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Phosphine-stailized complexes of Tantalum and Rhodium McConville, David Hugh 1992

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PHOSPHINE-STABILIZED COMPLEXES OFTANTALUM AND RHODIUMByDAVID HUGH MCCONVILLEB. Sc., The University of Windsor, 1987A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIESDepartment of ChemistryWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIANOVEMBER 1991© David Hugh MeConville, 1991In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.Department of______________The University of British ColumbiaVancouver, CanadaDate NV /99/DE-6 (2/88)UABSTRACTThe chemistry of the transition metals is largely governed by the electronic andsteric properties of the ancillary ligands. One of the most widely encountered ligandsis the phosphine donor which has steric and electronic properties that can be easilyaltered by varying the substituents at phosphorus. Furthermore, incorporating thephosphorus donor into a chelating array enhances the stability of the correspondingcomplex toward loss of phosphine. This thesis describes the use of bulky chelatingdiphosphines to stabilize unusual complexes of tantalum and rhodium.Two new binuclear polyhydrides of tantalum containing bulky chelatingdiphosphines were synthesized by the reduction of[(R2S)TaClJ(i-Cl)p.-SR (R= -(CH2)4- (THT), CH3 {SMe2J) in the presence of the diphosphine underclihydrogen. The polyhydride complex, [{Pr’P(CH2)3r1} TaC1H]2Qi-H)(p.-S)(Pr1 = -CHMe2), results from the unexpected S-C bond cleavage of the bridgingthioether moiety (SMe2) in the starting material, [(MeS)TaC1](p-Cl)j.t SMe.The hexahydride binuclear complex, [( P(CH2)3Pr}TaH(t-H)is formedunder similar reducing conditions from the parent starting material containing thebridging THT moiety; however, no evidence of S-C bond cleavage was observed inthis instance. The site exchange of bridging hydrides is normally facile in binuclearcomplexes, however the hydrides in [{Pr’P(CH2)3- Pr12}TaH2](L- )are rigidlybound. The electronic structure of an appropriate model of[{Pr12P(CH)3}Ta](p-H)was studied by the Extended Hückel method inorder to help understand the unusual rigid coordination of the bridging hydrides.Amido-diphosphine complexes of tantalum were prepared by the reaction ofLi{N(SiMe2CHPR)}(R = Me, C6H5 {Ph}, Pr) with Ta(CH2R’)Cl3(R’ = CMe3{But}, Ph). The reaction proceeds via an a-elimination of RH through a highly-111ordered transition state yielding alkylidene compounds. The alkylidene, amidodiphosphine complexes serve as good starting materials for the preparation ofpolyhydride and dinitrogen species; the latter complexes reveal dinitrogen bound in anend-on fashion. A full INDOI1 (Intermediate Neglect of Differential Overlap) semi-empirical molecular orbital calculation on a model of the zirconium side-on bounddinitrogen complex [ZrCl(N(SiMe2CHPPr )}](.t),previously prepared in ourlaboratory, is presented. An analysis of the frontier orbitals of the dinitrogencomplexes was used to help understand the nature of dinitrogen binding (i.e. “sideon” versus “end-on”).Rhodium-zinc and rhodium-magnesium bonds were formed by the reaction ofdialkylzinc (ZnR2, R = CH26H5 {Bz), C5H {Cp}, C3H5 {allyl}) anddialkylmagnesium (MgBzTHF))(THF = -O(CH2)4)reagents with the binuclearrhodium hydride dimer [{PriP(CH3}Rh](.t-H) In the case of zinc, twoproducts are obtained, a Rh(I) species {Pri2P(CH)3}RhR (R = ‘q3-Bz, ‘q5-Cp,i3-allyl) and a tetranuclear derivative [{ PrP(CH2)3PPr} Rh]2(j.i-H)p -ZnR),the latter being formed by an unique fragmentation/recombination reaction. Amechanism for this process has been proposed based on product analysis and twocrossover experiments. In the case of magnesium only the mononuclear species,{Pr2P(CH)3r1Rh fl3-Bz) and{Pri2P(CH}Rh(.t )MgBz wereisolated with no evidence of the tetranuclear zinc analogue present.The reaction of ZnBz2 or MgBz2(THF) with [(COD)Rh]2(p-Cl) (COD =1,5-cyclooctadiene) yields the mononuclear benzyl derivative (COD)Rh(13-Bz). Thiscomplex is a useful precursor to diphosphine rhodium3-benzyl derivatives by simpledisplacement of the COD ligand, (i.e. (P-P)Rh(’r13-Bz), P-P = But2P(CH)3But,Pr2(CH)3P i,Pr2(CH)Pr,Pr’2CHP ’2 and CyPCHy (Cy =C6H11)). The resultant diphosphine complexes react rapidly with dihydrogen to giveivhydride dimers of various composition. In the case of the bulky diphosphinesBut2P(CH)3Bu,Pr2(CH)3Pr1Pri2(CH)Pr1,the classic dihydridebridged species are obtained. For the complexes incorporating the one carbonbackbone diphosphines,Pr12CHPr and Cy2PCH2PCy2, binuclear hexahydridespecies are obtained. The small chelate ring size of these ligands precludes directisolation of the dihydride bridged complexes. 3-Benzyl derivatives of iridium of theform, (PP)fr(q3-Bz) (P-P = BuP(CH2)3PBut andPr’2(CH)3Pr1,have alsobeen prepared by the reaction of ZnBz2 with [(P-P)frj(p Cl),however, thesecomplexes yield several products when exposed to clihydrogen.VTABLE OF CONTENTSABSTRACT iiTABLE OF CONTENTS vLIST OF TABLES ixLIST OF FIGURES xLIST OF ABBREVIATIONS xiiiACKNOWLEDGEMENTS xviiDEDICATIONCHAPTER 1 General Introduction1.1 Phosphines in Inorganic and Organometallic Chemistry 11.2 Electronic and Steric Properties of Phosphines 11.3 Metal-to-Phosphorus Back-bonding 41.4 Synthesis of Alkyiphosphines 51.5 Synthesis of Alkyldiphosphines 61.6 Phosphorus-31 NMR 81.7 Complexes Incorporating Bulky Chelating Diphosphines 91.8 The Scope of this Thesis 101.9 References 11CHAPTER 2 Binuclear Polyhydride Complexes of Tantalum2.1 Introduction 162.2 Reduction of Diphosphine Complexes of Tantalum under Hydrogen 192.2.1 Molecular Structure of [{dippp}TaClH]2(.t-S)(.i.-H)2 252.2.2 Molecular Structure of [{dippp}TaClH]2(.t-H)2 292.2.3 Electronic structure of[(H3P)2Ta](I.L-H) 36vi2.3 Synthesis and Characterization of Binuclear HexachiorideDiphosphine Complexes 442.3.1 Reduction of [(diphosphine)TaC12]2(J.L-Cl)2 under Hydrogen 462.4 Synthesis and Characterization of Diphosphine Alkylidene Complexes 462.4.1 Reduction of (diphosphine)TaC13=CHBut) under Hydrogen 482.5 Reactivity of Tantalum Binuclear Polyhydride Complexes 482.6 Summary and Future Considerations 492.7 Experimental Procedures 512.8 References 62CHAPTER 3 Amido-Diphosphine Complexes of Tantalum3.1 Introduction 683.2 Aniide Complexes of Tantalum 693.3 Preparation and Structure of Amido-Diphosphine Complexes ofTantalum 713.4 Kinetics of the a-Elimination of CH3R fromCl2Ta(CHR){N(SiMe2CHPPr’)} 783.5 Reduction of lTa(CHR){N(SiMePPri)}under Dihydrogen 833.6 Preparation of Anñdo-Diphosphine Imido Complexes of Tantalum 863.7 Dinitrogen Complexes Incorporating the Amido-Diphosphine Ligand:Factors Influencing Side-on vs. End-on Binding of Dinitrogen 883.7.1 Tantalum End-on Dinitrogen Complexes 903.7.2 Zirconium Side-on Dinitrogen Complex 913.7.3 Reduction ofCl2Ta(CHR)(N(SiMeHPPr1)underDinitrogen 943.7.4 Frontier Orbital Analysis of Dinitrogen Complexes 963.7.4.1 Frontier Orbitals of {H3P}2ZrCl(NH) 97vu3.7.4.2 Frontier Orbitals of{H3P}2Ta(=CH)(NH .1003.7.5 Mechanism of Formation of Dinitrogen Complexes 1043.8 Summary and Future Considerations 1053.9 Experimental Procedures 1073.10 References 114CHAPTER 4 The Reaction of Binuclear Rhodium Hydrides withDialkylzinë and Dialkylmagnesium Reagents4.1 Introduction 1204.2 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(CH2Ph) withBinuclear Rhodium Hydrides 1234.2.1 Molecular Structure of [{ dippp }Rh]2(p.-H).t-ZnCHP ) 1254.3 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(C5H)2withBinuclear Rhodium Hydrides 1294.3.1 Molecular Structure of [{dippp)Rh]2(I-H)2(I-ZnC5) 1314.4 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(C3H5)2withBinuclear Rhodium Hydrides 1354.5 Fluxional behavior of [{dippp}Rh]2(L-H)2(j.L-ZnR)2 1364.6 Bonding in Bridging Allcylzinc Complexes 1384.7 Mechanism of formation of [(dippp}RhJ(j.t-H)p -Zn ) 1414.7.1 Crossover Experiment 1434.8 Reaction of [{dippp}Rh]2(.L-H)($.L-ZnR) with Dihydrogen 1454.9 Formation of Rhodium-Magnesium Bonds: The Reaction of MgR2with Binuclear Rhodium Hydrides 1494.10 Summary and Future Considerations 1544.11 Experimental Procedures 1554.12 References 163vu’CHAPTER 5 Synthesis, Structure and Hydrogenation of fl3-Benzyl Derivatives of Rhodium and Iridium5.1 Introduction 1665.2 Synthesis and Characterization ofr3-Benzyl Derivatives of Rhodiumandiridium 1695.3 Molecular Structure of {dippp}Rh(fl3-CH2P ) 1775.4 Synthesis and Structure of Binuclear Rhodium Hydrides 1795.5 Summary and Future Considerations 1875.6 Experimental Section 1875.7 References 196AppendixA.1 Details of the Molecular Orbital Analyses 200A.2 X-ray Crystallographic Analysis of [{dippp}TaCll{J2(J.i-H)(.L-S) 206A.3 X-ray Crystallographic Analysis of [{dippp)TaC1H]2Q.t-H)2 210A.4 X-ray Crystallographic Analysis of [{ dippp }Rh]2(iI-H)ji- ZnB z)2 215A.5 X-ray Crystallographic Analysis of [(dippp}h]2(p.-H)2(p.-ZnCp)2 221A.6 X-ray Crystallographic Analysis of {dippp}Rh(fl3-CH2P ) 228Biographical Information 234ixLIST OF TABLESTable 2.1. Binuclear polyhydride complexes .18Table 2.2. Selected bond lengths for [(dippp}TaC1H]2(,.t-S)(i.L- ) 25Table 2.3. Selected bond angles for [{dippp}TaC1HI2(j.L-S)(J.L-H)2 25Table 2.4. Selected bond lengths for [(dipppTaC1H]2(J1.-H)2 32Table 2.5. Selected bond angles for [{dippp}TaC1H]2(p.-H)2 34Table 2.6. Extended Hückel eigenvalues for [(H3P)Ta(i.t-H) 39Table 3.1. Rate data for the a-elimination of CH3R fromC12Ta(CHR){N(SiMe2CHPPr)} 81Table 3.2. Erying data for the a-elimination of CH3R fromClTa(CHR){N(SiMeHPPr)} 82Table 3.3. Enthalpy and Entropy data for the a-elimination process ofknown tantalum ailcylidene complexes 83Table 3.4. Tantalum end-on dinitrogen complexes 91Table 4.1. Selected bond lengths for [(dippp}Rh]2(. -H)-ZnC 2P ) 127Table 4.2. Selected bond angles for [{dippp)Rh](j.t-H)j.t-ZnCHPh) 127Table 4.3. Selected bond lengths for [(dippp}Rh]2(p.-H)(i-ZnC5H5)2 133Table 4.4. Selected bond angles for [(dippp}Rhj2(.t-H)i-ZnC5H) 133Table 5.1. Selected bond lengths for {dippp)Rh(r3-CHPh) 177Table 5.2. Selected bond angles for (dippp)Rh(q3-CH2P ) 177xLIST OF FIGURESFigure 2.1. 299.94 MHz 1H NMR spectrum of [{dippp}TaC1HI2(p.-S)(J.L-H)2, 1, in6D 24Figure 2.2. (a) Chem 3D Plus® representation of [(dippp)TaClH]2-(i-S)(i-H)2. (b) Chem 3D Plus® drawing of 1 showing the proposedpositions of the hydrides 26Figure 2.3. 299.94 MHz 1H NMR spectrum of Ta2H(dippp)2, 2, in C6D 31Figure 2.4. (a) Chem 3D Plus® representation of [{dippp)TaClH]2(p-H)2.Hydrogen atoms are omitted for clarity. (b) Chem 3D Plus® viewdownthe Ta-Ta axis showing the twisting of the plane generated by thebridging hydrides 33Figure 2.5. Summary of the Extended Hückel eigenvalues for the modelcompound [(H3P)2Ta](i.L-H),2’ 38Figure 2.6. (top) Isosurface plot of the 6ag level of 2’ for N’ = 0.05 a.u..(bottom) Isosurface plot of the 4b level for ‘ = 0.05 a.u.. Dark greyarea = ‘-Ni’ light grey area = -N’ 41Figure 2.7. (top) Isosurface plot of the 7b level of 2’ for Ni = 0.05 a.u..(bottom) Isosurface plot of the 7ag level for Ni = 0.05 a.u.. Dark greyarea = +\ji, light grey area = -Ni 42Figure 3.1. 400.00 MHz 1H NMR (top) and NOEDIFF spectrum (bottom)of compound 2 in C6D 76Figure 3.1. (a) The first-order rate plot for the a-elimination fromClTa(CHBut)(N(SiMeHPPr}.(b) The first-order rate plotfor the a-elimination from l2Ta(CHPh){N(SiMeCHPr} 80Figure 3.2. Eyring plot for the a-elimination of CH3R fromCl2Ta(CHR)-(N(SiMeCHPPr)} 81xiFigure 3.3. A possible transition state for the a-elimination of CH3R fromCl2Ta(CHR){N(SiMeHPPr’)2} 82Figure 3.4. Proposed active site in nitrogenase as determined bymolybdenum and iron EXAFS analysis 89Figure 3.5. (top) Isosurface plot of the 6bg level of[(H3P)2ZrCl(NH)](p.-N2) for N’ = 0.03 a.u.. (bottom) Isosurface plot of the 8bg level for =0.03 a.u.. Dark grey area=-i-’qi, light grey area= -Ni 93Figure 3.6. Molecular orbital interaction diagram for the model compound[{ HP )2ZrCl(NH](1.L-N2), showing the important N2 bondingorbitals 98Figure 3.7. Molecular orbital interaction diagram for the model compound[{HP}2Ta(=CH)(NH2)]($L-N2), showing the important N2 bondingorbitals 102FIgure 4.1. 121.42 MHz P{hH} NMR spectrum of a 1:1 mixture ofZn(CH2Ph) and [{dippp}Rh]2(I-H)2 in C6D 124Figure 4.2. Chem 3D Plus® representation of [{dippp)Rh]2(p.-H)2(I-ZnCH2Ph) (1). Hydrogen atoms have been omitted for clarity 126Figure 4.3. (a) Chem 3D Plus® view of the rhodium-zinc core of[{dippp}Rh](.L-H)2(.t-ZnCH2Ph)2 (1). (b) Chem 3D Plus® view ofthe rhodium coordination sphere 128Figure 4.4. (a) Chem 3D Plus® representation of [(dippp)Rh]2(.t-H)2(L-ZnC5H)2(3). Hydrogen atoms have been omitted for clarity. (b)Chem 3D Plus® representation of the core of the dimer 132Figure 4.5. (a) Mainly ionic interaction of a cyclopentadienyl group with zinc.(b) Mainly covalent interaction of a cyclopentadienyl group with zinc 137Figure 4.6. Bonding molecular orbitals for the fragment(15-CH)Zn 142xi’Figure 4.7. 121.42 MHz 31P{1H} NMR spectrum of the crossover between[{dippp}Rh]2(.L-H)2, [{dippe}RhJ2(.t-H)2 and Zn(CH2Ph)in C6D 146Figure 4.8. (a) 31P decoupled 1H NMR spectrum of the hydride region of{dippp}RhH2(L-H)2MgCPh(11). (b) 1H NMR spectrum of thehydride region 153Figure 5.1. Exchange processes in fl3-benzyl complexes. (A) Antarafacialexchange of ortho protons only. (B) Antarafacial exchange of syn andanti protons only. (C) Suprafacial exchange of ortho, syn and antiprotons 168Figure 5.2. 121.42 MHz 31P{’H} NMR spectrum of {dippm}Rh(fl3-CH2Ph)in C6D 172Figure 5.3. 299.94 MHz 1H NMR spectrum of {dippe}Rh(i3-CH2Ph)inC6!) 174Figure 53. Chem 3D Plus® representation of the molecular structure of{dippp)Rh(-CH2Ph) 178Figure 5.5. Results of the decoupling experiments for [(dippm}RhH3]2 184xfflLIST OF ABBREVIATIONSThe following list of abbreviations, most of which are commonly used in thechemical literature, will be employed in this thesis:A angstrom (10-10 m)Anal, analysisatm atmospherebr broadBz benzylBut tertiary butylb.p. boiling point‘C degree centigradeCalcd. calculatedChem 3D Plus® molecular modelling program for the Macintosch‘3C{ 1H} observe carbon while decoupling protoncm1 wave numberC1 ipso-carbonCm mera-carbonC0 ortho-carbonCp para-carbonCOD 1 ,5-cyclooctadieneCOE cycloocteneCp cyclopentadienyl anion, C5HçCy cyclohexylheatIH enthalpy of activationxivAS entropy of activation6 chemical shiftd doubletdd doublet of a doubletdcypm bis(dicyclohexylphosphino)methanedippe 1 ,2-bis(diisopropylphosphino)ethanedippm bis(diisopropylphosphino)methanedippp 1 ,3-bis(diisopropylphosphino)propanedmpe 1 ,2-bis(dimethylphosphino)ethanedmpm 1,1 -bis(dimethylphosphino)methanedppe 1 ,2-bis(diphenylphosphino)ethanedppp 1 ,3-bis(diphenylphosphino)propanedtbpp 1 ,3-bis(dit-butylphosphino)propaneEt ethylEXAFS extended X-ray absorption fme structureeV electron Voltfac facialg gramGCMS gas chromatography, mass spectrometryh Planck’s constanth hour1H(31P} observe proton while decoupling phosphorus2H { 1H } observe deuterium while decoupling protonHb bridging hydrideHm meta-hydrogenH0 ortho-hydrogenHp para-hydrogenxvH terminal hydrideHz HertzINDO intermediate neglect of differential overlapIR infraredn-bond coupling constant between A and B atomsK degree Kelvink rate constantkcal kilocaloriekB Boltzmann constantKeq equilibrium constantobserved rate constantHOMO highest occupied molecular orbitalLUMO lowest unoccupied molecular orbitalm multipletM molarMe methylmer meridionalmg milligramMHz megaHertzmJ milliljtremm millimetremmol millimolemol molen-Bu normal butyl (-CH2C3)15N{H} observe nitrogen while decoupling protonNOE nuclear Overhauser effectNMR nuclear magnetic resonancexviNp neopentylp pentetPES photoelectron spectroscopyPh phenylppm parts per million31P{1H) observe phosphorus while decoupling protonPr1 isopropylpz (pyrazolyl)hydroborateR gas constantROMP ring opening metathesis polymerizationRT room temperatures singlets secondsept septetS.H.E. standard hydrogen electrodet triplett-butyl tertiary butylTHF terahydrofuranTHT tetrahydrothiopheneV voltXcL type of molecular orbital programxviiACKNOWLEDGEMENTSFirst and foremost, I would like to thank my supervisor Mike Fryzuk for hisendless enthusiasm with regards to chemistry. Although Mike will cease to be myresearch supervisor, I will always consider him a good friend. Thank-you, Myl, Tim,Lisa, Guy, Cam, Neil, Chas, Randy, Kiran, Jesse, Craig, Cindy, Brian, Dave, Bobbi,Warren, Graham, Pauline and Patrick for your helpful comments and friendship.I would also like to acknowledge the help ‘I had from all the support staff hereat UBC: the people in the electrical, mechanical and glass-blowing shops, the NMRstaff, P. Borda the elemental analysis expert and Steve Rettig, the crystallographerwho solved four of the crystal structures in this thesis. A special thanks to DougStephan who also solved a structure.Many thanks to all the graduate students whose interests (apart fromchemistry) such as soccer, flag football, football pools, and auto-repair have allowedme a great deal of variation in my leisure time.Finally, I would like to thank the Natural Sciences and Engineering ResearchCouncil of Canada and the University of British Columbia chemistry department forfinancial assistance.xvfflFor my loving and supportive wifeAnne Marieand our beautiful children,may our chemistry never endChapter 1CHAPTER 1General Introduction1.1 Phosphines in Inorganic and Organometallic ChemistryTransition metals, and to a lesser extent main group elements, show atendency to form stable complexes with certain trivalent phosphorus compounds, andthis makes the phosphine donor one of the most frequently encountered ancillaryligands in inorganic and organometallic chemistry.1 Since the chemistry of thetransition metals is largely governed by the electronic and steric properties of theancillary ligands,2 the variability of phosphorus-based ligands allows the reactivity ofa metal complex to be fine-tuned. The steric bulk and electronic properties of aphosphine can be altered easily by varying the substituents at phosphorus.Furthermore, incorporating the phosphorus donor into a chelating array enhances thestability of the corresponding complex toward loss of phosphine (chelate effect).3 Incontrast to amines, the inversion at phosphorus’ in phosphines is quite slow allowingfor the synthesis of enantiomerically pure chiral phosphines. Transition metalcomplexes incorporating chiral phosphine ligands have been used for theenantioselective synthesis of important drugs.4 Because phosphines play a pivotalrole in this thesis, a brief review of this area is in order.1.2 Electronic and Steric Properties of PhosphinesPrior to about 1970, nearly all the reactivity associated with transition metalphosphine complexes was rationalized in terms of electronic effects, although someauthors did refer to steric effects.5 The electronic properties of phosphines werethought to be crucial when phosphine dissociation was desired. For instance,RhC1(PPh3) (Wilkinson’s catalyst)6 will hydrogenate olefins under very mildReferences p.11Chapter 1 2conditions (25°C, 1 atmosphere H2); however RhC1(PMe3)does not hydrogenateolefins even under extreme conditions7(scheme 1.1).Scheme 1.1HPg1,,,...SH2 -H2Sc1””hh’p I-C2H6An important step in the mechanism of the hydrogenation of olefins with Wilkinson’scatalyst is the dissociation of triphenyiphosphine. Dissociation of trimethylphosphinefrom RhC1(PMe3)is very slow which does not allow for the formation of thecoordinatively unsaturated intermediate A and this shuts down the catalytic cycle.The rest of the steps in the hydrogenation mechanism in scheme 1.1, oxidativeaddition, insertion and reductive elimination,1all form the basis of the catalytic cyclewhich has been extensively studied.8I-’ ,- H!—,liIl,.. •Ø,%1 t’CI P-H2HPPciH — PP-PP = P(C6H5)3S = solventMe3P11,,, Rh*PMe3CI PMec=cH•••,id’ Hc=cCHNo HydrogenationH2, OlOfiflReferences p.11Chapter 1 3In the early 1970’s, the effect of the steric bulk of a phosphine was realizedwith the measurement of equilibrium constants for the phosphine dissociation fromgroup 10 complexes;9 for example, PPr13 dissociates to a greater extent than PPh3from zero valent paladium complexes’° even though PPr13 is more basic than PPh3(equation 1.1).Keq.PdP4 P + PdP3 Keq (PPh3)< Keq (PPr’3) [1 .1]The presence of several bulky phosphine donors about the palladium metal centrecauses inter-ligand repulsion leading to facile ligand dissociation. The steric bulk of aphosphine is generally at least as important as the electronic effects and can dominatein many cases. Thus the phosphine dissociation proposed in the formation ofintermediate A in scheme 1.1 is as much an effect of the steric bulk of the PPh3(versus PMe3) as it is the electronic nature of the phosphine donor.A method used for the measurement of steric bulk of a phosphine ligand is thecone angle.5 In its simplest form, the cone angle is defined as the angle (ct) of acylindrical cone, centred 2.28 A from the phosphorus, which touches the outermostatoms of the substituent R groups (I).IThe angle a can vary from 118° for PMe3 to z182° for PBut3. For unsymmetricalphosphines or chelating diphosphines a different formula9 is used to calculate a coneReferences p.11Chapter 1 4angle. One of the bulky ligands used throughout this thesis, Pr’P(CH2)3rhas acone angle estimated to be l4O° about each phosphorus donor making this ligandquite sterically demanding. In comparison, the cone angle about each phosphorus inMe2PCHCMeis only iOi•Y1.3 Metal-to-Phosphorus Back-bondingFor a number of years, alkyl and aryiphosphines were thought to stabilizetransition metal hydride and alkyl complexes through dit-dic back-bonding from thefilled metal d-orbitals to the unfilled, high energy phosphorus 3d-orbitals.1 In fact, atextbook explanation’1 for it-back-bonding suggests that electronegativesubstituents on phosphorus lower the energy of the 3d orbitals making them moreavailable for it-accepting of electron density from the metal. Yet there are theoreticalcalculations on phosphines such as PMe3,PH3 and PF3 which suggest that the back-bonding to phosphorus is mainly into phosphorus 3p orbitals12 or a* type orbitals’3and not into phosphorus d-orbitals.Experimentally (PES) it has been found that the ic-acceptor ability of atrialkylphosphine is similar to that of a trialkylamine, that is, they are very weakacceptors at best.14-’8 However, a recent report19 showed that ic-back-bonding byalkylphosphines can also be important in low oxidation state early transition metalcomplexes.Observed features such as trans-bond weakening, previously thought to be aneffect of it-back-bonding in phosphine complexes, are satisfactorily explained by thestrong a-donation of a phosphine (II and III).References p.11Chapter 1 5CI2.29AEt3P Pt CI CIPEt3II ifiComplex II, which bears cis phosphines, displays a longer Pt-Cl bond length than theisomer with trans phosphines (III).20 Further evidence for strong a-donation fromphosphines is observed in the IR studies on Ni(CO)3PR by varying the phosphinedonors.2’ An increase in the amount of electron density at the metal has the effect ofreducing the carbonyl stretching frequency. The a-donor ability of the phosphinesstudied increase in the order PMe3 <PEt <PBu3.1.4 Synthesis of AlkyiphosphinesThe number of phosphorus compounds is truly remarkable; a seven volumeseries devoted to organophosphorus compounds lists, until 1976, over 100,000derivatives.22 The classic synthesis of alkyiphosphines involves reaction of PX3(normally X = Cl, Br) with an alkyl Grignard reagent at low temperamre as shown inequation 1.2.low temp.PX3 + z RMgX z MgX2 + PRX3.. [1 .2JEt20With sufficiently bulky alkyl groups the primary (RPX2) and secondary (R2PX)halophosphines can be isolated. However, a different preparative route is required forvolatile phosphine derivatives such as PMe3•24,25 Tertiary phosphines are waterstable but do react with oxygen to form phosphine oxides (R3P=O). Primary andsecondary halophosphines are less reactive with oxygen but very reactive with waterPEt3References p.11Chapter 1 6yielding alkyiphosphinic acids. The ability of phosphorus to increase its oxidationstate, P(III)— P(V), is the basis of the Wittig reagent which is used industrially26 toconvert aldehydes to olefms (equation 1.3).R3P=CHR + R’CHO R3P=O + RHC=CHR [1.3]Treatment of the primary or secondary halophosphines with lithium aluminiumhydride (LiA1H4)yields the primary or secondary phosphines27 as shown in equation1.4.low temp.PRX3.. + L1AIH4 PRH3.. [1.4]Et20Primary and secondary phosphines are water stable but again react with oxygen toform phosphine oxides (i.e. RH2P=O andR2HP=O).L5 Syntfresis of AlkyldiphosphinesDiphosphines containing a backbone of more than two methylene units aremost easily prepared by reacting an aliphatic dihalide with lithium dialkyiphosphide(LiPR2)as shown in equation 1.5.low temp.2 LiPR2 + X(CH2)X R2P(CH)PR + 2 LIX [1.5]X = Br, Cl; y 3LiPR2 is easily prepared by deprotonating HPR2 with one equivalent of butyllithium inhexanes.28 A representative example is the synthesis of Pr’2P(CH2)3PPr1from 1,3-dibromopropane and LiPPr2,9 an ailcyldiphosphine ligand used throughout this thesis.The synthesis of diphosphines incorporating one or two methylene units mustbe approached from a different route since the addition of LiPR2 to aliphatic halidessuch as XCH2X and XCH2CH yields elimination products. The simple addition ofReferences p.11Chapter 1 7four equivalents of an alkyl Grignard reagent toC12PCH13°yields the desireddiphosphine (equation 1.6).low temp.4 RMgX + CI2PCHI R2PCHCR [1.6]Et20X = Br, ClIn a similar fashion the single methylene backbone chlorodiphosphine,C12PCH13can be converted to the corresponding alkyldiphosphine. Prior to the synthesis ofC12PCHH 12 simple chelating ligands such as Me2PCH2CH2PMe2 wereprepared from toxic, hazardous materials such as PH32 and Me2P-PMe2.33’4The diphosphines mentioned above are normally incorporated into a chelatingarray once they are bound to a metal complex (V) which maintains the phosphorusdonors in a mutual cis-disposition.LV\%%(CH2)T”The bite angle, (x, of these ligands can range from 75° for the one carbon backbone,—85° for the two methylene unit backbone, to as high as 1050 in chelating diphosphinesincorporating the three carbon backbone. By varying the steric bulk, as measured bythe cone angle, and the mutual disposition of the phosphorus donors, as measured bythe bite angle, it is clear that the steric environment about the metal can be greatlyinfluenced.Alkyldiphosphines that maintain a trans-disposition of the phosphorus donorsare not as common as cis chelating diphosphines but can lead to different reactivityReferences p.11Chapter 1 8patterns once bound to a metal complex. A few representative examples of transdisposed chelating diphosphines are shown below (VI? VII,36aVllI,36’and 1X37).PR( PR2VIIN—H VIPR2PR2PR2 ,,—PR2Me2SiVIII /NLI ixMe2SI\PR2Complexes incorporating the amido-diphosphine ligand IX will be the subject of someof the studies in this thesis.1.6 Phosphorus-31 NMRUndoubtedly, one of the major reasons that the use of phosphines has gainedsuch prominence in inorganic and organometallic chemistry is the fact thatphosphorus-31 has a nuclear spin of 1/2 and is 100% abundant, making it readilyobservable by common nuclear magnetic resonance techniques.38 The receptivity ofphosphorus-31 is about 6% that of normal 1H NMR. The chemical shift window for31P NMR is rather large (700 ppm, from +250 ppm — -450 ppm) thus phosphines indifferent chemical environments are easily discernable. Furthermore, P-P’ coupling aswell as coupling to other spin active metal nuclei such as 195Pt, 103Rh, 183W, and 89Yis normally large yielding valuable stereochemical information.References p.11Chapter 1 91.7 Complexes Incorporating Bulky Chelating DiphosphinesThe use of bulky chelating diphosphines to stabilize unusual transition metalspecies has gained notoriety in recent years.392 The large bulky substituents onphosphorus can lead to coordinatively unsaturated metal centres. The preparation ofthe chromium(II) species, [(Pr1P(CH2)PPriCrC1]43demonstrates the use of abulky phosphine to generate coordinative unsaturation. With smaller diphosphinessuch as Me2PCHCMe,bis(diphosphine) derivatives such as(Me2PCH2CH2PMe}2CrC1 are obtained.44 Subsequent alkylation of[{Pr(CH)Pr} CrC1] yields the four-coordinate, square-planar Cr(II) ailcyls(X).45xAs well as generating coordinative unsaturation, bulky chelating diphosphinescan also protect reactive portions of a molecule. In the nickel complex46 below (XI),the bulky cyclohexyl substituents on phosphorus surround the di-benzyne moiety,possibly protecting it from further reaction.References p.11Chapter 1 101.8 The Scope of this ThesisThis thesis is divided into two parts: one dealing with phosphine complexes oftantalum (chapters 2 and 3), and the other with phosphine complexes of rhodium(chapters 3 and 4). The common theme is the use of builcy chelating diphosphines inan attempt to generate coordinatively unsaturated compounds as well as unusualmodes of reactivity.Chapter 2 deals with bulky chelating diphosphine complexes of tantalum47incorporating the three, two and one carbon backbone diphosphines,Pr2P(CH2)3r,Pr’2P(CHr1and Pr’2PCH2PPr1. The goal was to preparephosphine deficient, coordinatively unsaturated polyhydride complexes and to studytheir reactivity in the context of the known reactivity of polyhydride species.The main focus of chapter 3 is the synthesis and reactivity of alkylidene amidodiphosphine complexes of tantalum. The reduction of these species under dinitrogenand the molecular orbital analysis (Extended Hückel and INDOI1) of the resultingdinitrogen complexes was made in an effort to understand the differences in the typesof bonding available to dinitrogen (“side-on” versus “end-on”).References p.11Chapter 1 11In chapter 4 the reactivity of the coordinatively unsaturated diphosphinecomplex [{Pr’P(CH2)3r’)Rh]2Qi-H) toward dialkylzinc48 and diallcylmagnesiumreagents was studied. The facile oxidative addition of the Zn-C and Mg-C bonds tothe rhodium dimer core resulted in an unusual fragmentation-recombination reaction.A possible mechanism for this transformation is given.Finally, chapter 5 describes the synthesis and hydrogenation of1]3-benzylcomplexes of rhodium incorporating the bulky chelating diphosphines,But2P(CH)3But,Pr2(CH)3Pr1,Pr2(CH)Pr1,Cy2PCHPCy andPrCHP .49 An improvement in the preparation of the binuclear complexes[{Pr2(CH)3Pr} Rh]2(i-H) and [(Pr12P CH)} Rh](p.