Preparation of New Cyclopentadienyl Molybdenum Carbonyl Complexes

PREPARATION OF NEW CYCLOPENTADIENYL MOLYBDENUM

CARBONYL COMPLEXES

KABONGO JOACHIM BUKASA

THESIS

submitted in fulfilment of the requirements

for the degree

MASTER OF SCIENCE

CHEMISTRY

in the

FACULTY OF SCIENCE

at the

RAND AFRIKAANS UNIVERSITY

SUPERVISOR: PROF. H.G. RAUBENHEIMER

JANUARY 1997 OPSOMMING

Die bereiding en die karakterisering van nuwe siklopentadienielmolibdeen-karbonielkomplekse is bestudeer. 'n Unieke isomeriese ewewig sowel as 'n nuwe pakkingspatroon van siklopentadieniel- (trikarboniel)molibdeenbromied is ook beskryf.

Die siklopentadienielmolibdeen-karbonielkomplekse, [CpMo(C0)31q, is berei vanuit [CpMo(C0)3X]- tipe verbindings wat reageer met alkiellitiums. [CpMo(C0)3I] is gereageer met fenielasetiliedlitium om [Cp(C0)3/vIoC--=-CPh] (1) te vorm. Die kristalstruktuur van verbinding 1 is bepaal en dit toon dat die lengte van die drievoudige binding korter is as enige van die bekende asetiliedkomplekse. Indien 1 gereageer word met elektrofiele CF3SO 3CH3 of (CH3)2SO4 word die kationiese kompleks [Cp(C0)3.Mo=C=C(CH3)(Ph)1 + (4) verkry. [CpMo(C0)31] is ook behandel met 1,3- ditianiellitium on [Cp(C0)3Moe(H)SCH2CH2CH2S] (2) te vorm en met metiellitium om die bekende verbinding [CpMo(C0)3CH3] (3) te vorm. Verbinding 2 kan maklik gedeprotoneer word op die gekoordineerde koolstof, , maar verdere reaksies was onsuksesvol.

[Cp(CO)3MoC=C(Ph)C(=S)S] (5) is verkry deur middel van 'n (2+2)-sikloaddisie reaksie van CS2 me 1. Omdat hierdie CS2 adduk nie gealkileer kon word nie, is addisionele eksperimente gedoen met Mo- verbindings waar 'n CO-ligand gesubstitueer is met PPh3 en PMe3. [CpMo(C0)3I] is met PPh3 gereageer om [CpMo(CO)2(PPh3)I] (6) te vorm. Verbinding 6 is 'n stabiele en goed gekarakteriseerd verbinding. [Cp(C0)2(PPh3)MoCCPh] (7) is verkry deur die reaksie van fenieletiniellitium met 6. [Cp(C0)2(PPh3)MoC=C(Ph)C(=S)S] (8) is verkry deur 7 met CS2 te behandel.

[CpMo(C0)3I] is met PMe3 gereageer om twee isomere [CpMo(CO)2(PMe3)I] (cis- 9) en (trans - 9) te vorm. Hierdie twee isomere is geisoleer en daar is waargeneem dat die cis-isomeer in oplossing stadig

omgeskakel het na die trans-isomeer. Die waarneming dui op 'n isomeriese ewewig. Cis - 9 en fenieletiniellitium is gereageer om [CpC0)2(PMe3)MoCE---CPh] (11) te vorm.

Laastens, gedurende onsuksesvolle pogings om die dimeriese verbinding [CpMo(CO)3]2 met alkiel- er ariellitium te reageer is die bekende verbindings [ri 5-CpMo(C0)3C1] en [1'e-CpMo(C0)3Br] (12) as 11 kristallyne produkte gevorm. Die kristalstruktuur van die neutrale kompleks 12 is bepaal. Bindings- lengtes in die molekules wat daarin saampak het baie ooreengestem met die literatuurwaardes van dieselfde kompleks. Verbinding 12 het egter 'n ander pakkingspatroon getoon. 111

SUMMARY

This study comprises the preparation and characterisation of new cyclopentadienylmolybdenum carbonyl complexes. In addition, an unique isomeric equilibrium as well as the new packing pattern of the known compound of cyclopentadienyltricarbonylmolybdenum bromide is also described.

The cyclopentadienylmolybdenum carbonyl complexes have been prepared from precursors of the type [CpMo(C0)3X] which reacts with alkyllithium reagent to -afford [CpMo(CO)3R] compounds. [CpMo(C0)3I] reacts with phenylacetylide lithium to form [Cp(C0) 3MoC-CP11] (1). The X-ray crystal structure of compound 1 has been determined and reveals that the length of the triple bond is somewhat shorter than any of the other known acetylide complexes. Treatment of 1 with the electrophiles CF3SO3CH3 or (CH3)2SO4 gives the cationic complex [Cp(C0)3Mo=C=C(CH3)(Ph)r CF 3S03" (4).

[CpMo(C0)3I] reacts with 1,3-dithianyllithium to form [Cp(C0)3Moe(H)SCH2CH2C1121 (2) which can easily be deprotonated on the coordinated carbon. [CpMo(C0) 3I] also reacts with methyllithium to form [CpMo(CO)3CH3] (3) which is a known compound.

The reaction of CS2 with 1 which occurs by a (2 + 2) cycloaddition affords [Cp(CO)3MoC=C(Ph)C(=S)S] (5). As we could not alkylate this CS 2 adduct, additional studies with molybdenum compounds in which a CO ligand has been substituted with PPh 3 and PMe3 have been carried out.

[CpMo(C0)3I] reacts with PPh3 to form [CpMo(CO)2(PPh3)I] (6), a stable compound, known and well characterised. The compound 6 also reacts with phenylethynyllithium to form [Cp(C0)2(PPh3)MoCE---CPh] (7). Treatment of 7 with CS2 leads to [Cp(C0)2(PPh3)MoC=C(Ph)C(=S)] (8).

[CpMo(C0)3I] reacts with PMe3 to yield two isomers [CpMo(CO)2(PMe3)I] (cis-9) and (trans- 9). These two isomers were isolated and we observed that in solution the cis isomer was slowly transformed into the trans isomer which indicated the existence of an isomeric equilibrium. Cis-9 react: with phenylethynyllithium to form [Cp(C0)2(PMe3)MoCCP11] (11). iv

Finally, during unsuccessful attempts to react the dimeric compound [CpMo(CO)3]2 with alkyl and aryllithium, the known compounds [115-CpMo(C0)3C1] and [re-CpMo(C0)3Br] (12) were produced in crystalline form. The X-ray crystal structure of the neutral complex 12 has been determined and the molecular structure has bond distances and angles very similar to the literature values of the same compound. However, the compound 12 exhibits a different packing pattern in the unit cell. V

ACKNOWLEDGEMENTS

I would like to express my gratitude to all who supported and encouraged me during this project. In particular I would like to thank the following people and institutions: Professor H.G. Raubenheimer for his supervision and encouragement through out the duration of this project Professor G.J. Kruger and Katherine for crystal structures determinations Dr Linda van der Merwe for running the numerous NMR spectra _ Dr Hugh Laue for help in proof-reading this manuscript Mr. Fanie Nel for using NCP's facilities in editing this thesis Sarii and Susan for the Afrikaans translation of the summary To my wife Alphonsine for her encouragement and my children Carolle, Danny, Sarah, Zenas and Priscille for their patience The FRD and RAU for financial assistance To my Lord Jesus Christ for strength and encouragement through the Holy Spirit. vi

CONTENTS

OPSOMMING SUMMARY iii ACKNOWLEDGEMENTS CONTENTS vi ABBREVIATIONS viii

CHAPTER 1 INTRODUCTION AND AIMS

1.1 General background 1 1.2 Aims and objectives 9

CHAPTER 2 PREPARATION OF PHENYLACETYLIDE, 1,3-DITHIANYL AND THIAZOLYL-MOLYBDENUM PRECURSORS

2.1 Introduction 12 2.2 Results and discussion 15 2.2.1 Preparation of cyclopentadienyl(phenylacetylide)tricarbonylmolybdenum 15 2.2.2 Preparation of cyclopentadieny1(1,3-dithianyl)tricarbonylmolybdenum 16 2.2.3 Preparation of cyclopentadienyl(methyl)tricarbonylmolybdenum 17 2.3 Conclusions and further work 26 2.4 Experimental 27 vii

CHAPTER 3 DERIVATIZATION OF A MOLYBDENUM ACETYLIDE COMPLEX

3.1 Introduction 31 3.2 Results and discussion 32 3.2.1 Vinylidene molybdenum [Cp(CO)3 Mo=C=C(Ph)(CH3)] 32 3.3 Unsaturated addition complex 5, phosphine complexes 6 and 7, CS2 adduct 8, isomers cis-9 and trans-9 and the-phosphine acetylides 11 39 3.3.1 Introduction 39 3.3.2 Results and discussion 40 3.4 Experimental 60

CHAPTER 4 CRYSTAL AND MOLECULAR STRUCTURE DETERMINATION OF TWO MOLYBDENUM COMPLEXES

4.1 Introduction 64 4.2 Results and discussion 65 4.2.1 Structure of [Cp(C0)3MoCECP11] 65 4.2.2 Structure of [CpMo(CO)3Br] 69

REFERENCES 73 viii

ABBREVIATIONS

A Angstrom (10-1° m) Cp Cyclopentadienyl IR Infrared MP Melting point MS Mass spectrometry NIMR Nuclear Magnetic Resonance Ph Phenyl PPin Parts per million THF Tetrahydrofuran

S Chemical Shift (ppm) d Doublet Iltiplet Singlet

t Triplet

st Strong w Weak 1

CHAPTER 1

INTRODUCTION AND AIMS

1.1 General background

Since ferrocene was first proposed as a sandwich compound in 1952, the field of organometallic chemistry has experienced explosive growth.

Metal carbonyls are one of the most widely occurring organo transition metal compound types. Many experiments carried out in our laboratory as well as in other laboratories worldwide often use homoleptic metal carbonyls as starting materials for the preparation of many other organometallic compounds. A family of compounds called half-sandwich complexes, have a "piano stool" structure with cyclopentadienyl as the seat and from three to four ligands serving as the "legs." These legs may also be carbonyl ligands.

The following compounds serve as typical examples of such half- sandwich complexes:

0 ff Mn CO co O C / / \ OC/ /m°-- co OC 'CO CO co CO CO

When ligands making up the legs are good n-acids such as CO or NO, such complexes adhere rigorously to the "18 electron rule" but when poor n-acceptor ligands are present, they may not satisfy this rule.

The cyclopentadienyl ligand has become one of the most extensively used ligands in organo transition metal research. Ten distinct bonding modes for the C5H5 ligand have been structurally 2 characterized up to 1996. 1 The is-05H5, C5H5 and 1 1 - C5H5 ligands are of particular interest due to their interconversion chemistry called "ring slippage." 2-6

5 3 1 1 11 11 1

The cylopentadienyl ligand has the ability to stabilize metals in both low and high oxidation states as indicated above, and it also has the ability to bond through one to five carbon atoms. This should explain its widespread use in synthetic and catalytic applications. A practical example of ring slippage i Casey's observation that n 3-05H5 and ill-05H5 are intermediates in the reaction of (1 5-05H5)Re(C0)3 with PMe3 as is shown below.' In this manner all the intermediates and products are 18 electron systems.

H PMe3 _ PMe3 'PMe3 0C-- _-Re 0C—iRe —CO 0C- 7 N; • PM e3e3 CO CO PMe3 tO CO

Re 0C- - / CO PMe3• Scheme 1 3

The non-nitrosyl containing compound [(r1 5-05H5)-Re(C0)31 reacts reversibly with PMe 3 at +64°C to give a stable compound [(r1 1-05H5)Re(C0)3(PMe3)2]. 8 The only reasonable 18-electron structure for this intermediate contains a 11 3-051-15 group.

