tne the reported spectrum of [CpFe(CO) 2] 2 *, high-resolution mass spectrum of the chromium dimer reveals sequential loss

of nitrosyl groups, but the most abundant species present is

+ the bimetallic Cp2Cr2(NO) ion. Indeed, ions containing two metal atoms are generally much more abundant for the chromium

compound. Migration of the cyclopentadienyl group between metal atoms occurs much less readily than for the iron com• pound as evidenced by the markedly less abundant chromocinium

ion. Fission of the chromium dimer also occurs in a sym•

+ metrical manner (i.e. no ions of the type CpCr(NO)3 are

detectable) , but various ions (such as the relatively abun•

+ + dant CpCr20 and Cr20 ) in the mass spectrum of the chromium

compound have no counterparts in the fragmentation pattern

of the iron compound. - 107 -

Table XXII. High-Resolution Mass Spectral Data for

t(C5H5)Cr(NO) 2]2

m/z m/z Rel Rel Assignment' (Fe) Me asd Calcd abund abund b

+ 35 3 .952 353 .951 45 (C5H5)2Cr2(NO)4 9

+ 323 .953 323 .953 34 (C5H5)2Cr2(NO)3 6

+ 293 .955 293 .955 10 (C5H5)2Cr2(NO)2 10

+ 263 .957 263 .957 100 (C5H5)2Cr2(NO) 4

+ 198 .919 198 .918 13 (C5H5)Cr2(NO) 0

+ 184 .915 184 . 915 74 (C5H5)Cr20 /0

182 .018 182 .019 10 (C5H5)2Cr 70

+ 176 .976 176 .976 14 (C5H5)Cr(NO)2 19

+ 146 .978 146 .978 12 (C5H5)Cr(NO) 19

+ 133 .879 133 .879 15 Cr2(NO) 0

+ 119 .876 119 . 876 44 Cr20 0

+ 116 .980 116 .980 24 (C5H5)Cr 100

+ 103 .881 103 .881 2 Cr2 2

66 .048 66 .047 5 C H + 6 5 6

+ 65 .040 65 .039 5 C5H5 6

51 .942 51 .941 48 Cr+ 41

Assignments are based on the 5 2Cr isotope.

^Data from reference 84, assignments are for the analogous

fragments of [ (C^H,-) Fe (CO) 2] 2 • - 108 -

The two compounds exhibit some chemical simil• arities, and these are summarized in equations (46) - (48)

CH Cl9

[CpM(L0)p]o + I9 2CpM(LO) I (46)

or CHC13 ^

EtOH

[CpM(LO)2J2 + 2HC1 * 2CpM(LO)2 C1 (47) °2

CH 9Cl9

[CpM(LO)2]2 + 2C1NO - 2CpM(LO)2Cl (48)

(M = Fe or Cr, L = C or N, respectively). Thus, [CpCr(NO)2]2 is cleaved by iodine, hydrochloric acid, or nitrosyl chloride at ambient temperature with - concurrent conversion of the bridging nitrosyl ligands into terminal nitrosyl ligands in

1 6 4 1 a manner identical to that reported l&l ' for [CpFe (CO) 2] 2,

the compounds CpCr(NO)2X (X = Cl or I) being the final products. However, in other aspects of their chemistry, the two dimers are significantly different.

Reduction of [CpFe(CO)2]2 by sodium amalgam in thf proceeds readily at room temperature, and virtually

quantitative yields of the [CpFe(CO)2] anion can be ob•

tained. In contrast, the reduction of [CpCr(NO)2]2 under identical conditions leads rapidly to complete decomposition of the compound. The nitrosyl dimer is found to be stable under less vigorous conditions and is unaffected by zinc amalgam in thf or benzene. The failure of a large number

of reducing agents to produce the anion [CpCr(NO)2] is surprising in view of the fact that such an anion should be stabilized by the presence of strong TT-acid ligands. - 109 -

However, it is in their reactions with halogen- containing species that the two dimers most clearly show their chemical differences. For example, the chromium dimer abstracts all the chlorine ligands from tin tetrachloride under the conditions indicated in equation (4'9) whereas the iron dimer reacts with SnCl^ in inert solvents to form a compound containing a heteronuclear metal-metal bond and the

85 compound CpFe(CO)2Cl (equation 50) . The progress of

thf

2 [CpCr (NO) 2] 2 + SnCl4 • 4CpCr(NO)2Cl + Sn (49) reflux

JCA:'<:

[CpFeCCO)2 ]2 + SnCl4 »> CpFe (CO) 2SnCl3 + CpFe(CO)2Cl reflux

(50) reactions such as (4 9) can be monitored very conveniently by infrared spectroscopy since the characteristic absorptions

due to nitrosyl groups of the reactant [CpCr(NO)2]2 occur at 1667 (terminal) and 1512 cm 1 (bridging) whereas those due to the two terminal nitrosyl groups of the product CpCr-

1 (NO)2C1 occur at 1815 and 1710 cm" (Figure 6).