-H) is given alongwith evidence that the one carbon backbone diphosphines form hexahydride dimersinstead of the classic dihydride dimers.1.9 References-(1) Coliman, 3. P.; Hegedus, L. S.; Norton, 3. R.; Finke, R. G. Principles andApplications of Organotransition Metal Chemistry; University Science Books:Mill Valley, Cal, USA, 1987.(2) McAuliffe, C. A. In Comprehensive Coordination Chemistry; G. Wilkinson, R.D. Gillard and 3. A. McCleverty, Ed.; Pergamon Press: London, England, 1987;Vol. 2; pp 989.(3) Huheey, 3. E. Inorganic Chemistry; Third ed.; Harper and Row: New York,USA, 1983, pp 527-535.(4) Knowles, W. S. Acc. Chem. Res. 1983, 16, 206.(5) Tolman, C. A. Chem. Rev. 1977, 77, 313.References p.11Chapter 1 12(6) Young, J. F.; Osborn, 3. A.; Jardine, F. H.; Wilkinson, G. J. Chem. Soc., Chem.Commun. 1965, 131.(7) Jones, R. A.; Real, F. M.; Wilkinson, G.; Galas, A. M. R.; Hursthouse, M. B.;Malik, K. M. A. J. Chem. Soc., Chem. Commun. 1979,489.p(8) Halpern, 3.; Olcamoto, T.; Zakhariev, A. .1. Mo!. Cat. 1976,2, 65.(9) Tolman, C. A.; Seidel, W. C.; Gosser, L. W. J. Am. Chem. Soc. 1974, 96, 53.(10) Musco, A.; Kuran, W.; Silvani, A.; Anker, M. W. I. Chem. Soc., Chem. Commun.1973, 938.(11) Huheey, 3. E. Inorganic Chemistry; Third ed.; Harper and Row: New York,USA, 1983, pp 832-833.(12) Xiao, S.; Trogler, W. C.; Ellis, D. E.; Berkovitch-Yellin, Z. J. Am. Chem. Soc.1983, 105, 7033.(13) Marynick, D. S. J. Am. Chem. Soc. 1984, 106, 4064.(14) Gerloch, M.; Woolley, R. G. Prog. Inorg. Chem. 1984,31, 371.(15) Bursten, B. E.; Darensbourg, D. 3.; Kellog, 0. E.; Lichtenberger, D. L. Inorg.Chem. 1984, 23, 4361.(16) Daamen, H.; Oskam, A.; Stufkens, D. 3. Inorg. Chim. Acta 1980,38, 71.(17) Yarbrough II, L. W.; Hall, M. B. Inorg. Chem. 1978, 17, 2269.(18) Higginson, B. R.; Lloyd, D. R.; Connor, I. A.; Hillier, I. H. J. Chem. Soc.,Faraday Trans. 1974,2, 1418.References p.11Chapter 1 13(19) Morris, R. J.; Girolami, G. S. Inorg. Chem. 1990,29, 4167.(20) Appleton, T. H.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev. 1973, 10, 335.(21) Tolman, C. A. J. Am. Chem. Soc. 1970,92, 2953.(22) Kosolapoff, G. M.; Maier, L. Organic Phosphorus Compounds; John Wiley &Sons: New York, USA, 1976; Vol. 1-7.(23) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; Fifth ed.; JohnWiley & Sons: Toronto, Canada, 1988, pp 392.(24) Wolfsberger, W.; Schmidbaur, H. Syn. React. Inorg. Met.-Org. Chem. 1974,4,149.(25) Zingaro, R. A.; McGlothlin, R. E. J. Chem. Eng. Data 1963, 8, 226.(26) Pommer, H. Angew. Chem., mt. Ed. Engi. 1977, 16, 423.(27) Powell, P. Principles of Organometallic Chemistry; Second ed.; Chapman andHall: London, England, 1988, pp 126.(28) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,24, 642.(29) Tani, K.; Tanigawa, E.; Tatsubo, Y.; Otsuka, S. J. Organomer. Chem. 1985,279, 87.(30) Burt, R. J.; Chatt, 3.; Hussain, W.; Leigh, G. 3. J. Organomet. Chem. 1979, 182,203.(31) Novikova, Z. S.; Prishchenko, A. A.; Lutsenko, I. F. J. Gen. Chem. USSR 1977,707.References p.11Chapter 1 14(32) Chatt, 3.; Hayter, R. G. J. Chem. Soc. 1961, 896.(33) Butler, S. A.; Chatt, 3. Inorg. Syn. 1974, 15, 185.(34) Parshall, G. W. J. Inorg. Nuci. Chem. 1960, 14, 291.(35) Edwards, P. G.; Jaouhari, R. G. Polyhedron 1989, 8, 25.(36) (a) Shaw, B. L.; Tucker, N. I. Organo-Transition Metal Compounds andRelated Aspects of Homogeneous Catalysis; Pergamon Press: New York,USA, 1973. (b) Moulton, C. 3.; Shaw, B. L. .1. Chem. Soc., Dalton Trans. 1976,1020.(37) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,24, 642.(38) Pregosin, P. S.; Kunz, R. W. NMR Basic Principles and Progress; Springer-Verlag: Heidelberg, 1979; Vol. 16, pp 55.(39) Baker, R. T.; Ovenall, D. W.; Harlow, R. L.; Westcott, S. A.; Taylor, N. J.;Marder, T. B. Organometallics 1990,9, 3028.(40) Bonrath, W.; Pörschke, K. R.; Wilke, G.; Angermund, K.; Kruger, C. Angew.Chem., mt. Ed. EngI. 1988,27, 833.(41) Pörschke, K. R. Angew. Chem., mt. Ed. Engi. 1988,26, 1288.(42) Hermes, A. R.; Girolami, G. S. Organometallics 1988, 7, 394.(43) Hermes, A. R.; Girolanil, G. S. Inorg. Chem. 1988,27, 1775.(44) Giralomi, G. S.; Wilkinson, G.; Galas, A. M. R.; Thornton-Pett, M.;Hursthouse, M. B. .1. Chem. Soc., Dalton Trans. 1985, 1339.References p.11Chapter 1 15(45) Hermes, A. R.; Morris, R. J.; Girolami, G. S. Organometalllcs 1988, 7, 2372.(46) Bennett, M. A.; Drage, 3. S.; Griffiths, K. D.; Roberts, K. K.; Robertson, G. B.;Wickramasinghe, W. A. Angew. Chem. 1988, 100, 1002.(47) Fryzuk, M. D.; McConvile, D. H. Inorg. Chem. 1989,28, 1613.(48) Fryzuk, M. D.; McConville, D. H.; Rettig, S. 3. Organometallics 1990, 9, 1359.(49) Fryzuk, M. D.; McConville, D. H.; Rettig, S. 3. J. Organomet. Chem. 1991,accepted for publication.References p.11Chapter 2 16CHAPTER 2Binuclear Polyhydride Complexes of Tantalum2.1 IntroductionPentahydride complexes of tantalum of the type TaH5P4 (P2 = dmpe’ or P =PMe32) are members of a large family of phosphine-stabilized polyhydrideTcomplexes having the general formula MHXPY. Other members of this family from thethird row transition series include WH6P3,WH4P,ReH7P2,5ReH5P3,6OsH4P3,7IrH3P,8 and IrH5P2;9 the stoichiometry of these complexes is dependent on themethod of preparation but more importantly on the number and size of the phosphinepresent. The strong a-donating character and steric bulk of the phosphines help tostabilize an otherwise highly reactive moiety (MHz). A characteristic feature of allthese systems is that they are all 18-electron complexes, in other words, they areelectronically and coordinatively saturated. Therefore, any reactivity by phosphinestabilized polyhydride complexes must be preceded by either phosphinedissociation1012 or loss of H2;135 this latter process may be facilitated by thepresence of a coordinated -dihydrogen moiety.’6 Several polyhydride complexeshave been reinvestigated in recent years due to the discovery of the2-dihydrogenligand. For example, complexes such as (Ph3P)2ReH7and [(dppe)RuH3J havebeen reformulated as (Ph3P)2ReH5H)17and [(dppe)RuH(H)],18respectively.The polyhydrides of rhenium and iridium have received considerable attention becauseof their ability to activate C-H bonds in saturated as well as unsaturatedhydrocarbons.’923The term polyhydride will be reserved for complexes that contain on average two or more hydridesper metal centre.References p.62Chapter 2 17The thermally induced loss of 112 from the polyhydride complex (Cy3P)ReH713and subsequent activation of solvent (C6D) has been well studied as shown inscheme 2.1.Scheme 2.1(Cy3P)2ReH7 80C-“(Cy3P)2ReH5” + H2+Cy2P—ReH6(PCy3)(Cy3P)2ReH5D(C6)Cy2P4çeH(PCy3)The transient complex “(Cy3P)2ReH5”is formally a 16-electron species andsusceptible to oxidative addition. C-D activation of the saturated hydrocarbonsolvent, C6D generates the electronically saturated perdeutero-phenyl derivative A.Further evidence for the electron-deficient intermediate is observed in theregioselective metalation of the cyclohexyl rings of the phosphine and subsequentdeuteration at these sites via the rhenium deuteride (species B and C). This studydemonstrated the highly reactive nature of the electronically unsaturated rheniumpolyhydride intermediate and suggested that such complexes could be useful C-Hactivation catalysts.Binuclear polyhydrides of the transition metals are less common than theirmononuclear analogues. This is not surprising since the majority of mononuclearcomplexes are coordinatively and electronically saturated and as such do not requireReferences p.62Chapter 2 18further stabilization. Table 2.1 lists some of the better known examples of binuclearpolyhydride complexes.Table 2.1. Binuclear polyhydride complexes.Rh2H4(P(NMe2)3)4 ref. 24[fr2H5(dppp)2] ref. 25Os2H4(PMe Ph)4 ref. 15Ru2H8(PPh3)4 ref. 26Re2H8(PEt2Ph)4 ref. 27’Besides the presence of bridging hydrides, a further characteristic of thebinuclear polyhydride complexes above is that they contain on average only twophosphine donors per metal. This “phosphine deficiency” can be secured by usingstoichiomethc amounts of phosphine but this sometimes leads to disproportionation28(scheme 2.2).Scheme 2.2{(MeO)3P}Rh(-CH5) {(MeO)3P}RhH[{(MeO)3P}2RhH] {(MeO)3P)4RhHA method used to generate phosphine-deficient complexes is to employ bulky,chelating diphosphines. In general, the steric bulk of the diphosphine precludesformation of bis(diphosphine) complexes when a 1:1 stoichiometry is employed. Theentropic chelate effect enhances the stability of these complexes with respect to lossof phosphine. Furthermore, the nature of the chelated diphosphine maintains a cisdisproportionationReferences p.62Chapter 2 19coordination of the phosphines which reduce potential steric interactions in binuclearcomplexes.This chapter describes the synthesis and characterization of binuclearpolyhydride complexes of tantalum incorporating bulky chelating diphosphines. Thebinuclear polyhydrides were synthesized by a variety of routes in an attempt tounderstand the mechanism of their formation. An Extended Hückel molecular orbitaldescription of the bonding in one of the polyhydride complexes is also included.2.2 Reduction of Diphosphine Complexes of Tantalum under HydrogenTwo different strategies have been used previously to prepare binucleartantalum complexes containing phosphine ligands. The first uses the binuclearstarting materials in the form of tris(thioether) complexes29 which are prepared by thesodium-mercury amalgam reduction of TaX5 in the presence of excess THT as shownin equation 2.1.-TaX5 + 2 Na/Hg + (xs) THT toluene 1/2 TaX6(THT)3[2.11THT=S(] X=Br,CIThe molecular structure3°of [(THT)TaC12]2(p-C1)2(I- HT) (I) was shown to be aconfacial bioctahedron with two chlorides and a thioether moiety forming theconnecting face of the dimer. The analogous complex [(Me2S)TaC12]2(J.t-Cl)2(J.L-SMe2) (11) has the same molecular structure.3°References p.62Chapter 2 20IThe binuclear tantalum complexes I and II contain formal metal-metal double bondsas evidenced by the short Ta-Ta distances of 2.681(1) A and 2.691(1)A, respectively.The addition of diphosphines to I and II demonstrated the formation of edge-sharingbioctahedral complexes31’2by simple displacement of the thioether ligands as shownin scheme 2.3.Scheme 2.3Et2 CI CI Et2- 2 depe 1111 \ ØLChul% / Ø%’ -cEt2 c ci Et2Me2 CI Ci Me22 dmpe r1141 \ / PIIMe2 Me2The second strategy employed for the formation of binuclear tantalumphosphine complexes involves the reduction of TaCl in the presence of PMe3(equation 2.2).CIReferences p.62Chapter 2 212 Na/HgTaCt5 + (xs) PMe3toluene1/2 [(Me3P)TaCI]Q.t- t) [2.21IIIIn a series of reports,33-7 the binuclear tantalum complex [(Me3P)2TaC12]2(.t-C1)(III) was shown to undergo oxidative addition of dihydrogen across the Ta=Ta doublebond (scheme 2.4). The hydrido-bridged complex IV could be reduced in high yield togive the dimeric derivative V; addition of dihydrogen to V yielded the tetrahydridebridged dimer VI. Further reduction of VI lead to intractable products.Scheme 2.4FMe3 CIH2c,,, \ CI% / PMeci PMe3PMe3 H CiIV2 Na/HgH2With the above mentioned complexes in mind, we became interested insynthesizing edge-sharing bioctahedral complexes of tantalum incorporating the bulky,chelating diphosphines Pr2P(CH)3r (dippp),Pr2(CHPr (dippe) andPr2CHPr (dippm), and investigating their reactivity toward dihydrogen. Theaddition of two equivalents of dippp or dippe to [(THT)TaCl](j.t-Cl)-THT (I) orIIIVIPMe3 CiVReferences p.62Chapter 2 22[(Me2S)TaCl2j(.t-Cl)2(I.t-S Me2) (II) yielded “dangling phosphine” complexes asevidenced by 31P{1H} NMR spectroscopy as shown in scheme 2.5. The 1H NMRspectrum of a mixture of I and dippp showed both a bridging THT group and free THTin a 1:2 ratio.Scheme 2.5RR‘FI or II + 2Pr’(CH)PPr’I R=R=-(CH2)4-;n 2,3 (H2C)II R=R=Me;n=2,3Similar dangling ligand structures have been observed for the complexes[(MeSCH2SMe)NbC1](p.-Cl).t-SMe)and [(dppm)TaCl2](i-Cl)j.t-SMe),38where the bridging thioether ligand could not be displaced. Prolonged heating (1O(YC)of a toluene solution of I and dippp, yielded an insoluble red powder which is probablya polymeric complex formed by the elimination of one equivalent of diphosphine. Thechelating diphosphine, dippm, proved to be too builcy as solutions of I or II and dippmshowed no evidence of any ligand displacement (i.e. no reaction) as monitored by both1H and 31P(1H} NMR spectroseopy.Based on the above results it was apparent that the bridging thioether moietywas too resistent to displacement under normal conditions. In an effort to generatethe desired binuclear polyhydride complexes, the binuclear precursors I and II werereduced with excess Na/Hg amalgam in the presence of two equivalents ofdiphosphine under dihydrogen. The reduction of[(Me2S)TaCl}(t-C1).t SMe),C[References p.62Chapter 2 23II, in the presence of 2 equivalents of dippp under 4 atmospheres of dihydrogenprovided air sensitive, black crystals of 1 in 70% yield as shown in equation 2.3.(xs) Na/Hg11 + 2 dippp Ta2CISH4{dippp} 2 34atmH21The microanalytical data for 1 showed a significant amount of sulfur (3.28%) waspresent. The temperature invariant 31P{1H) NMR spectrum of 1 shows two doublets,one at 18.8 and one at 15.6 ppm, indicating that two spectroscopically inequivalentcoordinated phosphines are present. The solution molecular weight39 of 1051 gmol1(calcd. 1021 grnol)obtained for 1 is indicative of a binuclear structure.The 1H NMR spectrum of 1 shows a broad triplet of multiplets at 12.38 ppmand a broad multiplet at 7.70 ppm (figure 2.1), which are attributable to two bridgingand two terminal hydrides respectively; these resonances are absent in the deuteriumanalogue 1-14. Similar downfield shifts have been observed for both bridging andterminal hydrides in binuclear tantalum complexes.3340 There was no exchangebetween the two hydride resonances from -80°C to +80°C as observed by 1H NMRspectroscopy. The hydrides in complex 1 do not exchange with free deuterium gas atroom temperature over a period of four weeks. The ligand region of the 1H NMRspectrum of 1 shows four isopropyl methine resonances, consistent with there beinginequivalent phosphines as well as asymmetry above and below the plane of thechelated diphosphine (a structure with only inequivalent phosphines would give rise totwo isopropyl methine resonances). The JR spectrum of 1 (KBr disk) shows twomedium broad bands at 1759 and 1553 cm1 that shift to 1263 and 1114 cm1,respectively, for 1-d4.In the 1H NMR spectrum of 1, decoupling of the hydride resonance at 7.70 ppmreduced the resonance at 12.38 ppm to a symmetric triplet (Jj-j,p = 44 Hz).References p.62SFigure2.1.299.94MHz1HNMRspectrumof[{dippp}TaC1H]2(p.-S)(p..H)2,1,inC6D6(*denotesC6DSH).Ta-HbTa-Hi—--CD1210II642PPMChapter 2 25Decoupling of the hydride at 12.38 ppm reduced the hydride resonance at 7.70 ppm to adoublet of doublets (JH,p =20 Hz; JH,P’ = 10 Hz).2.2.1 Molecular Structure of [{dippp}TaClH](.t-S)(.t-H) 1.An X-ray crystal structure analysis of 1 revealed the molecular structureshown in figure 2.2. Selected bond distances and bond angles are given in Tables 2.2and 2.3, respectively.Table 2.2. Selected bond lengths for [{dipppTaClH]2(j.t-S)(i-H),1.Bond Length (A) Bond Length (A) Bond Length (A)Tal-Ta2 2.689(1) Tal-Cl 2.409(3) Tal-Pi 2.616(3)Tal-P2 2.613(3) Tal-S 2.537(5) Ta2-S 2.541(5)P1-C4 1.92(2) P1-C7 1.90(2) P2-ClO 1.94(2)P2-C13 1.91(1) P1-Cl 1.81(1) P2-C3 1.80(1)Table 2.3. Selected bond angles for [(divpp)TaC1HJ2(j.t-S)(j.t- ),1.Bonds Angles (deg) Bonds Angles (deg)P1-Tal-P2 90.1(1) Tal-S-Ta2 64.1(2)S-Tal-Cl 103.0(2) P1-Tal-Ci 92.1(1)P2-Tal-Cl 92.1(1) S-Tal-P1 75.5(1)S-Tal -P2 159.4(1) Cl-Tal-Ta2 114.0(1)S-Tal-Ta2 58.6(1) Pl-Tal-Ta2 129.0(2)P2-Ta 1 -Ta2 128.9(2) S-Ta2-Tal 57.0(1)References p.62Chapter 2 26(a)(b)C2cliC6Figure 2.2. (a) Chem 3D Plus® representation of [{dippp)TaC1H]2(.i.-S)(p.-H).(b) Chem 3D Plus® drawing of 1 showing the proposed positions of the hydrides. Thebridging and terminal hydrides were placed at 1.86 A and 1.80 A from the tantalum,respectively. Hydrogens and methyl carbons are omitted for clarity.C8SHbReferences p.62Chapter 2 27The sulfur atom that bridges the symmetry related tantalum atoms was foundto occupy two locations each with 50% site occupancy. Therefore the model has acentre of symmetry. Only one site occupied by the .t-S ligand is shown for clarity.Although the hydrides did not appear in the fmal difference Fourier analysis, theirprobable positions are shown in figure 2.2 (b). The dliphosphine ligands lie above andbelow the plane defmed by the two tantalum atoms and the bridging sulfur ligand. TheTa-Ta single bond distance of 2.689 (1) A is consistent with the presence of twobridging hydrides as is the compressed Ta-S-Ta angle of 64.1 (2)°. Although the endsof the molecule are related by a C2 axis (through the S in the Ta2S plane), eachphosphorus donor of a particular diphosphine is inequivalent, being either transoid (STa-P, 159.4 (1)° or cisoid (S-Ta-P, 75.5 (1)) to the bridging sulfido ligand. The solidstate structure is in accord with the solution spectroscopic data above.The formation of [{dippp}TaC1Hj2(J.t-S)(.L-H)2, 1, from [(Me2S)TaCl}(p-Cl)2(p,-SMe),II, involves conversion of a bridging thioether ligand to a bridgingsulfide. Analysis of the headspace gas from several reactions indicated the formationof CH3 and no detectable CH4 (by GCMC). The same result was obtained whenthe reaction was performed under 4 atmospheres of D2. Similar types of carbon-sulfurbond cleavage have been reported41’2 for group 5 metals. Interestingly, a recentreport43 demonstrated the abstraction of sulfur under similar reducing conditions asshown in equation 2.4.2 Na/HgTaCI5 + 2 PMeh1/2 PhSSPh P*[2.4]P*P=PMe2h VIIReferences p.62Chapter 2 28It was proposed that at some key step in the reduction the sulfur atoms of thedisulfide (PhSSPh) unit were abstracted. However, reducing conditions may not benecessary to promote S-C bond cleavage. Several binuclear complexes previouslythought to contain bridging chlorides38 have been reformulated43 as binuclearcomplexes containing bridging sulfido (S2) ligands. These complexes are formed bythe direct abstraction of sulfur from ligands such as MeSSMe, SMe2 andEtSCH2CHSEt. Shockingly, no microanalytical data for the bulk material werepresented in these published reports,38’43 demonstrating the need for both structuraland analytical data in Ta-S systems.Although no kinetic analysis of the S-C bond cleavage transformation wasattempted several key points can be ascertained from the data available. The mostlikely source of the S2- fragment is from the bridging SMe2 moiety which is already- present in the complex, although the terminally bound SMe2 groups cannot beexcluded. The high yield of this reaction (70%) suggests that the process that leadsto S-C bond scission is facile. Under reducing conditions the crude reaction mixture ofII with dippp under dihydrogen revealed only the product 1 and free diphosphine (by31P{1H} NMR spectroscopy) which would seem to eliminate the possibility of thephosphines being involved in the reaction via a phosphinesulfide (R3P=S). Thechemical evidence obtained showing the formation of CH3during the reduction ofII (equation 2.3) is significant since the reaction is performed under dihydrogen. Thusthe coupling of the methyl fragments to generate CH3 probably occurs in theabsence of metal hydrides (i.e. before oxidative addition of dihydrogen to the lowvalent tantalum centres) since this would most certainly produce some methane. Apossible mechanism for the sulfur abstraction is given in scheme 2.6.References p.62Chapter 2 29Scheme 2.6H3C H3 H3c p3xNaIHg‘S/“ \ -xNaCI ,/ \L2CI3Ta TaCI3L2 L2CI3.Ta TaCI3..L2VIIIL2 = dippp S-C cleavage/S\-CH3C/S\L2CI3..Ta TaCI3..L2 L2CI3Ta TaCI3..L2xH3C OH3IxReduction of the dangling phosphine complex, [(dippp)TaCl2j2(J.t-Cl)2()I-SMe2), and loss of NaC1, could generate the highly reduced tantalum complex, VIII,which could be stabilized by the chelation of the dangling phosphine (L). Oxidativeaddition of the methyl groups to the reduced tantalum centres (IX) and subsequentloss of CH3CH3could give S2 fragment as in X. There is no evidence that both metalcentres are involved in this process although fragmentation to mononuclear species isunlikely since a metal-metal multiple bond exists between the tantalum centres.2.2.2 Molecular Structure of [{dippp}TaClH]2(jt-H)With the above results in mind, we became interested in investigating thegenerality of this transformation. The reduction of [TaC12( HT)]II- l)i.-TH1’ , I,in the presence of dippp under 4 atmospheres of dihydrogen provided deep greencrystals of 2 in 50% yield as shown in equation 2.5.References p.62Chapter 2 30(xs) Na/HgI + 2 dippp Ta2H6{dippp) 2 54atmH22The microanalytical data for 2 did not show any sulfur to be present but did indicatethat one diphosphine was present per tantalum. The solution molecular weight39 of905 gmol-1 (calcd. 920 gmol1)for 2 is indicative of a binuclear structure. The 31P{1H}NMR spectrum of 2 shows a singlet at 45.3 ppm, thus all the phosphines areequivalent. The1HNMR spectrum of 2 shows a broad triplet (JH,P = 55 Hz) at 11.24ppm and a broad singlet at 6.42 ppm integrating in the ratio of 2:4 with respect to thedippp ligand, which is attributable to two bridging and four terminal hydrides,respectively (figure 2.3). These peaks are absent in the deuterium analogue 2-d6,generated under deuterium gas. The 2H(1H} NMR spectrum of 2 shows a triplet at11.11 ppm and a singlet at 6.22 ppm, slightly shifted from the observed 1H NMRresonances. The broadness of the hydride peaks can be attributed to the largequadrupole moment of tantalum.44 The ligand region shows two septets for theisopropyl methines and four sets of doublet of doublets for the isopropyl methyls whichindicates some asymmetry above and below the plane of the chelated diphosphine.The IR spectrum of 2 shows medium bands at 1737 cm1 and 1113 cm-1 which shift to1245 cm1 and 776 cm-1, respectively, in 2-d6.Several crystals of 2 were mounted for an X-ray structure analysis but thecrystals would not diffract. On one fortuitous occasion a single crystal diffracted welland the structure was solved. Unfortunately, the structure was not the anticipatedhexahydride but rather a tetrahydride dichioride binuclear complex. The molecularstructure of [(dippp}TaC1HJ2(p.-H)2 is shown in figure 2.4. Selected bond lengthsand bond angles appear in Tables 2.4 and 2.5, respectively.References p.62CD ITa-HbTa-Hi*II,p,I,,uIIIIIIIii108III11111111111IIII642PPMFigure2.3.299.94MHz111NMRspectrumof Ta2H6{dippp}2,2,inC6D6(*denotesC6D5H).Chapter 2 32Several attempts to prepare pure [{dippp}TaClH12(p-H)2 by various routes havebeen unsuccessful although it can be observed admixed with complex 2. If fourequivalents of amalgam are used in the reduction of I in the presence of dippp underdihydrogen, the yield of [{dippp}TaClHj2(L-H)2 is 15%. The bridging hydrideresonance in the 1H NMR spectrum of [(dippp}TaClH](.t-H)2 is seen as a triplet at10.08 ppm (JH,p = 60.2 Hz) and the terminal hydride as a singlet at 7.57 ppm. Thiswas confirmed by obtaining the 1H NMR spectrum of the single crystal used for the Xray structure determination.A view down the tantalum-tantalum axis in [{dippp)TaClHj2(.t-H)2 reveals atwisting of the bridging hydride-metal plane of 50.6 with respect to the chloride-metalplane as shown in figure 2.4(b). In the isoelectronic binuclear complex{(Me3P)2TaCl(1I-H)(V from scheme 2.4), the bridging hydrides were located ona diagonal plane 450 to either chloride-metal plane.PMe3 CIci II \ H / PMe3Ta T V [P]C[ I[P]ci \% ,/ PMe3 HPMe3 H CI P[Ci]Table 2.4. Selected bond lengths for [{dippp}TaC1H]2W.