The "half sandwich" compounds used in the present study are firstly a dimeric compound [CpMo(C0)3]2 and then also its derivative which is of the [CpMo(CO)3 X]- type ( X= Cl , Br , I ) .

The structure of the dimer has been redetermined in 1974 and it consists of two Cp(CO)3Mo halves joined by an unbridged Mo - Mo bond . The metal - metal bond length is 3.24 A° . 9

CO OC F CO Mo

1,4( OCR/ 0 CO CO Scheme2

1.1.1 Reactivity of [ CpMo(CO)3 ]2 Our focus here centres on two types of reactions to illustrate the versatility of the system: those that occur with retention of the Mo-Mo bond those that result in rupture of the Mo-Mo bond and formation of complexes of the [CpMo(C0)3X]-type.

1.1.1.1 Reactions in which the Mo-Mo bond is retained

CO-substitution reactions A variety of two-electron donor ligands (including phosphines, isocyanides and phosphites) can displace only one or, consecutively, two carbonyl groups to afford the following types of derivatives :

Cp(CO)3Mo — Mo(CO)3Cp + L Cp(CO)3Mo —Mo(CO)2LCp + CO (1)

Cp(CO)3Mo—Mo(CO)2LCp + L Cp(C0)2LMO— Mo(CO)2LCp + CO (2)

Although we know from the literature that a large variety of reactions have been carried out with [Cp2Mo2(CO)n] (n = 4 or 6, see below) and that during the production of new dinuclear complexes the Mo-Mo bond is retained (among these are sulfur compounds), 1° particular attention will here be paid to an interesting reaction in which CO loss from the dimer in the absence of nucleophiles occurs. One carbonyl is ejected from each molybdenum centre and the complex Cp(C0)2MomMo(C0)2Cp forms_ 11'12 The unsaturated Moa-Mo triple bond is susceptible to reaction with a wide range of nucleophiles under mild condition (Scheme 2). 13,14

[CpMo(C0)312 1-2C0 110 - 1500C C •ON CN [Cp(C0)2Mo----Mo(C0)2CP] NO [M]=NO [M]—[ RC°CR\itr2CN2

Nr2

Scheme3 [1\4] = Cp(CO)2Mo ; X2 = 12, RSSR, HI

As a further example, an interesting study has been carried out involving alkynes and [ Mo2(C0)4CP2 forming 1:1 adducts (see III below). In these 1:1 adducts the alkyne acts as a four donor bridging the /R CKt

OC / cp

0C—Mo Mo

Cp CO

R = H, Et, Ph 5 metal-metal bond . The structural arrangement in compounds such as (III) arises as a consequence of steric crowding on formation of the alkyne adduct." According to the nature of the substituents on the alkyne, the complex (HI) reacts further with alkynes. The solvent used in this case is octane. The following results have been reported :

Treatment of the 1:1 adduct (R= Ph) with C2Ph2 gives exclusively (IV)

= R2= Ph

Cp Mo Mo--Cp

\r/ O (IV)

Treatment of the 1:1 adduct (R=H) with alkynes progresses with loss of CO , to the formation of

[Cp2Mo2 (RC -R) 4 .1 complexes in which all four alkyne moieties are linked into one C8R8 ligand 16

• Cp Cp

R2 Ri = H R2 = CO2Me 6

The dimeric complex of molybdenum [ Mo(C0)3CP]2 further reacts via [Mo(CO)2Cp]2 to form [Mo(C0)2Cp2(P-C8H8)l-

Cp (v1) This complex (VI), isomerizes in polar solvents to form a pseudo sandwich compound(VII).

Mo CO

CO Cp

(VII) In the work described in this dissertation no neutral alkynes were involved, but a deprotonated alkyne was coordinated in a a-fashion to molybdenum in some experiments.

1.1.1.2 Reactions in which there is rupture of the Mo—Mo bond The direct reactions of [CpMo(CO)3]2 with oxidizing agents , e.g. halogens result in the rupture of the Mo-Mo bond and formation of complexes of the [CpMo(C0)3X]-type. Simple subsequent carbonyl substitution with two-electron donors, e.g. phosphines, affords numerous covalent complexes that can also undergo a further oxidation addition. (reactions 3 and 4).

[CpMo(CO)3X] + nL 1 CpMo(C0)3-nLnX + nCO (3)

CpMo(C0)3-nl-nX + X2 CpMo(C0)2-nLnX3 (4) i = [CpMo(CO)X]2

[CpMo(CO)3X] - compounds are useful starting materials in organometallic synthesis and have also been used in the present work. Another reaction that does not necessarily follow the same route a the substitution in (3), is the reaction of alkynes with [CpMo(CO)3X]. Such reaction results in three different product types:

[CpMo(C0)(i-C2R2)X] ii [CpMo(i1-C2R2)2X] iii complexes formed by coupling of alkyne units.

For example, treatment of [CpMo(CO) 3X] (X= CI, Br, I) with C2Ph2 results in the formation of the tw , complexes [CpMo(C0)(r1-C2Ph2)X] and [CpMo(C0)(i 4-C4P114)X1. 17 Contrary to the initial expectation , treatment of [CpMo(CO)3 X] (X = Cl) with C2R2 (R = Me, CF 3) leads to [CpMo(n-C2R2)2X]." Two alkynes displace three carbonyl groups to afford 16 electron complexes. Further reactions of the prodixt are shown in Scheme 4. 8

[CpMo(CO) 3X]

—R

+ c- r -X- R \o2(CO)8 r(0 / Cp R Co2(C0)8 \ M° R Mo ..••• OC Ro R OC CO Scheme 4

In the present research, X in [CpMo(CO)3X] was substituted with an alkynyl by transmetallation to give a reactive stable compound for further reactions.

1.1.2 Infrared Spectroscopy

Spectral characteristics of carbonyl complexes The infrared spectrum is extremely useful for the characterization and identification of complexes containing carbonyl ligands and has been utilized in this work. The intense v(CO) bands of carbonyl- containing metal complexes are found in a region of the infrared spectrum largely free of other absorption bands ( see Table 1). The type of carbonyl ligand present in a compound can be identified by the position of the carbonyl frequency.

Table 1: Type Carbonyl Frequencies - M-C-0+ Terminal CO 2140 - 1800 cm' 9

0 Doubly bridging 1850 - 1700 cm"' II C 1,4-m

0 Triply bridging down to - 1625 cm' II C

1 0M 4

CO Free 2143 cm'

Furthermore, the number and frequency of the CO stretching bands are also helpful in assigning their geometric arrangement in space. The course of a reaction can also be monitored by measuring changes in the stretching carbonyl frequencies. The number of IR active bands cannot exceed but may be less than the number of CO groups in the complex. n-Backbonding from the metal reduces the v(CO) frequency due to a lowering in CO bond order. Thus, in general, anionic carbonyl complexes have lower, and cationic carbonyl complexes highe v(CO) frequency values than their neutral isoelectronic complexes. °

1.1.3 13C NMR spectroscopy

'3C NMR data are also useful in the identification of carbonyl complexes. The chemical shifts typically occur in the 200 - 230 ppm region. NMR spectroscopy ('H & ' 3C) can distinguish between ch and trans groups. Carbene character in M- C bonds can also be characterized quite easily since the carbene carbon'exhibits carbocation characteristics.

1.2 Aims and objectives of the present study

In this thesis , the focus centres mainly on the reactivity of the molybdenum dimer [CpMo(CO)3]2 and the preparation and reactivity of its derivatives of the type [CpMo(CO)3R]. These two types of compound are linked by the useful synthetic scheme below (Scheme5) in which two route toward the final product type are outlined. We did not plan to use route 2, but rather 1 a as strategy A t

10 prepare the complex [CpMo(CO)3X] and then lb as strategy B with an alkyllithium reagent to afford [CpMo(CO)3R] complexes.

Mo(CO

C101-11 2

[115-05H5Mo(COM2

l a X2/ lb R N2 [15-05H5Mo(C0)3X] 1°. [-ri5-05H5Mo(COR] LiR X = Cl, Br, I R = Me, Et

Scheme 5 Lithiated thiazole reagents are being used in our laboratory to prepare, by transmetallation, compound! which can be transformed into carbene complexes by protonation or alkylation. In these specific cases, the chromium group 6 halides anion, [(C0) 5MCLI (M= Cr, Mo, W),20 the iron(II) chloride [CpFe(C0)2C1]21 as well as the gold(I) chlorides [Au(Cl)tht] and [Au(COPPh3], 27-23 are used to form ti initial thiazolyl complexes. The intention in the present study was also to follow this same procedure and to use a complex of molybdenum to prepare various precursor thiazolyl complexes which would then be protonated or alkylated as follows:

r.,44 (N Cp(C0)3Mo Cp(C0)3Mo ==c S

Thiazolyllithium, methylthiazolyllithium and benzylthiazolyllithium were the reagents of choice. CH3 Li-

Carbene formation, was not the only process to be investigated. Other pertinent questions relating to cyclopentadienyl molybdenum carbonyls to be addressed were:

(I) Does phenylethynyllithium react with the [CpMo(CO)3X]- type of compound to form acetylide derivatives, and could such a product be used in further transformations? 24'25 Especially the pioneering work of Selegue using iron compounds (see summary of this work in Chapter 3) 26 would have to be compared with new results in the molybdenum field. A specific goal was the subsequent reaction with CS2 and then, again, conversion to a carbene complex (vide infra).

(ii) Could the transmetallation product between [CpMo(C0) 3I] and lithiated 1,3-dithiane, successfully be functionalized by initial a-deprotonation (the proton is activated by the two neighbouring sulphurs or desulphurization (according to Corey and Seebach) 27 to afford an [M]CHO compound. Both these conversions, although now part of mainstream organic chemistr3 have not yet been explored in organometallic synthesis.

Our final aim with the present study was to investigate the interaction of the carbonyl ligands in the neutral dimer [CpMo(CO) 3]2 with alkyllithium reagents. Apart from the work by Stone (expounded in Chapter 428), no other results have yet been reported.

CHAPTER 2 PREPARATION OF PHENYLACETYLIDE, 1,3 DITHIANYL AND THIAZOLYL MOLYBDENUM PRECURSORS

2-1 Introduction

Transition-metal acetylide complexes CpL-r1MCCR are fairly common precursors to vinylidene complexes. Their structural features and reactivity provide an opportunity to explore transition-metal substituent effects upon GEC triple bond properties. Acetylide complexes of electron-donating L, 1M- units (M= metal, Li= ligands) should be nucleophilic at Co of LiM— C = C - R due to the resonance

LiaCL -CC--- —R —R forms We have made the cyclopentadienyl phenylacetylide tricarbonyl molybdenum complex [CpMo(C0)3(C-=-CPh)], with the purpose of using it in the preparation of cationic vinylidene carbene complexes (see Chapter3). Ipaktschi in 1993 discovered an interesting pathway for the synthesis of vinylidene metal complexes. He was attempting the preparation of the chiral alkoxycarbene complexes {(n5-05H5)(C0)(NO)Mo[=C(OCH3)(C-=CR)]) from [(n5-051-15)(C0)2(NO)Mo] by the general Fischer methodology when he unexpectedly isolated a (methyl)phenyl vinylidene compound (Scheme 2.1). 29

1) —R' Mq Mo 2)CF3 S03 CH3 N OTC /N R'= C6H5 at Scheme 2.1 13

The formation of ((n5-C5H5)(CO)(NO)Mo(=C=CR'CH3)) apparently proceeds via an associative or a single electron transfer (SET)- induced dissociative process and affords after elimination of a CO molecule, the anionic alkynylmolybdenum complex (2.1) as an intermediate before alkylation.