The propensity of the nitrosyl dimer to abstract halogen atoms dominates its reactions with inorganic and

organometallic halides.. Hence, treatment of [CpCr(NO)2]2 with the chlorides of.bivalent mercury, tin, or lead results in the formation of the elemental metals and the customary

CpCr(NO)2Cl, i.e. as in equation (51) (M = Hg, Sn, or Pb) .

[CpCr(NO)2]2 + MC12 • 2CpCr(NO)2Cl + M (51) reflux - 110 -

Infrared spectral changes accompanying the reactions

[CpCr(NO)2]2 +RX Jfe*

Frequency (cm-1) 2000 1800 1600 1400 I I I I I I I Initial

Final

Figure 6 - Ill -

The iron carbonyl dimer, on the other hand, undergoes an

oxidative-addition reaction with SnCl2 under, comparable ex• perimental conditions (equation 52) to yield a product which

n-BuOH

SnC1 (52) [CpFe(CO)2 ] 2 + SnCl2 • [CpFe (CO) ] 2 2 reflux

contains covalent iron-tin bonds85, and it apparently does

82 not react with PbCl2 . Furthermore, [CpCr(NO)2]2 functions

as a Wurtz coupling reagent when treated with appropriate

organometallic halides, as illustrated in equations (5 3)

thf

[CpCr(NO)2l2 + 2CpFe(CO)2Cl • 2CpCr(NO)2Cl + reflux

[CpFe(CO)2]2 (53)

and (54). Both conversions proceed smoothly in refluxing

thf

[CpCr(NO)2]2 + 2Mn(CO)5Cl * 2CpCr(N0)2C1 + reflux

Mn2(CO)1Q (54)

tetrahydrofuran, but reaction (5 3) is hampered by the fact

that CpFe(CO)2Cl is not particularly stable under the exper•

imental conditions employed. Interestingly, if CpFe(CO)2I

is used in place of its chloro-analogue in reaction (53),

or if reaction (5 3) is allowed to proceed at room temper•

ature for 8 d, detectable amounts of [CpFe(CO)2]2 are not

formed despite the fact that halogen abstraction by the

chromium nitrosyl dimer still occurs. Attempts to extend

this reaction to the preparation of the unknown dimers

[CpM(NO)2]2 (M = Mo or W) met with little success. Hence, - 112 -

when CpW(NO)2Cl is treated with [CpCr(NO)2]2 in thf at reflux

in the usual 2:1 stoichiometry the expected CpCr(NO)2Cl is

formed in good yields, but no nitrosy1-containing complexes

of tungsten can be detected in the final reaction mixture.

Similar reactions carried out in benzene at reflux or in thf

or benzene at. ambient temperature^.also lead to the formation

of CpCr(NO)2C1 as the only nitrosy1-containing product and

no new organometallic products containing molybdenum or

tungsten are isolated.

The reaction between the chromium dimer and Ph^SnCl

in refluxing thf (equation 55) has been recently reported87.

[CpCr(N0)9] + Ph^SnCl "CpCr(NO) „C1 + z 1 J reflux 8 d ^

Cp2Cr2(NO)3(NH2) (55)

The two chromium-containing products are formed in approx•

imately equal amounts, and.it is clear.that halogen abstrac•

tion by the nitrosyl reagent has again occurred. (The exact

nature of the tin product was not ascertained, but it was

not hexaphenyldistannane). The origin of the bimetallic

amido compound in reaction (55) remains uncertain at the

present time, but it is of interest to note that the same

compound can be obtained in 15% yield by heating a toluene

solution of [CpCr(NO)2l2 under gentle reflux for 24 h. This

amido . complex was first isolated as a by-product92, during

the preparation of [CpCr(NO)2]2, and it was presumed to be

formed by the unusual reduction of a Cr-NO linkage in the - 113 -

latter compound to a Cr-NH2 group by the reducing agent

s not employed. Consequently, even though [CpCr(NO)2]2 i-

detectably changed by refluxing in thf for 24 h, it is possible that during the prolonged time (8 d) required to effect completion of reaction (55) some thermal conversion

(involving the reduction of a Cr-NO group by either thf or

Ph^SnCl) into Cp2Cr2(NO)3(NH2) may have occurred.