-H)2.Bond Length (A) Bond Length (A) Bond Length (A)Ta-Ta 2.5547(7) Ta-Cl 2.466(2) Ta-Pi 2.603(1)Ta-P2 2.608(1) Ta-Hi 1.50 Tai-H2 1.74TaiH2* 1.82 P1-C4 1.858(5) P1-Cl 1.832(6)P1-C5 1.863(6) P2-C6 1.855(5) P2-Cl 1.863(5)P2-C3 1.838(6) Ci-C2 1.546(7) C2-C3 1.537(8)References p.62Chapter 2 33(a)(b)C2P2Figure 2.4. (a) Chem 3D Plus® representation of [{dippp}TaClHj2(.t-H)2.Hydrogen atoms are omitted for clarity. (b) Chem 3D Plus® view down the Ta-Taaxis showing the twisting of the plane generated by the bridging hydrides.C14H2*CIReferences p.62Chapter 2 34Table 2.5. Selected bond angles for [{dippp}TaC1H]2(JJ.-H)2.Bonds Angles (deg) Bonds Angles (deg)P1-Ta i-P2 96.52(4) Tal-Ta2-Cl 118.65(4)Ta 1 -Ta2-P 1 128.24(3) Tal -Ta2-P2 128.84(3)Tal-Ta2-H1 109 Tal-Ta2-H2 46Ta1Ta2H2* 43 Cl-Ta-Hi 133Cl-Ta1-P 1 84. 68 (5) Cl-Ta 1 -P2 84.66(5)Cl-Ta-H2 137 ClTaH2* 88In order to account for the observed bridging hydride pattern in the 1H NMRspectrum of [(Me3P)2TaCl](p-H)2, V, which is seen as a first order 1:4:6:4:1pentet (JH,p = 13.4 Hz), it has been proposed34 that the bridging hydrides in V arerotating about the metal-metal bond. If the hydrides were rigidly bound in thediagonal plane as shown in the Newman projection above, the hydrides would clearlybe cisoid and transoid to the phosphines resulting in dramatically different H-Pcoupling constants due to magnetic inequivalence. These observed spectralparameters for V did not change from -80°C to +30°C.The bridging hydrides in both [{dippp)TaC1HI2(I.L-H)2and Ta2H6{dippp}2,2,are seen as triplets with JH,P = 60 Hz and JH,P = 55 Hz, respectively. If the hydrideswere indeed rotating about the tantalum-tantalum axis, a similar 1:4:6:4:1 pentetwould be expected. In addition, the ligand region of the 1H NMR spectrum of 2 showsasymmetry above and below the plane of the chelated ligand. A rigid coordination ofthe two hydrides in a 45° diagonal plane would certainly account for this asymmetry.In complex V no such stereochemical argument is available since the phosphines andchlorides are located in a staggered conformation. The obvious difference betweenReferences p.62Chapter 2 35[(Me3P)2TaC11(Ii-H)CV) and [{dippp}TaClHj2(L-H) is the chelated ligand andthe significant increase in steric bulk of the substituents on phosphorus for the dipppcomplex. The phosphines on each metal in complex V are staggered while thephosphines in [{dippp}TaClH12(.i-H) are nearly eclipsed. Furthermore, complex Vcontains two chlorides per metal as ancillary ligands while [{dippp}TaC1HI2(ji-H)has one chloride and one hydride per metal, aside from the bridging hydrides.We have no reason to believe that TaH6{dippp} (2) differs structurally from[(dippp } TaC1H]2(ii-H) although a complex with staggered phosphines (XI) and asimilar twisting of the hydride plane would also be in agreement with the spectraldata.Interestingly, in the binuclear rhenium octahydride complexes6’2745 of the form[(R3P)2ReHJ(p.- )4(XI) where no stereochemical restraints are imparted on thephosphines, the eclipsed conformation is preferred. Removal of two bridging hydridestrans to one another would generate the coordination geometry of[{ dippp } TaC1Hj2(p.-H)2.)H HPR3R3PHXIIPR3HReferences p.62Chapter 2 36For the reasons mentioned above, the proposed structure of Ta2H6{ dippp)2 isanalogous to the solid state structure of [{dippp}TaC1HI2(p-H)2, that is, eclipseddiphosphine ligands and hydrides canted at 45° to the Ta2P4 plane.2.2.2.1 Electronic structure of [(H3P)2Ta]Qi- ),2’.The ground state electronic structure of the model compound[(H3P)2TaClJ(.t- ) (V’) has been described33 using the multiple scattering Xcimethod46 in order to rationalize the rotation of the hydrides about the metal-metalaxis. The calculations suggest that there is no electronic barrier to hydride rotation.In contrast, Extended Hückel calculations47 suggest that the barrier for hydriderotation in a representative d6-d dimer of the form [L4M]2(t-H) should be 125 kcalmol1. Clearly the energetic barrier associated with hydride rotation variesdramaticaliy from metal to metal and is also highly dependent ott the ancillary ligandspresent.Extended Hückel48 calculations were first applied to the model complex[(H3P)2TaCl](.t- ) (V’) in order to test the validity of a such a calculation. Theresults of the calculation predicted the correct molecular orbitals as compared to theXci method, albeit at elevated energy values. Since we were only interested in aqualitative description of the bonding in our model complex, the calculations wereperformed on [(H3P)2Ta](p- ) (2’). Note that substituents have been removedto facilitate the calculation, specifically the bulky isopropyl groups on phosphorus andthe three carbon backbone of the ligand. If hydride rotation about the metal-metal coreis indeed the process that exchanges the bridging hydrides, the model is valid.However, if the exchange process involves end group rotation then certainly stericeffects would be as important if not more important than the electronic barrier torotation, and the model would be meaningless. The results of the calculations areReferences p.62Chapter 2 37displayed in figure 2.5. The energies of the levels and the atomic contribution to themare presented in Table 2.6.The model compound [(H3P)2Ta](j.t-H) (2’) was confined to C2hsymmetry with the phosphines eclipsed across the dimer. Likewise, the terminalhydrides were also eclipsed. The bridging hydrides were positioned on a plane 450 tothe plane generated by the phosphines and the tantalum. The P-Ta bond lengths, theTa-Ta bond length as well as the P-Ta-P angle were taken from the structure of[{dippp}TaClH]2(L-H)2. The distal hydrogens on the phosphines were held in theplane generated by the phosphines and the tantalum, as shown in XII. The terminalhydride bond length, estimated at 1.80 A, was taken from the neutron diffractionanalysis of (Me3P)4TaH2C1.9 The bridging hydride bond length was taken to be1.86A as determined in the neutron diffraction analysis27 of[(Et2PhP)ReH](J.L-H>4. Other details are given in the experimental (section 2.7).[P] xiixzWhy do the bridging hydrides in Ta2H6{ dippp } 2 2, remain static while thehydrides in [(Me3P)2TaCl2]2(p.-H)2 (V) rotate about the metal-metal bond? Theanswer may lie in the conformation of the ancillary ligands. The molecular orbitals thatform the basis of the bridging hydride and metal-metal interaction in the model[(H3P)2Ta](p- ),2’, are worth noting.H HyReferences p.62Chapter 2 38[(H3P)2TaH2](ji-H)—11LUMO-127b HOMO Ta-Ta t7ag Ta-Ta 013-14 Ta-He 7tTa-He 7tTa-He 0_________Ta-Hb 0-15uag Ta-PTa-He 016 4b Ta-Hb-17 Ta-P_ }PH3Ta-P-18_ __ __} PH3-19-20-21-22 } PH3Figure 2.5. Summary of the Extended Hückel eigenvalues for the model compound[(H3P)2TaH2]2(.t-H),2’.References p.62Chapter 2 39Level8ag6a7b7ag6bSbg5a6ag4bg5bSag4b4a3bg3b4ag3a3ag2bg2b2a2ag1blbglaglaEnergy(eV)-11.560-11.587- 12.584- 12.669-14.331-14.415-14.881-14.921- 14.952- 14.967-15.210-16.069-17.102-17362-17.415-17.674-17.703-17.806-17.962-17.963-18. 184-18.206-21.527-21.53 1-21.708-21.7 14001 41 4 10 21 0 1 50 66 2 100 72 2 100 34 18 246 4 16 349 0 34 14 240 52 3 3 210015 851 9918 8235 652 9816 831002 98The HOMO is 7b and LUMO 6a. (i) Hb refers to the bridging hydrides. (ii) Htrefers to the terminal hydrides. (iii) H refers to the phosphine hydrogens.Table 2.6. Extended HUckel eigenvalues for [(H3P)2Ta](.t- ),2’LUMOHOMO% Contribution % Ta atomic contributionsTa Hb Ht P H s p d96819423174429References p.62Chapter 2 40The Ta-Hb a-bond interaction (6ag) is shown in figure 2.6 (top). This orbitalarises from the overlap of a hybrid on Ta (combination of 6p, 5d2 and the 5d) andthe in-phase combination of two is orbitals on the two bridging hydrogens. Anothermolecular orbital of interest is the Ta-Hb it-bond interaction (4b) shown in figure 2.6(bottom). The tantalum contribution to this molecular orbital is mainly from the 5dand 5d atomic orbitals which overlaps with an out-of-phase combination of the twobridging hydrogen is orbitals. The Ta-Ta a- and it-bond orbitals are shown in figure2.7. The Ta-Ta a-overlap (figure 2.7 (bottom)), involves the overlap of two dZ.2orbitals which are derived from a linear combination of the d2..y2 and the d2.47 TheTa-Ta it-bond, derived from a combination of the 5d and 5d (figure 2.7 (top)), isperpendicular to the Ta-Hj, it-bond interaction. Thus, there should be no electronicbarrier to hydride rotation as has been seen in complex [(Me3P)2TaC1](p.-H)(V)since rotation into the Ta-Ta it -bond molecular orbital is symmetry allowed.A bending back of the terminal hydrides (155°) away from the bridginghydrides and the core of the dimer is restricted due to the stereochemical restraints ofthe P-Ta-P angle of 95°; in fact this terminal hydride angle may be underestimatedsince an angle approaching 180° would lead to greater overlap with the metal basedorbitals.47 The monodentate phosphines in compound [(Me3P)2TaCl](j.t-H)(V),which contain no stereochemical restraints, form a P-Ta-P angle of 156° allowing for asignificant contraction in the Cl-Ta-Cl angle (128°). This type of distortion for theML2P fragment in binuclear complexes is well documented,32’43 and illustrated inscheme 2.7.References p.62Chapter 2 41Figure 2.6. (top) Isosurface plot of the 6ag level of 2’ for v = 0.05 a.u.. (bottom)Isosurface plot of the 4b level for i = 0.05 a.u.. Dark grey area =-i-i; light grey area=-v.References p.62Chapter 2 42Figure 2.7. (top) Isosurface plot of the 7b level of 2’ for g = 0.05 a.u.. (bottom)Isosurface plot of the 7ag level for ‘qc = 0.05 a.u.. Dark grey area = +ijc; light grey areaReferences p.62Chapter 2 43Scheme 2.7a increase a decrease Pgs.,,______a______The key aspect of these ligand arrangements is that as the angle a between thephosphine donors increases, the ML2P2 fragment adopts a structure as in XIII.Conversely, as the angle a decreases the ML2P2 fragment becomes more like thatshown in XIV.Although no calculations of hydride rotation for a d2-d complex are available,the calculations47of the rotational barrier for the d6-d complex [L4M]2(p.-H) serveas a good starting point. The model complex [L4M]2(J.t-H)2 (XV) was restricted toD2h symmetry as shown below in scheme 2.8.Scheme 2.8,ryzXV XVIRotation of the hydrides into an eclipsed conformation with the axial ligandsrepresents the high energy intermediate (XVI). This high energy structure is aconsequence of the hybridization of the orbital which occurs due to the donorLReferences p.62Chapter 2 44ligands in the equatorial coordination sites. Rotation of the hydrides is facilitated bythe L4M groups adopting a structure more like XIII (scheme 2.7); thus, the two metalbased 2t-orbitals become more energetically similar leading to an equally favorableoverlap of either orbital with the hydrides. Therefore it is believed that the structure ofthe TaC12Pfragment of [(Me3P)2TaClJ(1.I-H) (V) is responsible for the observedhydride rotation. The complex TaH6(dippp}2 (2) adopts a structure more like XIV(scheme 2.7) which likely raises the energy associated with the intermediate (XVI)shown in scheme 2.8, accounting for the rigid nature of the bridging hydrides.2.3 Synthesis and Characterization of Binuclear HexachiorideDiphosphine ComplexesThe search for other binuclear starting materials that contained the desireddiphosphines in a chelated fashion was prompted by the substitutionally inertthioether moiety in the binuclear starting materials [(THT)TaCl2](p-Cl)j.t- HT)(I) and [(Me2S)TaC12J2(1’-Cl)2(1’- SMe2) (II). A literature report5° demonstratedthe high yield (87%) synthesis of a diniobium edge-sharing bioctahedral complexesincorporating monodentate phosphines as shown in equation 2.6.(xs) Mg2 NbC!5 + (xs) PMe2h Nb2C!6(PMePh)4 [2.6]- MgCI2However, the attempted synthesis of binuclear chelating diphosphine complexesutilizing the small diphosphine, l,2-bis(dimethylphosphino)ethane, yielded only bisdiphosphine mononuclear complexes.5’In an effort to synthesize tantalum analogues the bulky chelating diphosphinesdippp, dippe and dippm were utilized. The unique behavior of the tantalum complex[(Me3P)2TaCl](1’- 1) (III in scheme 2.3) made these bulky chelating diphosphinecomplexes attractive as precursors to binuclear polyhydride derivatives. The sodium-References p.62Chapter 2 45mercury amalgam reduction of TaC15 in the presence of bulky chelating diphosphinesyields the desired dimers in high yield as shown in equation 2.7.2 Na/Hg2 TaCI5 + 2 P2 Ta2CI6{P} [2.7]- NaCI3 P2=dippp4 =dippe5 P2 = dippmComplex 5 could be prepared with sodium sand, which avoids the use of mercury. Allthree complexes are soluble in toluene and methylenechioride with the exception ofTa2Cl6 { dippp } 2 (3) which reacts rapidly with methylenechioride to give an insolubleproduct. Normal shifts were observed for the ligand in the 1H NMR spectrum ofcomplexes 3-5 as well as a high degree of symmetry indicated by the presence of onlytwo sets of doublet of doublets for the isopropyl methyl protons. A singlet in the31P{1H} NMR spectra of complexes 3-S also indicates symmetrical coordination ofthe phosphines. The solution molecular weight39 of 1052 gmol1 (calcd. 1098 gmoll)determined for Ta2C16(dippe}2 (4) is indicative of a binuclear structure. Although nosolid state structural evidence is available for these compounds an edge-sharingbioctahedral structure is proposed (XVII) based on the spectroscopic data above.XVIIThe hexachioride dimer Ta2Cl6tdippp}2 (3) reacts with excess dihydrogen (4atmospheres) as evidenced by a broad singlet at 14.11 ppm in the 1H NMR spectrum.Removal of the excess dihydrogen regenerates the hexachloride dimer quantitatively.We have no evidence of the nuclearity of the hydride intermediate but based on thedownfield location of the hydride resonance a binuclear bridging hydride is proposed.References p.62Chapter 2 46In contrast, complexes 4 and 5 do not react with dihydrogen, even at elevatedtemperatures (80°C). Other binuclear tantalum complexes have also be shown to beunreactive toward dihydrogen.322.3.1 Reduction of [(diphosphine)TaCI]j. -CI )2 under HydrogenThe sodium-mercury amalgam reduction of Ta2C16{dippp}2(3) under 4atmospheres of dihydrogen proceeds smoothly to yield the hexahydride complexTa2H6{dippp} (2) in excellent yield.(xs) Na/HgTa2CI6(dippp} Ta2H6{dippp} [2.8]4 atm H2Most surprisingly, complex 4 incorporating the two carbon backbone diphosphine,dippe, does not react with sodium amalgam under hydrogen or in the absence ofbydrogen The reductinn potential of Na/Hg amalgam (-2.71 V vs. S.H.E.)52 iscertainly sufficient to reduce this type of complex, however no reaction has beenobserved. The reduction of complex 5 containing dippm was also unsuccessfulyielding large amounts of free dippm as evidenced by 31P{1H} NMR spectroscopy.2.4 Synthesis and Characterization of Diphosphine AlkylideneComplexesIn the two previous sections (2.2 and 2.3) the synthesis of binuclearpolyhydride complexes was demonstrated using binuclear starting materials.Mononuclear complexes with the appropriate ancillary ligands could provide someinformation into the mechanism of formation of the binuclear polyhydride complexes. Areport53 detailing the syntheses of mononuclear phosphine complexes of tantalumprovided a starting point for this investigation; as shown in equation 2.9, the additionof monodentate phosphines to bis(neopentyl) tantalum trichioride results in theReferences p.62Chapter 2 476 n=37 n=28 n=1formation of a neopentylidene complex. Substituting the monodentate phosphineswith bulky chelating diphosphines would yield a mononuclear starting material bearingthe coordinated diphosphine ligand intact.Ta(CH2But)C)3+ 2 PR3 Ta(CHBu) )3(PR2+ CMe4 [2.9]The hydrogenation of (MeP)TaHC1CHBut)33to give the tetrahydrido-bridgedcomplex [(Me3P)2TaCl]2(p-H)4(VI) shows how binuclear complexes may beaccessed from mononuclear starting materials.With the above results in mind, three ailcylidene complexes were prepared bythe addition of the bulky chelating diphosphines dippp, dippe and dippm toTa(CH2But)Cl3as shown in equation 2.10.CH2ITa(CH2But)C13+ Pr2(CH)PP’_______\CI [2.10]Pr2CIAn alternative synthesis to that shown in equation 2.10 is to generate the THFligated alkylidene complex in situ53 (xs THF + Ta(CH2But)C13—‘Ta(=CHBut)Cl3(T F)2+ CMe4) then add diphosphine; this procedure avoids the useof chlorinated solvent. The 31P{ 1H} NMR spectrum of complexes 6-8 shows tworesonances indicating inequivalent coordinated phosphines are present. The 1H NMRspectrum of complexes 6-8 shows two isopropyl methine protons indicating that thealkylidene fragment lies in the plane generated by the two phosphines and thetantalum. The direction in which the But group is pointing cannot be determined byReferences p.62Chapter 2 48spectroscopic means but the most reasonable position would be toward the chloride tominimize steric interaction with the isopropyl groups on phosphorus. The solutionmolecular weight39 of 604 gmol (calcd. 633 gmol1) for (dippp}TaC13CHBut) (6)confirms the mononuclearity of the complexes.2.4.1 Reduction of (diphosphine)TaC13=CHBut) under HydrogenThe reduction of complex 6 under dihydrogen gave good yields (8 1%) of thedesired binuclear hexahydride complex TaH6{dippp}. In contrast, the reduction of 7and 8 yielded large amounts of free ligand. The free ligand observed in these reactionssuggests that at some point in the reduction the chelating ligands are unstable towarddissociation. In fact during the reduction of 7, a mononuclear complex having theformula TaH5(dippe} was isolated in =10% yield. The 1:4:6:4:1 hydride pattern(2JH,P = 36.1 Hz) for TaH5{dippe} at -1.95 ppm is similar to that seen for bothTaH5(PMe3)4(2JH,P = 41.2 Hz) and TaH5(dmpe)2(2JH,P = 35.0 Hz). Clearly thethree carbon backbone diphosphine is bound more firmly to the tantalum centre than isthe two or one carbon analogues.The high yield synthesis of Ta2H6{ dippp } 2 (2) from a mononuclear startingmaterial indicates that the pre-formation of a Ta-Ta double bond is not necessary. Infact the key step in the synthesis is the coordination of the diphosphine. Yields of 2starting from TaC15 and dippp are low (29%), indicating that the ligand mustcoordinate early before the complex over-reduces and forms tantalum metal.2.5 Reactivity of Tantalum Binuclear Polyhydride ComplexesComplex 1, [{dippp}TaC1H]2(p-S)(ji-H) reacts with acetylene to givepredominantly trans polyacetylene54as determined by IR spectroscopy. Similarly,polyethylene is formed when 1 is treated with excess ethylene. The addition ofReferences p.62Chapter 2 49excess of 1,3-butadiene produced large amounts of a white solid which is believe to bepolybutadiene. The above polymerizations were monitored by 31P NMR spectroscopywhich showed virtually no coordinated ligand to be present in the reaction mixtures.Furthermore, each reaction required an induction period before the polymerizationbegan; in the case of [{dippp)TaClH]2Qi-S)(i-H) and 1,3-butadiene severalminutes past before an uptake of the diene was observed. The above results wouldseem to suggest that the diphosphine must be lost before any polymerization canoccur.Surprisingly TaH6(dippp} (2) is quite stable and does not react withethylene, acetylene or 1,3-butadiene even at elevated temperatures (80C). Thisstability coupled with the lack of exchange of the hydrides with deuterium would seemto suggest that the core of the binuclear complex is very well protected, likely due tothe steric bUlk of the diphosphine.2.6 Summary and Future ConsiderationsThe preparation of a stable binuclear polyhydride complex of tantalumTa2H6{ dippp ) 2, 2, stabilized by bulky chelating diphosphines has been realized inseveral ways starting from both mononuclear and binuclear species. The electronicstructure of [(H3P)2Ta](.t- ),2’, has been investigated in order to understandthe rigid coordination of the bridging hydride ligands. The stereochemical restrictionsof the chelated diphosphine are believed to be responsible for the observed rigidity ofthe bridging hydrides. Disappointingly, the less bulky diphosphines dippe and dippmdid not form stable binuclear polyhydride complexes. The large amounts of freediphosphine ligand generated during attempted syntheses using these ligands,indicates that the ligands are not firmly bound to the reduced tantalum complexes.References p.62Chapter 2 50The unexpected S-C bond cleavage observed in the formation of[(dippp}TaClH]2(p.-S)(.L-H)2, 1, has shed light on the prospects of obtainingpolyhydride complexes from starting materials that contain bridging thioethermoieties. The observation that CH3is formed upon cleavage of the bridging SMe2ligand suggests that this process is fast compared to hydride formation at the metalcentre.The alkylidene diphosphine complexes,P2Ta(=CHBut)C13should beinvestigated further. For instance, the reaction of Ta(=CHBut)C1 with alkyllithiumreagents such as NpLi may yield five-coordinate bis(alkylidene) species such asP2Ta(=CHBut)CButvia a second a-elimination. A comparison of the relativestability of these complexes with respect to the diphosphine used (i.e. dippp, dippeand dippm) would be of interest. These complexes,P2Ta(=CHBut)CBut, couldalso be used as precursors to bis(imido) compounds, Ta(=NR)CHBut, by reactionwith imines (RHC=NR). With a single alkyl group remaining, reactions with smallmolecules such as carbon monoxide would be more easily monitored.The hexachioride dimers of the form, [P2TaCl](t-Cl) should also beinvestigated further. The alkylation of these dimers with reagents such as MeLi mayyield peralkylated dimers (i.e. [P2TaRj(.t- )). Again a comparison of the relativestability of these complexes with respect to the diphosphine used (i.e. dippp, dippeand dippm) would be of interest.Finally, an X-ray crystallographic analysis or even better a neutron diffractionanalysis of a binuclear hexahydride species would be of tremendous interest sincethen, and only then, will the structure of these species be known unambiguously. Theobvious change that could be made to access these species would be to replace theisopropyl substituents on phosphorus with other bulky groups. The three carbonReferences p.62Chapter 2 51backbone diphosphine ligand, CyP(CH2)3 Cy, has similar steric properties to theligand dippp and may yield more ordered crystalline material. A more detailedelectronic analysis of the hexahydride complex that is, one that takes into accountrelativistic effects, could be used as a comparison to similar detailed analyses in theliterature.2.7 Experimental Procedures2.7.1 General Information. All manipulations were performed under prepurifiednitrogen in a Vacuum Atmospheres HE-553-2 glovebox equipped with a MO-40-2Hpurifier or in standard Schlenk-type glassware on a vacuum line.55 The description“reactor bomb” refers to a cylindrical, thick-walled pyrex vessel equipped with a 9 mmKontes® teflon needle valve and a ground glass joint for attachment to a vacuum line.Toluene, hexanes and THF were predried over CaH2 for 24 hours. Toluene,hexanes, pentane, diethyl ether and THF were dried by refluxing over sodiumbenzophenone ketyl followed by distillation under argon. CH21 was predried overCaH2, then distilled from P205. Deuterated benzene (C6D) and toluene (C7D8)were purchased from Aldrich, dried over activated 4A molecular sieves, vacuumtransferred and “freeze-pump-thawed” three times prior to use. Hydrogen gas waspurified by passing through a column packed with activated molecular sieves andMnO. Microanalyses of all air- and moisture-sensitive compounds were expertlyperformed by Mr. Peter Borda of this department.All NMR spectra were recorded at room temperature (20° C) unless otherwiseindicated. 1H NMR spectra were recorded on either a Varian XL-300 (299.94 MHz)or a Bruker WH-400 (400.00 MHz) spectrometer and referenced to C6D5H orC6D5D2Hset at 7.15 ppm and 2.09 ppm respectively. 1H homonuclear decouplingexperiments were performed on a Varian XL-300 (299.94 MHz). T1 measurementsReferences p.62Chapter 2 52were made on a Varian XL-300 (299.94 MHz) using the inversion-recoverymethod.56 13({ 1H} and 3lp1H} NMR spectra were recorded on a Varian XL-300spectrometer (75.43 MHz and 121.42 MHz respectively). The 31P{1H} NMR spectrawere referenced to external P(OMe)3 set at 141.00 ppm relative to 85% H3P04 and13C{ 1H} to C6D set at 128.00 ppm. 1H{31P} NMR were recorded on a BrukerAMX-500 (500.13 MHz) spectrometer. Infrared spectra were recorded on a Nicolet5DX Fourier Transform spectrophotometer with samples as KBr pellets. Theabbreviations used for identification of IR bands are: vs. very strong; s, strong; m,medium; w, weak. Molecular weight determinations were made using the Signermethod.39 The measurements were made in benzene using [(dippe)Rhj2(i-H)(MW = 732.53) as the reference. The accuracy of this method is estimated at ±10%.Molecular orbital calculations were performed on the CAChe Worksystem, aproduct developed by Tektronix. The parameters used for the Extended Hückelcalculation of the tantalum model, [(H3P)2Ta](.t- ) were taken from theliterature58 and are listed in the appendix. The bond lengths and angles used for themodel are as follows: Ta-Ta, 2.550 A; Ta-P, 2.600 A; ; Ta-Hb, 1.860 A; Ta-Ht, 1.800A; P-H, 1.380 A; P-Ta-P, 96.0°; Ht-Ta-Ht, 155.0°. The Cartesian coordinates of themodel can be found in the appendix.2.7.2 Syntheses. TaC15 (99.9%) was purchased from Aldrich Chemical Company,Inc. and used as received. THT (tetrahydrothiophene, SC4H8) and SMe2 weredistilled from CaH2. [(Me2S)TaClJ(i- Me) p-Cl)30and [(THT)TaCl2](i-THT)(j.i-Cl)29 were prepared according to the literature. The ligandsPr(CH)Pr(dippe)59 andPr12CHPr(dippm)6°were also preparedaccording to the literature. A slightly modified preparation ofPr2(CH3Pr(dippp)61 is given below. Neopentyl chloride (99%) was purchased from AldrichReferences p.62Chapter 2 53Chemical Company, Inc., and used as received. Zn(CH2But)62 andTaC13(CH2But)53were prepared according to the literature. TaC13(=CHBut)(THF)was generated in situ by the addition of THF to TaCl3(CH2But) at -30°C.2.7.3 [{dippp}TaC1HJ(p-S)(.t-H) (1). In the glovebox, a —1% sodiumamalgam was generated in a 350 mL reactor bomb by dissolving 241 mg Na (10.5mmol) in 24 g Hg. A 50 mL toluene solution containing 1.001 g (1.3 12 mmol) of[(MeS)TaC1](j.t-SMe) L- l) and 727 mg (2.63 mmol) of dippp was thenintroduced to the reactor bomb along with a 2 cm stir bar. The reactor bomb solutionwas sealed and taken to a vacuum line. The reactor bomb was degassed three timesand cooled to -196°C. Purified hydrogen was introduced at -196°C and the reactorbomb sealed. The solution was slowly warmed to room temperature and stirredvigorously. The colour of the solution gradually turned red from brown, as NaC1formed. After 48 hours the excess hydrogen was remove-d under vacuum and thereactor bomb taken into the glovebox. The solution was filtered through a mediumporosity frit with the aid of Celite® being careful to leave the mercury residues behind.The solution volume was reduced to 20 mL toluene and 10 mL hexanes added. Thedeep red solution was cooled to -40°C for 24 hours to yield 929 mg (70%) of 1. Anal.Calcd forC30H7212P4STa:C, 35.27; H, 7.10; Cl, 6.94; S, 3.14. Found: C, 34.99; H,7.10; Cl, 6.98; S, 3.28%. 