Mo Li+ N C 0 N C\ R' 0

2.1 This intermediate compound is alkylated by methylfluoromethanosulfonate to yield the vinylidene complex (Scheme 2.1). Both possible mechanistic pathways could be facilitated by the strong TC acceptor effect of the NO ligand in [(n 5-C5H5)Mo(CO)2(NO)].

Sterzo, in 1995, focused on iodide complexes of the type [CpM(CO) nI] ( M=Mo , W, n=3; M=Ru, n=2). These complexes react with some representative tributyltin acetylides 30 Bu3Sn-CC-R (R=H, Pr, Ph) in the presence of a catalytic amount of [(CH3CN)2PdC12] to produce acetylide product! (Scheme 2.2).

[(CH3CN)2PdC12], 25 0C (0C)nMI + Bu3Sn—C--=-C —R a (0C)3MC -C —R - Bu3SnI

Scheme 2.2

The reaction takes place at room temperature with stirring overnight. The stannyl derivative in slight excess, produces the active Pd catalyst via the in situ reduction of the [(CH3CN)2PdC12]. In the absence of palladium, or when PdC12 (which is not reduced to Pd(0) under the ruling reaction 14

conditions) is used, the coupling reaction does not occur and the starting materials are recovered unchanged. This shows that Pd(0) is probably the active species in promoting the coupling reaction.

Villernin and Schigeko" synthesized cr-alkyne organometallic compounds from phenylacetylenc and organometallic halides using copper(I) iodide in triethylamine (Scheme 2.3).

Et3N Et3NH±X

C6H5C --CH C6H5CCu CuI [MLI]

+ C6HSC= CML

M = Mo, W, Pt L = Cp(CO)3 Scheme 2.3

The purpose of preparing metal-a-acetylide compounds has been to explore their role as models and precursor ligands in the preparation of polyalkyne polymers containing transition metals in the main backbone chain. As will be indicated in chapter 3, metal a-acetylides can also be used in other transformations in the presence of transition metals.

In our laboratory, the cyclopentadienyl phenylacetylide tricarbonyl molybdenum compound [Cp(C0)3MoC=CC6H5] has now been successfully prepared. The product was obtained in a good yield of 90% and in a shorter period of time (2 hours) than Sterzo's reaction discribed above (overnight). The preparation of the known compound [Cp(CO)3MoCH3], 32 according to the same transmetallation method, proved more successful than the literature procedure and the methylated product could be obtained in 78% yield. Cronje" recently made a cationic (thio)carbene complex of iron. The preparation involves the - addition of 4-methylthiazolyl- or benzylthiazolyllithium to an iron chloride complex [CpFe(CO)2C1] to form thiazolyl complexes. These thiazolyl complexes may be protonated with CF3SO3H to afford the corresponding cationic thiazolinylidene complexes (Scheme 2.4) 15

H +

/C1 Li —e) H+ e CF3SO3

CO CO CO CO CO

CH3

Or Scheme 2.4

We attempted the same method for the preparation of molybdenum thiazolidene complexes. Unfortunately, the experiments were unsuccessful. A reason could be that the substitution does not occur at the low temperature (-50°C) necessary to avoid decomposition of the thiazolyllithium precursors. This assumption was strengthened by the fact that both LiMe and LiCECPh only substituted a halide at -30°C. We successfuly lithiated 1,3 - dithiane in order to utilize it for transferrinE a dithianyl group to the metal. The preparation of cyclopentadienyl 1,3 - dithianyl tricarbonyl molybdenum was accomplished in THF-hexane as solvent. Our attempts to explore the properties of th new products are described in the next chapter whereas all the initial preparations are discussed in this chapter.

2.2 Results and discussion

2.2.1. Preparation of cyclopentadienyl(phenylacetylide)tricarbonylmolybdenum, 1 The neutral cyclopentadienyl(phenylacetylide)tricarbonylmolybdenum was prepared by reacting phenylacetylide lithium with [CpMo(C0)3I] in THE at - 30°C. The neutral complex was obtained as a yellow powder after purification by column chromatography. Dissolving the yellow powder in CH2C12/hexane and cooling of the solution to -25 °C afforded yellow crystals (Scheme 2.5).

Mo — I + Li—C —C / I OC NCO CO 1 Scheme 2.5

A complete, single crystal X-ray structure determination of this complex was carried out. It represents the first example of a carbonyl- containing molybdenum acetylide characterized in this manner.

2.2.2. Preparation of cyclopentadieny1(1,3 -dithianyl)tricarbonyl molybdenum, 2 1,3-Dithiane was lithiated with BuLi in THF-hexane at - 30 °C 27 and the temperature was allowed to rise to 10 °C. The lithiated dithioacetal reacted in THE at -30 °C with [CpMo(C0)3I] to afford the 1,3 dithianyl complex of tricarbonyl cyclopentadienyl molybdenum, after purification by column chromatography and crystallization from CH2C12/hexane. This complex, unexpectedly, is exceptionally sensitive to air .

S)_ > + BuLi—THE Hexane 0 ). Li S -30 ---111" + 1 0 C S

0/ 1 6 S / O -I Mo LiI Li CO M \ CO CO/ ICoNC 3S CO CO 4 2

Scheme 2.6 17

2.2.3. Preparation of cyclopentadienyl(methyl)tricarbonyl molybdenum, 3 The preparation of methyl cyclopentadienyl tricarbonyl molybdenum complex involves the addition of LiMe in excess to a solution of [CpMo(C0) 3I] in diethylether. After completion of the reaction the solvent was removed in vacuum and the residue chromatographed on Si0 2. Ether/hexane 1:1 was used as eluent. The final product was obtained as an air stable, yellow, microcrystalline powde

her Mo —I + LiMe et MO - Me

COO I CO \ CO COC O CO 3 Scheme 2.7

Using longer reaction times in these three preparations did not improve the yield but resulted in the formation of the unwanted dimer [CpMo(C0)3]2-

Spectroscopic characterization of [Cp(C0)3Mo—CPh] (1) [Cp(C0)3MoCHgCH2CH2CH2k] (2), [CpMo(C0)3CH3] (3)

The numbering system indicated below will be referred to in the NMR spectroscopy for the assignment of peaks and in the IR characterization tables.

Mo —C C OCZ 8 7 0 ° 18

1-NMR spectroscopy The 'H NMR data and ' 3C NMR data for complexes 1, 2, and 3 are summarized in Tables 2.1 and 2.2. The proton resonances of the cyclopentadienyl ligand in complexes 1, 2 and 3 are shifted somewhat upfield (8 5.54 , 5.52 and 5.28) compared to the proton resonances of cyclopentadienyliodotricarbonyl molybdenum at 8 5.59.This indicates a small increase in electron density, probably due to the diminishing n-acceptor ability of the new ligands which is especially true for Me being known for having a positive inductive effect. In free 1,3- dithiane the CH2 protons H4 an H6 are equivalent. In complex 2, however, the IFINMR shows three non-equivalent CH 2 proton resonances at 8 3.01, 2.47 and 2.09. These multiplets indicate that each a-thio CH2-group is in a different chemical environment. The '11NMR spectrum complex 3 shows one signal for the CH3 group at 8 0.36 that peak for a high electron-density on this group and is partly in contradiction of the shift towards high field found for the cyclopentadienyl group in this complex.

Table 2.1 'H NMR data for complexes (1), (2) and (3)

Complex* 8 (Assignment

1 5.54 (5H, s, Cp) 7.22 (5H, m, C6H5)

2 5.52 (5H, s, Cp) 4.40 (1H, s, CHS2) 3.01 (2H, m, H4 orH6) 2.47 (2H, m, H4 and H6) 2.09 (2H, In, H5)

3 5.28 (5H,s Cp) 19

0.36 (3H, s, CH3)

*Measured in CDCI3 relative to internal TMS.

The 13C-ell) NMR data for the new complexes are summarized and assigned in Table 2.2. These show that carbonyl groups for complexes 1, 2 and 3 resonate respectively at 5 238.8 and 222.3 for 1; at 5 240.0 and 226.6 for 2 and at 5 226.6 for 3 (3 shows one peak the cis-due to too low concentration) which showed the characteristic number of peaks with the correct intensities, and the absorbances were in the correct region of the spectrum. Furthermore the chemical shift follows the order l< 2 — 3.

Table 2.2

13C NMR for complexes (1), (2) and (3)

Complexes* 5(Assignment)

1 238.8 CO 222.3 2C0 130.9 C2 & C6 129.4 C4 127.9 C3 & C5 127.2 Cl 126.0 C8 87.3 C7 93.0 C5H5 240.0 CO 226.6 2C0 93.7 C5H5 37.3 C2 & C4 20

26.7 C3 21.4 Cl

3 226.6 CO 92.4 C5H5 -22.3 CH3

*Measured in CDC13 relative to internal TMS

Both C7 and C8 carbons in complex 1 (8 87.3 and 126.0) resonate at higher chemical shifts than in free acetylene (wherein these signals appear at 8 77.6 and 83.6). Also, the coordinated carbon is much mon

shielded in complex 3 5 - 22.3 than in the other two compounds (2: 5 21.4). This comparison can only be drawn from the given results if one remembers that the two cis ligands have stronger signals than th one trans, and in addition that the trans signal could not be seen in the spectrum of compound 3 due tc too low concentration. The relative carbonyl positions above could mean that the ligand in 1 is transferring more negative charge on to the carbonyl carbons than the other ligands. Unfortunately this result could not be substantiated by infrared measurements (vide infra). Further, the two typical alkylic ligands in 2 and 3 show approximately no differentiation in the CO chemical shifts. The cyclopentadienyl groups in the three compounds (1, 8 93.0; 2, 8 93.7; 3, 5 92.4) are not significall ■ influenced by the C- donor ligands which is approximately in line with the small difference in shifts observed in the 'H NMR spectra.

2- Infrared spectroscopy

The carbonyl stretching frequencies of complexes 1, 2 and 3 are summarized in Table 2.3. Villemin and Schigeto31-34 measured the infrared spectra of [Cp(C0)3MoC...CP11] and [Cp(C0)3WCmCP11]. They found the v(CO) vibrations of the first compound at 2041 cm -land 1966 cm and of the second compound at 2040 cm -land 1950 cm-1. These results agree with the present findings. The infrared spectrum of complex 1 is shown in Fig 3.1. 21

Table 2.3 IR spectra for complexes (1), (2) and (3)

Complex v (CO) / cm"'

1 2045 (st) 1963 (st)

2 2031 (st) 1942 (st)

3 2019 (st) 1929 (st)

Solution spectra recorded in dichloromethane.

All three compounds exhibit two strong v(CO) infrared frequencies in the 2000 crn -1 region indicating the presence of terminal CO groups. The following frequency order is established: 1 (2045, 1963 cm') > 2 (2031, 1942 cm'') > 3 (2019, 1929 cm') .

From this result we draw the conclusion that TC backdonation from metal to the carbonyl ligands is less for 1 than for 2 than for 3, which means that the contribution (a) below becomes more important from compound 1 to 3.