The principal product from the pyrolysis of [CpCr-

(NO)2]2 is a red-brown cluster compound whose exact formula•

tion has yet to be determined. It is soluble in polar

organic solvents and slightly soluble in toluene. Its solu•

tions exhibit one terminal nitrosyl absorption (at 1670 cm 1)

in their infrared spectra and there are no absorptions

observed due to bridging nitrosyl ligands either in solution,

mull, or KBr disc spectra. The mass spectral data collected

+ at 270° C exhibit fragments of the type (C5H5)3Cr2(NO)3 ,

+ + X (C5H5)2Cr20 , and (C5H5)2Cr . The H NMR spectrum of the

compound in CDC13 consists of a broad complex peak in the

region normally associated with Tr-cyclopentadieny 1 protons.

All of this evidence points to a cluster containing three or

four chromium centres surrounded by cyclopentadienyl and

terminal nitrosyl ligands. With the observation of the for•

mation of the bridging amido-complex in the same reaction

which produces this polymetallic compound, it is not unlikely

that amido bridges may also be present and necessary for the

stability of the cluster complex. It is, however, quite

apparent that this product is not a simple oligomer of - 114 -

[CpCr(NO)]. (Pyrolysis of [CpFe(CO)2]2 leads to the form• ation of [CpFe(CO)] in low yields88).

In view of the reactions of [CpCr(NO)2J2 and

[CpFe(CO)2]2 considered previously in this chapter, it was of interest to determine how the related.manganese dimer,

[(MeCp)Mn(CO)(NO)32, reacts with halogen-containing reactants under comparable experimental conditions. Unfortunately, the manganese compound is quite thermally labile and reacts

with SnCl2 in refluxing thf to produce only intractable decomposition products which do not contain carbonyl or nitrosyl ligands. In fact, the dimer itself readily decom• poses in refluxing thf and is converted in low yields into

(MeCp)Mn(CO)3 and (MeCp)3Mn3(NO)4 as the only detectable organometallic carbonyl and nitrosyl products.

The new trimetallic compound forms black crystals which are freely soluble in common organic solvents (except paraffin hydrocarbons) to give air-stable green-black solutions. When heated in an open capillary the crystals decompose at 15 7° C. The 1H NMR spectrum of the compound consists of two sharp resonances at 6 4.78 and 1.83 of rel• ative intensity 4:3, thereby indicating the equivalence of the three methylcyclopentadienyl rings and the diamagnetism of the.compound. The IR spectrum in dichloromethane exhibits three strong bands at 15 38, 1483, and 1333 cm 1 attribu• table to bridging nitrosyl groups. The major peaks in the

mass spectrum of the compound are due to the ions (C^H^)3 ~

+ + Mn3(NO)x (x •= 4, 2, or 1) and (C6Hy)2Mn2(NO)y (y = 2 or 1) , - 115 -

the (CgH7)3Mn3(NO) ion being the most abundant. The com• pound is thus apparently isostructural with its cyclopenta•

dienyl analogue, Cp3Mn3(NO)4, which possesses three doubly bridging nitrosyl groups and one triply bridging nitrosyl group 8 9 .

Selective Removal of Halogen from Organic Halides.

An extension of the study of the chemical reactivity of [CpCr(NO)2^2' Particularly its halogen abstraction ability, is an examination of the effectiveness of the dimer as a reagent for the dehalogenation of organic substrates. The studies can be divided into two parts:

(1) the reaction of [CpCr(NO)2]2 with benzylic, allylie, and alkyl halides, and

(2) the reaction of [CpCr(NO)2]2 with vic-dihaloalkanes.