1H NMR (C6D,6, ppm): 12.38 (t of m, Nb, 2H, 2JH,P =44Hz); 7.70 (d of m, H, 2H, 2H,P = 20 Hz); 2.82 (d of sept, PCH(CH3)22H, 2JH,P =5.4 Hz, 3JH,H = 7.2 Hz); 2.55 (d of sept, PCH(CH3)22H, 2JH,P = 8.7 Hz, 3JH,H = 7.2Hz); 2.07 (d of sept, PCH(CH3)24H, 2JH,P = 7.2 Hz,3JH,H = 7.2 Hz); 2.04 (d of sept,PCH(CH3)2,2H, 2JHP = 7.2 Hz, 3JH,H = 7.2 Hz); 1.63 (m, PCH2 and PCH2C,12H); 1.45 (d of d, PCH(CH3)26H, 3JHP = 12.9 Hz, 3JH,H = 7.2 Hz); 1.39 (d of d,PCH(CH3)2,3H, 3JH,P = 13.8 Hz, 3JH,H = 7.2 Hz); 1.34 (d of d, PCH(CH3)23H,3JH,P = 14.1 Hz, 3JH,H = 7.2 Hz); 1.29 (d of d, PCH(CH3)23H, 3JH,P = 12.9 Hz,References p.62Chapter 2 543JH,H = 7.2 Hz); 1.23 (d of d, PCH(CH3)23H, 3JH,P = 13.8 Hz, 3JH,H = 7.2 Hz); 1.17(d of d, PCH(CH3)23H, 3H,P = 11.7 Hz, 3JH,H = 7.2 Hz); 1.08 (d of d, PCH(CH3)23H, 3JH,P = 11.1 Hz, 3JH,H = 7.2 Hz). 1H NMR {1H selective) (C6D,6, ppm):12.38 {H at 7.70) (t, Hb,2JH,P = 44 Hz); 7.70 {Hb at 12.38) (d of d, Ht,2JH,P = 20Hz, 2J,p’ = 10 Hz). T1 measurements (seconds): 12.38 ppm, Hb, 0.302(5); 7.70ppm, H, 0.261(4); 2.82 ppm, PCH(CH3)20.729(8). 31p NMR (C6D,6, ppm):AA’MM’ spin system, 18.82 (PA,2JP(A),P(M) = x Hz,3JP(A),P(A’) = x Hz); 15.59(PM,2JP(A),P(M) = X Hz,3JP(A),P(A’) = x Hz). IR (KBr, cm1): VTa..H 1759 (m);VTa..H..Ta 1559 (m).2.7.4 [{dippp}TaCID](p-S)(p-D) (1-d4). The preparation of 1-d4 isanalogous to the preparation of 1 with the exception that deuterium gas was utilizedinstead of dihydrogen gas. The hydride signals present in the 1H NMR of 1 wereabsent in 1-d4, confirming full deuteration. The 31p NMR of 1-d4 was slightlybroadened but at the correct chemical shift. IR (KBr, cm-1): VTa..D 1263 (m); VTa..D.Ta1114 (m). 2H NMR (C6D,6, ppm): 12.10 (t, Db,2JD,P = 42.9 Hz); 7.41 (d, Dt,= 18.1 Hz).2.7.5 Synthesis of [{dippp}TaH2](.t-H) (2)2.7.5.1 From [(THT)TaCl(p-THT)(t- l) In the glovebox, a —1%sodium amalgam was generated in a 350 mL reactor bomb by dissolving 125 mg Na(5.44 mmol) in 12 g Hg. A 50 mL toluene solution containing 761 mg (0.907 mmol) of[(THT)TaCl2] p.-THT)(p- l) and 501 mg (1.81 mmol) of dippp was then introducedto the reactor bomb along with a 2 cm stir bar. The reactor bomb was sealed andtaken to a vacuum line. The reactor bomb solution was degassed three times andcooled to -196°C. Purified hydrogen was introduced at -196°C and the reactor bombsealed. The solution was slowly warmed to room temperature and stirred vigorously.References p.62Chapter 2 55The colour of the solution gradually turned red from brown, as NaC1 formed. After 48hours the excess hydrogen was removed under vacuum and the reactor bomb takeninto the glovebox. The solution was filtered through a medium porosity Mt with theaid of Celite® care being taken to leave the mercury residues behind. The solutionvolume was reduced to 20 mL toluene and 10 mL hexanes added. The deep redsolution was cooled to -40°C for 24 hours to yield 929 mg (50%) of green crystalline 2.The green crystals can be redissolved to give red solutions. Anal. Calcd forC3oH74P4Ta2:C, 39.14; H, 8.10. Found: C, 39.01; H, 8.00%. 1H NMR (C6D,6,ppm, 23°C): 11.24 (br t, Hb, 2H, 2H,P = 55 Hz); 6.42 (br s, H, 4H); 2.03 (sept,PCH(CH3)2,4H, 3JHH = 7.5 Hz); 1.98 (sept, PCH(CH3)24H, 3JH,H = 7.5 Hz); 1.52(m, PCH2 8H); 1.46 (d of d, PCH(CH3)212H, 3JH,H = 7.5 Hz,3JH,P = 13.5 Hz); 1.44(m, PCH2C 4H); 1.35 (d of d, PCH(CH3)212H, 3JH,H = 7.5 Hz, 3JH,P = 12.3 Hz);1.28 (d of d, PCH(CH3)212H, 3JH,H = 7.5 Hz, 3JH,P = 12.6 Hz); 1.19 (d of d,PCH(CH3)2,12H, 3JH,H = 7.5 Hz, 3JH,P = 11.4 Hz). T1 measurements (seconds):11.24 ppm, Hb, 0.303(3); 6.42 ppm, H, 0.258(2); 2.02 ppm, PCH(CH3)20.823(9).3lp NMR (C6D,6, ppm): 45.3 (s). IR (KBr, cm-i): VTa.H 1737 (w); VTa.H..Ta 1113(m). Decoupling of either hydride only sharpens the remaining hydride. Mol. weightcalcd. forC30H74P4Ta2:920 gmol-1. Found: 905 gmol-1.2.7.5.2 From [{dippp}TaCIJ(j.t-Cl) In the glovebox, a -1% sodium amalgamwas generated in a 350 mL reactor bomb by dissolving 41 mg Na (1.8 mmol) in 4 g Hg.A 25 mL toluene solution containing 251 mg (0.221 mmol) of [{dippp}TaCl2j(.L-Cl)2(3, see 2.7.7) was then added to the amalgam. The reactor bomb was sealed andtaken to a vacuum line. The reactor bomb solution was degassed three times andcooled to -196°C. Purified hydrogen was introduced at -196°C and the reactor bombsealed. The solution was slowly warmed to room temperature and stirred vigorously.The red solution gradually lightened in colour, as NaC1 formed. After 48 hours theReferences p.62Chapter 2 56excess hydrogen was removed under vacuum and the reactor bomb taken into theglovebox. The solution was filtered through a medium porosity fit with the aid ofCelite® care being taken to leave the mercury residues behind. Concentration to 5 mLand cooling to -40°C yielded 183 mg of 2 (90%).2.7.5.3 From TaCI5 and dippp. In the glovebox, a —1% sodium amalgam wasgenerated in a 350 mL reactor bomb by dissolving 385 mg Na (16.8 mmol) in 39 g Hg.A 10 mL toluene solution containing 772 mg (2.79 mmol) of dippp was added to theamalgam. Solid TaCl5 (1.000g, 2.791 mmol) was introduced to the bomb and washeddown with 100 mL toluene. The reactor bomb was sealed and taken to a vacuum line.The reactor bomb solution was degassed three times and cooled to -196°C. Purifiedhydrogen was introduced at - 196°C and the reactor bomb sealed. The solution wasslowly warmed to room temperature and stirred vigorously. The colour of the solutiongradually turned red from yellow, a NaC1 formed. After 48 hours the excess hydrogenwas removed under vacuum and the reactor bomb taken into the glovebox. Thesolution was filtered through a medium porosity fit with the aid of Celite® care beingtaken to leave the mercury residues behind. The solution volume was reduced to 40mL toluene and cooled to -40°C to yield 381 mg of 2 (29%).2.7.5.4 From {dippp}TaC13(=CHBuI). In the glovebox, a —1% sodiumamalgam was generated in a 350 mL reactor bomb by dissolving 44 mg Na (1.9 mmol)in 5 g Hg. A 25 mL toluene solution containing 243 mg (0.383 mmol) of{dippp}TaC13(=CHBut) (6, see 2.7.10) was then added to the amalgam. The reactorbomb was sealed and taken to a vacuum line. The reactor bomb solution wasdegassed three times and cooled to -196°C. Purified hydrogen was introduced at-196°C and the reactor bomb sealed. The solution was slowly warmed to roomtemperature and stirred vigorously. The colour of the solution gradually turned redfrom purple, as NaC1 formed. After 48 hours the excess hydrogen was removed underReferences p.62Chapter 2 57vacuum and the reactor bomb taken into the glovebox. The solution was filteredthrough a medium porosity frit with the aid of Celite® care being taken to leave themercury residues behind. Concentration to 5 mL and cooling to -40°C yielded 143 mgof 2 (81%).2.7.6 [{dippp}TaD2](j.t-D) (2-d6). The synthesis of 2-d6 is identical to theprocedure for 2 with the exception that deuterium gas was used. Since the yields for 2were highest when starting from [{dippp}TaCl]2(I-Cl)2, this is the preferred route(see 2.7.5.2). There was no change in the reported yields. 2H NMR (C6D,3, ppm):11.11 (t, Db,2JD,P = 55 Hz); 6.22 (s, Di). IR (KBr, cm-i): VTa..D 1245 (m); VTa..D..Ta776 (m).2.7.7 [{dippp}TaCI2](p-Cl) (3). In the glovebox, a 0.2% amalgam wasgenerated in a 350 mL reactor bomb by dissolving 256mg (11.1 mmol) of Na in 128 gHg. A 10 mL toluene solution containing 1.543 g (5.583 mmol) dippp was added to thereactor bomb. Solid TaC15, 2.000 g (5.582 mmol), was added and washed into thebomb with 250 mL toluene. The bomb was taken to a mechanical shaker and fastenedhorizontally (the bomb should not only be clamped but taped to the shaker so itdoesn’t become dislodged). Shaking is initiated so that the toluene and amalgammove quickly from one end of the bomb to the other. If the shaking is too slowconsiderable amounts of tantalum metal will form and the yields will be poor. Thecolour of the solution changed from yellow to green (5 minutes) to purple (2 hours).After 12 hours of shaking the toluene was removed under vacuum and the productextracted with 100 mL THF. The solution was filtered and the solution concentrated to50 mL. Cooling to -40°C for 24 hours yielded 2.34 1 g of 3 (74%). Anal. Calcd forC30H681P4Ta2•1/4toluene: C, 33.15; H, 6.13. Found: C,33.35; H, 6.50. Exhaustivedrying could not remove all toluene, but the residual toluene was confirmed byintegration of the methyl peak of toluene with respect to the isopropyl methine of theReferences p.62Chapter 2 58ligand. 1H NMR (C6D,8, ppm): 2.65 (d of sept, PCH(CH3)28H, 3JH,H = 7.2 Hz,2JHP = 4.0 Hz); 1.81 (m, PCH2 8H); 1.21 (m, PCH2C 4H); 1.08 (d of d,PCH(CH3)2,3JH,P = 10.8 Hz,3JH,H = 7.2 Hz); 1.03 (d of d, PCH(CH3)2,3JH,P = 10.2Hz, 3JH,H = 7.2 Hz). 3lp NMR (C6D,6, ppm): -21.4 (s).2.7.8 [{dippe}TaCl](t-CI) (4). In the glovebox, a 0.2% amalgam wasgenerated in a 350 mL reactor bomb by dissolving 128 mg (5.56 mmol) of Na in 64 gHg. A 10 mL toluene solution containing 733 mg (2.79 mmol) dippe was added to thereactor bomb. Solid TaC15, 1.001 g (2.792 mmol), was added and washed into thebomb with 250 mL toluene. The work-up of 4 is identical to 3 except that 100 mLCH21 is used to extract the product. Concentration of the solution to 30 mL followedby cooling to -40°C for 24 hours yielded 1.155 g of 4 (75%). Anal. Calcd forC28H641P4Ta•CH:C, 29.41; H, 5.62. Found: C, 29.34; H, 5.70. 1H NMR(C6D,6, ppm): 2.31 (d of sept, PCH(CH3)28H, 2JH,P = 7.2 Hz, 3H,H = 7.2 Hz);1.62 (d of m, PCH2 8H, 3H,P = 12.6 Hz); 1.32 (d of d, PCH(CH3)23H,H = 7.2 Hz,3JH,P = 13.8 Hz); 1.07 (d of d, PCH(CH3)23JH,H = 7.2 Hz, 3JH,P = 11.7 Hz). 31PNMR (C6D,6, ppm): 9.77 (s). Mol. weight calcd. forC28HCl6P4Ta:1098gmol1.Found: 1052 gmol-1.2.7.9 [{dippm}TaCI2](p-CI) (5). In the glovebox, 64 mg Na sand wereintroduced into a 350 mL reactor bomb along with a 2 cm stir bar. A 10 mL toluenesolution containing 346 mg (1.39 nimol) dippm was added to the reactor bomb. SolidTaC15, 500 mg (1.39 mmol), was added and washed into the bomb with 250 mLtoluene. The workup of 5 is identical to 3. The solution was filtered and the solutionconcentrated to 50 mL of THF. Cooling to -40°C for 24 hours yielded 553 g of red-purple 5 (74%). Anal. Calcd for26H60C1P4Ta:C, 32.36; H, 6.27. Found: C,31.99; H, 6.02. 1H NMR (C6D,6, ppm): 2.24 (sept, PCH(CH3)22H, 3JHH = 7.0Hz); 2.18 (m, PCH2 2H); 1.11 (d of d, PCH(CH3)26H, 3H,p = 13.2 Hz, 3JH,H = 7.0References p.62Chapter 2 59Hz); 1.08 (d of d, PCH(CH3)26H, 3JH,P = 12.2 Hz, 3JH,H = 7.0 Hz). 3lp NMR(C6D,3, ppm): 2.81 (s).2.7.9 {dippp}TaCI(=CHBUt) (6). To a 25 mL Et20 yellow coloured solutioncontaining 1.474 g (3.43 1 inmol) of TaCl3(CH2But) at -30°C was added 5 mL THF(excess) in a 100 mL reactor bomb. The solution was warmed to room temperatureand stirred for 6 hours. 948 mg (3.43 mmol) of dippp was then added to the purplesolution at room temperature and stirred 12 hours. The Et20 and excess THF wereremoved under vacuum to yield a red solid. The complex was dissolved in 40 mLtoluene and filtered. Concentration to 20 mL followed by cooling to -40°C for 24 hoursyielded 1.978 g of red crystalline 6 (9 1%). Alternatively, 6 can be made directly fromTaC13(CH2But) and dippp at -30°C in CH21. Anal. Calcd forC20H4413PTa: C,37.90; H, 6.99. Found: C, 38.19; H, 7.24%. 111 NMR (C6D,6, ppm): 4.25 (d,=CHBu, UI, 3J,p = 2.5 Hz); 2.46 (d of sept, PCH(CH3)22H,3JH,H = 7.1 Hz,2JH,P= 2.1 Hz); 2.23 (d of sept, PCH(CH3)22H, 3JH,H = 7.1 Hz,2JH,P = 7.1 Hz); 1.73 (m,PCH2C,2H); 1.48 (m, PCH2 4H); 1.40 (s, =CHC(CH3)9H); 1.21 (d of d,PCH(CH3)2,6H, 3JH,P = 13.3 Hz, 3JH,H = 7.1 Hz); 1.19 (d of d, PCH(CH3)26H,= 13.8 Hz, 3JH,H = 7.1 Hz); 1.17 (d of d, PCH(CH3)26H, 3JHP = 12.4 Hz,3JH,H = 7.1 Hz); 1.06 (d of d, PCH(CH3)26H, 3JH,P = 11.3 Hz, 3JH,H = 7.1 Hz). 31PNMR (C6D,6, ppm): 25.2 (s, PA); -16.9 (s, PM). Mol. weight calcd. forC20HCl3PTa: 633 gmolt.Found: 604 gmol1.2.7.10 {dippe}TaCI3(=CHBut) (7). The preparation of 7 is identical to thepreparation of 6. 1.520 g (3.542 mmol) ofTaC13(CH2But) and 928 mg (3.54 mmol) ofdippe yielded 1.974 g of red crystalline 7 (90%). Anal. Calcd forC19H4213PTa: C,36.82; H, 6.83; Cl, 17.16. Found: C 36.43; H, 6.79; Cl, 17.00%. 1H NMR (C6D,6,ppm): 3.92 (d, =CHBut, 1H, 3JH,P = 2.0 Hz); 2.31 (d of sept, 2H, 3JHH = 7.2 Hz,= 7.2 Hz); 2.19 (d of sept, 2H, 3JH,H = 7.2 Hz, 2H,p = 7.2 Hz); 1.64 (m, PCH2References p.62Chapter 2 602H); 1.58 (m, PCH2 2H); 1.40 (d of d, PCH(CH3)26H, 3JH,P = 13.1 Hz 3JH,H = 7.2Hz); 1.37 (s, =CHC(CH3)9H); 1.28 (d of d, PCH(CH3)26H, 3JH,P = 12.8 Hz3JH,H= 7.2 Hz); 1.10 (d of d, PCH(CH3)26H, 3JH,P = 13.8 Hz3JH,H = 7.2 Hz); 1.02 (d of d,PCH(CH3)2,6H, 3JH,P = 11.9 Hz3JH,H = 7.2 Hz). 31p NMR (C6D,8, ppm): 45.1(d, A,2Jp,p’ = 13 Hz); 3.4 (d, M,2Jp’,p = 13 Hz).2.7.11 {dippm}TaC1(=CHBut) (8). The preparation of 8 is identical to thepreparation of 6. 1.643 g (3.83 1 mmol) of TaC13(CH2But) and 950 mg (3.83 mmol) ofdippm yielded 2.039 g of red crystaffine 7 (88%). Anal. Calcd forC18H401P2Ta:C, 35.69; H, 6.66. Found: C, 36.01; H, 6.93. 1H NMR (C6D,8, ppm): 3.62 (d,=CHBut, 1H, 3H,P = 2.0 Hz); 2.25 (sept, PCH(CH3)22H, 3JHH = 7.0 Hz); 2.23(sept, PCH(CH3)22H, 3H,H = 7.1 Hz); 2.20 (m, PCH2 2H); 1.31 (s, =CHC(CH3)9H); 1.24 (d of d, PCH(CH3)26H, 3JH,P = 13.2 Hz, 3JH,H = 7.1 Hz); 1.19 (d of d,PCH(CH3)2,6H,3J P = 12.8 Hz, 3JH,H = 7.0 Hz); 1.08 (d of d, PCH(CH3)26H,3H,P = 12.2 Hz, 3JH,H = 7.0 Hz); 1.05 (d of d, PCH(CH3)26H, 3JHP = 13.8 Hz,= 7.1 Hz). 31p NMR (C6D,6, ppm): 28.7 (d, A,2Jpp’ = 109 Hz); -15.1 (d,M,2Jp’,p = 109 Hz).2.7.12 Modified Preparation of dippp. Step 1. Under nitrogen in a 3 L, 3-neckflask equipped with a double-coil condenser, 500 mL dropping funnel and a mechanicaloverhead stirrer was generated 2 moles of isopropyl Grignard by adding 183 mL (2.01mole) of 2-chloropropane over 2 hours to 57 g Mg° in 500 mL diethyl ether (Et20) at0CC. 1,2-dibromoethane can be used to activate the magnesium. The isopropylGrignard was filtered into a 500 mL dropping funnel (adjust volume to 500 mL),titrated and stored for use in step 2.Step 2. Under nitrogen in a 3 L, 3-neck flask equipped with a double coilcondenser, 500 mL addition funnel containing 500 mL of the isopropyl Grignard (3.56M) from step 1, and a mechanical overhead stirrer was generated PrPCl by addingReferences p.62Chapter 2 61the isopropyl Grignard dropwise over 1 hour to a stirred solution of 79.2 mL (0.908mole) PCi3 in 2 L Et20 at -40°C. Once half the isopropyl Grignard was added theaddition was interrupted for 1 hour to allow the first equivalent to react fully. Thecooling bath may be removed during this time. After 1 hour, the cooling bath wasreplaced and the second equivalent of isopropyl Grignard was added dropwise over 30minutes at -40°C. The mixture was filtered through a coarse 2 L frit under nitrogeninto a 2-neck, 3 L flask and stored overnight.Step 3. In a separate 3 L, 3-neck flask equipped with a double coil condenser,500 mL addition funnel and a mechanical overhead stirrer was added 37.95 g (1 mole)of LiA1H4 (LAH) and 100 mL Et20. The solution from step 2 was added to the 500mL dropping funnel in 500 mL aliquots. The Pr’PCl solution was added dropwise withstirring at room temperature at a rate that permits the ether to reflux. Each 500 mLaliquot was added over 1 hour. The mixture was stirred overnight under nitrogen.Step 4. The excess LAH from step 3 was hydrolyzed with 500 mL degassedH20 at 0°C by adding the water via a dropping funnel “slowly”. Extreme care wastaken as this step is exothermic and large amounts of H2 gas are evolved. Once allthe water had been added the ether layer was separated from the aqueous layer andthe aqueous layer extracted with 500 mL ether. The combined ether portions weredried over Na2SO4 overnight.Step 5. The ether from the step 5 was removed by distillation and the Pr2Hdistilled under nitrogen at atmospheric pressure (b.p. 118°C). The yield based on PCi3is usually around 60%.Step 6. To a 1 L, 3-neck flask equipped with a stirbar, condenser and 250 mLdropping funnel was added 24.89 g (0.211 mole) of Pr2H and 250 mL THF. Thedropping funnel was charged with 132 mL (1.6 M, 0.212 mole) of n-BuLi. The BuLiwas added dropwise with stirring to the cooled (-20°C) solution of Pr2H. Once theBuLi was added the solution was warmed to room temperature and stirred for 30References p.62Chapter 2 62minutes. The cooling bath was replaced and 1/2 equivalent of 1 ,3-clibromopropaneadded until the yellow color of the lithium phosphide disappeared (avoid adding excess1,3-dibromopropane). Once the addition was complete the THF was removed undervacuum. 100 mL degassed water and 250 mL ether were added and the twotransferred to a separatory funnel. The ether layer was separated from the aqueouslayer and the aqueous layer extrated with an additional 250 mL ether. The combinedether extracts were dried over Na2SO4 overnight.Step 7. The ether from step 6 was removed under vacuum and the productdistilled under full vacuum (b.p. = 102°C @ 0.1 mm Hg). Normal yields are 70% fromPr’PH.2.8 References(1) Tebbe, F. N. J. Am. Chem. Soc. 1973, 95, 5823.(2) Tebbe, F. N. U.S. Patent 3 933 876, Jan 20, 1976.(3) Moss, J. R.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1968, 632.(4) Bell, B.; Chatt, J.; Leigh, G. L.; Ito, T. .1. Chem. Soc., Chem. Commun. 1972, 34.(5) Chatt, J.; Coffey, R. S. .1. Chem. Soc. (A) 1969, 1963.(6) Chatt, J.; Coffey, R. S. J. Chem. Soc., Chem. Commun. 1966, 545.(7) Douglas, P. G.; Shaw, B. L. J. Chem. Soc., Chem. Com,nun. 1969, 624.(8) Mann, B. E.; Masters, C.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1970,846.(9) Mann, B. E.; Masters, C.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1970,703.References p.62Chapter 2 63(10) Muralidharan, S.; Ferraudi, G.; Green, M. A.; Caulton, K. G. J. Organomet.Chem. 1984,244, 47.(11) Green, M. A.; Huffman, 3. C.; Caulton, K. G.; Rybak, W. K.; Ziollcowski, J. 3. J.Organomet. Chem. 1981,218, C39.(12) Green, M. A.; Huffman, 3. C.; Caulton, K. G. J. Am. Chem. Soc. 1981, 103, 695.(13) Zeiher, E. H. K.; Dewit, D. G.; Caulton, K. G. J. Am. Chem. Soc. 1984, 106,7006.(14) Bruno, J. W.; Huffman, J. C.; Caulton, K. G. .1. Am. Chem. Soc. 1984, 109, 1663.(15) Green, M. A.; Huffman, 3. C.; Caulton, K. G. J. Organomet. Chem. 1983,243,C78.(16) Kubas, G. J.; Ryan, R. R.; Swanson, B. I.; Vergamini, P. 3.; Wasserman, H. 3. J.Am. Chem. Soc. 1984, 106, 451.(17) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 4126.(18) Bautista, M.; Earl, K. A.; Morris, R. H. J. Am. Chem. Soc. 1987, 109, 3780.(19) Fisher, B. J.; Eisenberg, R. Organometallics 1983,2, 764.(20) Baudry, D.; Ephritikhine, M.; Felkin, H. J. Chem. Soc., Chem. Commun. 1982,606.(21) Green, M. A.; Huffman, 3. C.; Caulton, K. G. J. Am. Chem. Soc. 1981, 103, 695.(22) Crabtree, R. H. Acc. Chem. Res. 1979, 12, 331.References p.62Chapter 2 64(23) Clerici, M. G.; DiGioacchino, S.; Maspero, F.; Perrotti, E.; Zanobi, A. J.Organomet. Chem. 1975,84, 379.(24) Meier, E. C.; Burch, R. R.; Muetterties, E. L.; Day, V. W. .1. Am. Chem. Soc.1982, 104, 2661.(25) Wang, H. H.; Pignolet, L. H. Inorg. Chem. 1980, 19, 1470.(26) Chaudret, B.; Devillers, J.; Poilbianc, R. J. Chem. Soc., Chem. Commun. 1983,639.(27) Bau, R.; Carroll, W. E.; Teller, R. G.; Koetzle, T. F. J. Am. Chem. Soc. 1977,99, 3872.(28) Green, M.; Bottrill, M. J. Organomet. Chem. 1976, 111, C6.(29) Templeton, J. L.; McCarley, R. E. Inorg. Chem. 1978, 17, 2293.(30) Cotton, F. A.; Najjar, R. C. Inorg. Chem. 1981,20, 2716.(31) Cotton, F. A.; Diebold, M. P.; Roth, W. J. Inorg. Chem. 1987,26, 4130.(32) Cotton, F. A.; Falvello, L. R.; Najjar, R. C. Inorg. Chem. 1983,22, 375.(33) Scioly, A. 3.; Luetkens Jr, M. L.; Wilson Jr., R. B.; Huffman, 3. C.; Sattelberger,A. P. Polyhedron 1987, 6, 741.(34) Wilson Jr., R. B.; Sattelberger, A. P.; Huffman, 3. C. J. Am. Chem. Soc. 1982,104, 858.(35) Sattelberger, A. P.; Wilson Jr., R. B.; Huffman, 3. C. Inorg. Chem. 1982, 21,2392.References p.62Chapter 2 65(36) Sattelberger, A. P.; Wilson Jr., R. B.; Huffman, J. C. Inorg. Chem. 1982,21,4179.(37) Sattelberger, A. P.; Wilson Jr., R. B.; Huffman, J. C. J. Am. Chem. Soc. 1980,102,7113.(38) Canich, J. A. M.; Cotton, F. A. Inorg. Chem. 1987, 26, 3473.(39) Clark, E. P. Indust. Eng. Chem., Anal. Chem. 1941, 13, 820.(40) LaPointe, R. E.; Wolczanski, P. T. J. Am. Chem. Soc. 1986, 108, 3535.(41) Tatsumi, K.; Sekiguchi, Y.; Nakamura, A.; Cramer, R. E.; Rupp, J. 3. J. Am.Chem. Soc. 1986, 108, 1358.(42) Skripkin, Y. V.; Eremenko, I. L.; Pasynskii, A. A.; Struchkov, Y. T.; Shklover,V. E. J. Organornet. Chem. 1984,267, 285.(43) Babaian-Kibala, E.; Cotton, F. A.; Kibala, P. A. Inorg. Chem. 1990,29, 4002.(44) NMR and the Periodic Table; Harris, R. K.; Mann, B. E., Ed.; Academic Press:New York, USA, 1978.(45) Freni, M.; Valenti, V. Gazzetta 1961, 91, 1357.(46) Johnson, K. H.; Smith, F. C. Phys. Rev. B 1972,5, 831.(47) Dedieu, A.; Aibright, T. A.; Hoffman, R. J. Am. Chem. Soc. 1979,101, 3141.(48) Hoffmann, R. J. Chem. Phys. 1963,39, 1397.(49) Luetkens Jr., M. L.; Hopkins, M. D.; Schultz, A. 3.; Williams, 3. M.; Fair, C. K.;Ross, F. K.; Huffman, 3. C.; Sattelberger, A. P. Inorg. Chem. 1987,26, 2430.References p.62Chapter 2 66(50) Hubert-Pfalzgraf, L.; Reiss, 3. Inorg. Chim. Acta 1978,29, L251.(51) Datta, S.; Wreford, S. S. Inorg. Chem. 1977,16, 1134.(52) CRC Handbook of Chemistry and Physics; Weast, R. C., Ed.; CRC Press, Inc.:Boca Raton, USA, 1984, pp D-158.(53) Rupprecht, G. A.; Messerle, L. W.; Fellmann, 3. D.; Schrock, R. R. J. Am.Chem. Soc. 1980, 102, 6236.(54) The JR spectrum of the polyacetylene was compared to the JR of an authenticsample. Baker, G. L.; Shelburne, J. A.; Bates, F. S. J. Am. Chem. Soc., 1986,108, 7377.(55) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive Compouds;2nd edition, John Wiley and Sons, Inc.: New York, USA, 1986.(56) Mullen, K.; Pregosin, P. 5. Fourier Transform NMR Techniques: A PracticalApproach; Academic Press: New York, USA 1976, pp 62.(57) This complex has been structurally characterized and determined to be a dimerin solution by the multiplicity of the bridging hydride pattern. Fryzuk, M. D.;Piers, W. E.; Einstein, F. W. B.; Jones, T. Can. J. Chem. 1989,67, 883.(58) Hoffman, D.; Hoffmann, R.; Fisel, C. R. J. Am. Chem. Soc. 1982, 104, 3858.(59) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984,3, 185.(60) Novikova, Z. S.; Prishchenko, A. A.; Lutsenko, I. F. J. Gen. Chem. USSR 1977,707.References p.62Chapter 2 67(61) Tani, K.; Tanigawa, E.; Tatsubo, Y.; Otsuka, S. J. Organomet. Chem. 1985,279, 87.(62) Schrock, R. R.; Fellmann, 3. D. .1. Am. Chem. Soc. 1978, 100, 3359.References p.62Chapter 3 68CHAPTER 3Amido-Diphosphine Complexes of Tantalum3.1 IntroductionAlthough the tantalum diphosphine complexes outlined in chapter 2 were easilyprepared, the subsequent reactivity of these complexes was thwarted by the loss ofdiphosphine in most cases. In an effort to prepare complexes which would be morestable toward the loss of phosphine, amido-diphosphine complexes were pursued.The goal was to “anchor” the soft’ phosphine donors to the metal by incorporatingthem into a tridentate ligand system which contained a hardt amide donor. The ligandsystem employed for this endeavor is shown below (I); the syntheses of these andother similar ligands have been reported previously2’3and will not be discussed here.Me2 Me2R=Ph,Pi,Me,But [IjJ’1 IR2P M PR2The simple metathetical exchange between Li{N(SiMeCHPR)and a metalhalide leads to the metal-ligand arrangement shown in I. The relatively strong Ta-Nbond and the chelate effect reduce the tendency for complete dissociation of thephosphine ligand donors.The amido-diphosphine ligand in I, has been shown to stabilize both early4’5and late6’7 transition metal complexes through the unique interdependence of the hardamide and soft phosphine donor types. Once chelated to a metal, the ligand can beviewed as a uninegative six-electron donor similar to the ubiquitous cyclopentadienylligand. The ligand can donate a further two electrons via the lone pair still remainingon the amide raising the total formal electron count to eight. It is debatable to whatReferences p.114Chapter 3 69extent the lone pair on the amide is delocalized into the silicon d-orbitals via a pit-dittype interaction versus a similar interaction with the transition metal dit orbitals,nevertheless it can be safely assumed that some multiple bond character is presentbetween the amide and the transition metal.Another feature of the amido-diphosphine hybrid ligand, I, is the meridionaldisposition of the phosphines which makes the amido-diphosphine ligand quitesterically bulky, especially when the substituents at phosphorus are isopropyl or tertbutyl. In octahedral complexes, the amido-diphosphine ligand is normally found tooccupy three sites arranged along a meridian whereas the Cp ligand occupies threesites on a face (facial); this makes a direct comparison of the steric bulk of the twoligand types difficult. However, reactivity studies reported in this chapter suggestthat complexes containing the amido-diphosphine ligand are much more thermallystable than their cyclopentadienyl or pentamethylcyclopentadienyl congeners.3.2 Amide Complexes of TantalumAmong the first amide complexes of the group 5 metals were the binarydimethylamido derivatives,8-10prepared by the metathesis of LiNMe2 and NbC15. Thestructure of Nb(NMe2)5(II) was shown to be square pyramidal.11IIMe2Me2N’,Nbcç..NMe2Me2N NMe2Amide complexes of tantalum have proven to be excellent precursors for thepreparation of alkyl and alkylidene derivatives;12’3 for example, the reaction of((Me3Si)2N } 2TaC13 with three equivalents of methyllithium yields the trimethylderivative {(Me3Si)2N}2TaMe.The role of transition metal alkyls in many catalyticReferences p.114Chapter 3 70processes’4has inspired the search for reactive ligand-stabilized complexes. Withmore sterically voluminous alkylating reagents such as LiCH2S Me3four-coordinatealkylidene derivatives are obtained (equation 3.1).