[M]= C =0 [M]—C 0 + (a) - (b) [M] = CpMo(C0)2L

By comparing the 13C NMR shift, it follows that metal-ligand TC bonding does not necessarily imply a large electron density on the CO carbonyl. I .! 22 I. ► 11 l'ill l.1 1 ! I f 1 1 1-1 1 ; iiim 'Il ! ir I I • I I • . ; • I 1 II 1 ;I i•1 I '• • I : .,11. 1 , 1 • ; , , ! ' • • Is • s• • ••• I. e• • • • 1 tv lo ; 1 :11: 1: 1 1. 1".!,! 7. ! i! . :...; : .: 1 1 I • IIIIIiiiiiii111; 1141:1 •Iv ' 11. 1 11. I1 1 /1111111.. LI 11.1 I . 1 11111 ..111111;1. 11. ;!: 1 1 .11 1: II :1; a,• •littl- ■ ••• ■ •••: 1 . .1 .,1 111•:: ! , ' • • ' 1 t ! • I .. : : i : . i . : ! : L.1 i iiiVsii, ji'siiI!Illi;;;;-: 1 II 1 1111 • !Iiiajilitil..11 ■ 11 1: ' 11 I : , 'III / 1...!i'et Itt••::1 , • ' . I 1 ' I f l!'•' I i 1 ' I : • ; i ll111 -111 ':', !'ll'i: • II 0 till ', iti;•• ■ •.11•1111, I .111. , • '11...i 11111;1 .; I .: . ■ •1•!• ••1• , I11•1:: -!:.I•1 .11 III* I1I! s• ••s• i. : . • 1 I • 1 . ; I li 11 111 !I I :h:I i ; l i i iiiiil l liiii! :.•. ' I • !I ! . •I •• I & , 1 ! I • • - ! • .... ... I 1 I i I I I I I I L 11 : 1 111 ; ; I I , : • • - ; • If • sat • • CL• e•. . • •, • • . i

; CO; • . i • • • . . ! : ! sett": • 1' •• 1. I • 1 1 I ; ' • •• • • e,- 5 I • : • • • • 1 : 1 1 : - • - •

• • • ! • 1 • • ; ; • • I.• ill. • ! I • i 'St ;:, I.; `t) d . •.i -* . I : ! I . , . eas ! ! 1 •• I ! I . r i : • el 11 • • \ l • • 1, to . : : . C'•1 • • C....) ; .iI. 1 1 .••• • '•,: :;; 0 ice ' ,I!1 tii , IIII .•.: 1 . ' • I Ii . x: • ., g i Ir.: 1. . !;....;. •111. 1 o • e• • • • I ! . I • -7- :-•-•1•••7 .... 1 •; ; : / II -• !I ! ' ! : • . • j I • . : l • .. • I • ' , • ..n. (ii I • • ! ••• ' 1 - - , ..;:, • 1 lj.j!! : .. l 1: • :.•sl : . • ; . 1 • 1 • sr te •: • • ; • 11 1-- I • 1 - i .:• 1 :H.! ."• 1 • • • •!!: - .1 1 : :111 : 1S!11• • •: 1-1 1 . I i !1 .... 1 . ' ... 1 I• • 1 -1 1• . : ! • . I et: • 4...4::...,,,:,...1... , : i .....- 1 : v.a .1.• I • . ,. . : . , V•i . 12-1. •••...... iiI: :i . • . I 1.4 .1.v. :.I. .• • • 4.• : . : 1. * : ••I•. •• • .I• ••1• ••• • 1! • •I .•:• .1.1. • I .; 1...• '1• F::: •• ..i:' ....:; - : • ' 'si; ■ le) J • : I. 1. i. 1 1 i 41 1. ' • 1 i. . • 61 • 1-1.1 • ; 1 . 1 : ; •, ; 111 - ; ; ; ; . : , .1.j1 ; •. ; I ; : j III: • , *. ' • : r-- , ... .10 1•I r•.I - ; 1 .1 . i . I . . - ■ . . . . , . . 1-i i f. 7..-• 1 ; !• ! • ., : ,- • , ;- t , : . ! • , i . • - . 1'. i • I s , : 1 7 • ; .1 ., ... i . :i 1 " -.5 : 1 . I 1 • I . ! 1 : II '.. I : i ! : 1 , ... , 1 : .... , r I, ; . . • • .1:.;• i 1 1 :" :: H 1 . : : • : .:;-. • •: - .11 **. 1 1 : ''!•::•"- -i•• -1-•• ':. 1•:1 :,:!:lt:1 ;;s - ;s1i 1!::•a;il I: i;:;•.1•1.- SIi . i .•" I ! ' I • t:,..; ... 8 -••• s •.•.s s ..• - • - • ;:, .• :. • • . 4 s • : -1. ' • • I. :1 . ' • , .:::'• • o! . • •I • I . . . i . III I:1 I1111 11 •t • . II. Illji11•11; ! •!,11111.•11. •is 11 ,• . . I 1 1 : : ! ; ; I ; ! 1 1 i . ; ' ./.. /, I ; I!. I I •: , i . ; 11 ,. . . • .: .i ." 1 .r: . , : , -• : , : , .. .. : 1 I !..:I.1.!;! I . •I• I !. • s., : , ■ s: I I : :::: 111.! •::1 . :.1 I: - !••• E iji ! i1 i • ,. I 1.' j •i• !II, .....•i•1 ; ••• I ' •I H I I j■ i li I I •!••1 0•11 1 14 1 . • ...... I...• :.;.! I ' ! ' I • .iv.v 1 1• 1. 1 .II:::•ill;;; •• ■ ••1 4•11. ' -••I•• VI, 1i I• .... !!!: ...• • .• • • ; • 1 • ...:i. i ll ••• ..J.J. .•._.2.:. .•..1 I • ••• . . : .. .I . i ! • . . : I 11.! •• !; ! 1.• V .1 IjI I1, :l• 111 • • 1 . s.o i . I _•• • I ! • • I • L.+ 1 I • • • • .11 • a IP • • ! 1 :fan 1. 1-1 I i : • i . I : . ! i • • I :es! /.1 : ; ; 0 Ifb.19 i I .. i .. ; 1 1311. 11 ! . •Ixi• t ; 1..1 ! -3, • 1,•1., . • . ; 1 ; - _ : _ : , ! -CA • ! • . i • ; 1": 1 1 I. ' • .iii • I . • i -... • ; • . I • • 4 ,. : ... • . . . e . : - • • ! ! : •• • : • • ' ! I i • ' : - i . I i 1 •1" I• i• 1,.1. ■ • ' • ; , ; • • i .• , . .• • • 1 : 1I•. 23

3- Mass spectrometry

The mass-spectra data of complexes (1) and (2) are summarized in Table 2.4 and 2.5.

Table 2.4 Mass spectra for complexes (1) and (2)

Complex m/z Fragment ions

1 348 [CpMo(C0)3C=CC6115] 320 [CpMo(C0)2C-=-CC6F15]± 292 [CpMo(CO)C--C6115] -4- 264 [CpMoC------CC6H5]+

2 364 [CpMo(C0)3CHkH2CH2C112§]+ 336 [CpMo(C0)2CFICH2CH2CH2k] + 308 [CpMo(CO)CHkH2CH2CH2]+

280 [CpMoCH§CH2CH2CF12§]+

266 [CpMoCHSCH2C}12r 252 [CpMoCH§CH2g]+ 238 [CpMoCHSS] +

The mass spectrum of 1 is shown in Fig 3.2. I ea _

1••"' ■•••••

to cr)

w cr, to a tmo

■•

1 x le mp co f o trum ec -sp mass he T 2

3. to

ure N ig F

to c.) N

ts• a) tr) 25

Complex 1 Complex 2

[CpMo(C0)3C1=CC6H5] [CpMo(C0)30-thCH2CH2CHA

-3C0 -3C0 [CpMoCCC61-15] [CpMoCH§CH2CH2C}121S] ± -CH2CH2CH2 [CpMoCHSS]+

It is generally true that metal carbonyls lose all the carbonyl groups easily in a mass spectrometer. This provides a convenient way of counting them. It is obvious that the carbonyls are fragmented first before the extensive central part fragments at all. In fact, the mass spectrum of these complexes of molybdenum are very complicated due to the many isotopes of Mo in relative high concentration. But we could identify a general pattern (Table 2.5). Our general patterns have previously also been mentioned for [Cp(C0) 3MoC:----CP11] and [Cp(C0)3WCmCP11].31'34 26

2.3 CONCLUSIONS AND FURTHER WORK

Making a molybdenum a-acetylide compound has now opened the opportunity to investigate properties of a-coordinated acetylide. Ca in the coordinated ligand is nucleophilic and susceptible to electrophilic attack. It is one of the methods of making vinylidene complexes, [LTIM=C=CRR1". Vinylidene complexes have recently attracted much attention and have been studied in considerable detail in the last decade. Many factors are responsible for this interest in them: 35 compounds containing metal-carbon double bonds show unique and diverse reactivity modes and structural properties; surface-bond vinylidene ligands play a key role in hydrocarbon chain growth in the heterogeneously- catalyzed Fischer-Tropsch process ("Mc Candlish mtchanism");36 vinylidene complexes are effective acetylene polymerization catalyst precursors;" vinylidene complexes show good potential for use in organic synthesis. 38

The dithianyl complex 2 was prepared with the exclusive intention of using it as an example of a compound which can easily be deprotonated on the coordinated carbon:

to be deprotonated

Unfortunately the reaction was unsuccessful in the sense that the product could not be utilized in further reaction (e.g. with CS2), and nothing further will be said about it. 27

2.4 EXPERIMENTAL 2.4.1 General remarks

All reaction involving organometallic reagents were carried out under an atmosphere of nitrogel using standard vacuum-line and Schlenk tube techniques. Clean glassware was taken directly from a drying oven and placed under vacuum before use. For low-temperature reactions dry ice/acetone (-78°C) baths were used.

All solvents were pre-dried in the following manner for two days before use: THF, diethyl ether were dried over sodium wire; and pentane , hexane and CH2C12 over potassium hydroxide. Before use all solvents were freshly distilled under nitrogen. THF and diethyl ether were distilled from sodium wire and benzophenone. Pentane, hexane and CH2C12 were distilled from CaH2.

Chromatographic purifications were performed under nitrogen using Silica gel as the stationary phase in double-layered columns.

All deuterated solvents were obtained from ALDRICH. THF, CF3SO3Me and CF 3SO3H were purchased from FLUKA and n-butyllithium (1.6 M ) was acquired from MERCK.

The 'H MAR spectra were recorded on Varian VXR 200 FT (200.6 MHz) spectrometer. The NMR spectra were recorded on the same instrument at 50.3 MHz. The melting points were determined on a standardized digital Buchi 535 apparatus and are corrected. The mass spectra (electron impact ) were recorded on a Finnigan Mat 8200 instrument and the infrared spectra on a Perkin-Elmer 841 spectrometer.