There are many reagents which effectively couple benzylic and allylie halides90. Similarly, the reaction of the nitrosyl dimer with diarylhaloalkanes results in the - 116 -

formation of the corresponding substituted ethanes (equation

56). However, unlike other coupling reagents, the nitrosyl

R' R1 R* 1 1 1 (56) (bb) 2 R2C-X - R2C-CR2 R = oryl i R'= aryl or H complex does not couple allyl or methallyl halides. In fact,

[CpCr(NO)2]2 does not even react with allyl halides or most simple alkyl or aryl halides, and the organic compounds may be recovered unaltered. For instance, no halogen abstrac• tion occurs from 3-chloropropene, 1-chloropqntane,

2-chloro-2-methylpropane, 1-bromo-2-phenylethane, 1-bromo-

2-phenylethene, or iodobenzene.

However, in contrast to this, [CpCr(NO)2]2 does react with vic-dihaloalkanes in a 1:1 ratio to produce the corresponding alkenes. Some typical transformations are shown below. Total dehalpgenation occurs in all reactions

(trans) - 117 -

trans-dibromide of cholesterol

producing the expected CpCr(NO)2Br and, more importantly, the olefins are isolable in >75% yields.

Since it was observed that no reaction occurred be•

and tween [CpCr(NO)2]2 non-vicinal non-benzylic haloalkanes, an attempt was made to perform selective vicinal halogen abstraction from vic-dihaloalkyl halides with the hope of leaving the third halogen unperturbed. Two such reactions have been studied to date and have resulted in the isolation of the desired haloalkene products in good yields (equations

5 7 and 5 8) .

57 C6HgCHBrCHBr2 • (^HgCH = CHBr 73% < > - 118 -

(58)

trans- dibromide of cholesteryl bromide

Consequently, as long as the remaining halide is non-benzylic, the nitrosyl dimer can apparently be used to effect such transformations generally. Similar reactivity is shown only

91 by the NaCH2S(0)CH3 reagent but it is not widely applic• able since it may also effect dehydrohalogenation. On the

other hand, [CpCr(NO)2]2 is specific to halogen only, can be used stoichiometrically, and is effective in very short per• iods of time (4 - 12 h) under very mild conditions.

Finally it should be noted that the nitrosyl com• plex appears to show no preference for cyclic or exocyclic halogens. Furthermore, although only trans-stilbene was isolated as a product from the dehalogenation of 1,2- dibromo-1,2-diphenylethane, the stereochemistry of these transformations has not yet been completely studied. - 119 -

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R.E. Botto, B.W.S. Kolthammer, P. Legzdins and J.D. Roberts. Carbon-13 and Nitrogen-15 NMR Spectroscopy of Some (n5- Cyclopentadienyl)nitrosyl Complexes of Group 6B Elements. Inorg. Chem., in press.

T.J. Greenhough, B.W.S. Kolthammer, P. Legzdins and J. 5 s a Trotter. [ (n -C5H5)Cr(CO)2]2 / Novel Organometallic Complex Possessing a Cr = S = Cr Linkage. .J. Am. Chem. Soc, submitted for publication.

T.J. Greenhough, B.W.S. Kolthammer, P. Legzdins and J. Trotter. The Thionitrosyl Ligand; Molecular Structure of Dicarbonyl(n5 -cyclopentadieny1)thionitrosylchromium. J. Chem. Soc, Chem. Commun., 1036-1037 (1978).

B.W.S. Kolthammer and P. Legzdins. Organometallic Nitrosyl 5 Chemistry. 7. Evidence for the Existence of (n -RC5H4)-

Mn (CO) (NO) I (R = H or CH3) . Inorg. Chem. , 18_, 8 89-891 (1979) ..

5 B.W.S. Kolthammer and P. Legzdins. Preparation of (n -C5H5)-

Cr(CO)2(NS). The First Organometallic Thionitrosyl Complex. J. Am. Chem. Soc., 100, 2247-2248 (1978).

B.W.S. Kolthammer, P. Legzdins and D.T. Martin. Selective

Removal of Halogen from Organic Halides Using [(n-C5H5)-

Cr(NO)2]2. Tetrahedron Lett., 323-326 (1978).

B.W.S. Kolthammer, P. Legzdins and J.T. Malito. Organo• metallic Nitrosyl Chemistry. 4. Additional Reactions of Nitrosyl Chloride with Neutral Carbonyl Complexes. Inorg. Chem., 16, 3173-3178 (1977).

B.W.S. Kolthammer and P. Legzdins. Organometallic Nitrosyl Chemistry. Part 3. Some Aspects of the Chemistry of Bis[(n-cyclopentadienyl)dinitrosylchromium]. J. Chem. Soc, Dalton Trans. , 31-35 (1978) .

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