{(Me3Si)2N}TaCI + 3 LiCHSiMeMe SiHCN(SiMe3)2Ta/ N(SiMe3)2Me3SiH2CWell-defined metal alkylidene complexes have been an integral part of thedevelopment of the ring opening metathesis polymerization’5(ROMP) process.Given the above precedents for the synthesis of group 5 amide complexes, itwas surprising that initial attempts to prepare amido-diphosphine complexes directlyfrom TaC15 and Li(N(SiMe2CHPR)}(R = Ph, Pr, Me, But) were completelyunsuccessful (equation 3.2).TaCI5 + Li{N(SIMe2CHPR)}--<--- TaCI4{N(SiMe2CHPR)}3 2]R = Ph, Pr’, Me, ButUpon mixing the lithium amide salt with TaC15 at -78°C a deep green solution resulted.1H and 31P{1H} NMR spectra showed only free ligand and what appeared to be aparamagnetic complex based on several extremely broad resonances. It is possiblethat the amide reduces TaC15 although the phosphines could also be involved in thereduction as has been observed with other phosphine-TaC15 systems.’6 Use of thepotassium salt of the amide, K{N(SiMe2CHPPh)},17also led to reduction.Several reports in the literature suggest that TaCl is easily reduced withalkyllithium reagents,’8 therefore the tin reagent,Bu3SnN(SiMe2CH2PMe2)2,’9wasprepared. However this route was also found to produce reduced material. Since ailcylReferences p.114Chapter 3 71zinc20 and aluminum21 reagents are known to effect metathesis without causingreduction, ClZn{N(SiMeHPPh)2was prepared. However, the addition ofC1Zn{N(SiMeHPPh)}to a toluene solution of TaCl5 again yielded a greensolution from which no diamagnetic material could be isolated. It became obvious thatamido-diphosphine complexes of tantalum prepared directly from TaC15 wereinaccessible due to the facile reduction of the metal in this oxidation state, thereforedialkyl derivatives of tantalum were employed as an alternative.A previous attempt’9 in our laboratory to prepare an amido-diphosphinecomplex from TaMe3Cl2 and Li(N(SiMe2CHPR)}(R = Me, Ph) met with limitedsuccess due to the thermal instability of the product formed.U It is interesting to notethat both CpTaCIMe3 and CpTaMe3 are thermally unstable, while TaMe5(dmpe)2is stable indefinitely at room temperature.26 Clearly, the choice of ancillary ligand inthese reactions can greatly influence the stability of the products. As mentioned inchapter 2, the addition of 2 equivalents of phosphine to Ta(CH2But)C13leads to theformation of alkylidene bis(phosphine) derivatives27in high yield (equation 3.3).Ta(CH2Bu’)C13 + 2 PR3 Ta(CHBu) 13(PR + CMe4 [3.3]This is the route of choice for the preparation of amido-diphosphine complexes oftantalum.3.3 Preparation and Structure of Amiclo-Diphosphine Complexes ofTantalumThe addition of one equivalent of Li(N(SiMe2CHPR)}(R = Pr, Ph, Me) toyellow Ta(CH2But)Cl3gives, by an apparent cz-elimination, the desired deep purpletantalum neopentylidene complexes in very high yield as shown in equation 3.4.References p.114Chapter 3 72Ta(CH2But)C13 + Li{N(SiMe2CHPR)}- CMe4[3.4]CI2Ta(=CH But){N(SiMe2CHPR}R=Pr’,lR = Ph, 2R=Me,3The alkylidene formulation is supported by the downfield resonance observed for thealkylidene a-carbon proton (CHa: 1, 7.19 ppm; 2, 7.94 ppm; 3, 7.61 ppm) in the 1HNMR spectra of compounds 1-3. The 13C { 1H} NMR spectrum ofC12Ta(=CHBut)(N(SiMeHPPr)}(1) shows a doublet at 263.3 ppm(1JC,H = 89Hz) due to the neopentylidene a-carbon atom. The chemical shift and couplingconstant are typical of electron-deficient ailcylidene complexes.28It is well established that a-elimination of benzyl groups is sluggish comparedto the corresponding reaction of neopentyl; for example, in order to effect a-eliminationfrom Ta(CH2Ph)C13with PMe3, prolonged heating is required.27 It was thereforesurprising to find that the reaction of Li{N(SiMe2CHPPr)}with Ta(CH2Ph)Cl3produced the benzylidene complex C1Ta(=CHPh) { N(S iMe2CH2PPr1)} (4) undersuch mild conditions (24 h, 20°C) (equation 3.5).Ta(CH2Ph)C13 + Li{N(S1MeCHPPr’)}- CH3Ph[3.5]CI2Ta(=CHPh){N (SiMe2CHPPr’)}4The 1H NMR spectrum of 4 reveals a resonance at 9.08 ppm due to the benzylidenea-carbon proton, CHa, and the 13C{1H} NMR spectrum shows a doublet at 255.3ppm(1JC,H = 98 Hz) again indicative of an alkylidene complex. Presumably the bulkReferences p.114Chapter 3 73of the phosphines as well as the rather large amide donor provide the correct stericenvironment for the facile elimination of toluene in complex 4.The degree to which the phosphines help promote a-elimination was onlyrealized after an attempt was made to prepare the benzylidene complex incorporatingthe phenyl substituted amido-diphosphine ligand. The reaction ofLi(N(SiMe2CHPPh)}and Ta(CH2Ph)C13did not give the desired benzylidenecomplex but rather a complex (Ill) with no coordination of the phosphines (danglingphosphine) as evidenced by 1H and 31P(1H} NMR spectroscopy.PPhMe2SI,,0T IIIciThe reduced basicity at phosphorus which is likely due to the electron withdrawingnature of the phenyl substituents, precludes coordination of the phosphines.Furthermore, prolonged heating of C12Ta(CH2Ph)2 { N(SiMe2CH2PPh2)2 } leads todecomposition with no evidence of any alkylidene intermediates as monitored by 1HNMR spectroscopy.The four alkylidene complexes 1-4 described above are monomers in solutionbased on their similar spectral parameters and the solution molecular weight29 of 701gmol’ found for Cl2Ta(=CHBut)(N(SiMePPr1)}(1) (calcd. 715 gmol’).The structure of the alkylidene complexes 1-4 was inferred from 1H and3lp { 1H) spectroscopy NMR as well as an NOE difference experiment on‘CH2PhReferences p.114Chapter 3 74l2Ta(=CHBut){N(SiMeCHPPh)}(2). The 31P{1H} NMR spectra of complexes1-4 appear as temperature invariant singlets indicating that the phosphines areequivalent on the NMR timescale. However, each alkylidene complex (1-4) showstwo silylmethyl resonances indicating that some asymmetry does exist in thebackbone of the coordinated amido-diphosphine ligands. The meridional coordinationof the amido-diphosphine ligand was confirmed spectroscopically (1H NMR) incomplexes 1-3 since all show a doublet of virtual triplets30 as the resonance for themethylene protons (PCH2) in the backbone of the ligand, arising from stronglycoupled, trans-disposed phosphines. In the 1H NMR spectrum ofC12Ta(=CHPh)-{N(SiMe2CHPPr)},4, the isopropyl methines signal appears as a virtual triplet ofseptets again confirming the meridional geometry of the ligand in solution. Based onthe above spectroscopic data there are 3 possible structures (IV, V. and VI) for theamido-diphosphine alkylidene complexes.RP.Me,,,. \Me’ \\____N Ta CIF,l es.,..Me ‘NL1VIRIP%;;..s, RRMet.....RReferences p.114Chapter 3 75Structure IV shows the meridionally coordinated amido-diphosphine ligandand the alkylidene which is trans to the amide donor. In structures V and VI thealkylidene moiety is oriented cis to the amido ligand which generates two possiblestructural isomers, that is, one with the R’ group anti to the amide group and the otherwith the R’ group syn to the amide group. In all 3 isomers the equivalency of thephosphines as well as the asymmetry of the ligand would be maintained. It is worthnoting that if alkylidene rotation is occurring in these complexes, that is rotation aboutthe Ta=C bond, it would only be measurable for isomer IV since alkylidene rotation inisomers V and VI would have no effect on the inequivalent groups of the amidodiphosphine ligand. We have seen no evidence of ailcylidene ligand rotation incomplexes 1-4 from -80°C to +80°C as monitored by 1H NMR spectroscopy butcannot rule out a rapid equilibrium between isomers V and VI (schcme 3.1).Scheme 3.1Of the structurally characterized alkylidene complexes known, the M-Ca-C angle ofthe alkylidene fragment invariably exceeds 160° due to an extensive agostic C-Hainteraction with the metal; this may enhance the multiple bonding between theailcylidene and the metal and increase the energy barrier for alkylidene rotation. Weturned to an NOE difference experiment in an attempt to determine the structure ofcomplexes 1-4 the results of which are shown in figure 3.1.Me2SI\R’Me2SI\V VIReferences p.114PhPhMe2Si— _C.CMirradiatet-butylgroupMe2Si\SPhCMe3Phm=CHPh0•1ISiMePPM,.IPCH2PCH2‘II2.1irradiateherePPMFigure31.400.00MHz1HNMR(top)andNOEDIFFspectrum(bottom)of compound2inC6D6(*denotesC6DSH).Chapter 3 77Irradiation of the tert-butyl protons of the neopentylidene group inC12Ta(=CHBut){N(SiMeHPP)},2, shows a nearly equal enhancement of thetwo types of ortho phenyl protons of the amido-diphosphine ligand and somewhatweaker enhancement of the meta and para protons. No enhancement of the ligandsilylmethyl or backbone-methylene protons was observed. A ligánd geometry such asthat depicted in structures V and VI would be expected to lead to some enhancementof one of the silylmethyl groups or one of the methylene protons and have little or noeffect on the phenyl protons opposite the neopentylidene group. Furthermore, a rapidequilibrium between isomers V and VI (scheme 3.1) can also be ruled out since thiswould likely lead to some enhancement of the silylmethyl protons. In structure IV thetert-butyl group of the neopentylidene ligand would lie quite far from the silylmethyland methylene protons and nearly between the four phenyl substituents of the amidodiphosphine ligand. This geometry correlates best with the NOE differenceexperiment as well as the 1H and 31P NMR data. The coordination geometry ofcomplexes 1-4 is best described by structure IV.rvl1 R=Pr,R’=Bu’2R=Ph,R=But3 R=Me,R’=Bu iv4 R=P,R=Ph Mei,,...,MeA common mode of decomposition for alkylidene complexes occurs viabimolecular coupling of the alkylidene ligands to give an olefin and reduced metalfragments. 6,25,27,31,32References p.114Chapter 3 782 LM=CHR RHC=CHR + 2 [LM] [36]cis, trans isomersIt was therefore rather surprising to find that complexes 1 and 4 could be heated to100°C in toluene for several days with no sign of decomposition by 31P{1H} NMRspectroscopy. The steric bulk of the phosphines as well as the chelate effect greatlyenhance the thermal stability of these complexes. Although the chlorides incompounds 1-4 can be replaced with a variety of alkyl groups, no attempt was madeto isolate these derivatives.Coordinatively saturated (six-coordinate) alkylidene complexes of the formC13Ta(=CHR)L2(R = But or Ph; L = tertiary phosphine) require loss of phosphine inorder to react with olefins.33 The alkylidene complexes 1 and 4 do not react witholefms, ketones or 02 even at high temperature (24h, 80°C) demonstrating again thecoordinatively saturated nature of these six-coordinate complexes.3.4 Kinetics of the a-Elimination of CH3R from CI2Ta(CHR)-{N(SiMe2CH2PPr1)Details of the a-elimination process have been described32 for the dialkylcyclopentadienyl derivative CpTaC12(CHBut) but similar measurements on thephosphine derivatives TaC13(CHR)PR’)(R = But or Ph) were hampered by theloss of phosphine.27 The stability of the amido-diphosphine complexes allowed for themeasurement of the kinetics of the a-elimination process since the problemsassociated with loss of phosphine are eliminated due to the chelating nature of theamido-diphosphine ligand.The addition of Li(N(SiMe2CHPPr))to a cooled (-30°C) ether solution ofTa(CH2But)C13or Ta(CHPh)C13results in the formation of the dangling phosphineReferences p.114Chapter 3 79complexes C12Ta(CHBut)(N(SiMe2CHPPr1(A) andCl2Ta(CHPh)-{N(SiMe2CHPPr1)}(B), respectively, analogous to the dangling phosphinecomplex III mentioned above. Inspection of the 31P(1H} NMR spectrum of bothcomplexes at -30°C revealed similar chemical shifts centred around that found for freeamine-diphosphine (— -4 ppm). No evidence of the alkylidene complexes 1 and 4 wasobservable by 31P{1H) NMR spectroscopy providing the temperature was maintainedbelow -30°C.The tantalum dangling phosphine complexes C12Ta(CHBut)2{ N( SiMe2-CH2PPr))(A) andCl2Ta(CHP )(N(SiMeHPr}(B) undergo clean firstorder kinetics eliminating neopentane and toluene, respectively; this generates thealkylidene derivatives 1 and 4 described in the previous section. The kinetics of thisreaction can be followed conveniently by 31P{1H) NMR spectroscopy by measuringthe decrease in the concentration of species A and B in C6D. The first-order rateand Eyring plots are shown in figures 3.2 and 3.3, respectively; the data are shown inTable 3.1 and the activation parameters in Table 3.2.The large negative AS t measured for the a-elimination from the danglingphosphine, five-coordinate complexes A and B requires that the transition state bemore ordered than the starting material. A four-centred transition state34 involvingthe alkyl substituents which is consistent with the data presented is shown in figure3.3.References p.114Chapter 3‘-4C-aC800 1000 2000 3000Time (seconds)4000(a)3______2(b)00 1000 2000 3000 4000Time (seconds)Figure 3.1. (a) The first-order rate plot for the a-elimination fromCI2Ta(CHBut)(N(SiMeHPPri)},A. (b) The first-order rate plot for the aelimination from C12Ta(CHPh){ N(SiMe2CHPPr}, B. The first orderdependency was determined by successive runs using different concentrations of bothA and B.References p.1140CTable 3.1. Rate data{N(SiMe2CHPPr)}.Chapter 3 81-12.00-12.50-13.00-13.50-14.00-14.500. 00295(K)tempFigure 3.2. Eyring plot for the a-elimination of CH3R from C12Ta(CHR)-(N(SiMe2CHPPr)}.for the a-elimination of CH3R from C12Ta(CHR)-0.00310 0.00325 0.00340R=But R=Ph. Temp (°C) k (s1) Temp (°C) k (s1)20.4 1.97 x iO-’ 30.2 2.42 x25.6 3.05 x i0 35.3 3.41 x iO-430.6 4.62 x 10-4 40.2 4.65 x iO35.5 6.74 x iO- 45.3 6.54 x i0-40.5 9.47 x 10-4 50.4 9.05 x iO-45.5 1.39 x 10-3 55.3 1.21 x 10-350.4 1.96 x lO- 60.2 1.62 x iO-References p.114Chapter 3 82Table 3.2. Erying data for the a-elimination of CH3R from Cl2Ta(CHR)-{N(SiMe2CHPPr)}.Parameter R = But R = PhASt (cal K-1 mole1) -28 ±4 -35 ± 4AH (kcal mole-1) 13 ± 1 12 ± 1Figure 3.3. A possible transition state for the a-elimination of CH3R fromC12Ta(CHR){ N(SiMe2CH2PPr)2}.The five-coordinate starting materials, A and B, would have a greater degree offreedom than the seven-coordinate transition state intermediate (figure 3.3),principally because of the dangling phosphines. Furthermore, in the five-coordinatestarting material the alkyl groups bound to tantalum would be free to occupy equatorialor axial sites since isomerization is rapid in five-coordinate ligated complexes. A cisdisposition of the alkyl groups is required for intramolecular a-elimination to occurwhich may be facilitated by the concomitant coordination of the phosphines. Althoughseven-coordinate complexes are also known to be highly fluxional, the chelatedamido-diphosphine may restrict or slow this process. A seven-coordinateCICIReferences p.114Chapter 3 83intermediate is well supported since a-elimination does not occur from six-coordinatedlialkyl complexes such asC13Ta(CH2Ph)(PMe).7The AH and ASI values for the a-elimination of CH3R from intermediates Aand B are comparable with published values32 for the a-elimination of neopentanefrom CpTaCl2(CHBut)in chloroform (Table 3.3).Table 3.3. Enthalpy and entropy data the a-elimination process for known tantalumailcylidene complexes.32Complex Solvent AH (kcal mole-1) AS1 (cal K mole)CpTaC12(CHBut) ether 19 ± 1 -16 ± 4CpTaC1(CHBut) benzene 21 ±2 -4 ± 10CpTaC12(CHBut) chloroform 10.7 ± 0.5 -36 ± 2CpTaBr(CHBut)2 ether 16±2 -13 ± 7It has been observed qualitatively that a-elimination occurs most rapidly in polarchlorinated solvents as this may aid in the stabilization of a polar transition state27(i.e. the transition state is highly solvated). The amido-diphosphine ligatedcomplexes, A and B, exhibit a similar large negative LS which suggests that thesolvent (benzene) may be involved in stabilizing the transition state. A more detailedkinetic analysis in several different solvents may reveal the role that the solvent playsin the a-elimination of alkane from these complexes.3.5 Reduction ofCl2Ta(=CHR){N(SiMePPr)}under DihydrogenIn chapter 2, the synthesis of the hexahydride complex Ta2H6 { dippp } 2 wasdescribed as being achieved by sodium-mercury amalgam reduction of thecorresponding alkylidene complexCl2Ta(=CHBut){dippp} under hydrogen. Thealkylidene complexes Cl2Ta(=CHR){N(SiMe2CH2PPr’)2) (1, R = But; 4, R = Ph)References p.114Chapter 3 84alkylidene complexes C12Ta(=CHR) {N(SiMe2CHPPr)} (1, R = But; 4, R = Ph)also react with dihydrogen under reducing conditions to give good yields of thehexahydrido binuclear derivativeTa6{N(SiMeCHPPr(5), as shown inequation 3.7.CI2Ta(=CH R){N (SiMe2CHPPr’)[3.7](xs) Na’Hg Ta2H6{N(SiMeCHPPr’)}1,R=Bu 4atmH22,R=Ph 5The binuclearity of the structure is corroborated by the solution molecular weight29 of1153 gmol-1 found for 5 (calcd. 1176 gmol1).The 1H NMR spectrum of 5 shows four silyl methyl, four isopropyl methine andeight isopropyl methyl resonances indicating considerable asymmetry in the molecule.The alkylidene moiety has been lost as RH (R = But or Ph) likely via the formation ofan alkyl followed by hydrogenolysis. Additionally, the 1H NMR spectrum of 5 showsfour different hydride resonances in the integrated ratio of 2:2:1:1. The downfieldresonance at 12.30 ppm appears as a broad triplet (2JH,P = 40 Hz) which ischaracteristic of a bridging hydride coupled to trans phosphines. The other threeupfield hydride resonances are broad and featureless likely due to coupling to thequadrupolar tantalum nucleus.35 The hydrides do not exchange rapidly on the NMRtimescale even at 80°C suggesting that the structure is rigid. Homonuclear andheteronuclear(1H{31P}) decoupling experiments revealed no additional informationregarding the multiplicity of the hydride patterns; however, the hydride resonanceswere absent in the hexadeutero analogue Ta2D6{N(SiMe2CH2PPr2)2}2 (5-d6). Acomparison of the JR spectrum of 5 and 5-d6 was ambiguous and the stretching bandscould not be assigned; these resonances are either too weak or obscured by ligandReferences p.114Chapter 3 85by 1H NMR spectroscopy, however several decomposition products were observed by31P(lH} NMR spectroscopy.The 31P(1H} NMR spectrum of 5 appears as an AA’BB’ spin system with thephosphines of one ligand donor being inequivalent. A possible structure consistentwith the above spectroscopic data is shown below (VII)Inspection of the proposed structure, VII, having C2 symmetry (C2 through HA andHe), reveals inequivalent phosphine donors as well as four different hydrides, thelatter in the ratio 2:2:1:1. The structure also shows the staggered conformation of thephosphines which would be preferred from a steric point of view. The structure is alsoconsistent with the asymmetry observed in the ligand region of the 1H NMR spectrumof complex 5. The proposed structure of complex 5 is reminiscent of the tetrahydridebridged dimer [(Me3P}2TaC12](J.t-H)4(VIII) which also has staggered phosphinesand rigidily bound hydrides.37I[P”]HB0Si’[H1F “‘DLVIISi’ = SiMe2p” = pp1i2PMe3VIIIClReferences p.114Chapter 3 86The hexahydride dimerTa2H6{N(SiMeCHPPr1)},5, is disappointinglystable; for example, the hydrides in 5 do not exchange with free deuterium (4atmospheres), the complex does not react with excess ethylene, 1 ,3-butadiene oracetylene, and appears to be air stable for short periods of time (10-15 minutes).Evidently, the amido-diphosphine is so sterically demanding that even smallmolecules cannot react with the metal centre.3.6 Preparation of Amido-Diphosphine Imido Complexes of TantalumAs mentioned in section 3.2, the alkylidene complexes Cl2Ta(=CHR’)-{N(SiMe2CHPR)}(1-4) do not react with simple olefins to give metathesisproducts because of the saturated coordination sphere of the metal (IV).1 R=Pr’,R=But2 R=Ph R1= But3 R=Me,R’=But ‘V4 R=Pr’,R’=PhAttempts to remove one of the chloride ligands with Ag(BPh4) as well as replacing achloride with a weakly coordinating ligand (CF3S03-) were unsuccessful leading todecomposition. In order to generate a coordinatively unsaturated complex, the twochlorides would have to be replaced with a suitable ligand which occupies a singlecoordination site and has a 2- charge; an imido donor (NR2) seemed reasonable.A convenient starting point for the preparation of tantalum imido compounds isthe octahedral, THF ligated complex Cl3Ta(=NPh)(THF)2,8 which, upon the additionMe,,,..URReferences p.114Chapter 3 87of Li(N(SiMe2CHPR)}toC13Ta(=NPh)(THF)2at room temperature gives thedesired imido complex as shown in equation 3.8.CI3Ta(=NPh) (TH F)2 + Li{N(SiMe2CHPR)}RT CI2Ta(=NPh){N(SiMe2CHPR) [3.8]Et20-6 R = Pr7 R = PhThe 1H MR spectrum of 6 shows three distinct resonances for the phenyl ofthe imido ligand as well as two isopropyl methine, four isopropyl methyl and two silylmethyl resonances. The temperature invariant 31P{1H} NMR spectra of 6 and 7appear as singlets indicating equivalency of the phosphine donors. As with theailcylidene complexes, there are three possible structures for the imido compounds: theimido ligand could be bent and oriented trans to the amide, the imido could be cis tothe amide and bent toward the arnide group, or the imido could be cis to the amide andbent toward the chloride. A linear imido ligand trans to the amide does not correlatewith the observed asymmetry in the amido-diphosphine ligand.The imido bis(phosphine) complex, C13Ta(=NPh)(PEt)2has a trans,mergeometry38 as shown below (IX).IxTherefore, based on the above spectroscopic data and literature precedence, the mostlikely structure of the imido complexes 6 and 7 is trans,mer with the imido ligandIReferences p.114Chapter 3 88possibly bent (X). An NOE difference experiment would be informative in thisinstance.6R=Pr’ x7 R = PhInitial reactivity studies suggest that an imido-alkylidene species is formedupon treatment of C12Ta(=NPh) {N(SiMe2CHPPh,7, with two equivalents ofneopentyl lithium as evidenced by 1H NMR spectroscopy. Further elaboration of thissystem may lead to stable five-coordinate imido-alkylidene species which mayundergo metathesis type reactions.3.7 Dinitrogen Complexes Incorporating the Amido-DiphosphineLigand: Factors Influencing Side-on vs. End-on Binding ofDinitrogenThe catalytic reduction of di.nitrogen by the enzyme nitrogenase39 to give twoequivalents of ammonia is an unique transformation in nature. For many years40researchers have devoted much effort to developing a well-defined analogue tonitrogenase, which is believed to contain molybdenum, iron and sulfur in a cubic array(figure 3.4). However no such catalytically active analogues have been prepared.41Me2ID112References p.114Chapter 3 89Figure 3.4. Proposed active site in nitrogenase as determined by molybdenum42’3and iron EXAFS analysis.The inermess of dinitrogen is apparent from its lack of reactivity with mostelements at room temperature.45 However, dinitrogen can be reduced by priorcoordination to a transition metal complex which lowers the energy of the it4’ orbitalson dinitrogen, allowing for formal electron transfer. The synthesis of simple well-defined transition metal dinitrogen complexes may help in the understanding of theprocess that is operative in nitrogenase; specifically, the nature of the bonding of thedinitrogen ligand to the metals present and how it relates to the reduction mechanism.The first report of dinitrogen bound to a transition metal46 was made in 1965. Themolecular structure47 shows an end-on coordination of dinitrogen (XI).NH3NHH3N Ru NN XIH3N INH3The nature of the bonding interaction between dinitrogen and a metal has beenthe subject of many reviews;48 for example, the side-on bonding of dinitrogen isproposed in the catalytic reduction of dinitrogen to hydrazine and ammonia as shownin equation 3.9.N2s’References p.114Chapter 3 900,‘ s,,,1 0’N 2 e, 2 H+N’”N ,.SNH + H2 + NH3ç [3.9](4 = SCH2CH(NH) 0Catalytic conversion of dinitrogen to ammonia has been observed although thesystems are not well defined.49 Stoichiometric conversion of dinitrogen to ammoniaemploying a molybdenum complex with two end-on coordinated dinitrogen ligands hasbeen achieved50 and the catalytic conversion of hydrazine to ammonia using amolybdenum catalyst has also been reported.5’3.7.1 Tantalum End-on Dinitrogen ComplexesThe reduction of dinitrogen by a highly-reduced transition metal complex is amethod that has been used to prepare bridging dinitrogen complexes. The reduction ofC13Ta(CHBut)(PMe)2under dinitrogen52 yields the dinitrogen bridged complex[ClTa(CHBut)(PMe]2(.tN2); the same compound is obtained from isolatedC1Ta(CHBut)(PMe3)4and free dinitrogen.52 Subsequent alkylation with LiCH2Butyields [Ta(CHBut)(CHBut)(PMe(j.tN(XII); the molecular structure of XIIdisplays a “diimido-like” linkage of the dinitrogen ligand whereby dinitrogen is actingas an N24 ligand.PMe3Me3P CH2ButBUtH2C,,,,His,.Ta N—N xii/ Me3P C—HBUt PMe3 IButReferences p.114Chapter 3 91Other structural features include a trigonal bipyramidal arrangement of the ligandsabout each tantalum and a twisting of the two ends of the molecule by 83. Ofparticular importance is the alkylidene It-system which is oriented perpendicular tothe Ta=N axis of each metal; this becomes significant in determining the bonding ofdinitrogen (side-on vs. end-on). Other members of this class of end-on dinitrogencomplexes appear in Table 3.4.Table 3.4. Tantalum end-on dinitrogen complexes.Complex N-N (A) Reference[Ta(CHBut)(CH2CMe)(PM]2(I.t-N2) 1.298 52[TaCl3( HF)p-N- 52[TaC1(PEt)2]2(p.-N2) - 52{TaC1(FBz3)(THF)1J.1.-N2) L282 53[(H4)TaC1(PMe3)2]2(p.-N- 52[Ta(S -2,6-C6H3-Pr2) (THF)] 20.t-N2) 1.290 54[Ta(O-2,6-C6H3-Pr2)3(THF)] 2(P.-N2) 1.320 54[Ta(OCMe)( HF)].i-N 1.290 553.7.2 Zirconium Side-on Dinitrogen ComplexA recent report5 from our laboratory described the synthesis of a side-onbridging dinitrogen complex by the reduction of ZrC13{N(SiMe2CH2PPr)}with twoequivalents of sodium-mercury amalgam under 4 atmospheres of dinitrogen. Thisgenerates the complex [ZrCl{N(SiMe2CH2PPr1)}](I- (XIII). Only a fewexamples of side-on bound dinitrogen have been reported.56References p.114Chapter 3 92Inspection of the molecular structure of [ZrCl (N(SiMe2CHPPr2)2} ](I.t-N) (XIII)shows that the amido-diphosphine ligand and the chloride of one zirconium fragmentoccupy the four basal positions of a pseudo square-based pyramid with the centroid ofthe dinitrogen ligand occupying the apical position. The unusual coordination of thedinitrogen moiety to the two zirconium centres prompted an investigation of thebonding in this complex.62Details of the ENDO/l semi-empirical molecular orbital calculation on themodel complex [{H3P}2ZrCl(NH)](j.t- can be found in the experimental section.A picture of the model compound is shown below (XIV).The two most intriguing molecular orbitals for this complex are the HOMO(8bg) andthe H0M09 (6bg) which are shown in figure 3.5.Pr’2 Pr2Xfflzx‘I4.‘4.yH3PHN’//HH3PPH3NN’ ciHPH3XIVReferences p.114Chapter 3 93Figure 3.5. (top) Isosurface plot of the óbg level of[{H3P}2ZrC1(NH)]Qi- for= 0.03 a.u.. (bottom) Isosurface plot of the 8bg level for ‘ig = 0.03 a.u.. Dark greyarea = +‘ig, light grey area=-ig.References p.114Chapter 3 94The molecular orbital (talcing the principal axis as coincident with the nitrogen-nitrogen axis), 8bg, arises from the overlap of two primarily zirconium basedorbitals with the ir orbital of dinitrogen. The it molecular orbital, 6bg, is generated bythe overlap of two orbitals with the other orthogonal it” orbital of dinitrogen. Theanalysis of the zirconium model complex suggested that ML4 formally d2 fragmentsincorporating the amido-diphosphine ligand could bind dinitrogen in a side-on fashion.Thus, we initiated a study to prepare other ML4 fragments containing the amidodiphosphine ligand in an effort to understand the role of the ancillary ligand in thesesystems.3.7.3 Reduction ofCI2Ta(CHR){N(SiMeHPPr)}under DinitrogenA group 5 valence isoelectronic analogue to the zirconium complex[ZrCl{N(SiMe2CHPPr)}j(j.t-Nwould have to have the chloride ligand replacedwith a 2- ligand. Formally, the alkylidene moiety (CHR2-) is such a ligand. Thus, thetwo fragments, ZrC1(N(SiMe2HPPri)} and Ta(=CHR)(N(SiMe2CHPPri},can be viewed as four-coordinate isoelectronic moieties. The reduction ofCl2Ta(=CHR){N(SiMePPr)(1, R = But; 4, R = Ph) under 4 atmospheres ofdinitrogen gives good yields of the desired dinitrogen complexes as shown in equation3.10.2 Na/HgCI2Ta(=CH R){N (SiMe2CHPPr’)} 4 atm N2[3.10]8, R= But9, R = Ph [Ta(=CHR){N(SiMe2CPPr’)](p,-Microanalytical data for the complexes [Ta(=CHBut){N(SiMePPr))](i(8) and [Ta(=CHPh){N(SiMe2CP r)](t- (9) are consistent with twoReferences p.114Chapter 3 95nitrogen atoms per tantalum while 1H and 31P(1H) NMR data suggest that theamido-diphosphine ligand and alkylidene ligand are intact and bound to the metal. Thesolution molecular weight29 of 1227 gmol1 found for 8 (calcd. 