2.4.2 Preparation of cyclopentadienyltricarbonylmolybdenum dimer [CpMo(C0)312

2 Mo(C0)6 + Cio1-112 [C5H5Mo(C0)3J2 + 6C0 + H2 This is a thermal reaction between molybdenum hexacarbonyl and dicyclopentadiene. The flask, fitted with a nitrogen inlet, magnetic stirrer, straight reflux condenser was charged with 16.0 g (606 'mop molybdenum hexacarbonyl and 80.0 ml of dicyclopentadiene. The reaction mixture was heated to 135 28

145°C (reflux) until no more molybdenum hexacarbonyl sublimes out of the reaction mixture. After completion , the reaction mixture was cooled to room temperature and red crystals of product separated. The red crystals of the product were filtered by suction and washed with hexane to remove excess dicyclopentadiene. The product was heated in a sublimation apparatus under vacuum to insure complete removal of any molybdenum hexacarbonyl. The bright red-violet residue consisted of [C5HsMo(C0)3]2- 39

Yield : 10.4 g (70 %)

2.4.3 Preparation of cyclopentadienyltricarbonylmolybdenum iodide [CpMo(CO)3(1)]

The dimer complex of molybdenum [C 5H5Mo(CO)3]2 (1.60 g , 3.30 mmol) in 10 ml of chloroform was added dropwise to iodine (0.84 g, 3.3 mmol) in 12 ml of CHC13 with constant shaking. After completion, the solution of chloroform was shaken with aqueous sodium thiosulfate (2 g/ 20 ml) to remove the excess iodine . After separation the chloroform was removed and the residue washed with light petroleum. 4°

Melting point : 118 °- 119 °C Yield : 1.70 g (70 %). 2.4.4 Attempted the preparation of

[Cp(C0)3Mo=CNHCH--CHk][CF3S03]

A solution of thiazole (0.101 g, 1.25 mmol) in 11-1F (15 ml) was cooled to -78 °C and treated with butyllithium (0.78 ml 1.25 mmol). The solution was allowed to stir at -60 °C for ± 15 minutes, thl the complex [CpMo(C0)3I] (0.47 g, 1.25 mmol) in THE (20 ml) was slowly added. The mixture was stirred for 2-3 hours at the same temperature -60 °C. The reaction was followed by TLC because a neutral complex was expected. No observable reaction occurred even after stirring overnight. The solution was recooled to -78 °C before CF3S03H (1.25 mmol, 0.11 ml) was added. The solution was allowed to warm up to room temperature for more than 1 hour . The experiment was unsuccessful ar we did not obtain the carbene expected. 29

2.4.5 The attempted preparation of [Cp(C0)3Mo=0 ■1(Me)CH=CH§1[CF3S03]

The same procedure as above was followed. A solution of 4-methyl thiazole (124 mg, 1.25 mmol) in 15 ml of THF was treated with BuLi (0.78 ml 1.6 M 1.25 mmol) at -78 °C. The solution was stirred at -78°C for 1 hour and cyclopentadienyltricarbonylmolybdenum iodide (0.465 g 1.25 mmol) in 20 ml of THF was slowly added. The mixture was stirred for 3 hours at -60 °C . This reaction was monitored by TLC. This reaction was also unsuccessful.

2.4.6 The attempted preparation of benzylcyclopentadienylthiazolylmolybdenum complex.

The same procedure as in 2.4 was used to try and prepare benzylcyclopentadienyltricarbonyl molybdenum . We did not get the result expected but only recovered starting materials.

2.4.7 Preparation of [Cp(C0)3Mo-Cm-CC6H5], (1)

A solution of phenylacetylene (0.20 g , 2.00 mmol) in 20.0 ml of THF cooled to -30 °C was treated with BuLi (1.25 ml , 2.00 mmol). The yellow solution was stirred for 30 minutes and the temperature was brought to - 10°C . The yellow solution became colourless. The solution was cooled I -30°C before [CpMo(C0)3I] (0.74 g 2.00 mmol) in 20.0 ml of THF was slowly added. The mixture was stirred for 1-2 hours at -5 °C. The solvent was removed and the residue chromatographed on Si02 using ether / hexane (1:5) as eluent. The solvent was removed and the residue , a yellow powder, was redissolved in CH 2C12/ hexane. Cooling to -25°C afforded yellow crystals of complex 1.

Melting point : 119 °- 120 °C 'Yield: 0.62 g (90%) 30

2.4.8 Preparation of [CpMo(C0)3CHkCH2CH2CH24 (2)

A solution of 1,3 dithiane (0.24 g 2.0 mmol) in 12.0 ml of THE cooled to -30°C was treated with BuL (1.35 ml 1.6 M 2.00 mmol) in 12.0 ml of hexane. Over a period of 20 minutes, the temperature was brought to + 8°C and the solution was stirred for 30 minutes. The solution was then cooled to -20 °C and [CpMo(C0)3I] (0.53 g 1.43 mmol) was added dropwise. After 1 to 2 hours, the solvent was removed and the residue chromatographed on Si02 using ether/ hexane (1:1) as eluent. The first fraction was discarded and the second fration collected as product. The solvent was removed under vacuum and the residue redissolved in CH 2C12/Hexane ; cooling to -25 °C afforded yellow crystals of complex 2. Yield: 0.43 g (83 %)

2.4.9 Preparation of [Cp (C0) 3MoCH3] (3) To a solution of [CpMo(C0)3I] (0.20 g, 0.50 mmol) in 25.0m1 of diethyl ether was added CH31 (1m1, 1.60 mmol) in excess. After completion of the reaction, the solution was chromatographed on Si02 using ether/hexane (1:1) as eluent. The solvent was removed under vacuum, yielding a yellow powder 3.

Yield: 0.11 g (78 %)

CHAPTER 3

DERIVATIZATION OF A MOLYBDENUM ACETYLIDE COMPLEX.

3-1 Introduction

Vinylidene H2C=C: is the simplest unsaturated carbene. 4' Several methods have been employed for the synthesis of vinylidene complexes in which the addition of electrophiles to the electron-rich C a metal acetylides is the most important. The general reaction may be formulated as in Scheme 3.1: 4244

R+ + M—C C —R' M-= vinylidene alkynyl Scheme 3.1

An example studied by Davison and Selegue45 concerning the protonation of the following iron complc (Scheme 3.2) is related to the attempts described in this chapter.

,H H± C— R Fe = C = C / Fe / CO\ CO \ CO CO C (I) Scheme 3.2 32

Upon coordination of the acetylide its nucleophilicity is transferred from C a to Cp. Electrophilic attack on the alkynyl Cp atom is charge controlled. Nucleophilic attack on C. is frontier orbital controlled. Several authors have described the addition of electrophiles to the electron-rich Cp atoms of metal acetylides. 41'46 Protonation or alkylation of [M(C2R)(C0){1 )(0Me)3}2(n-05H5)] (M=Mo , W ; R=Bu +, Ph) gives the corresponding vinylidene complexes. The reactivity of cationic vinylidene complexes depends on the nature of the metal and donating properties of the ligands coordinated to the metal atom. The protonation of [Cp(C0)2FeCE---CP11] (I) by HX (X= C104 or BF 4) described above, gives a reactive vinylidene complex [Cp(CO)2Fe= C = CHPNX (II) which, in the absence of a competing nucleophile, reacts with a second molecule of I, to yield a binuclear complex of iron containing a cyclobutenylidene ligand. 47'48 The protonation of acetylide complexes with increased electron density a the iron atom gives vinylidene compounds more stable and less reactive than 11. 454" However, from recent work which includes theoretical studies on [Fe(CCH)L2(n-05115)] (L= CO or PH3)," it can be concluded that in these examples the alkynyl ligand acts essentially as a simple a- donor in bonding to transition metal.

We applied similar electrophilic addition methodology to the reaction of [CpMo(CO)3(C2Ph)] with a methyl cation and protons. The conversion involves the addition of alkylating agents such as CF3SO3CH3 and (CH3)SO4 to the acetylide complex [CpMo(CO)3(C2Ph)] to produce a complex 4. Protonation with CF3SO3H was unsuccessful.

In this chapter, the reaction of the acetylide compound with CS2 is also described. When modifying our starting materials by triphenylphosphine substitution, we discovered the presence of isomers in solution. An unique isomeric equilibrium is also dealt with in the present chapter.

3.2 Results and discussion 3.2.1 Vinylidene molybdenum complex 4 A- Preparation The vinylidene molybdenum complex was prepared by reacting phenylethynyllithium with q5-cyclopentadienyltricarbonylmolybdenum iodide. Treatment of this mixture with CF 3S03CH3 gave 4. The same procedure was repeated with another alkylating agent (CH3)2SO4 with the same result (Scheme 3.4). 33

IwoI —I + Li—C =C

OC ( `CO CO IMF

1_- I / 70—C C OC CO CO

CF3SO3CH3, -780C or (CH3)2SO4, 00C

1 + M O =C=C CF3SO3 / I \ \ TT Or OC CO C3ri CO CH3OSO3

Scheme 3.4 34

CH2C12 was the solvent of choice for the alkylation since polymerization of TI-IF occurred when this solvent was utilized. B- Spectroscopic characterization of complex 4 1- NMR spectroscopy The 'H NMR and 13C NMR data for complex 4 are summarized respectively in Table 3.1 and 3.2. The proton resonances of the cyclopentadienyl ligand in complex 4 is shifted somewhat upfield (5 5.28) with respect to those of complex 1, the precursor (8 5.54). But the multiplet of the phenyl in complex 4 is shifted downfield (5 7.42) compared to the multiplet shown by 1 (8 7.22). Notice also the appearance of another singlet at 5 0.37 , which was assigned to CH3 protons. The 13C-{ 111} NMR data for the carbonyl groups in compound 4 show resonances at S 239.7(C0), 226.6(2C0). They are shifted downfield compared to the carbonyl positions in complex 1. The chemia shift of the cyclopentadienyl is not affected by the reaction. Comparison of the results for complex 4 with that of the only known vinylidenemolybdenum complex of the type {(n5-05H5)(C0)(NO)Mo[=--C=C(CH3)(Ph)]), 29 show that the aromatic group resonates in the 13C NM] spectrum at 5135.4, 128.4, 126.6, 125.3 and 124.9 that is in the same region in which the aromatic group resonates in complex 4 (5 132.6, 129.2, 128.4 and 121.9). The aromatic protons in 4 appear as multiplet at approximatively 8 7.4. C o and CH3 in {(n5-051-15)(C0)(NO)Mo[=C a=Cp(CH3)(Ph)]) resonate at 8 134.7 and 814.8 while in the new compound these resonances are found at 8 81.6 and 8 15.3 respectively, confirming its constitution. Unfortunately, even with pulse delay, the coordinated carbon was not found. The 'H NMR and 13C NMR spectra of complex 4 are shown resPectively in Figures 3.1 and 3.2.

Table 3.1 '1-1NMR data for complex 4 Complex* 8 (Assignment)

4 0.37 (3H, s, CH3) 5.28 (5H, s, C5H5) 7.42 (5H, m, C6H5) 35

*Measured in CDC13.

Table 3.2

13C- NMR data for complex 4

Complex* 8 (Assignment)

4 239.7 CO (trans) 226.6 2C0 (cis) 132.6 C2 & C6 129.2 C4 128.4 C3 & C5 121.9 C1 81.6 C7 74.0 C8 92.4 C5H5 15.3 CH3

*Measured in CDC13.

2- Infrared spectroscopy The carbonyl stretching frequencies of complex 4 are summarized in Table 3.3. The two strong CO bond stretching frequencies at 2055 and 2019 cni l increased considerably and furthermore, a very weak additional peak now appears at 1926 cm' compared to those of complex 1 (v(CO) 2045 cm', 1963 cm-I). It is clear that in the vinylidene complex 4 the electron density decrease on the central Mo atom, thereby decreasing the d -47C backbonding and raising the CO bond order anc stretching frequencies. Comparison between ri 5-cyclopentadienylphenylethynyltricarbonyltungsten and complex 4 shows similarity and their respective carbonyl frequencies occur in the same region of the 36 infrared spectrum. When compound I is protonated in the presence of triphenylphosphine a cation II forms. It also has three carbonyl vibrations of lower energy than that of the present compound.