1316 gmol’) confirmsthe binuclearity of the clinitrogen complexes in solution.While the absolute structure of the dinitrogen complexes 8 and 9 is difficult todetermine in the absence of an X-ray crystallographic study, several key features arereadily deduced from the 1H, 31P{1H} and 15N(1H} NMR data. The 1H NMR spectraof complexes 8 and 9 show two silylmethyl, two isopropyl methine and four isopropylmethyl resonances indicating inequivalency in the backbone of the amido-diphosphineligand. The temperature invariant 31P(1H} NMR spectra of complexes 8 and 9 showa singlet indicating a chemically equivalent environment of the two phosphine donorsper ligand. The phosphine donors in the solid state structure of[Ta(CHBut) (CH2But)(PMe32j(iN(XII) are inequivalent; however, a singlet isobserved in the 31P{1H} NMR spectrum.52 Free rotation about the N-N bond islikely operative in these complexes. The 15N { H} NMR spectrum of{Ta(=CHBut){N(SiMeCPPr}]($.ll5N(5’) shows a single resonance at 419ppm which is very close to the chemical shift of 414 ppm reported for the end-on 15Nlabelled analogue [Ta(CHBut)(CH2But)(PMe3(I lSN52and is typical for acomplex containing an N24- bridging ligand.57 A structure consistent with the datapresented is shown in XV.Pr’2Me2SiN8,R=But S...Me2Si Ta N—N T9,R=PhPr2Pr2XVReferences p.114Chapter 3 96The exact orientation of the alkylidene ligand could not be determinedspectroscopically; however, the positioning of the R-group toward the core of thedimer would certainly reduce steric interactions with the amido-diphosphine ligand.3.7.4 Frontier Orbital Analysis of Dinitrogen ComplexesIn an effort to understand the ligand arrangement of an ML4 fragmentnecessary for side-on vs. end-on binding of dinitrogen, an Extended HUckel analysisof the fragments ZrCl(N(SiMe2CHPPr)}and Ta(=CHR){N(SiMe2CPPr)}was undertaken. The idealized model fragments, C and D, used for the analysis areshown below.H HzCI ZrH’1NHL’LSLFor both models the metal is raised above the plane of the four ligands by 20°, as thisbest represents the coordination sphere observed in the structure of [ZrC1{N(SiMe2-CH2PPr12)2}]2(.t-N (XIII) and the conformational restrictions of the amidodiphosphine ligand. Details of the calculations can be found in the experimentalsection. The frontier orbitals for an idealized ML4 fragment of C4h symmetry are wellknown and the results presented here compare well with published58 theoreticalstudies.HDReferences p.114Chapter 3 973.7.4.1 Frontier Orbitals of{H3P)2ZrCI(NH)Inspection of the orbital interaction diagram for the zirconium fragment (figure3.6) reveals two metal-based d-orbitals (la” and 2a”) which have the correctsymmetry to overlap with the? orbitals of dinitrogen. The out-of-phase combinationof the 1 a” orbital, which is comprised mainly of the atomic orbital, with theappropriate ? orbital of dinitrogen generates the It-symmetry orbital, 6bg. Thismolecular orbital is bonding with respect to Zr-N but antibonding with respect to N-N. As mentioned above, INDO/l calculations on the zirconium model,[{H3P}2ZrCl(NH2)](I.L- 2 , suggest that this orbital, 6bg, is remarkably stable(HOMO-9). This is in contrast to the It-type molecular orbitals generated for atypical end-on dinitrogen complex, which invariably appear as HOMO or HOMO-1.Thus it would appear that the it-overlap for side-on bound dinitrogen is much moreenergetically favorable than the same it-overlap in an end-on dinitrogen complex in-the context of this particular system. The second molecular orbital of interest is the 6interaction, 8bg, which involves the other? orbital on dinitrogen and an in-phasecombination of the metal-based virtual orbital, 2a”. This orbital appears as theHOMO as would be expected for the less favorable overlap predicted for 6-typebonds. Again the interaction is net bonding between Zr-N and antibonding betweenN-N. The predicted bond order for the zirconium model,[{H3P}2ZrCl(NH)](i-,is 0.85 which is consistent with the observed N-N bond length of 1.548 A in themolecular structure of Xffl.References p.114Chapter 3 981/ —Itt.0gtgtots.,5to,tOIstoSt0 0StS •0 s5 04,0Figure 3.6. Molecular orbital interaction diagram for the model compound[(HP}2ZrCl(NH)J(p-,showing the important N2 bonding orbitals.1 a”—N2r1i \P/P”cIZReferences p.114Chapter 3 99The importance of the availability of the virtual orbital was recently59demonstrated with the synthesis of the titanium end-on dinitrogen complex[TiC1 {Me2NCHCHMe)(N(SiMe3)2)](p.-N2)(XVI).S1Me3Me3Si..../Me2N/N SiMe3CWith no conformational restrictions such as those present in the chelating amidodiphosphine ligand, the amido group (N( SiMe3 } 2) is free to rotate into a lesssterically demanding position; the pt orbital of the aniide in complex XVI is orientedperpendicular. to the Ti-Ti axis thus generating a pit-dit interaction with the virtualorbital on titanium. With the orbital involved in a it-bond with the amide, itappears that the end-on coordination of the dinitrogen ligand is preferred. The frontierorbital analysis6°of the model fragment (H3N}2TiC1(NH)clearly shows themetal-based orbital occupancy which would seem to negate the possibility of forminga side-on dinitrogen complex.The amide ic-orbital and a chloride p-orbital in the fragment,{ H3P} 2ZrC1(NH2), interact with the virtual frontier orbital on the zirconiumfragment (XVII).References p.114Chapter 3 100HHantibondi ngXVIIIThis generates a stable bonding molecular orbital (HOMO-4) which in turn raises theenergy of the corresponding antibonding combination (XVIII) above both the la” and2a” frontier orbitals (see figure 3.7); the cooperative role of the amide and chloride inthis system cannot be underestimated. It is believed that the absence of this secondIt-type frontier orbital on the zirconium fragment is in part responsible for theformation of the side-on dinitrogen complex.The two it orbitals on dinitrogen interact in a a and it fashion with combinationsof the virtual Py and d2-2 orbitals on the zirconium fragment (not shown). The la”and 2a” frontier orbitals on the zirconium fragment do not have the appropriatesymmetry for suitable overlap with the it orbitals of dinitrogen. Additionally, the filledmolecular orbitals that can be thought of as the lone pairs of electrons on thedinitrogen moiety are essentially non-bonding as they are not directed toward anymetal-based orbitals.3.7.4.2 Frontier Orbitals of {H3P}2Ta (= C H 2) (NH2An interaction molecular orbital diagram for the overlap of the frontier orbitalsof fragment D,{H3P}2Ta(=CH2)(NH2), with dinitrogen is shown in figure 3.7. Thefrontier orbitals a’ and a” are the virtual and tantalum based orbitals,respectively, which have the correct symmetry for overlap with the it and It orbitals ofdinitrogen. The in-phase combination of two a” frontier orbitals of the tantalumbondingXVIIReferences p.114Chapter 3 101fragment and the it orbital on dinitrogen generates the it-symmetry molecular orbital,a. This molecular orbital is bonding with respect to the Ta-N as well as the N-N.The next interaction, b, is composed of two in-phase a’ tantalum frontier orbitals andthe second it orbital of dinitrogen. This molecular orbital is also bonding with respectto Ta-N and N-N.The out-of-phase combination of the a” frontier orbitals and the it molecularorbital on dinitrogen generates the orbital, bg, which is bonding with respect to Ta-Nbut antibonding with respect to N-N. A second out-of-phase combination, ag, isorthogonal to bg. The lone pairs of electrons on the dinitrogen moiety are involved insimple a-bonds with the appropriate unfilled frontier orbitals on the tantalum fragment(not shown). The theoretical bond orders obtained for the N-N interaction are l.24and for the Ta-N interaction 2.14. This is in agreement with the proposed freerotation about the N-N bond and the N-N bond distances reported in the literature.57Again the amide it-orbital and a p-orbital on carbon are involved in bondingwith the virtual orbital on tantalum (XIX).This generates a stable bonding molecular orbital (HOMO-3) which in turn generatesthe corresponding antibonding molecular orbital (XX) which is depicted as thefragment orbital a’ in figure 3.7.bonding antibondingXIX XXReferences p.114Chapter 3 102It‘II— —— — — — et__tet•0agbgj44JI,,,TaPFigure 3.7. Molecular orbital interaction diagram for the model compound[{H3P}2Ta(=CH)(NH2)]2(-N2), showing the important N2 bonding orbitals.References p.114Chapter 3 103The Ta=C double bond consists of a pit-orbital on carbon interacting with thevirtual orbital on the tantalum fragment (XXI).PH32 <It is believed that the formation of a side-on dinitrogen complex is unfavorable notonly because the virtual orbital is occupied but because the antibondingcombination of XXII is raised in energy above the antibonding combination XX. Thisenergy difference between XXII and XX may account for the observed end-oncoordination of dinitrogen.Returning to the molecular structure52 of [Ta(CHBut)(CH2Bu )(PMe3)2}2(I.L-N2), XII, the it-system of the alkylidene is oriented perpendicular to the Ta-Ta axisas shown below (XXIII).zHBUt.HH__________H(7,PH3bondingXXIantibondingXXIIXXIIIMe3References p.114Chapter 3 104The pit-orbital on carbon overlaps with the virtual orbital on tantalum leaving theand orbitals for bonding to dinitrogen. Again the orientation of the alkylideneis believed to be responsible for the observed end-on coordination of dinitrogen.3.7.5 Mechanism of Formation of Dinitrogen ComplexesOther d2, ML4 fragments are currently being investigated in our laboratory inorder to test the validity of our approach to bind dinitrogen in different modes. Forexample, the side-on dinitrogen complex, [Zr(2,6-OC6H3Me2)(N(SiMe2CH2-PPri2)](p.N,6and the end-on dinitrogen complex, [CpZr{N(S1Me2HPPr}}(i.t-N),62have recently been prepared and these results are in agreementwith the calculated availability of the appropriate frontier orbitals.Although much has been learned concerning the nature of the bonding in thesesystems, the actual mechanism of formation is still unclear. In order to form thezirconium and tantalum dinitrogen compounds, three separate molecules mustconverge: the two ML4 metal fragments and the dinitrogen ligand. However, thedinitrogen ligand is not restricted in its coordination to only the formally reduced ML4fragments. At any point during the reduction process one or more dinhtrogen ligandscould act as donors, possibly stabilizing the reactive reduced fragment. However, it istempting to speculate that the amido-diphosphine ligand initially generates a pseudosquare-planar arrangement of the ML4 fragment which restricts the approach ofdinitrogen to the two faces of this square plane (cf. XXIV).SiMe2Pr’2N2Me2xsI—N2References p.114Chapter 3 105A square-planar arrangement of ligands is not unrealistic for a d2, ML4 fragmentcontaining a second or third row transition metal.3.8 Summary and Future ConsiderationsAlkylidene complexes of tantalum can be prepared by reacting the diallcylderivatives TaR2C13 (R = Np, Bz) with a variety of amido-diphosphine ligands. Thereaction proceeds via an i-elimination of RH through a highly-ordered transitionstate. An NOE difference experiment suggests a trans,mer arrangement of theamido-diphosphine ligand and ailcylidene moiety. This appears to be the only viablemethod for the preparation of mononuclear amido-diphosphine complexes of tantalum.The alkylidene amido-diphosphine complexes serve as good starting materials for thepreparation polyhydride derivatives. Imido complexes of tantalum incorporating theamido-diphosphine ligand can also be prepared in high yield and these materialsappear to yield imido-alkylidene derivatives upon reaction with an appropriate alkyilithium. The high yield synthesis of dinitrogen bridged derivatives incorporating theamido-diphosphine ligand has also been demonstrated.Extended HUckel calculations on the tantalum ML4 fragment,{H3P}2Ta(=CH)(NH,suggest that the orientation of the alkylidene ligand may beresponsible for the observed end-on coordination of dinitrogen. The full INDOI1calculations on the model, {H3P}2Zr(NH)Cl, suggest that the it-overlap of the itorbital on dinitrogen and the appropriate it-symmetry orbital on zirconium is quite lowin energy suggesting that this overlap is more favorable than the correspondingoverlap in end-on complexes.We are currently searching for other fragments, not necessarily ML4, which areisolobal to the zirconium fragment. Preliminary theoretical studies suggest thatReferences p.114Chapter 3 106porphyrin derivatives of zirconium (XXV), ClV{N(SiMe2HPPr)2)(XXVI) andCl2Ta(N(SiMeHPPr)}(XXVII) have the correct symmetry and orbital orderingto form side-on dinitrogen complexes.60XXVXXVIXXVIIIn the case of the vanadium complex, ClV{N(SiMe2HPPr)J(XXVI), a furtherreduction to a nitrido complex, ClV(N) {N(SiMeCHPPr2)2), may be possible,although this will require population of the a*orbital of dinitrogen, a potentially highenergy process. The preparation of other side-on bound dinitrogen complexes mayhelp in the search for a system that can catalytically reduce dinitrogen to ammonia.Further studies on the imido complexes of tantalum are also in order aspreliminary studies indicate the presence of an imido-alkylidene species. These typesof compounds may be precursors for the ring opening metathesis of cyclic olefms.Pr’2Me2S1References p.114Chapter 3 1073.9 Experimental Procedures3.9.1 General Information. See section 2.7.1 (chapter 2) for further details.All molecular orbital calculations were performed on the CAChe Worksystem,a product developed by Tektronix. The parameters used in the INDO/1 semi-empirical molecular orbital calculations on the model compound,[{H3P}2Zr(NH)Cl]( ,were taken from the literature.63 A full list of eigenvaluesand symmetry labels can be found in the appendix. The bond lengths were taken fromthe X-ray crystal structure analysis5 of [ZrCl{N(SiMe2CHPPr)}j(ii-N)and themodel was restricted to C2h symmetry. The Cartesian coordinates of the models canbe found in the appendix. For all models the following standard bond lengths wereused: P-H, 1.380 A; C-H, 1.090 A; N-H, 1.070 A.The parameters used for the Extended HUckel calculation of the tantalummodel fragment, {H3P}2Ta(=CH)(NH,were taken from the literature64aand arelisted in the appendix. The bond lengths and angles used for the model are as follows:Ta-N, 2.175 A; Ta-P, 2.770 A; Ta-C, 1.930 A; P-Ta-P, 140.00; C-Ta-N, 140.0°. TheCartesian coordinates of the models can be found in the appendix.The parameters used for the Extended HUckel calculation of the zirconiummodel fragment, (H3P}2Zr(NH)Clwere taken from the literature641’and are listed inthe appendix. The bond lengths and angles used for the model are as follows: Zr-N,2.175 A; Zr-P. 2.770 A; Zr-Cl, 2.493 A; P-Zr-P, 140.00; Cl-Zr-N, 140.0°. TheCartesian coordinates of the models can be found in the appendix.3.9.2 Syntheses. TaCl5 (99.9%) was purchased from Aldrich Chemical Companyand used as received. Ta(CH2But)l3lSand Ta(CH2Ph)C1366 were preparedaccording to literature procedures. The amido-diphosphine ligandsReferences p.114Chapter 3 108Li {N(SiMe2CHPPr)} ,3 LifN(SiMe2CHPPh)} , and Li {N(SiMe2CHPMe)}as well as TaC13(=NPh)(THF),8were prepared by published routes.3.9.3CITa(=CHBut){N(SiMePPr},1. To a stirred yellow Et20solution (200 mL) of Ta(CH2But)C13(1.841 g, 4.291 mmol) at RT was added anEt20 solution (30 mL) of Li{N(SiMeCHPPr (1.713 g, 4.292 mmol) over 5minutes. Within 30 minutes the solution turned purple. The solution was stirred for24 hours and the ether was removed under vacuum. The crude product extracted withhexanes (100 mL) and filtered through a layer of Celite® to remove LiC1.Concentration of the solution to 25 mL followed by cooling to -40°C overnight yielded2.002 g of purple crystalline 1. Further concentration of the solution to 5 mL gaveanother 513 mg (total yield 82%). Anal. Calcd forC23H541NPSiTa: C, 38.66;H, 7.62; N, 1.96. Found: C, 38.37; H, 7.82; N, 1.79%. 1H NMR (C6D,6, ppm): 7.19(t, CHBut, 1H, 3Jjp = 1.5 Hz); 2.79 (t of septPCH(CH3)2H,[2JH,P +4Jjj,p] ÷ 2 =3 Hz, 3JH,H = 7 Hz); 2.33 (t of sept, PCH(CH3)22H,[2JH,p +4JH,PJ ÷ 2 = 3 Hz,3JH,H = 7 Hz); 1.59 (d of t, PCH2 2H, 2JH,H = 14 Hz,[2JH,p +4JH,P1 + 2 = 3 Hz);1.44 (s, CH(CH3)9H); 1.43 (d of d, PCH(CK3)26H, 3JHP = 14 Hz,3JH,H =7 Hz);1.21 (d of d, PCH(CH3)26H, 3JH,P = 15 Hz3H,H =7 Hz); 1.18 (d of d, PCH(CH3)26H, 3JH,P = 14 Hz, 3JH,H =7 Hz); 1.13 (d of d, PCH(CH3)26H, 3H,P = 14 Hz, 3JH,H= 7 Hz); 1.04 (d of t, PCH2 2H, 2JH,H = 14 Hz,[2JH,P +4JHP] ÷ 2 = 3 Hz); 0.43 (s,SiCH3, 6H); 0.24 (s, SiCH3 6H). 31P{1H} NMR (C6D,6, ppm): 37.7 Cs).13C{H} NMR (C6D,6, ppm): 263.3 (d, CHBut, 1JC,H = 89 Hz); 45.5 (s,C(CH3);36.1 (s, C(CH3)2;28.3 (s, PCH(CH3)2;26.8 (s, PCH(CH3)2;20.9 (s,PCH(CH3)2;20.1 (s, PCH(CH3)2;19.4 (s, PCH(CH3)2;18.8 (s, PCH(CH3)2;14.7(s, PCH2); 5.3 (s, SiCH3); 3.3 (s, SiCH3). Mol. weight calcd for 715. Found 701gmol 1References p.114Chapter 3 1093.9.4C12Ta(=CHBut){N(S1MeHPPh),2. To a stirred yellow toluenesolution (100 mL) of Ta(CH2Bu’)2C13(1.072 g, 2.491 mmol) at RT was added atoluene solution (30 mL) of Li{N(SiMeCHPPh}(1.332 g, 2.491 mmol) over 5minutes. The metathesis reaction took place immediately as evidenced by theformation of LiC1 but no colour change was evident for several days. The solution wasstirred for 7 days and filtered through a layer of Celite® to remove LiC1. Concentrationof the solution to 25 mL followed by cooling to -40°C overnight yielded 2.0 13 g ofpurple crystalline 2 (94%). Anal. Calcd forC35H4612NPSiTa: C, 49.41; H, 5.45;N, 1.65. Found: C, 49.71; H, 5.55; N, 1.54%. 1H NMR (C6D,, ppm): 8.02 (m, H0,4H); 7.94 (br s, CHBut, 1H); 7.83 (m, H0, 4H); 7.06 (m, Hm, 8H); 7.01 (t, Hp, 4H);2.44 (d of t, PCH2 2H,2JH,H = 13 Hz,[2JH,P +4JH,P] ÷ 2 =2 Hz); 1.93 (d of t, PCH22H, 2JH,H = 15 Hz, [2JH,P +4JH,P] ÷ 2 = 3 Hz); 1.07 (s, C(CH3)9H); 0.37 (s,SiCH3,6H); 0.30 (s, SiCH3 6H). 31P{1H} NMR (C6D,, ppm): 21.5 (s).3.9.5 ITa(=CHBut){N(SiMePMe},3. The preparation complex 3is identical to that of compound 1 above except that the reaction was performed at-40°C. 439 mg (1.02 mmol) of Ta(CH2But)C13and 294 mg (1.02 mmol) ofLi{N(SiMe2CHPMe)}gave 444 mg of red-purple 3 (68%). 1H NMR (C6D,,ppm): 7.61 (s, CHBut, 1H); 1.48 (t, PCH3 6H,[2JH,p +4JH,P] ÷ 2 = 3 Hz); 1.39 (s,CH(CH3),9H); 1.28 (s, PCH3 6H); 1.01 (d of t, PCH2 4H,2H,H = 13 Hz,[2JH,P +4JH,P] ÷ 2 = 3 Hz); 0.29 (s, SiCH3 6H); 0.14 (s, SiCH3 6H). 31P{1H} NMR(C6D,3, ppm): 2.5 (s).3.9.6 ITa(=CHPh){N(SiMeCP r1},4. To a stirred orange-red Et20solution (200 mL) of TaC13(CH2Ph)2 (4.59 1 g, 9.782 mmol) at RT was added an Et20solution (30 mL) of Li{N(SiMeCHPPri}(3.911 g, 9.781 mmol) over 5 minutes.The metathesis reaction was evident by the formation of LiC1 but no colour changeReferences p.114Chapter 3 110occurred for 6 hours. The solution was stirred for 24 hours and the ether was removedunder vacuum. The crude product extracted with toluene (200 mL) and filtered througha layer of Celite® to remove LiC1. Concentration of the solution to 50 mL followed bycooling to -40°C overnight yielded 6.573 g of deep green crystalline 4 (91%). Anal.Calcd for25H5OC12NPSiZTa: C, 40.87; H, 6.86; N, 1.91. Found: C, 40.97; H, 7.05;N, 2.08%. H NMR (C6D,8, ppm): 9.08 (t, CHBut, 1H, 3JH,P = 1.6 Hz); 7.56 (d,H0, 2H, 3JH,H = 7 Hz); 7.35 (t, Hm, 2H, 3H,H =7 Hz); 6.69 (t, Hp, 1H, 3JH,H = 7 Hz);2.67 (t of sept, PCH(CH3)22H, 3JH,H = 7 Hz,[2JH,P +4JH,P] ÷ 2 = 4 Hz); 2.09 (t ofsept, PCH(CH3)22H, 3JH,H = 7 Hz, [2JH,p +4JH,p] ÷ 2 = 4 Hz); 1.38 (d of d,PCH(CH3)2,6H, 3H,p = 16 Hz, 3JH,H = 7 Hz); 1.18 (d of d, PCH(CH3)26H, 3JHP =15 Hz, 3JH,H = 7 Hz); 1.09 (m, PCH2 4H); 1.02 (d of d, PCH(CH3)26H, 3JH,p = 14Hz, 3JH,H = 7 Hz); 0.98 (d of d, PCH(CH3)26H, 3JH,p = 16 Hz, 3JH,H = 7 Hz); 0.41(s, SiCH3 6H); 0.29 (s, SiCH3 6H). 31P{1H} NMR (C6D,6, ppm): 40.1 (s).13C{H} NMR (C6D,8, ppm): 255.3 (d, CHBut,1JC,H = 98 Hz); 145.2 (s, ofphenyl); 133.2 (s, C0 of phenyl); 131.1 (s, Cm of phenyl); 125.4 (s, C, of phenyl); 27.4(s, PCH(CH3)2;25.6 (s, PCH(CH3)2;19.8 (s, PCH(CH3)2;19.4 (s, PCH(CH3)2;19.1 (s, PCH(CH3)2;18.1 (s, PCH(CH3)2;13.1 (s, PCH2); 4.8 (s, SiCH3); 3.7 (s,SiCH3).3.97 [Tall3{ N (Si Me2C H2PPr2)2)]2 5. In the glovebox, a —1% sodiumamalgam was generated in a 350 mL reactor bomb by dissolving 94 mg Na (4.1 mmol)in 10.0 g Hg. A 50 mL toluene solution containing 1.001 g (1.362 mmol) ofCl2Ta(=CHPh){N(SiMeP r)(4) was then added to the amalgam. Thereactor bomb was sealed, taken to a vacuum line and the solution degas sed threetimes. The bomb was cooled to -196°C and purified dihydrogen introduced. The bombwas sealed at - 196°C. The solution was slowly warmed to room temperature andstirred vigorously. The green solution gradually turned deep red in colour, as NaC1References p.114Chapter 3 111formed. The solution was stirred for 48 hours and the toluene was removed undervacuum. The crude product was extracted with hexanes (25 mL) and filtered througha medium porosity frit with the aid of Celite®, care being taken to leave the mercuryresidues behind. Concentration to 10 mL and cooling to -40°C yielded 572 mg of 5(72%). Anal. Calcd forC36H94N2P4SiTa:C, 37.49; H, 8.23; N, 2.43. Found: C,37.17; H, 8.05; N, 2.35%. 1H NMR (C6D6,8, ppm): 12.30 (br t, Ta-H, 2H,2JH,P =40Hz); 6.62 (br s, Ta-H, 1H); 5.34 (br s, Ta-H, 2H); 3.34 (br s, Ta-H, 1H); 2.67 (d ofsept, PCH(CH3)22H, 3JH,H = 7 Hz,3JH,P = 7 Hz); 2.22 (d of sept, PCH(CH3)22H,3H,H = 7 Hz, 3JH,P = 7 Hz); 2.01 (br d of sept, PCH(CH3)2211); 1.94 (d of sept,PCH(CH)22H, 3JH,H = 7 Hz, 3JH,P = 7 Hz); 1.65 (d of d, PCH(CH3)26H, 3H,P =14 Hz, 3JHH = 7 Hz); 1.61 (d of d, PCH(CH3)26H, 3JH,P = 14 Hz, 3JH,H = 7 Hz);1.51 (d of d, PCH(CH3)26H, 3JH,P = 13 Hz,3JH,H = 7 Hz); 1.39 (overlapping d of d,PCH(CH3)2,12H, 3JH,P — 14 Hz, 3JH,H = 7 Hz); 1.28 (d, PCH2 4H); 1.24 (d, PCH2411); 1.10 (overlapping d of d, PCH(CH3)218H, JH,P 14Hz, 3JH,H = 7 Hz); 0.66(s, SiCH3 6H); 0.46 (s, SiCH3 6H); 0.39 (s, SiCH3 6H); 0.23 (s, S1CH3 6H).3lp{1H} NMR (C6D,8, ppm): AA’BB’ spin system, 45.3 (m). Mol. weight calcdforCH942P4SL(l’a:1176. Found: 1153 gmol-1.3.9.8 lTa(=NPh){N(SiMeHP r)},6. To a stirred yellow Et20solution (50 mL) ofTaC13(=NPh)(THF)2(551 mg, 1.05 mmol) at -10°C was added anEt20 solution (10 mL) of Li(N(SiMeCHPPr (422 mg, 1.05 mmol) over 5minutes. As the mixture was warmed to RT, the colour of the solution turned orange.The solution was stirred for 24 hours and the ether was removed under vacuum. Thecrude product extracted with hexanes (100 mL) and filtered through a layer of Celite®to remove LiCl. Concentration of the solution to 10 mL followed by cooling to -40°Covernight yielded 616 mg of yellow-orange crystalline 6 (79%). 1H NMR (C6D,6,ppm): 7.60 (d, H0 of phenyl, 2H, 3H,H = 7 Hz); 7.28 (t, Hm of phenyl, 2H, 3JH,H =7References p.114Chapter 3 112Hz); 6.76 (t, Hp of phenyl, 1H, 3JH,H = 7 Hz); 2.39 Ct of sept, PCH(CH3)22H, 3JH,H= 7 Hz, [2JH,P ÷4JH,P] ÷ 2 = 3 Hz); 1.95 (t of sept, PCH(CH3)22H, 3JH,H = 7 Hz,[2JH,P +4JH,PJ ÷ 2 = 3 Hz); 1.44 (d of t, PCH2 2H, 2JH,H = 14 Hz,[2JH,P +4JH,P] +2 = 3 Hz); 1.40 (d of t, PCH2 2H,2JH,H = 14 Hz,[2JH,P +4JHp] ÷ 2 = 3 Hz); 1.23 (dof d, PCH(CH3)26H, 3JH,H = 7 Hz, 3JH,P = 15 Hz); 1.13 (d of d, PCH(CH3)26H,3JH,H = 7 Hz, 3JH,P = 14 Hz); 0.98 (d of d, PCH(CH3)26H, 3JH,H = 7 Hz, 3JH,P =113 Hz); 0.95 (d of d, PCH(CH3)26H, 3JH,H = 7 Hz, 3JH,P = 15 Hz); 0.53 (s, SiCH36H); 0.42 (s, SiCH3 6H). 31P{1H} NMR (C6D,6, ppm): 33 8 (s).3.9.9CITa(=NPh){N(SiMeHP h,7. The preparation of 7 is identicalto the procedure outlined for 6 above. 161 mg (0.308 mmol) ofTaC13(=NPh)(THF)2and 165 mg (0.308 mmol) of Li(N(SiMe2CHPPr}yielded 242 mg of 7 (90%).Anal. Calcd forC36H41N2PSTa: C, 49.60; H, 4.74; N, 3.21. Found: C, 49.32;H, 4.87; N, 3.20% 1H NMR (C6D,8, ppm): 7.81 (d, H0 of phenyl, 6H, 3JH,H = 7Hz); 7.68 (d, H0 of phenyl, 4H, 3JH,H = 7 Hz); 7.25-7.11 (m, Nm of phenyl, 1OH); 7.01(t, Hp of phenyl, 4H, 3JH,H = 7 Hz); 6.61 (t, Hp of phenyl, 4H, 3JHH = 7 Hz); 2.13 (dof t, PCH2 2H, 2JH,H = 13 Hz, [2JH,P +4JH,PJ ÷ 2 = 2 Hz); 2.04 (d of t, PCH2 2H,2JHH = 15 Hz,[2JH,P +4JH,P1 + 2 = 3 Hz); 0.38 (s, SiCH3 6H); 0.22 (s, SiCH3 6H).31P{1H} NMR (C6D,6, ppm): 18.2 (br s).3.9.10 [CITa(=CHBut){N(S1Me H2PPr)](i-N, 8. In theglovebox, a —1% sodium amalgam was generated in a 350 mL reactor bomb bydissolving 27 mg Na (1.2 mmol) in 2.7 g Hg. A 25 mL toluene solution containing 211mg (0.295 mmol) ofC1Ta(=CHBut)(N(SiMePPr}(1) was then added tothe amalgam. The reactor bomb was sealed and taken to a vacuum line. The reactorbomb was degassed three times and cooled to -196°C. Dinitrogen was introduced at-196°C and the reactor bomb sealed. The solution was slowly warmed to roomtemperature and stirred vigorously. The purple solution gradually turned yellow inReferences p.114Chapter 3 113colour, as NaC1 formed. The solution was stirred for 48 hours and the toluene wasremoved under vacuum. The crude product was extracted with hexanes (25 mL) andfiltered through a medium porosity frit with the aid of Celite®, care being taken toleave the mercury residues behind. Concentration to 5 mL and cooling to -40Cyielded 171 mg of 8 (88%). Anal. Calcd for46H108NPS1Ta2:C, 41.99; H, 8.27;N, 4.26. Found: C, 41.43: H, 8.43; N, 4.09%. The percent carbon was slightly low forthis complex due in part to the difficulty encountered in the oxidation of the Ta=Ndouble bond. On several occasions the carbon percentage was within 0.3%, yet thenitrogen percentage was roughly half the expected value. Thus the compound had tobe oxidized with a combination of Co304/Ag or CuOINaF. 1H NMR (C6D,8, ppm):7.20 (br s, CHBut, 2H); 2.41 (br t of pentets, PCH(CH3)24H); 2.09 (t of pentets,PCH(CH3)2,4H, 3JH,H =7 Hz,[2JH,P +4JH,P] + 2 = 3 Hz); 1.44 (d of d, PCH(CH3)212H, 3JHH = 7 Hz, 3j11 = 14 Hz); 1.42 (s, CH(CH3)218H); 1.34 (d of d,PCH(CH3)2,12H,3J11j=7 Hz, 3H,p = 15 Hz); 1.32 (d of d, PCH(CH3)212H, 3JH,H=7 Hz, 3JH,P = 14 Hz); 1.26 (d of d, PCH(C113)212H, 3JH,H =7 Hz, 3H,P = 14 Hz);1.06 (d of t, PCH24H,2JH,H = 15 Hz,[2JH,P +4JH,P] ÷ 2 = 3 Hz); 1.02 (d of t, PCH24H,2J= 15 Hz,[2JH,P +4JH,P1 ÷ 2 = 3 Hz); 0.44 (s, SiCH3 12H); 0.36 (s, SiCH312H). 31P{1H} NMR (C6D,8, ppm): 48.8 (br s). 15N{H) NMR (C7D8,6,ppm): 419 (s). Mol. weight calcd for 1316. Found 1227 gmoi1.3.9.11 [CITa(=CHPh){N(SiMeP r}](p.-,9. The preparationof 9 is identical to the procedure outlined for complex 8 above. 1.000 g (1.36 1 mmol)of C12Ta(=CHPh){N(SiMePPr)(4) yielded 736 mg of 9 (79%). Anal.Calcd forC5oHiojN4SiTa:C, 44.30; H, 7.44; N, 4.13. Found: C, 44.72; H, 7.52;N, 3.90%. See the discussion of the analysis above (section 3.9.10) 1H NMR(C6D6, 6, ppm): 9.35 (br s, CHPh, 2H); 7.47 (d, H0 of phenyl, 4H, 3JH,H = 7 Hz); 7.35(t, Hm of phenyl, 411, 3JH,H = 7 Hz); 6.84 (t, Hp of phenyl, 2H, 3JH,H = 7 Hz); 2.40 (brReferences p.114Chapter 3 114sept, PCH(CH3)24H, 3JHH = 7 Hz); 2.08 (br sept, PCH(CH3)24H); 1.28(overlapping d of d, PCH(CH)224H, 3JH,P = 14 Hz, 3JH,H = 7 Hz); 1.19(overlapping d of d, PCH(CH3)224H, 3JH,P = 13 Hz, 3JH,H = 7 Hz); 0.81(overlapping d of t, PCH2 8H, 2JH,H = 15 Hz,[2JH,P +4J,p] ÷ 2 = 3 Hz); 0.51 (s,SiCH3, 12H); 0.39 (s, SiCH3 12H). 31P{1H} NMR (C6D,6, ppm): 51.1 (s).3.9.12 Kinetics of the x-Elimination. The first order decomposition of thecomplexesClTa(CH2R){N(SiMePPr )}(A, R = But; B, R = Ph) wasmonitored using 31P(1H} NMR spectroscopy. In order to insure accurate integrationsa five second delay between 20° pulses was utilized. Typically, the spectra werecollected at variable temperatures in C6D solutions (0.12 molL1) in sealed NMRtubes. The observed rate constants were determined from the slope of the graph:ln{ ([A]0 / [A]0-x)) versus time by plotting the ln(1 I % starting material) versus time(least squares fit). The AH and ASI: were determined from the Eyring plots: ln(kobs /temp) versus 1 / temp (least squares fit). AHI: = -R(slope) and AS = R[intercept -ln(kB / h)] where R = gas constant, h = Planck’s constant and kB = Boltzmannconstant. The estimated error bars for the values of Ht and AS are the result ofrepeated runs for the neopentyl complex.3.10 References(1) Pearson, R. G. J. Chem. Ed. 1968,45, 581, 643.(2) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. 3.; Secco, A. S.; Trotter, 3.Organometallics 1982, 1, 918.(3) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,24, 642.(4) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. 3. Organometallics 1988, 7, 1224.References p.114Chapter 3 115(5) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J. J. Am. Chem. Soc. 1990, 112, 8185.(6) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. 3. .1. Am. Chem. Soc. 1985, 107, 6708.(7) Fryzuk, M. D.; Joshi, K.; Rettig, S. J. Organometallics 1991, 10, 1642.(8) Bradley, D. C.; Thomas, I. M. Can. J. Chem. 1962,40, 1335.(9) Bradley, D. C.; Thomas, I. M. Can. .1. Chem. 1962,40, 449.(10) Bradley, D. C.; Gitlitz, M. H. J. Chem. Soc. (A) 1969, 980.(11) Heath, C.; Hursthouse, M. 0. J. Chem. Soc., Chem. Commun. 1971, 143.(12) Santini-Scampucci, C.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1976, 1766.(13) Anderson, R. A. Inorg. Chem. 1979, 18, 3622.(14) Coliman, J. P.; Hegedus, L. S.; Norton, 3. R.; Finke, R. G. Principles andApplications of Organotransition Metal Chemistry; University Science Books:Mill Valley, USA., 1987, pp chapter 11.(15) Grubbs, R. H. In Comprehensive Organometallic Chemistry; G. Wilkinson, F.G. A. Stone and E. W. Abel, Ed.; Pergamon Press: Oxford, England, 1982; Vol.8; pp 499.(16) Hubert-Pfalzgraf, L. G.; Tsunoda, M.; Reiss, 3. 0. Inorg. Chim. Acra 1981,52,231.(17) Haddad, T. S. Ph.D. Thesis, University of British Columbia, Canada, 1990.(18) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978,100, 3359.References p.114Chapter 3 116(19) Williams, H. D. 1983, unpublished results.(20) Schrock, R. R.; Parshall, G. W. Chem. Rev. 1976, 76, 243.(21) Nishimura, K.; Kuribayashi, H.; Yamamoto, A.; Ikeda, S. J. Organomet. Chem.1972, 37, 317.(22) McConville, D. H. 1990, unpublished results, this complex has been identifiedby ‘H and 31P NMR spectroscopy.(23) Juvinall, G. L. J. Am. Chem. Soc. 1964,86, 4202.(24) McConville, D. H. 1990, unpublished results, the complex (R = Ph) has beenidentified by ‘H and 31P NMR spectroscopy at low temperature butdecomposes rapidly at room temperature.(25) Schrock, R. R.; Sharp, P. R. J. Am. Chem. Soc. 1978, 100, 2389.(26) Schrock, R. R. J. Organomet. Chem. 1976, 122, 209.(27) Rupprecht, G. A.; Messerle, L. W.; Fellmann, 3. D.; Schrock, R. R. J. Am.Chem. Soc. 1980, 102, 6236.(28) Schrock, R. R. Acc. Chem. Res. 1978, 12, 98.(29) Clark, E. P. Indust. Eng. Chem., Anal. Chem. 1941, 13, 820.(30) Brookes, P. R.; Shaw, B. L. J. Chem. Soc. (A) 1967, 1079.(31) Turner, H. W.; Schrock, R. R.; Fellmann, J. D.; Holmes, S. 3. .1. Am. Chem. Soc.1983, 105, 4942.(32) Wood, C. D.; McLain, S. 3.; Schrock, R. R. J. Am. Chem. Soc. 1979, 101, 3210.References p.114Chapter 3 117(33) Rocklage, S. M.; Fellmann, 3. D.; Rupprecht, G. A.; Messerle, L. W.; Schrock,R. R. J. Am. Chem. Soc. 1981, 103, 1440.(34) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. 3.; Nolan, M. C.;Santarsiero, B. D.; Schaefer, W. P.; Bercaw, 3. E. J. Am. Chem. Soc. 1987, 109,203.(35) Hanis, R. K.; Mann, B. E. NMR and the Periodic Table; Acedemic Press: NewYork, NY, 1978.(36) Sattelberger, A. P.; Wilson Jr., R. B.; Huffman, 3. C. J. Am. Chem. Soc. 1980,102,7111.(37) Wilson Jr., R. B.; Sattelberger, A. P.; Huffman, 3. C. J. Am. Chem. Soc. 1982,104, 858.(38) Rocklage, S. M.; Schrock, R. R. J. Am. Chem. Soc. 1980, 102, 7809.(39) Eady, R. R.; Postgate, 3. R. Nature 1974,249, 805.(40) Coucouvanis, D. Acc. Chem. Res. 1981, 14, 201 and references therein.(41) Challen, P. R.; Koo, S.-M.; Kim, C. G.; Dunham, W. R.; Coucouvanis, D. J. Am.Chem. Soc. 1990, 112, 8606.(42) Conradson, S. D.; Burgess, B. K.; Newton, W. E.; Hodgson, K. 0.; McDonald,3. W.; Rubinson, J. F.; Gheller, S. F.; Mortenson, L. E.; Adams, M. W. W.;Mascharak, P. K.; Armstrong, W. H.; Hoim, R. H. J. Am. Chem. Soc. 1985, 107,7935.References p.114Chapter 3 118(43) Conradson, S. D.; Burgess, B. K.; Newton, W. E.; Mortenson, L. E.; Hodgson,K. 0. J. Am. Chem. Soc. 1987,109, 7507.(44) Antonio, M. R.; Teo, B. K.; Orme-Johnson, W. H.; Nelson, M. J.; Groh, S. E.;Lindahi, P. A.; Kauziarich, S. M.; Averill, B. A. J. Am. Chem. Soc. 1982, 104,4703.(45) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, Fourth ed.; JohnWiley & Sons: New York, USA, 1980, pp 253.Allen, A. D.; Senoff, C. V. J. Chem. Soc., Chem. Commun. 1965, 621.Bottomley, F.; Nyburg, S. C. .1. Chem. Soc., Chem. Commun. 1966, 897.Dilworth, J. R.; Richards, R. L. In Comprehensive Organometallic Chemistiy; G.Wilkinson, F. G. A. Stone and E. W. Abel, Ed.; Pergarnon Press: Oxford,England, 1982; Vol. 8; pp 1073.(49) Vol’pin, M. E.; llatovskaya, M. A.; Kosyakova, L. V.; Shur, V. B. .1. Chem. Soc.,Chem Commun. 1968, 1074(50) (a) Chatt, J. Nature 1975, 253, 39. (b) Chatt, 3. J. Organomet. Chem. 1975,100, 17.(51) Schrock, R. R.; Glassman, T. E.; Vale, M. G. .1. Am. Chem. Soc. 1991, 113,725.(52) Turner, H. W.; Fellmann, 3. D.; Rocklage, S. M.; Schrock, R. R.; Churchill, M.R.; Wasserman, H. 3. J. Am. Chem. Soc. 1980, 102, 7809.Churchill, M. R.; Wasserman, H. J. Inorg. Chem. 1982,21, 218.Schrock, R. R.; Wesolek, M.; Liu, A. H.; Wallace, K. C.; Dewan, J. C. Inorg.Chem. 1988,27, 2050.(46)(47)(48)(53)(54)References p.114Chapter 3 119(55) Rocklage, S. M.; Schrock, R. R. J. Am. Chem. Soc. 1982, 104, 3077.(56) (a) Evans, W. 3.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988, 110, 6877and references therein. (b) Pez, G. P.; Apgar, P.; Crissey, R. K. J. Am. Chem.Soc. 1982, 104, 482. (c) Gynane, M. 3. S.; Jeffery, 3.; Lappert, M. F. J. Chem.Soc., Chem. Commun. 1978, 34.(57) O’Regan, M. B.; Liu, A. H.; Finch, W. C.; Schrock, R. R.; Davis, W. M. J. Am.Chem. Soc. 1990, 112, 4331.(58) Dedieu, A.; Aibright, T. A.; Hoffmann, R. J. Am. Chem. Soc. 1979,101, 3141.(59) Duchateau, R.; Gambarotta, S.; Bensimon, C. 1991, private communication.(60) McConvile, D. H. 1991, Extended Hückel calculations were performed on asuitable model complex using appropriate bond distances and angles.(61) Mylvaganam, M. 1991, unpublished results.(62) Mylvaganam, M.; Fryzuk, M. D.; McConvile, D. H.; Haddad, T. S.; Rettig, S. J.Fourth Chemical Congress of North America New York, USA, 1991.(63) Anderson, W. P.; Cundari, T. R.; Drago, R. S.; Zerner, M. C. Inorg. Chem.1990,29, 1.(64) (a) Hoffman, D. M.; Hoffmann, R.; Fisel, C. R. J. Am. Chem. Soc. 1982, 104,3858 and references therein. (b) Hoffmann, R. J. Chem. Phys. 1963,39, 1397.(65) Messerle, L. W.; Jennische, P.; Schrock, R. R.; Stucky, G. J. Am. Chem. Soc.1980, 102, 6744.References p.114Chapter 4 120CHAPTER 4The Reaction of Binuclear Rhodium Hydrides with Dialkyizincand Dialkylmagnesium Reagents4.1 IntroductionCompounds containing a direct transition metal-to-zinc bond have been knownfor some time;’3 they include zinc-bis(transition metal) compounds (e.g.Zn[Co(CO)4]2),transition metal-zinc halides (e.g. (Co)4Fe(ZnC1 25),organozinctransition metal compounds (e.g. CpZnMn(CO)56)and cluster complexes such asCpNiZn4.7One of the methods8 used to generate transition metal-zinc bonds is thereaction of a transition metal hydride with a dialkylzinc derivative via elimination ofhydrocarbon to give the unsymmetrical product LM-ZnR as shown in scheme 4.1.Scheme 4.1LXMH + ZnR2 -RH LM—ZnRLM—ZnR_____- 1/2 ZnR2 + 1/2 [LM]ZnThe equilibrium between the unsymmetrical complex LM-ZnR and the symmetricproducts of disproportionation,9ZnR2 and [LMj2Zn, usually lies so far to the rightthat LM-ZnR species cannot be isolated. However, the equilibrium can be shiftedto the left by employing polyhaptic6ligands such as cyclopentadienyl, which providecoordinative saturation to the zinc atom. For example the reaction of Cp2NbH3 withZnEt2’° leads to the formation of the symmetrical dimer [Cp2NbH]Zn (equation4.1), whereas the reaction of the same niobium complex with ZnCp21t’2 generatesthe mononuclear, unsymmetrical derivative Cp2NbHZ(ZnCp) (equation 4.2).References p.161Chapter 4 121Cp H____ZnEt2 ,‘ \ 1CpNb H Zn Nb [4.1]/ H -2CH6 \ / CpCp Cc HCp Cpzncp2 \ HNb’ H Nb—ZnCp [4.2]/ H -C5H6 / ‘HCp CpIn some ways Zn2 is very similar to Mg2, both have a closed shellconfiguration (Zn2,1s2p63d0;Mg2,1s2p6)and have only s and porbitals with which to form bonds. In the solid state, MgMe213 and MgEt2’4 arepolymeric with symmetrically bridging alkyl groups. The bonding may be regarded aselectron-deficient three-centre two-electron polar links between the alkyl residue andthe magnesium atom, with the metal adopting a formalsp3-hybridized structure.15The Pauling electronegativity’6of magnesium is 1.2, thus any interactions with carbon(E.N. = 2.5) will tend to be ionic in nature.In contrast, dialkyizinc complexes are monomeric in solution and only weaklyassociated in the solid state.’7 The stereochemistry of zinc is determined by its sizeand electrostatic forces which are a consequence of the filled d shell.18 Therefore, thezinc-carbon bonds in ZnMe2 can be regarded as occupying two sp-hybridizedmolecular orbitals, resulting in a linear geometry. The Pauling electronegativity’6forzinc is 1.6, which suggests that the interaction between zinc and carbon is somewhatmore covalent than between carbon and magnesium.In comparison to zinc, the number of known transition metal-magnesiumbonded species is few.1922 The magnesium atom in the iron complexCpFe(dppe)MgBr(THF)2(I) is tetrahedrally coordinated with an iron-magnesiumbond length of 2.593(7)A.’References p.161Chapter 4 122THF iPh2PPhI is best described as an inorganic Grignard since replacement of the iron moiety withan alkyl group would give the standard organic Grignard reagent.The interest in forming transition metal-zinc or -magnesium bonds stems fromthe observation that certain nickel-magnesium alloys reversibly absorb dihydrogen23as shown in equation 4.3.325CMg2Ni . 2H Mg2NiH4 [4.3]Similar copper alloys, Mg2Cu,24 and zinc alloys, MgZn,25 have also been shown toundergo this reaction. Hydrogen rich phases such as Mg2NiH4can have a density ofhydrogen higher than liquid hydrogen and thus have been explored as potentialhydrogen storage materials. These materials are all solids and their chemicalcomposition is exceedingly difficult to ascertain. Soluble polynuclear organometallicanalogues may shed some light on the fundamental processes involved in thesereactions.This chapter describes the reactivity of the electron rich, coordinativelyunsaturated rhodium hydride dimer, [{ PrP(CH2)3PPriRh]2(I.t-H), towarddialkyizinc and dialkylmagnesium. Unusual polynuclear clusters are obtained in aseries of fragmentation/recombination reactions. The reactivity of the rhodium-zincand -magnesium complexes toward dihydrogen is also discussed.BrReferences p.161Chapter 4 1234.2 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(CH2Ph)with Binuclear Rhodium HydridesIn an effort to build polynuclear clusters containing bare electropositive metalswith only bridging hydrides as ancillary ligands, a study was initiated on the reacthrityof simple organometallic reagents of group 12 with the electron-rich binuclear hydride[(dipppRh]2(p.-H)2 (II) (dippp = Pr’P(CH2)3r12).—(s.)-- —(s..)-\ /( Rh Rh ) 11\_/ NHI/ \J—(‘I--The reaction of [{dippp)Rh]2(p.-H)2 CII) with 1 equivalent of Zn(CH2Fh)26 intoluene did not lead to the expected symmetrical complex [{dippp)Rh]2Zn, byelimination of 2 equivalents of toluene (equation 4.4), but rather gave two newproducts in a 1:1 ratio by 31P(1H} NMR spectroscopy as shown in figure 4.1.-2 CH3Ph[{dippp}Rh]2(i.-H) + Zn(CH2Ph) —.___. [{dippp}Rh]2Zn [44]The two compounds could be separated by fractional crystallization from toluene at-40°C.One of the species observed in the reaction of [{dippp}Rh12(J.i-H)2(II) andZn(CH2Ph)2 by 31P{1H} NMR spectroscopy (figure 4.1) shows an AMX pattern,indicating inequivalent phosphines coupled to 103Rh. Extraction of the solid from thecrude reaction mixture of [{dippp}Rh]2(.L-H)2 and Zn(CH2Ph) with hexanesfollowed by cooling yields complex 2.References p.16 1*55504540353OPPMFigure4.1:121.42MRz31P{1H}NMRspectrumof a1:1mixtureof Zn(CH2Ph)2and[{dippp)Rh]2(Ii-H)2inC6D6.*denotescomplex1Vdenotescomplex2VVII...Chapter 4 125On the basis of spectroscopic and analytical data coupled with the known structure of1 (vide infra), the second species was identified as the mononuclear3-benzylderivative (dippp }Rh(i3-CH2Ph) (2). In fact 2 can be synthesized directly from[(dippp}Rh]2(p.-C1)27and a variety of benzylating reagents (see chapter 5).The 1H NMR spectrum of the less soluble dark-red, crystalline complex 1showed a singlet at 2.33 ppm and a multiplet at -9.38 ppm which are attributable tofour benzylic protons and two hydrides with respect to the ligand, respectively. Themultiplet at -9.38 ppm was found to be a pentet of triplets(1JH,1Th = 14 Hz; 2JH,P = 20Hz) upon simulation, revealing the binuclearky of 1 in solution. Further evidence forthe binuclearity of the complex is observed in the 31P{1H} NMR spectrum whichshows a symmetrical doublet of multiplets resonance normally associated withbinuclear rhodium diphosphine complexes. Phenyl resonances associated with abenzyl moiety were observed in the appropriate region. The ligand region showed oneisopropyl methine and two isopropyl methyl resonances indicating a symmetricenvironment above and below the plane of the coordinated ligand. Microanalytical andspectroscopic data were consistent with the presence of one zinc per rhodium and onlyone benzyl moiety per rhodium, therefore an X-ray crystallographic analysis of 1 wasundertaken in order to determine its structure and the nature of the bonding in thecomplex.4.2.1 Molecular Structure of [{dippp}Rh]2(.t-H).t-ZnCHPh),1The molecular structure of [{dippp}Rh12(i-H)2(.t-ZnCHP )(1) is shownin figure 4.2, selected bond lengths and bond angles appear in Tables 4.1 and 4.2,respectively. The dimeric structure consists of two {dipppRh fragments bridged bytwo ZnCH2Ph units and two hydrides, which were located in the final differenceFourier map.References p.161Chapter 4 126Figure 4.2: Chem 3D Plus® representation of [{dippp}Rh]2(I-H)2(J.L-ZnCH2Ph)2(1). Hydrogen atoms have been omitted for clarity.c19 C20Cl C21C4cliClC2C3C14 C7C15References p.161Chapter 4 127Table 4.1: Selected bond lengths for [{dippp}Rh]2(p-H)J.L ZnCHPh),1.Bond Length (A) Bond Length (A) Bond Length (A)Rhl-Rh2 2.764(1) Rhl-Znl 2.513(1) Rh2-Znl 2.558(1)Rh 1 -P1 2.255(2) Rh 1 -P2 2.261(2) Rh 1-Hi 1.8(1)Rh2-H1 1.4(1) Znl-C16 2.020(8) P1-cl 1.838(8)Pl-C4 1.862(8) P1-C5 1.867(8) P2-C3 1.846(7)P2-C6 1.847(8) P2-c7 1.852(8) cl7-c18 1.34(1)Table 4.2: Selected bond angles for [{dippp)Rhj2(J.t-H)2(.L-ZncH2Ph)2, 1.Bonds Angles (deg) Bonds Angles (deg)P1-Rhl-P2 96.12(7) P1-Rhi-Hi 136(3)P1-Rhl-Znl 113.58(6) P1-Rhl-H2 171(3)Rhi-Znl-Rh2 66.05(4) Rhl-H1-Rh2 116(5)Zn 1-Rh i-Zn2 72.94(4) P2-Rh 1-Zn2 169.86(6)P2-Rh 1 -Znl 111.82(6) Pi-Rhl-Zn2 89.77(6)The bridging hydrides and bridging zinc benzyl moieties are both involved in bondingwith the rhodium centres giving the dimer as a whole a formal electron count of 28.Removal of the ancillary ligands from the binuclear complex (bridging hydrides anddiphosphines) reveals a tetrahedral arrangement of the two rhodium and two zincatoms (figure 4.3 (a)).References p.161Chapter 4 128(a) A(b)Figure 4.3: (a) Chem 3D Plus® view of the rhodium-zinc core of [{dippp}Rh]2( .-H)2(J.L-ZnCHPh)(1). (b) Chem 3D Plus® view of the rhodium coordination sphere.The Zn-Zn separation of 3.015 A is rather long for a Zn-Zn bond and preliminaryINDO/1 semiempirical28molecular orbital calculations on the model, [{H3P)2RhJ(p.-H)2(j.t-ZnH),suggest that the interaction is weak with a bond order of 0.28. Asimilar arrangement of two cobalt and two zinc atoms has been observed in the solidstate structure29 of [(CO)3Co]2(.L- O)(I.I-Zn o(CO)4(III); in this case the zincatoms are separated by 3.568 A which precludes any significant Zn-Zn bonding.H2P2-Rhl-Zn2 = 169.86(6)Pi-Rhi-Hi = 171(3)References p.161Chapter 4 129Zn- Zn(CO)3Co%7o(CO)Zn = Zn[Co(CO)4]The arrangement of the zinc moieties in 1 can be interpreted of as the addition productof PhH2CZn-ZnCHhacross the rhodium hydride dimer [(dippp}Rh]2(.I-H)2 (II).While organodizinc species (RZn-ZnR) do not exist due to the weakness of Zn-Znbonds,30 there are analogues such asR3Sn-SnR and RS-SR which may undergo asimilar addition across the electron-rich rhodium hydride dimer.A second interesting feature of the tetranuclear complex [{dippp}Rh]2( -H)2(I.L-ZflCHPh)2 (1) is the coordination geometry of the ligands around eachrhodium atom as shown in figure 4.3 (b). The donor atoms of the diphosphine, one ofthe bridging hydrides, and one of the bridging zinc-benzyl moieties form a nearlyperfect square plane about the rhodium. Therefore, the dimer can be viewed as twointerlocked square planar rhodium units, [(dippp) RhH(ZnCH2Ph)J, which areseparated by a Rh-Rh distance of 2.764 A. The Rh-Rh separation is well within rangeto invoke a single bond, however, a Rh(I)-Rh(III) structure is also valid. The squareplanar fragments are twisted by about 85.8.4.3 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(C5H)2with Binuclear Rhodium HydridesIn an effort to study the generality of the above reaction other dialkyizincreagents were employed. The reaction of one equivalent of Zn(C5H)23’to thehydride dimer [{dippp}Rh]2(J.L-H)2 (II) in toluene or THF yields the tetranuclearReferences p.161Chapter 4 130complex [{ dippp }Rh]2(ii-H)2 ( p.-Zn(C5H)} 2 (3) and { dippp ) Rh(i5-CH)(4) inquantitative yield by 31P{1H} NMR spectroscopy as shown in equation 4.5.11-IFII + Zn(C5H)2 [4.5]Pi42IPPr’The tetranuclear complex 3 could be obtained as orange crystals in high yield (88%)by cooling (-40°C) a toluene solution containing a mixture of 3 and 4. While complex4 could not be separated from 3 easily, it has been prepared in quantitative yield byreacting Zn(C5HS)2 with [(dippp}Rh]2(p.-C1)2.27The 1H NMR spectrum of 3 shows a singlet for the Cp group at 6.48 ppm whichis close to free cyclopentadienyl anion, suggesting an ionic interaction between theCp- group and zinc.32 A symmetrical 1:6:15:20:15:6:1 septet is seen at -12.12 ppmwhich has been assigned as two bridging hydrides with equal coupling to two 103Rhnuclei and four 31P nuclei(1JH,Rh 2JH,P = 14.7 Hz). Again a single resonance isseen for the isopropyl methines, and two resonances for the isopropyl methyls,indicating a high degree of symmetry in the complex in solution. The temperatureinvariant 31p(1H} NMR spectrum of [{dippp}Rhj2(I.L-H)2{.L-Zn(CsHs)}2(3) shows+References p.161Chapter 4 131a doublet of multiplets centred at 44.7 ppm with coupling to 103Rh of 151 Hz. Thecoupling to rhodium and the location of the doublet pattern is very close to thatobserved for [(dippp}Rh]2(j.t-H).t-ZnCHPh)(1) (figure 4.1).4.3.1 Molecular Structure of [{dippp}Rh]2(j.t-H)p-ZnC5H 5)2, 3The molecular structure of [(dippp)Rh](i-H)p. ZnC5H)(3) is shown infigure 4.4 (a), selected bond lengths and bond angles appear in Tables 4.3 and 4.4,respectively. Complex 3 crystallizes as a 1:1 toluene solvate, however there are noclose contacts between the toluene molecule and 3, therefore the toluene is notshown. The structure of 3 consists of two (dippp}Rh fragments bridgedunsymmetrically by two ZnCp units and one hydride. The two zinc atoms, Znl andZn2, are significantly closer (0.13 A) to Rh2 than to Rhi. Furthermore, the ratherlarge Rh-Rh separation of 2.9507(9) A would seem to suggest that a Rh(I)-Rh(Ill)formalism Ia in order. Unexpectedly, a second hydride was found to occupy a bridgingposition between the Zn2 and Rhi centres. The hydrides were located in thedifference Fourier map but would not remain stationary upon further refinement. Thereare few examples of structurally characterized complexes which bear hydrides bounddirectly to zinc.33The core of the tetranuclear complex is shown in figure 4.4 (b). The degree ofasymmetry in the tetranuclear complex is undoubtedly due to the presence of thehydride bridging the zinc (Zn2) and the rhodium (Rh 1). Inspection of the coordinationsphere of Rh2 reveals a similar nearly square planar arrangement of two phosphines(P3 and P4), a hydride (Hi) and a ZnR group (Zn 1) as seen in the molecular structureof [{dippp}Rh](t-H)p.-ZnCHh 1.References p.16 1Chapter 4 132(a)C26p3(b)Figure 4.4: (a) Chem 3D Plus® representation of [(dippp)Rh]2(L-H)2(.t-ZnC5H)2(3). Hydrogen atoms have been omitted for clarity. (b) Chem 3D Plus®representation of the core of the dimer.doC33cliC24C9C8CiC16C2020C3014 C27C28C15Zn 24—H2cç ZnlRhp4P2References p.161Chapter 4 133Table 4.3: Selected bond lengths for [(dippp}Rh]2(t-H)2(.L-ZnC5H)2,3.The Rhi centre is coordinated differently, with one of the phosphines (P2) nearly trans(171.3) to the hydride which bridges the zinc and rhodium centres. The secondphosphine (P1) is basically trans (157.00) to the hydride which bridges the tworhodium centres.The two cyclopentadienyl groups in [{ dippp }Rhj2(JI-H)(p-ZnC5H)(3) arebound in a pseudo i3 fashion with one short and two long contacts between the zincand the carbon atoms. A space filling model of 3 suggests that there is sufficient roomBond Length (A) Bond Length (A) Bond Length (A)Rhl-Rh2 2.9507(9) Rhl-Znl 2.6115(8) Rhl-Zn2 2.5854(7)Rhl-P1 2.251(2) Rhl-P2 2.288(1) Rh2-Znl 2.4812(9)Rh2-Zn2 2.453(1) Rh2-P3 2.290(1) Rh2-P4 2.313(1)Znl-Zn2 2.8200(8) Znl-C31 2.131(5) Znl-C32 2.656(7)Znl-C35 2.706(6) Zn2-C36 2.127(4) Zn2-C37 2.471(5)Zn2-C40 2.659(5) Rhl-H2 1.57 Zn2-H2 1.66Rhl-H1 1.72 Rh2-H1 1.74Table 4.4: Selected bond angles for [{dippp)Rh]2(.t-H)2(J1-ZnC5H) ,3.Bonds Angles (deg) Bonds Angles (deg)P1 -Rh 1-P2 95.86(5) P3-Rh2-P4 96.55 (5)Rh 1 -Zn 1 -Rh2 71.64(2) Rh 1 -Zn2-Rh2 70.76(3)Zn 1 -Rh 1 -Zn2 65 .72(2) Zn 1 -Rh2-Zn2 69.71(3)Rhl-H1-Rh2 117.2 Rhl-H2-Zn2 106.1References p.161Chapter 4 134for the cyclopentaxlienyl fragment to adopt an r5 coordination. This type of distortionof a cyclopentadienyl fragment bound to a group 12 metal is well documented.31’4-6The hexanuclear complexZn4Ni2(C5HR)6(IV) (R = SiMe3) shown below containscyclopentadienyl groups bound in an ‘qi, ‘q3 and ri5 fashion.IvThe extent of the cyclopentadienyl distortion is measured by the ring slippagewhich is defined as the distance between the ring centroid and the perpendicularprojection of the metal atom on the least-squares ring plane. In complex IV the 111bonded cyclopentadienyl groups show a large ring slippage of 1.88 A, while the 3bonded cyclopentadienyl groups show a smaller slippage of 0.72 A. In[{dippp}Rh]2(I-H)2(I.L-ZnCSH5)2,3, the ring slippage for the cyclopentadienyl groupbound to Znl is 1.56 A while that for Zn2 is only 1.22 A. These values fall roughlymidway between the ‘qi and ‘q3 bonding values.The nature of the bonding between zinc and cyclopentadienyl ion has been thesubject of several studies.3’ The degree of covalency between the cyclopentadienylgroup and zinc is reflected in the angle generated by the centroid of the Cp group, thenearest carbon, and the zinc, as shown in figure 4.5.RR = SIMe3References p.161Chapter 4 135(a) 90 (b)Figure 4.5. (a) Mainly ionic interaction of a cyclopentaclienyl group with zinc. (b)Mainly covalent interaction of a cyclopentadienyl group with zinc.An interaction between zinc and the cyclopentadienyl ligand that ischaracterized as being mainly ionic is manifested by a 90° angle between the least-squares plane of the Cp, and the zinc, and by statistically equal carbon-carbon bondlengths ((a) in figure 4.5).A mainly covalent interaction results in an angle of 54° between the least-squares plane of the Cp group and the zinc with well-defined alternating long-shortcarbon-carbon bond lengths which differ by =0.15 A throughout the Cp unit. Thecyclopentadienyl group bound to Znl in [{dippp}Rh]2Qi-H)2( .-ZnC) ,3, formsan angle of 80.0° while the bond lengths differ by only =0.04 A (i.e. statistically thesame, well within 3a). The cyclopentadienyl group attached to Zn2 displays an angleof 89.4° and again the carbon-carbon bond lengths in the Cp group differ by only =0.04A. Based on the above analysis, the cyclopentadienyl ligands in [(dippp}Rh]2(p.-H)2(j..t-ZnC5)(3) are bound in a mainly ionic fashion. This conclusion issupported by the downfield shift of the Cp group in the 1H NMR spectrum of 3.4.4 Formation of Rhodium-Zinc Bonds: The Reaction of Zn(C3H5)2with Binuclear Rhodium HydridesThe reaction of one equivalent of Zn(C3H5)27 with [{dippp)Rhj2(j.t-H)2 (II)in toluene or THF yields the tetranuclear complex [(dippp}Rh}2(.t-H)( -ZnC54References p.161Chapter 4 136(5) and (dippp}Rh(3-CH)(6) in quantitative yield by 31P(1H} NMR spectroscopy(equation 4.6). The presence of complex 6 was confirmed spectroscopically bycomparison to an authentic sample.38toluene [4.6]II + Zn(C3H5)2Rh1.6r2FØJP 2The 31P{1H} NMR spectrum of 5 shows a complex doublet pattern at 47.4 ppm(1Jppj = 155 Hz) which is quite comparable to the 31P(1H) NMR data of complexes1 and 3. The 1H NMR spectrum of 5 shows the typical thplet of pentets resonance forthe hydrides at -9.34 ppm. The allyl group is undergoing a rapid exchange of syn andanti protons as evidenced by the pentet pattern for the central proton. Complex 5 isassumed to be structurally similar to both 1 and 3.4.5 Fluxional behavior of [{dippp}Rh]2(i-H)p-Zn )The 1H and 31P{1H} NMR spectra of the complexes [{dippp)Rh](p.-H)2(I-ZnCH2Ph) (1), [{ dippp }Rh]2(I.L-H)lI-ZnC5)(3) and [(dippp }RhJ2(p-H).-ZnC3H5)2(5) are temperature invariant down to -90°C. The coordination geometryabout each rhodium in the solid state structure of 1 shows clearly that the phosphorus+References p.161Chapter 4 137donors of each ligand are inequivalent, one being trans to a zinc benzyl moiety and theother trans to the bridging hydride (figure 4.3 (b)). Furthermore, the chemicalenvironment above and below the plane of the chelated diphosphine ligand is differentwith a zinc benzyl moiety above and a bridging hydride below. As for the molecularstructure of the tetranuclear derivative 3, all four phosphine donors are inequivalentowing to the distortion imparted by the hydride which bridges Zn2 and Rhi. Thepattern associated with the bridging hydrides in the 1H NMR spectrum of complexes1, 3 and 5 show equivalent coupling to all four phosphines, indicating a rapid exchangeprocess is operative. Fragmentation yielding mononuclear species can be ruled out asa mechanism for exchanging the hydrides and phosphines based on the binuclearity of1 in solution (vide supra) and the absence of crossover product when solutions of[(dippp }Rhj2(I.t-H)t-ZnCHP )(1) and [(dippp}Rh]2(.i-H)p.