[Cp(C0)3WCCP11] + HBF4 + PPh3 —+ [Cp(C0)3W-C(PPh3)+ = CHPh]BF4 (I) ( 1) The infrared spectrum of II measured in CH2C12 exhibits CO vibrations at 1860, 1965 and 2040

Table 3.3 IR spectrum for complex 4

Complex* v (CO) /

4 2055 (st) 2019 (st) 1926 (st)

*Solution spectra recorded in CH2C12-

3- Mass spectroscopy Attempts to collect a mass spectrum of complex 4 resulted in a spectrum of its alkynyl precursor complex 1. It thus can be deduced that the alkylation is thermally reversible in the solid state. ▪ 3/

C C O 1 C .C • X+

C. 0 C. 0 A C. 0

CDC O

i t 7.49b0 as c. r..11U1

1. •

.1 r.: C. f C CO flo

,- 5.2774

t. S.2716- - •

a .

ca—

it .2. A. X1 C Cu ''' — 16E3 .1. C I— ... r 0.3E04 c ... t... I. *a. X --- 239.702 ' s .10

.:28 . 621

-- 215.373 s— L14.41G

— CD CD

— —a— 129.182 128.429

--- 121.867 c —, 0

0— O

--- 92.4202

.m1

1 C • — 81.5778

U 77.63.13 77.GC.14 —N .-76.3615 73.96a. ;.

65.8099

•

ru -

--- 15.2508

3.3 - Unsaturated addition complex 5, phosphine complexes 6 and 7, CS2 adduct 8, isomers cis- and trans-9 and the phosphine acetylide 11

3.3.1- Introduction

Carbon disulfide is an unsaturated electrophile. Typically CS2 reacts with metal alkyls or hydrides by insertion, giving dithiocarboxylate or dithiorformate complexes. Selegue, in 1982, reporte his work on electrophilic attack on a metal alkynyl by carbon disulfide. 52 It occurred by a (2 + 2) cycloaddition to form a complex containing a 2H-thiete - 2 -thione functional group (Scheme 3.5).

Fe C—CH3 + CS2 Fe —C C=S SZ CO CO CO CO

Scheme 3.5

This new mode of CS 2 reactivity, with an electron-rich iron alkynyl complex, has now been extended to include our molybdenum alkynyl complex 1. The conversion involved the addition of CS2 excess to [Cp(C0)3MoC.Ph] in THE to form a neutral deep purple complex. Additional studies witl molybdenum compounds in which a CO ligand has been substituted with PPh3 and PMe 3 have been carried out because we could not alkylate the first CS2 adduct.

A variety of procedures are available for the substitution of carbonyls in metal carbonyl complexes. 53-55 Coville recently published the use of a metal dimer catalyst to bring about single carbonyl substitution. 56'57 The preparation was carried out by heating [CpMo(C0) 3I] with the appropriate phosphine ligands, L, in the presence of [CpMo(CO)3]2 as catalyst in refluxing benzene. 40

3.3.2- Results and discussion 3.3.2.1 [Cp(C0)3Mo=C(Ph)C(S)SI 5 ; [CpMo(CO) 2(PPh3)I] 6; [Cp(C0)2(PPh3)MoC---ECP111

[Cp(CO)2(PPh3)MoC=C(Ph)C(S)S1 8; [CpMo(C0)2(PMe3)11 cis- 9; [CpMo(C0)2(PMe3)11 1712113'- 9; [Cp(C0)2(PMe3)MoC=CPh] 11.

A- Preparations A-1 - [Cp(C0)3MoC=C(Ph)C(S)S], 5

To a solution of the acetylide complex 1, CS2 was added in excess at room temperature. The mixture was stirred for four days and the solvent removed under vacuum. The residue yielded a deep purple powder of complex 5 after chromatography. The product is air stable and quite soluble in polar and non polar solvents. The complex 5 may be formulated in either an open (5a) or a closed (5b) form (Scheme 3.6).40 Another resonance form of 5b (5c) is also shown in the Scheme below. Compound 5 is stable in solution and in the crystalline form. It is soluble in more polar organic solvents.

(c) / Mo—C =C + C [Cp(C0)3M0= C=C 0/ ICO \CO 10) C=S S/ 5a 2 1 i +% _ "-NA ikC7.0.\ (--,A Cp(C0)3Mo----C/ C —S CP(C0)3Mo —C C= S 8\ / 9 S 5c 56 Scheme 3.6

Attempts to react [Cp(C0)3Moa=C(Ph)C(S)IS] with CF3S03CH3 and [Cr(CO)5(THF)] have been unsuccessful. CF 3S03H resulted in decomposition, which means that resonance form 5c could not be utilized in further reaction.

A-2 [CpMo(C0)2(PP63)I] , 6

This complex has been made before and is well characterized. 5"° [CpMo(CO)2(PPh3)I], PPh3 and [Cp(CO)3Mo]2 (as catalyst) in benzene were heated under reflux. The product was isolated by column chromatography. The complex 6 is a stable compound.

A-3 [Cp(C0)2(PPh3)MoC---XPh], 7

Phenylacetylene was treated with BuLi in THF at -30 °C. After stirring the solution for 30 minutes, [CpMo(CO)2(PPh3)I] was added slowly to the mixture. The solvent was removed under vacuum and the residue chromatographed, yielding a pale yellow powder (Scheme3.7). The compound is stable at room temperature when in the crystalline form. Crystals of 7 were obtained from CH2Cl2/hexane at -20°C.

THF BuLi + H CPh s Li C

THF z M —I + Li—C —C z

OC I `CO OC I PPh3 PPh3 7

Scheme 3.7 42

A-4 [Cp(C0)2(PPh3)Mo i)(S)g ], 8

CS2 used also as solvent, was added in excess to complex 7. After four days, the unreacted CS2 was removed under vacuum and the residue chromatographed. The final product was a deep purple powder (Scheme 3.8), stable at room temperature and even in solution. It is also soluble in more polar organic solvents.

S C)1 S r.? / MOI —C cp• (c0)2(PPh3)mcic---c ) oc \CO = s PPh3 - s

C C + / ‘ _ •"1/4 _ (")k [C p(C0)2(PPh3)Mo---- C t —S ■1111-11111■ [Cp( C0)2(PPh3)Mo—c C = S

\S / \ si 8b

Scheme 3.8

It was expected that alkylation of 8 should occur more readily than that of 5, due to the weaker IC accepting ability of the phosphine compared to CO." The thione moiety should be particularly electron-rich due to conjugation with the highly donating alkenyl-molybdenum unit. Nevertheless, no reaction was detected upon treatment with alkylating agents or acids.

A-5 Complex [CpMo(C0)2(PMe3)I1 cis- 9, trans - 9

A CO substitution with PMe3 was also carried out in order to prepare another more viable starting material, but also in an attempt to obtain information (NMR) concerning the possible formation of cis and trans isomers as proposed before (page 32). To the complex [Cp(C0)3MoI] in benzene, PMe3was added carefully and the mixture stirred at room temperature. The solvent was removed under vacuum and the residue chromatographed yielding two

isomers cis- 9 and trans - 9 . We did not find any report on complexes cis- 9 and trans - 9 (Scheme 3.9) in the existing literature.

C6H6 / M —1 + PMe3 RT low OC I \CO 06.- I \ PMe3 CO PMe3

cis-9

' J CO

trans-9

Scheme 3.9

These two isomers were separated by column chromatography and characterized. Compounds having the formula [n-05115Mo(C0)2LX] where L= PPh3, P(nBut)3, P(OMe)3 and X= Cl, Br, I, H have been studied by Fallen and Anderson.62 They could be regarded as seven coordinate complexes with the cyclopentadienyl ring occupying three coordination positions. Alternatively the Cp-group can be taken 44 as one ligand and the other four occurring with the metal in a square pyramidal arrangement. This square-pyramidal geometry suggests the possibility of the existence of two geometric isomers.

...Mo...... / CO

trans cis The isoinv: HIMsz;02) 12 Risoipcomplexn Comparisons of the isomer ratios in a given solvent reveal the trends in free energy and enthalpy differences, regardless of solvent. These stability differences can be explained by the effect of steric interactions on the enthalpy of formation of each isomer. Hence the trans configuration should be favoured for the iodide more than for the chloride. Within a series of halides containing the same L group the percentage of cis isomer decreases in the order Cl > Br > I. Unfortunately, this approach fails to explain the observation that, for a given ligand L, the relative stability of the trans isomer of a hydride complex is often comparable to that of the iodide e.g. when L = P(n-but)3 or PPh3.

Suffice it to say that steric effects are an important contributing factor in determining the equilibrium ratio of isomers but they do not always dominate in the control of configuration preference. It thus appears that electronic factors must also be responsible in large measure for the isomer ratios which are observed. Correlation of thermodynamic, as well as kinetic, phenomena in the Pt(II) system (where molybdenum systems may represent a rather large departure from a model system based on Pt(II) complexes) leads to a decreasing trans effect order as follows : CO > PR 3 > — If — CH3> T > Br >C1.

Suffice it to say that in all of the [it-051-15Mo(C0)2LR] compounds a delicate balance between steric and electronic effects exist. In the reaction represented in Scheme 3.9, the cis isomer has been isolated as major product and trans isomer as minor. All the results have also been confirmed by NMR

45 spectroscopy. Furthermore we observed in solution that the cis isomer was slowly transformed into the trans isomer which indicated the existence of an isomeric equilibrium (Figure 3.5).

A-6 complex [Cp(C0)2(PMe3)MoC- CP11] 11

Phenylacetylene was treated with BuLi in THE at -30 °C. After stirring the solution for 30 minutes, [Cp(CO)2(PMe3)MoI] was added slowly to the mixture. After stripping of solvent in vacuo, and separation by column chromatography, pale yellow complex 11 was obtained (Scheme 3.10).

BuLi + H CPh THE Li C -300C

+ Li —C lr-

OC CO OC PMe3I \ PMe3

11 Scheme 3.10

The product was stable but the yield so low that no further reactions could be undertaken.

B - Spectroscopic characterization of complexes (5) -(11)

The NMR data for complexes 5 - 11 are summarized in Table 3.4. The proton resonances of the cyclopentadienyl ligand in the adduct complex 5 are shifted somewhat upfield 5 5.49 with respect to the proton resonances of Cp in the acetylene complex 1 (5 5.54). Complex 5 with the closed form, [MoJC=C(Ph)C(=S)S, is a 3 dithiolactone (2H-thiete-2thione). No previous report of a 2H thiete -2 thione of molybdenum has been found in the literature for 46

comparison. The only complex similar in the literature is the one reported by Selegue that has been mentioned before and which is formed by electrophilic attack on an iron alkynyl by carbon disulfide. 32 Complex 6 has been made and characterized a long time ago. Barnet 63reported the proton resonances of

the cyclopentadienyl group in the cis- isomer at 8 5.33 (singlet) and at 8 5.07 (doublet) for the trans- isomer which could, however, not be separated_ These results confirmed our chemical shifts for this -

compound, i.e. the Cp, (cis) at 8 5.32 (singlet) and a doublet at 8 5.05 for the trans - isomer. The proton resonance of the cyclopentadienyl ligand in complex 7 (8 5.34) is shifted downfield compared to that in complex 6. The low field positions of the cyclopentadienyl resonances in the proton spectra of complex 8 (8 5.5) indicate that the C=CPhCS(S) ligand is a stronger electron withdrawing ligand than [CE:CPh] in complex 7 8 5.34. Iodo-complexes such as these with general formula [7t-CpMo(C0)2LI] may exist as cis or trans isomers and the chemical shift due to the cyclopentadienyl protons of the cis isomers appears as a singlet whereas a 1:1 doublet is observed at somewhat higher 8-values for the trans derivatives." These

results are now confirmed for the complex [Cp(CO)2Mo(PMe3)I] cis- 9 and trans - 9.The proton

resonances of the cyclopentadienyl group in complex cis- 9 is a singlet at 8 5.30 whereas a doublet is

observed at 8 5.20 for complex trans - 9. This is also in line with the results for complex 6 where both a singlet and doublet were found for the mixture of cis and trans isomers in solution. Our results for 6 also agree with those in the literature. 63

The 'H NMR spectra of complexes cis- 9 and trans - 9 are shown in Figures 3.3 and 3.4.

Table 3.4

'H -NMR data of complexes 5, 6, 7, 8, cis- 9, trans - 9 and 11

Complex* 8 (Assignment)

5 5.49 (5H, s, C5110 7.43 (5H, s, C6115)

6 5.05 (5H, d, C5H5 ,trans) 47

5.32 (5H, s, C5H5 ,cis) 7.40 (15H, m, 3C6H5)

5.34 (5H, s, C5H5) 7.35 (15H, m, 3C6H5) 7.47 (5H, m, C6H5)

8 5.50 (5H, s, C5H5) 7.45 (15H, in, 3C6H5) 7.70 (5H, m, C6H5) cis- 9 5.30 (5H, s, C5H5) 1.74 (9H, d, 3CH3)

trans- 9 5.20 (5H, d, C5H5) 1.61 (9H, d, 3CH3)

11 7.26 (5H, m, C6H5) 5.30 (5H, t, C5H5) 1.75 (9H, d, 3CH3 cis) 1.61 (9H, d, 3CH3 trans)

*Measured in CDC13 relative to internal TMS. 48

The numbering system indicated below will be referred to in the ' 3C NMR spectroscopy for the assignment of peaks. 4

rC•i M o 8 „C 7 OC I •-C$0 10 Cp(CC)3M0 —C S 8\ /9 11 5 12 13

0I ic`--,C =s mo— 8\ /9 OCR CO S lj 10 11 12

The 13C-(H) NMR data for complexes 5, 7, 8, cis- 9, trans- 9 are summarized and assigned in Table

3.5. The '3C NMR spectrum of complex cis- 9 is shown in Figure3.8. 49

Table 3.5 The 13C-{H} NMR for complexes 5, 6, 7, cis-9 and trans-9

Complex* 6 (Assignment)

5 247.5 2C0 204.9 CO 132.2 C2, C6 129.7 C4 128.5 C3, C5 121.3 Cl 96.8 C7 88.7 C8 92.6 Cp

7 238.2 CO 219.1 CO 133.6 C10 & C14 130.1 C12 128.2 C11 & C13 135.5 C9 133.6 C2, C6 130.1 C4 128.1 C3, C5 127.3 Cl 124.7 C7 107.0 C8 92.6 Cp 50

8 256.7 CO 132.3 C11 & C15 131.6 C4 131.5 128.5 C12 & C14 133.9 C10 132.2 C2, C6 129.7 C4 128.5 C3, C5 121.4 Cl 92.6 Cp cis- 9 237.1 CO 199.2 CO 92.5 Cp 21.2 3CH3 20.5 trans- 9 232.5 CO 232.0 CO 92.4 Cp 21.2 3CH3 20.5

*Measured in CHC13. Pulse delay of 7 seconds. — 0 — 51

C Th C

C e 1

(0— H NMR s pect rum of

com pl e x ci s -9 [C

-- 7.2400 pM o(C0

= ) 2(PM e 3)1 1

•

••• 1 7F14

C1 :

1.3440

/NO

C • C to-

7.2397

O UI

O (a

01— N

O ga

1 t. . —4 5.3020 1 t. I r r ,. — 1

gm.

..11h..••■•

1.7626 • /— 1.6243 7 1.5464 53

'41 oco 0 0 O O C Ul O CD

CIrr.

= M C 0 O

Q . Cr O Oa

el rs

es9

D. • ._.r _ r- 7.4464 As - 7.2395 co

0 re CA -

- 0 ese° B0 rP

•••" 1 I Ca. • r- r • s-

-4

Ul CC US X

Q •

-- 1. ea36 -"%- 1.576G

--- 1.2279

1.1989

--- 1.1684 54

J. -.

z.; - /r.s4,14

•

/O.

41.1Fit1 55

2- Infrared spectroscopy

No reference to the differences in the stretching frequencies of cis and trans isomers of the type

found for cis- 9 and trans -9, has been made in the literature. It is now clear that these frequencies appea a somewhat lower wave number for the cis than for the trans isomer. Furthermore the v (CO) vibrations occur at higher frequenciesfor the PPh3 ligand compounds than for PMercontaining ones.

The carbonyl stretching frequencies of complexes 5, 6, 7, 8, cis- 9, trans - 9 and 11 appear in Table 3.7.

TABLE 3.7 IR spectra for complexes (5) - (11)

Complex* v (CO) / cm'

5 2056 (st) 1974 (st) 1906 (st)

6 1964 (st) 1884 (st)

cis-9 1956 (st) 1865 (st)

trans-9 1959 (st) 1875 (st)

11 1964 (st) 1879 (st)

*The infrared spectra were recorded in CH2C12. 56

3- Mass spectrometry

It is generally true that metal carbonyls lose all the carbonyl groups readily in the mass spectrometer. This was also found for the complexes 7, cis- 9, trans-9 and 11 that lose all their CO groups successively in the spectrometer followed by a loss of the other ligands. Molybdenum does not have just one isotope, but a whole series (m/z 100, 98,97,96,95,94,92). The highest intensity is found for isotope 98. The multitude of peaks complicated the peak assignments, nevertheless certain fragmentations could be assigned. The mass spectra of complex 7 is summarized in Table 3.8 and that_of cis-9 in Table 3.9.

Table 3.8 Mass spectrum of complex 7

Complex m/z Fragment ions 7 582 [Cp(C0)2(PPh3)MoC CC6115i±

-CO

550 [Cp(C0)(PPh3)MoC=CC6H5i ±

-CO 522 [Cp(PPh3)MoC---C ]+ -Ph 445 [Cp(PPh3)MoCC]+ 57

Table 3.9

Mass -spectra of complex cis- 9

Complex m/z Fragment ions

cis- 9 422 [CpMo(C0)-2(PMe3)Tr 4,-CO 394 [CpMo(C0)(PMe3)11 + 4--CO + 366 . [CpMo(PMe3)I] 4.-PMe3 290 [CpMoI]+

The mass-spectra of complexes cis- 9 and trans - 9 are shown in Figures 3.6 and 3.7.

Mass Spectrum Bata: BU313 R17 Base a/z: 290 85/22/95 12:29:88 + 1:86 Cali: CAL5495 113 RIC: 187776. Sample: Conds.: 188.8 5384.

29 5384.

58.0 — 394

14114 i3.11 loft, ‘3141 3 -117 - I t ) fir% 1 419, • u/z 388 358 488 458 588 SPEC:

Figure 3.6 The mass-spectra of complex cis-9

Mass Spectrum Data: BU315 #34 Base m/z: 290 05/22/95 12:55:00 + 2:13 Cali: CAL5495 #3 RIC: 221696. Sample: Conds.: 100.0 -- 9321

50.0

_ 366

50. 0 394

26 422

) 1 I II t rt t l11 I 1 ~ 1 r 411111,h 1 NOLTIr.. u/z 250 300 350 400 450 SPEC:

Figure 3.7 the mass-spectra of complex trans - 9 59

Table 3.11 The mass spectra of complex 11

Complex m/z fragment ions

11 394 [CpMo(C0)2(PMe3)(C-=-CPh)r 4--CO 366 [CpMo(C0)(PMe3)(Ca-CPh)] + 4,-CO 340 [CpMo(PMe3)(CFECPh)] + 4-CH3 322 [CpMo(PMe2)(07--CPh)r 4,-CH3 307 [CpMo(PMe)(Ca-CPh)]+ 4-CH3 290 [CpMoP(C---s.CPh)J+

267 [CpMo(Ca--CPh)]+

The fragment ions confirm the number of CO ligands present and the molecular masses in these complexes. The carbonyl groups were the first to be lost. In most cases we cannot further identify the fragment ions because of overlapping with the peaks of molybdenum. By recognizing the different possible fragments (Tables 3.8 -3.15), the identification of complexes 7, cis- 9, trans- 9 and 11 was achieved. 60

3.4 EXPERIMENTAL

3.4.1 General The same experimental techniques apply as in section 2.4.1. The following starting materials were used without further purification: CS2 ,PPh3 and PMe3.

3.4.2 Preparation of Cp(C0)3Mo=C=C(Ph)(CH3) 4 A solution of phenylacetylene (0.205 g, 2.01 mmol) in 20 ml of THF cooled at -30 °C was treated with BuLi (1.25 ml 2.00 mmol). The yellow solution was stirred for 30 minutes and the temperature was brought to -10°C. The yellow solution became colorless . The solution was cooled to - 30°C before it was slowly added to [CpMo(C0)3I] (0.50 g, 1.34 mmol) in 20 ml of THF. The mixture was stirred for 1-2 hours at -5°C and then recooled to - 78 °C before CF3SO3Me (0.23 ml 2.00 mmol) was added. After one hour at this temperature the solvent was removed and the residue chromatographed on Si02 using ether/ hexane 1:1 as eluent yielding a yellow powder 4.

Melting point : 600- 61C. Yield: 0.22 g (45 %)

3.4.3 Preparation of [Cp(C0)3Mo(C=C(Ph)C(=S)S] 5

To a solution of 1 (0.27 g 0.76 mmol) in THF (12 ml) at room temperature was added CS2 (1.3 ml). The mixture was stirred for four days . The solution changed color from dark red to a deep purple. The solvent was removed and the residue chromatographed on Si02 using ether/ hexane (1:9) as eluent, yielding a deep purple powder of 5.

Melting point : 117 °- 118 °C Yield: 0.21 g (65 %) 61

3.4.4 Preparation of [Cp(C0)2Mo(PPh3)11, 6

The iodo complex of [CpMo(C0)3I] (1 g, 2.7 mmol) and the ligand PPh3 (0.72 g, 2.75 mmol) were added 25 ml to benzene. The solution was heated under reflux with [CpMo(CO)3]2 (10 mg) as a catalyst. The product was chromatograhed on silica gel using hexane as a stationary phase and benzene as eluent. The solvent was removed yielding an orange powder cis- 6 and trans - 6.

Yield: 1.50 g (92 %)

3.4.5 Preparation of [CpMo(C0) 2(PPh3)(C:=-CPh)], 7

A solution of phenylacetylene (0.302 g 3 mmol) in 20 ml of THF cooled at -30°C was treatec with BuLi(1.9 ml, 3 mmol). The yellow solution was stirred for 30 minutes and the temperature was brought to -10°C. The yellow solution became colorless. The solution was cooled to -30 °C before it was slowly added complex 6 (1.5 g, 2.5 mmol) in 25 ml of THF. The mixture was stirred for 1-2 hours at - 5°C . The solvent was removed and the residue was chromatographed on Si02 using hexane as stationary phase and benzene as eluent. The solvent was removed, yielding a pale yellow powder 7.

Yield: 1.27 g (88 %)

A solution of [Cp(C0)31VloCCP11] (1) (0.35g, 1 mmol) and the ligand PPh3 (0.29 g, 1.1 mmol) were added to benzene 20 ml. The solution was heated under reflux with [CpMo(CO)3]2 (10 mg as a catalyst. The product was chromatographed on Si02 using hexane (stationary phase) and benzene as eluent. The solvent was removed yielding a pale yellow powder 7.

Melting point : 184 ° - 185 °C. Yield: 0.38 g (66 %) 62

3.4.6 Preparation of [Cp(C0)2(PPh3)MoC=C(Ph)C(=S)S], 8

To a solution of 7 (0.15 g, 0.26 mmol) in CH2C12 (12 ml) at room temperature was added CS2i] excess. The mixture was stirred for one week . The solution changed from yellow to a deep purple. The solvent was removed and the mixture chromatographed on silica gel using ether / hexane 1:9 as eluent , yielding a purple powder 8.

Yield: 0.13 g (76 %)

3.4.7 Preparation of [CpMo(C0) 2(PMe3)(1)] cis- 9 and trans- 9.

The iodo complex [CpMo(C0) 3I] (1.75 mmol 0.65 g) and the ligand PMe3 (0.187 ml 1.85mmol) were dissolved in 20 ml of benzene. The solution was stirred at room temperature with [CpMo(CO)3]2 (15 mg). After completion, the product was chromatographed on silica gel using hexane as stationary phase and benzene as eluent_ The solvent was removed , affording two isomers cis 9 and trans-9.

Melting point cis-9: 120 °- 121 °C Melting point trans-9 : 123 ° - 12 4 °C Yield: 0.58 g (80 %) cis-9 Yield: 0.06 g (8 %) trans -9

3.4. 8 Preparation of [CpMo(C0) 2(PMe3)(CCPh)] 11

1- A solution of [Cp(C0)3MoC.----CPh] (0.39 g 1.16 mmol) and the ligand PMe3 (0.17 ml , 1.7 mmol) were added to 25 ml of benzene. The mixture was stirred at room temperature in the the presence of [CpMo(C0)3]2 (15 mg) as catalyst. After completion, the product was chromatographed on silica gel using hexane as stationary phase and benzene as eluent. The solvent was removed , affording a yellow compound 11. Yield: 0.08 g (18 %) 63

2- A solution of phenylacetylene (51 mg 0.5 mmol) was lithiated with BuLi (0.31 ml, 0.5 mmol) in THF according to the procedure in 2.4.7. Complex [CpMo(CO)2(PMe3)(I)] (0.15 mg, 0.4 mmol) in 15 ml of THF was slowly added at -30°C. The mixture was stirred at -5°C and the progress of the reaction was followed by TLC as we were expecting to have a neutral compound. The solvent was removed and the residue chromatographed on silica gel using hexane / benzene , yielded a yellow powder 11. Yield: 0.03 g (21 %)

3.4.9 Attempted preparation of [Cp(C0)3Mo +=C=C(Ph)(C(=S)SCH3)]

To a solution of 5 (0.135 g , 0.319 mmol) in 12 ml of CH2C12 cooled at - 78°C was added CF3SO3Me (0.06 ml, 0.5 mmol). The reaction did not give the expected result. Using CF3SO3H (0.05 ml, 0.5 mmol) decomposition occurred.

3.4.10 Attempted preparation of [Cp(C0)31V1o+=C=C(Ph)(C(=S)SCr(C0)5)]

The pentacarbonylchromium(0) complex is prepared as follows: Cr(CO)6 + THF [Cr(CO)5(THF)] + CO

Hexacarbonylchromium(0) (0.66 g, 3 mmol) was placed in the reaction vessel and dissolved in 60 ml of dry peroxide-free tetrahydrofuran (THF). This was irradiated for one hour and an orange solution was obtained, which was placed (avoiding air contact) in a Schlenk tube. An attempt to react with complex 5 was unsuccessful. 64

CHAPTER 4

CRYSTAL AND MOLECULAR STRUCTURE DETERMINATION OF TWO MOLYBDENUM COMPLEXES

4.1 Introduction

Single X-ray crystal structure determinations provide valuable information about the structure and, indirectly, the type of bonding occurring in complexes. In this chapter the crystal and molecular structures of complexes [re-0 5I-15(C0)3MoCCPh] (1) and [i5-C5H5Mo(CO)3Br] (12) are discussed. Both X-ray crystal structures unambiguously show a "piano stool" structure with cyclopentadienyl as the seat and four ligands serving as the legs. In addition, very few molybdenum complexes in which an acetylide ligand appears are Icnown, 6549 so we decided to investigate the structure of this compound in detail since it is the first example of such a type containing carbonyl and cyclopentadienyl ligands.

The structural characteristics of this acetylide complex is compared to those of other phenylethynyl molybdenum compounds. The Mo-C (ethynyl) bond length is of special interest as one would like to ascertain whether this bond is influenced significantly by the other ligands coordinated to the metal.

The structural characteristics of bromide complex 12 have proved to be very similar to the literature values of the same compound. However, the present compound exhibits a different packing pattern that was deduced from its unit cell during initial X-ray experimentation.

During unsuccessful attempts to react the dimeric compound [Cp2Mo2(CO)6] with alkyl and aryllithium, no new products could be isolated. However, the known compounds [115-05H5Mo(C0)3C1]70 and [n5-05115Mo(C0)3Br]71 mentioned above were produced in crystalline form. They probably resulted during substitution of the reactive adducts by halides or halide-containing 65 compounds present in the solution. For example, CH2C12 was used as solvent after the reaction with MeLi during attempted work-up and LiBr is present in a self prepared PhLi solution. Details of the X-ray structure determinations as well as crystal data are available from professor G.J. Kruger of the Chemistry Department at RAU, P.O. Box 524, Aukland Park, 2006.

4-2 Results and discussion 4.2.1 Structure of [Cp(C0)3MoC-CP11], (1)

The molecular structure of compound 1 is shown in Fig 4A, while selected bond lengths and bond angles are given in Tables 4.1 and 4.2. The crystal structure of the title compound consists of three carbonyl groups and a hapto-5 Cp ring coordinating to the molybdenum. The C---C triple bond any the phenyl ring form a flat plane, with atom C(4) having the greatest deviation from the plane (0.028A) As mentioned before, no other acetylide complexes of molybdenum containing carbonyl ligands have been subjected to a crystal structure determination. One may add: no such structure of a complex with cyclopentadienyl ligand is known. Therefore, it is difficult to compare the bond lengths in 1 meaningfully with that of known compounds. Structures of the following mononuclear compounds hav been reported (important bond distances and angles are given alongside):

Ph--P —Ph Ph— —Ph \ \ Ph Ph/ Ph Mo- C 2.137 A Ph Mo- C 2.067A C=C 1.205A C=C 1.195A Mo- C=C 178.5:4

BF4- Mo-C=C CC 174.6A 66

Ph ph ple"PN / '`- Ph PV. \ Ph H3Mot—c_c---tBu Ph p , P Phi p Ph' Ph Phi Ph Mo- C 2.094 A Mo- C 2.175A C=C 1.237A C=C 1.209A Mo- C=C 175.6 A Mo- CC 176.9A C

In these complexes the Mo-C (acetyl) separation varies between 2.067A (in A) and 2.175A (in D). The corresponding distance in 1 (2.145A) also falls in this region. The length of the triple bond in complex 1 is, however, somewhat shorter than in any of the other acetylide complexes in which their bond lengths varies between 1.195A and 1.237A. If this result is due to the effect of different ligands, one should have seen it also in the Mo-C separation, which is not the case. All these compounds except (B) have a significant deviation in linearity present in the Mo-CEC arrangement. The molecular structure of complex 1 is shown in Figure 4.1.

In (B) this angle is nearly 180° (178.5°). From all these results it is also clear that the compared bond distances are not significantly influenced by the oxidation state of the metal.

In contrast to compound 12 to be discussed below, all the Mo-CO, distances (ay. 1.98A) as we as the C- 0 bond lengths (ay. 1.14A) are very similar in compound 1. The fact that the Mo- C (carbonyl) distances are shorter than the Mo- C(acetyl) length of 2.145A, indicates the importance of 7t-back donation in the former ligands. 67 ' `o a fD M ol e cul ar st r uct ur e of c om pl e x 1 sh o wi n g th e n umb eri n g sch

• • . em e 68

Table 4.1 Selected bond lengths (A) for complex 1 with e.s.d.s in parentheses

Mo -C(1) 1.978(4) Mo -C(2) 1.984(4) Mo -C(3) 1.986(4) Mo -C(4) 2.145(4) Mo -C(12) 2.308(4) Mo -C(14) 2.308(4)

Mo -C(15) 2.347(4) -Mo -C(15) 2.347(4) Mo -C(16) 2.316(4) C(4) -C(5) 1.177(6) C(5) -C(6) 1.435(6) C(1) -0(1) 1.153(5) C(2) -0(2) 1.141(5) C(3) -0(3) 1.141(6)

Table 4.2 Selected bond angles (°) for complex 1 with e.s.d.s. in parentheses

C(1) -Mo-C(2) 110.0(2) C(1)-Mo-C(3) 77.5(2) C(1)-Mo-C(4) 70.3(2) C(2)-Mo-C(3) 80.1(2) C(2)-Mo-C(4) 75.4(2) C(3)-Mo-C(4) 129.0(2) Mo-C(1)-0(1) 178.7(4) Mo-C(2)-O(2) 176.7(3) Mo-C(3)-O(3) 178.6(4) Mo-C(4)-C(5) 175.1(3) C(4)-C(5)-C(6) 177.3(4) C(5)-C(6)-C(7) 121.7(4) C(5)-C(6)-C(11) 122.1(4) 69

4.2.2 Structure of [re-05H5Mo(C0)3Br] (12)

The molecular structure of complex 12 is shown in Fig 4.2. Selected bond lengths and bond angles are in Tables 4.3 and 4.4. The structure is of the "half sandwich" type in which the molybdenum is coordinated to the cyclopentadienyl ring on one side and to the bromide and carbonyl groups on the other. In other words, the far ni ligands adopt a distorted square pyramidal coordination about the Mo atom.

In Boyle's publication on compound 12, no comparison with other compounds has been reported. We decided to compare 12 on one hand with similar complexes like [ir-CpMo(CO)3C1] and also to 1, to ascertain whether differences do exist, and on the other hand to compare the packing pattern with the same compound previously reported. n The average Mo -C(carbonyl) distance in compound 12 is 2.016 A, which is slightly greater than in the chloride complex (1.99 A) and in compound 1 (1.983 A). From that we conclude that the distance between the metal and the carbonyl is not affected drastically by the substitution of ligands.

The very short average C -O distance of 1.113 A is shorter than that of both the chloride (1.16A) and acetylide (1.145A) complexes. The Mo -Br distance is longer(2.651 A) than Mo -Cl (2.493 A) and Mo -C(acetylide) (2.145 A) which does shows the importance of donor atom size. The molecular structure of complex 12 is shown in Figure 4.2. Table 4.3 Bond lengths (A) for complex 12 with e.s.d.s. in parentheses

Mo -C(1) 2.021(6) Mo -C(2) 2.031(5) Mo -C(3) 1.996(6) Mo -Br 2.651(1) 0(1) -C(1) 1.125(7) 0(2) -C(2) 1.103(7) 0(3) -C(3) 1.110(7) S./ 71

Table 4.4 Selected bond angles (°) for complex 12 with e.s.d.s. in parentheses

Br-Mo-C(1) 77.1(2) Br-Mo-C(2) 76.8(2) Br-Mo-C(3) 130.7(2) C(1)-Mo-C(2) 114.3(2) C(1)-Mo-C(3) 76.4(2) C(2)-Mo-C(3) 77.4(2) Mo-C(1)-0(1) 176.4(5) Mo-C(2)-O(2) 178.5(5) Mo-C(3)-O(3) 178.8(5)

The packing consists of flat sheets, layered on top of one another. These layers are made up of pairs of molecules (shown in circle A in diagram). In the two crystal modifications the layers are stackec differently. In our compound, layer molecules register as in circle B, for example with Cp rings parallel, and with a centre of symmetry between them, whereas in Boyles' structure Cp rings of registering molecules are at right angles to each other. In short, the difference is a shift of one molecule in the relative positions of layers. The packing patterns of complexes 12 and Boyle's are shown in Figures 4.3 and 4.4. Figure 4.3 Packing pattern of complex [CpMo(CO) 3Br], 12

Figure 4.4 Packing pattern of Boyle's complex [CpMo(CO)3Br] 73

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