-ZnC5H)(3)are mixed together.In the tetrahydride binuclear rhodium complex [{dippp)RhH2]2 (V),38 thehydrides are seen as a single resonance in the 1H NMR spectrum at roomtemperature due to a rapid exchange process; a bridge-terminal exchange has beenproposed to account for the hydride equivalency.39VHowever, the exchange process could be “frozen-out” at -80°C and the variousinequivalent hydrides observed in the 1H NMR spectrum. Furthermore, the 31P{1H}NMR spectrum of V at -80°C revealed inequivalent phosphines and P-Rh couplingPrPr2Pr’2References p.161Chapter 4 138constants (1JRh(I),p = 167.3 Hz and1JRh(III),p = 105.8 Hz) atthbutable40’1to aformally Rh(I)-Rh(ffl) complex.The main difference between the organozinc bridged complexes 1, 3 and 5, andcomplex V is the presence of the two organozinc moieties and two hydrides instead offour hydrides. A direct comparison of solid state structure of [{dippp)Rh)2(L-H)2(I-ZnC5H)2,3, and V above reveals some interest features.cP/\ /p— Rhi Rh2 3I”z7 \3.H2—Zn2The bridging hydride H2, previously the terminal hydride shown in structure V. hasadopted a bridging position between Rhl and Zn2. Interestingly, Znl and Zn2 areboth statistically closer to Rh2 than to Rhi, thus a Rh(I)-Rh(ffl) framework, as in V,is likely present. It is conceivable that the zinc centres aid in the exchange of thehydrides from one rhodium centre to the other in complexes 1, 3 and 5. In order toaccount for the equivalency of the phosphines a butterfly motion of the bridgingorganozinc moieties above and below the rhodium-diphosphine plane concomitantwith hydride exchange is advanced. However, it should be noted that because wewere unable to observe any decoalescence to give some information on the fluxionalprocess, the proposals presented here are purely speculative.4.6 Bonding in Bridging Alkyizinc ComplexesThe bonding of the allcylzinc fragments to the rhodium centres (Rh-Zn-Rh) incomplexes 1, 3 and 5 can be viewed as a three-centre two-electron bond (VI) orReferences p.161Chapter 4 139alternatively as a three-centre four-electron interaction (VII) with a further pair ofelectrons being donated from a filled d-orbital on rhodium.R RI IThis difference in bonding depends on whether all the atomic orbitals on zinc are beingused. As mentioned in the section 4.1 (introduction), the bonding in mononucleardiallcylzinc complexes can be viewed as an appropriate orbital on carbon interactingwith an sp hybrid on zinc giving rise to a linear geometry of the zinc and alkyl groups.In complex 1, which bears a bridging ZnCH2Ph moiety, the bonding is best describedas a three-centre four-electron type between zinc and the two rhodium centres withthe zinc adopting a formal sp2 hybridization. This is supported by the sum of the threeangles about Zn in the structure of [{dippp}Rhj2(.L-H)2(p.-ZnCH2Ph)2, 1, whichequal 355.6°. The remaining p-orbital on zinc may interact with other filled d-orbitalson the rhodium atoms. INDO/1 semiempirical28molecular orbital calculations on themodel, [{H3P}2Rhj2(p,-H)(I.L-Zn predict a bond order of 0.58 for each Rh-Zninteraction.The bonding in the (ri5-CH)Zn fragment involves a weak a-donation andtwo somewhat stronger it-donations of electron density from the C5H HOMO’s to ansp hybridized zinc centre (figure 4.6).VIRh RhVIIRh RhReferences p.161Chapter 4 140Figure 4.6. Bonding molecular orbitals for the fragment (fl5-C5H5)Zn.The interaction between zinc and the rhodium centres in complexes 3 and 5 is againbest described as a three-centre, four-electron bond with the zinc adopting a formalsp2 hybridization. This is supported by the observed coordination of the Cp group inthe solid state structure of [(dippp}Rh]2(t-H)i-ZnC5H)3, which can not beaccounted for on steric considerations, if the Cp group were to adopt an T5 geometryonly a single orbital would remain on the zinc centre (VIII), whereas the icoordination releases one of the zinc based p-orbitals (IX). This is achieved byremoval of one of the it bonding molecular orbitals of the CpZn fragment (figure 4.6).The distortion of the Cp group is likely due to a more favorable overlap between theZn orbital and a filled d-orbital on rhodium as opposed to a filled p-orbital of the Cpgroup.a It ItReferences p.161Chapter 4 1414.7 Mechanism of formation of [{dippp}Rh]2(j.t-H).t-ZnThe reaction between Zn(CH2Ph) and [(thppp}Rh]2(.t-H)2 is complete at-8OC therefore a detailed kinetic analysis was somewhat impractical; howeverproduct analysis was quite useful in formulating a mechanism. The reaction ofZn(CH2Ph) and [{dippp}Rh]2(t-D)238(II-d2) resulted in the formation of[{dippp}Rh]2(L-D)2(I-ZnCH2Ph) (1-d2 and {dippp)Rh(’q3-CH2Ph) only, with nodetectable deuterium incorporation in the ‘q3-benzyl moiety or anywhere else asmeasured by 2H(1H} NMR spectroscopy. A possible mechanism consistent with thedeuterium labelling experiment and product analysis is shown in scheme 4.2.Oxidative addition of the Zn-C bond42 across the rhodium hydride core of[{ dippp } Rh]2(t-H) would generate the trimetallic derivative A; upon asymmetriccleavage of A, the Rh(il1) fragment B and the Rh(I) fragment C would be generated.Dimerization of B followed by (or concomitant with) loss of 112 completes theformation of complex 1. Alternatively, fragment B could lose H2 to give a monomericrhodium-zinc benzyl complex and then recombine with another fragment of B to givethe tetranuclear derivative 1. The Rh(I) fragment C must isomerize to the r3 form,which presumably stabilizes an otherwise reactive Rh(I) 14e complex.In a similar fashion the diallcylzinc reagents Zn(C5H)2and Zn(C3H5)2reactto give the observed products. It is believed that this sequence of reactions is generalfor all dialkylzinc reagents. For example, preliminary studies with ZnEt2,ZnNp andZn(HC=CMe2)appear to give the desired tetranuclear derivatives; however, theaccompanying Rh(I) species P2RhEt, P2RhNp andP2Rh(HC=CMe),respectively,are unstable, and decomposition of these fragments complicates isolation of theproducts.References p.161Chapter 41Scheme 4.2Pr2142-ç+ mcPr’2Pr’2 ZnPigs.,,.C 1,Rh% +Pr’2RI2References p.161Chapter 4 143With this in mind, the reaction of the binuclear hydride dimer [{dippp)RhJ2(t-H),II,with ZnH243 would be most interesting, since the two fragments formed couldrecombine as shown in equation 4.7.[{dippp}Rh]2(t-H) + ZnH2Pr2 [4.7]I,,,jt H i..,HRh___Pr’2A key intermediate in the mechanism outlined in scheme 4.2 is species B,{dippp}RhH2(ZnCPh), which is formed by the fragmentation of A. Given thepresumed reactivity of such an intermediate and our inability to observe such aspecies by low temperature 31P{1H) NMR spectroscopy, a crossover experiment wasdevised in order to demonstrate its existence..10P1’2 ZnI H BRh”The goal was to have fragment B recombine with a similar, but different fragment andobserve the unsymmetrical derivative by 31P(1H} and 1H NMR spectroscopy.Replacing the three carbon backbone diphosphine with the two carbon analogue,Pr4.7.1 Crossover ExperimentReferences p.161Chapter 4 144Pr2CHCPr (dippe),44 results in a subtle chemical change; however, thespectroscopic difference is large since dippp (six-membered chelate) and dippe (fivemembered chelate) phosphorus resonances45 are normally separated by 30-60 ppm inthe 31P(1H) NMR spectrum of analogous species.It was first established that similar products were obtained. Thus, the reactionof one equivalent of Zn(CH2Ph)2 with the corresponding binuclear hydride dimer[{dippe}Rh]2(J.t-H)244having the two carbon backbone diphosphine results in theformation of two complexes by 31P(1H) NMR spectroscopy. One of the complexeswas identified as {dippe}Rh(fl3-CH2P ) (8) by comparison to an authentic sample(see chapter 5). The other complex (7) was identified analytically andspectroscopically as the tetranuclear complex [(dippe }Rh]2(,.t-H)ii-ZnCH2Ph)(equation 4.8), as observed for the dippp analogue.[{dippe}Rh]2(.t-H)toluene [4.81Zn(CH2Ph)p — %q% p1i2The crossover experiment was performed with one equivalent of Zn(CH2Ph)2added to a mixture of 1/2 equivalent of [{dippp}Rh]2(I.t-H)2(II) and 1/2 equivalent of8References p.161Chapter 4 145[{dippe}Rh]2(p.-H)2. Besides the formation of the symmetrical products, a newcompound was present as shown by 31P{1H NMR spectroscopy (figure 4.7). Thenew species showed a doublet in the “dippe region” at 104.4 ppm and a seconddoublet in the “dippp region” at 50.4 ppm. Closer inspection of the two new doubletsrevealed identical secondary couplings of 4.9 Hz which can be attributed to long rangethree bond PdipppPdippe coupling across the newly formed dippp-dippe dimer[{ dippp ) Rh](p.-H)2.t-ZnCHPh)[Rh(dippe)] (9).9Further evidence for this new mixed diphosphine complex comes from the 1H NMR ofthe mixture which shows a new hydride multiplet at -7.81 ppm and a third benzylicproton resonance (ZnCH2Ph) at 2.12 ppm.The above mentioned crossover experiment demonstrates the likely existenceof the mononuclear Rh(llI) fragment {P2}RhH2(ZnR) which is presumed to be theintermediate in the formation of the bridging alkyizinc complexes 1, 3,5, 7 and 9.4.8 Reaction of [{dippp}Rh]2(j -H)p..Zn ) with Dihydrogen.As mentioned above, the formation of the tetranuclear complexes 1, 3, 5, 7 and9 likely proceeds through an intermediate such as {dippp}RhH2(ZnR) (B). The lossof H2 from this fragment occurs either before or concomitant with the dimerizationprocess.Pr2 Pr’2References p.161HILiC)Figure4.7.121.42MHz31P{1H)Zn(CH2Ph)inC6D6.VdenotescrossoverproductVIIIlJTIIIIIITliiiIJTITTFTIIIJITIIIIIlIIIjIIIIIIIIIiIIj1041021009896949290vW 1hhh1hh11(1(11115048IIIIIIIIhf,4644424038NMRspectrumofthecrossoverbetween[(dipppJRh]2(.L-H),[fdippe)Rh]2(i-H)and3634PPM-Chapter 4 147If H is lost from the dimeric intermediate, then addition of dihydrogen to complexessuch as [(dippp}Rh]2(p.-H)L-ZnCHPh)2(1) may yield this intermediate. Theaddition of excess (4 atmospheres) dihydrogen to complexes 1 or 3 in a sealed NMRtube yields new complexes as evidenced by 31P( IH) NMR spectroscopy (equation4.9).4atmH2[{dippp}Rh]2(.t-H)p,-ZnR) w- [{dippp)RhH2(ZnR)]2 [49]10 R = CH2Ph11R=C5HThe temperature invariant 31P{1H) NMR spectrum of complexes 10 and 11displays reduced 1Jp,Rh coupling constants of 103 Hz and 106 Hz, respectively,indicating the presence of a Rh(Ill) species.40’ Complexes 10 and 11 readily loseH2 when exposed to vacuum and revert back to the dehydrogenated tetranuclearprecursors 1 and- 3, thus the nuclearity- of the complexes could not be unambiguouslydetermined. However, they are most likely tetranuclear species and not simply thedinuclear species {dippp)RhH(ZnR).Interestingly, a solution of [1 dippp)Rh]2(p.-H)2(p.-ZnCH2Ph)2 (1) and[{dippe}Rh]2(L-H)2(l.L-ZnCPh)2(7) when exposed to dihydrogen (4atmospheres) for 5 minutes followed by dehydrogenation under vacuum yields about10% of the crossover product [{dippp}Rh](,.t-H)(l.L-ZnCH2Ph)2[Rh{dippe)} (9)(scheme 4.3). In the absence of dihydrogen this same solution monitored 24 hourslater showed no further crossover. Exposure of the same solution again to 4atmospheres of dihydrogen followed by heating to 50°C for 10 minutes showed, afterremoving the dihydrogen under vacuum, approximately 25% crossover. Based on thisresult it is proposed that the hydrogenated intermediate is a dirhodium species but inequilibrium with some monomeric Rh(ffl) complex as shown in scheme 4.3.References p.161Chapter 4 148Pr2 ZnP1111, I H2Pr2Scheme 4.3+2 [{dippp}RhH2(ZnCHPh){dippe}RhH2(ZnCHPh)]Pr2[{dippp}RhH2(ZnCHP )] [{dippe}RhH2(ZnCHP )]22 9References p.161Chapter 4 1494.9 Formation of Rhodium-Magnesium Bonds: The Reaction of MgR2with Binuclear Rhodium HydridesAs mentioned in the introduction, Zn2+ and Mg2+ are similar in many regards.In the context of the reaction with rhodium hydride dimers, a direct comparison ofZnR2 versus MgR2 would be of interest since reactivity studies on {ri3-HB(3-Butpz)3}ZnR46and(q3HB(3.Butpz)}MgR47(pz = (pyrazolyl)hydroborate) haveshown that Mg-R bonds are much more reactive than Zn-R bonds. Although manymonomeric dialkylzinc reagents are known few dialkylmagnesium species aremonomeric. Furthermore, the purity of dialkylmagnesium reagents is normallysomewhat suspect due to the method of preparation,48 which usually involvesdisproportionation of the parent Grignard reagent with 1,4-dioxane via the Schlenkequilibrium (equation 4.10).(xs) 1 ,4-dioxane2 RMgX — RMg + MgCI2(1,4-dioxane)2.1. [4.10]Mg(CH2Ph)2(THF)26and Mg(C5H5)249 are among the few well-defined monomericdialkylmagnesiun reagents known which are soluble in non-coordinating solvents.Dialkylmagnesium reagents can also be prepared from HgR2 and Mg0, however, thisis normally avoided due to the toxicity of mercury.5°As described above for the zinc reagents, the reaction of one equivalent ofMg(CH2Ph)2(THF)2with [{dippp)Rh]2(L-H)2 (II) was found to generate twocompounds by 31P{1H} NMR spectroscopy (equation 4.11).References p.161Chapter 4 150[{dippp}Rh]2(t-H)+Mg(CH2Ph)(THF)tolueneRTPh2p1J2\/22[4.11]One of the compounds was identified as the3-benzyl derivative {dippp}Rh(3-CH2Ph) (2) by 1H and 31P{ 1H} NMR spectroscopy. The other complex{dippp}Rh([.t-H)MgCHPh (12), which was isolated as a yellow powder, did notresemble the Rh2-Zn tetranuclear complexes described above as evidenced bysolution spectral measurements; in particular, the 1H NMR spectrum showed asecond-order hydride pattern at -6.64 ppm and a simple symmetrical doublet in the3lp { 1H} NMR spectrum. The complex is thermally sensitive which thwarted allattempts to obtain accurate microanalytical data. The compound is stable at -40°C formonths.A square-planar arrangement of ligands about the rhodium centre in 12 wouldgenerate a second order pattern for the hydrides in the 1H NMR spectrum.Furthermore, this geometry would maintain a symmethcal environment above andbelow the plane of the coordinated diphosphine ligand which is in agreement with theobserved spectroscopic data.+p,,212References p.161Chapter 4 151Precedent for the proposed structure of {dippp)Rh(-H)2MgCPh,12, is thecation-anion interaction suggested5’for Cp2NbH2(Li) (XI).XIThus, complex 12 could be viewed as the cation, (MgCH2Ph), stabilizing the anion,-(dipppRhH2),via the hydride bridges. Further evidence for the structure of 12 is thecomplex (dippp } RhHPhLi (XII) which was synthesized in our laboratory52 by thereaction of two equivalents of PhLi with [(dippp}Rh12(Ji-H)2(II).Pr2XIIIsolated {dippplRh(p.-H)2MgCH2Ph (12) reacts with 1 atmosphere ofdihydrogen to give a single product as evidenced by 31 { 1) NMR spectroscopy(equation 4.12); specifically, a new resonance is observed at 55.1 ppm which shows areduced 1JP,Rh coupling of 94 Hz indicative of a Rh(Ill) species.40’PReferences p.161Chapter 4 152{dippp)RhQ.t-H)2MgCHP 12H2 (1 atm)C’R:H:IM[4.12]p \‘H”2gPh2 \ .- 1 3HThe 1H NMR spectrum of 13 shows a ten-line pattern at -9.18 which is attributableto two terminally bound hydrides on rhodium. A second hydride resonance at -10.28which also integrated to two protons appears as a second-order multiplet. Withrespect to integration of the diphosphine ligand, only one benzyl ligand was present.The1H{31P} NMR spectrum of 13 revealed the multiplicity of the two hydridepatterns the results of which are shown in figure 4.8. Decoupling of the 31P nuclei in13 reduces the terminal hydride pattern to a simple doublet of triplets due to couplingto 103Rh and coupling to two equivalent bridging hydrides. The pattern for the bridginghydrides is reduced from a second-order pattern to a simple doublet of tripletsbecause of coupling to 103Rh and coupling to two equivalent terminal hydrides. Thestructure of 13 shown in equation 4.12 is consistent with the spectral data presented.As with the zinc system discussed above, the reaction of MgH2 with thebinuclear rhodium hydride dimer, [{dipppRhj2(p-H) would be of interest; the Rh(I)species formed, { dippp } RhH, could recombine with (dippp ) Rh(.t-H)2Mg to givecomplex { dippp )Rh(p.-H)2Mg(ph(dippp } (XIII).Pr’2•H ,,. ....“MgHRh___XfflPr’2Pr’2References p.161Chapter 4Figure 4.8. (top) 3P decoupled 1H NMR spectrum of the hydride region of(dippp}RhH2(.L-H)2MgCHP (13). (bottom) 1H NMR spectrum of the hydrideregion.153—iO.5pp.References p.161Chapter 4 1544.10 Summary and Future ConsiderationsThe reaction of dialkylzinc (ZnR2; R = CH2Ph, C5H,C3H5)complexes withthe binuclear hydride dimers [(P2}Rh](t-H) (P2 = dippp, dippe) yields twoproducts. The first is a mononuclear Rh(1) derivative P2RhR and the second is atetranuclear complex of the general formula[{P2}Rh](p.-H)ji-ZnR)2. Two of thetetranuclear species have been studied crystallographically and the data revealunusual structural features including a hydride found to bridge a rhodium and a zincatom. This reaction appears to be completely general, although the isolation of theproducts is facilitated when the Rh(I) derivative is stable. The complexes reactreversibly with dihydrogen to give binuclear polyhydrides which are in equilibrium withmonomeric Rh(llI) complexes of the formP2RhHZnR. A mechanism based onproduct analysis and two separate crossover experiments has been proposed whichinvolves fragmentation and recombination of rhodium-zinc fragments.The reaction of dibenzylmagnesium with [(dippp}Rh]2(.t-H)2 is similar in thatthe same Rh(I) species is formed; however, the second product is believed to be theheterobimetallic complex,P2RhHMgCH,which does not dimerize. Similarly, thiscomplex reacts readily with dihydrogen to yield a rhodium-magnesium tetrahydridederivative.The reactions of ZnH2 and MgH2 with [(dippp}Rh]2(J.L-H)2 should beattempted since these reactions appear to be promising in terms of preparingcomplexes which contain electropositive metals stabilized by the anionP2RhH. Thereversible addition of dihydrogen to the tetranuclear complex [{P}Rh](p-H)ii-ZnR)2 is promising since a similar behaviour is observed for materials such asMgNi.23 The observation that hydrides can indeed interact in a bridging fashion withReferences p.161Chapter 4 155electropositive metals such as zinc and magnesium suggests that higher nuclearityspecies may be useful models for hydrogen storage materials.4.11 Experimental Procedures4.11.1 General Information. See section 2.7.1 (chapter 2) for further details.4.11.2 Syntheses. Hydrated rhodium trichioride, RhCl3(H2O), was obtained fromJohnson-Matthey and used to prepare[(fl4-C8H12)Rh]2($.t-C )2.53 The ligands 1,3-bis(diisopropylphosphino)propane (dippp)54 and 1 ,2-bis(dilsopropylphosphino)ethane(dippe)44 were synthesized by literature methods. [{dippp}Rh]2(I-H)38wasprepared by hydrogenating (dippp)Rh(3-CH2Ph)as outlined in chapter 5 of thisthesis. [{dippe}Rh]2(p.H) was prepared by literature methods.4[{dippp}Rh]2(p.-Cl) was prepared27 by adding 2 equivalents of dippp to [(fl4-C8H12)Rhj(p-Cl).Zn(CH2Ph) and Mg(CH2Ph)(THF) were prepared by literature methods.26Zn(C5H)2was prepared31 using a modification of the procedure outlined in theliterature.55 Zn(C3H5)2 was prepared56 by adding ZnMe2 to B(C3H5).7 Amodification of the preparation57 of ZnMe2 is given below. Full analytical data for{dippp}Rh(fl3-CHP ) and {dippe}Rh(fl3-CHP ) are given in chapter 5 of thisthesis. The spectral data for (dippp}Rh(i-C5)compared well with publishedresults.394.11.3 [{dippp}RhJ2(t-H)-ZnCHPh,1. To a stirred green toluenesolution (25 mL) of [(dippp}Rh]2(1-H)2(203 mg, 0.266 nimol) was added dropwise atoluene solution (5 niL) of Zn(CH2Ph) (66 mg, 0.27 mmol). The colour of the solutionturned orange-red instantly. The solution was filtered through Celite® andconcentrated to 15 niL. Cooling the solution to -40°C for 24 hours yielded 118 mg ofReferences p.161Chapter 4 156red crystalline 1 (83% based on rhodium). Anal. Calcd forC44H8PRh2Zn:C,49.22; H, 7.88. Found: C, 49.07; H, 7.73%. 1H NMR (C6D,6, ppm): 7.25-6.92 (m,phenyl protons, 1OH); 2.34 (s, CH2Ph, 4H); 1.69 (d of sept, PCH(CH3)28H, 2JH,P =7.0 Hz, 3JHH = 7.0 Hz); 1.17 (m, PCFI2 and PCH2C,12H); 1.12 (dd, PCH(CH3)224H, 3JH,P = 13.1 Hz, 3JH,H = 7.0 Hz); 0.95 (dd, PCH(CH3)224H, 3H,P = 13.3 Hz,3JH,H = 7.0 Hz); -9.37 (t of pentet, Rh-H, 2H, 2JHP = 20 Hz, 1JH,P = 14 Hz).31P{1H} NMR (C6D,8, ppm): 46.7 (d of m, 1JP,1h = 154 Hz).4.11.4 Spectral data for {dippp}Rh(3-CH2Ph), 2. The preparation of pure 2can be found in chapter 5 of this thesis. 1H NMR (C6!),6, ppm): 7.24 (t, Hme, 2H,3JH,H = 6.9 Hz); 6.63 (t, Hpara, 1H, 3JH,H = 6.9 Hz); 5.87 (d, Hoho, 2H, 3JH,H = 6.9Hz); 2.25 (d, CH2Ph, 2H, 3JH,P = 7.1 Hz); 1.92 (d of sept, PCH(CH3)22H, 2H,P =7.1 Hz, 3H,H = 7.1 Hz); 1.68 (m, PCH2 2H); 1.64 (d of sept, PCH(CH3)22H, 2H,p= 7.1 Hz, 3JH,H = 7.1 Hz); 1.26 (m, PCH2 2H); 1.23 (m, PCH2CH2, 2H); 1.12 (dd,PCH(CH3)2,6H, 3JH,P = 12.8 Hz, 3JH,H = 7.1 Hz); 1.04 (dd, PCH(CH3)26H, 3JH,P =13.6 Hz, 3JH,H = 7.1 Hz); 0.96 (dd, PCH(CH3)26H, 3H,P = 13.2 Hz, 3JH,H 7.1Hz); 0.85 (dd, PCH(CH3)26H, 3JHP = 13.0 Hz, 3JH,H = 7.1 Hz). 31P{1H} NMR(C6D,6, ppm): 48.3 (dd, A,1Jp,RJ = 242 Hz; 2Jp,p’ = 40.8 Hz); 33.9 (dd, B,1JP,ih= 172 Hz; 2Jp’,p = 40.8 Hz).4.11.5 [{dippp}Rh](.t-H)p-ZnC3. To a stirred green THF solution(25 mL) of [{dippp)Rh]2(p.-H)2 (623 mg, 0.819 mmol) was added dropwise a THFsolution (5 mL) of Zn(C5H)2(178 mg, 0.910 mmol) (10% excess). The colour of thesolution turned orange-red instantly. The THF was removed under vacuum and theproduct extracted with toluene (25 mL). The solution was filtered through Celite®and concentrated to 15 mL. Cooling the solution to -40°C for 24 hours yielded 330 mgof orange crystalline 3 (79% based on rhodium). Anal. Calcd forC40H8PRhZn:C, 47.03; H, 7.89. Found: C, 46.84; H, 8.02%. H NMR (C7D8,6, ppm): 6.48 (s,References p.161Chapter 4 157C5H, 1OH); 1.90 (d of sept, PCH(CH3)28H, 2JH,P = 7.1 Hz, 3JH,H = 7.1 Hz); 1.69(m, PCH2 and PCH2C,12H); 1.19 (dd, PCH(CH3)224H, 3JH,P = 12.9 Hz,3JH,H =7.1 Hz); 1.12 (dd, PCH(CH3)224H, 3JH,P = 13.1 Hz, 3H,H = 7.1 Hz); -12.12 (t ofpentet, Rh-H, 2H, 2H,P = 14.7 Hz, 1JH,Rh = 14.7 Hz). 31P{1H} NMR (C7D8,6,ppm): 44.7 (d of m, 1Jp,p1 = 151 Hz).4.11.6 {dippp}Rh(5..C5H ), 4. Compound 4 was observed in the crudereaction mixture of [(dippp)Rh12(p.-H)2and Zn(C5H)2and was synthesized directlyfrom [{dippp)RhJ2(.t-Cl)2 and Zn(C5H)2.To stirred toluene suspension (25 mL) of[{dippp)Rhj2(I-C1)2 (201 mg, 0.242 mmol) was added Zn(C5H)2(49 mg, 0.25mmol) as a solid. The mixture was stirred for 24 hours as the solution turned darkorange. The toluene was removed under vacuum and the product extracted withhexanes (25 mL). Concentration of the solution to 10 mL followed by cooling for 24hours provided 132 mg of orange crystalline 4 (71%). 1H NMR (C6D,8, ppm): 5.32(s, C5H 5H); 1.49 (d of sept, PCH(CH3)24H, 2H,p = 7.0 Hz, 3JH,H = 7.0 Hz); 1.05(dd, PCH(CH3)212H, 3JH,P = 13.4 Hz, 3JH,H = 7.0 Hz); 0.95 (dd, PCH(CH3)212H,= 12.9 Hz, 3JHH = 7.0 Hz); 0.84 (m, PCH2 and PCH2C,6H). 31P{1H}NMR (C6D,8, ppm): 59.7 (d, 1JP,Rh = 210 Hz).4.11.7 [{dippp}Rh](p-H).t-ZnC55. To a stirred green THF solution(25 mL) of [{dippp)Rh]2(p-H)2 (224 mg, 0.294 mmol) was added dropwise a THFsolution (5 mL) of Zn(C3H5)2(46 mg, 0.31 mmol) (10% excess). The colour of thesolution turned orange-red instantly. The THF was removed under vacuum and themixture dissolved in hexanes (20 mL). Concentration of the sample to 10 mL followedby cooling yielded 81 mg of red crystalline 5 (57%). The reaction is quantitative by31P{ 1H} NMR spectroscopy. The product 5 was slightly contaminated with{dippp)Rh(r-CH)(6) thus accurate microanalysis was not obtained. 1H NMR(C6D,6, ppm): 6.54 (pentet, H of allyl, 2H, 3JH,H = 11 Hz); 3.58 (d, Hsyn,anti ofReferences p.161Chapter 4 158aflyl, 8H, 3JH,H = 11 Hz); 1.88 (d of sept, PCH(CH3)28H); 1.73 (m, PCH2 andPCH2C,12H); 1.09 (d of d, PCH(CH3)224H); 1.01 (d of d, PCH(CH3)224H);-9.34 (t of pentets, Rh-H, 2H, 2JHP = 21 Hz, 1JH,Rh = 18 Hz). 31P{1H) NMR(C6D,6, ppm): 47.4 (d of m, 1Jp,pj = 155 Hz).4.11.8 Spectral data for {dippp)Rh(3-CH),96. 1H NMR (C6D,8,ppm): 4.80 Cd of t of t, Hm, 1H, 3JH,H = 12 Hz, 3JH,H =7 Hz,3JH,Rh = 2 Hz); 3.61 (d,2H, 3JH,H = 7 Hz); 2.19 (dd, 2H, 3H,H = 12 Hz,2JH,P = 5 Hz); 1.92 (d ofsept, PCH(CH3)22H, 2JH,P = 7 Hz,3JH,FI = 7 Hz); 1.80 (d of sept, PCH(CH3)22H,=7 Hz, 3JH,H =7 Hz); 1.20 (dd, PCH(CH3)26H, 3JH,P = 14 Hz, 3JH,H =7 Hz);1.10 (dd, PCH(CH3)26H, 3JH,P = 13. Hz,3JH,H = 7 Hz); 1.08 (dd, PCH(CH3)26H,3JH,P = 12 Hz, 3JHH = 7 Hz); 1.01 (dd, PCH(CH3)26H, 3JHP = 13 Hz, 3JH,H = 7Hz); backbone resonances were obscured. 31P{hH} NMR (C6D,6, ppm): 43.3 Cd,1Jp,Rh = 188 Hz).4.11.9 [{dippe}Rh]2(j.t-H).t-ZnCHPh)7. The synthesis of 7 is identicalto the procedure outlined for 1. [{dippe)Rh]2(.L-H)2 (86 mg, 0.12 mmol) andZn(CH2Ph) (30 mg, 0.12 mmol) gave 43 mg of red crystalline 7 (71% based onrhodium). Anal. Calcd forC42H80PRhZn:C, 48.25; H, 7.71. Found: C, 48.24; H,7.80%. 1H NMR (C6D,6, ppm): 7.28-6.92 (m, phenyl protons, 1OH); 2.22 (s,CH2Ph, 4H); 1.78 (d of sept, PCH(CH3)28H, 2JHP = 7.2 Hz, 3JH,H = 7.2 Hz); 1.16(d of m, PCH2 8H, 3JH,P = 13.2 Hz); 1.15 (dd, PCH(CH3)224H, 3JH,P = 15.6 Hz,3JH,H = 7.2 Hz); 0.88 (dd, PCH(CH3)224H, 3JH,P = 12.6 Hz, 3JH,H = 7.2 Hz); -7.84(t of pentet, Rh-H, 2H, 2JHP = 21.4 Hz, 1HRh = 19.2 Hz). 31P{1H} NMR (C6D,6, ppm): 107.7 (d of m, 1JP,Rh = 165 Hz).4.11.10 {dippe}Rh(3-CH2Ph), 8. The preparation of pure 8 can be found inchapter 5 of this thesis. 1H NMR (C6D,6, ppm): 7.29 (t, Hmeta, 2H, 3JH,H = 7.0References p.161Chapter 4 159Hz); 6.57 (t, Hpara, 1H, 3JH,H = 7.0 Hz); 5.91 (d, Hortjio, 2H, 3JH,H = 7.0 Hz); 2.47 (d,CH2Ph, 2H, 3JH,P = 7.5 Hz); 1.88 (d of sept, PCH(CH3)22H, 3JHH = 7.0 Hz,2JH,P =7.0 Hz); 1.69 (d of sept, PCH(CH3)22H, 3JH,H = 7.0 Hz, 2JH,P = 7.0 Hz); 1.19 (m,PCH2, 4H); 1.07 (dd, PCH(CH3)26H, 3JHP = 13.2 Hz, 3JH,H = 7.0 Hz); 0.92 (dd,PCH(CH3)2,6H,3JH,p = 13.0 Hz,3JH,H = 7.0 Hz); 0.87 (dd, PCH(CH3)26H, 3JH,P =13.6 Hz, 3JH,H = 7.0 Hz); 0.82 (dd, PCH(CH3)26H, 3JH,P = 13.4 Hz, 3JH,H = 7.0Hz). 31P{H} NMR (C6D,8, ppm): 97.9 (dd, A, Vp,Rh = 245 Hz; 2Jp,p’ = 20.5Hz); 91.0 (dd, B, 1Jp,pj = 177 Hz; 2Jp,p = 20.5 Hz).4.11.11 Spectral Data for [{dippp}Rh](p.-H)(.t-Zn C H2Ph)-[Rh{dippe}], 9. H NMR (C6D,6, ppm): 2.12 (s, CH2Ph, 4H); -7.81 (t ofpentets, Rh-H, 2H, 2Hp = 20 Hz, 1JH,Rh = 15 Hz); phenyl and ligand resonanceswere obscured. 31P{1H} NMR (C6D,6, ppm): 104.4 (d of d of m, Pdippe 1JP,Rh =155 Hz, 3Jp,p 4.9 Hz); 50.4 (d of d of m, Pdippp, 1JP,Rh = 155 Hz, 3Jp’,p = 4.9 Hz).4.11.12 {dippp}Rh(.t-H)MgCHPh, 10. To a stirred green toluene solution(25 mL) of [(dippp}RhJ(.t-H) (478 mg, 0.630 mmol) was added dropwise a toluenesolution (5 mL) of Mg(CH2Ph)(THF) (221 mg, 0.63 1 mmol). The colour of thesolution turned yellow-orange instantly. The solution was filtered through Celite®and the toluene removed under vacuum. The mixture was suspended in hexanes (10mL) and the product collected on a fine fit to give 141 mg of crude 12 (90%). Theproduct can be recrystallized from toluene/hexanes. 1H NMR (C7D8,8, ppm): 7.25-6.75 (m, phenyl protons, 5H); 2.07 (s, MgCH2Ph, 2H); 1.63 (d of sept, PCH(CH3)24H, 2JH,P = 14.2 Hz, 3JH,H = 7.1 Hz); 1.21 (m, PCH2 and PCH2C,6H); 1.10 (dd,PCH(CH3)2,24H, 3JH,P = 13.8 Hz, 3JH,H = 7.1 Hz); -6.64 (d of d of m, Rh-H, 2H,= 63.9 Hz, 1H,Rh = 29.2 Hz). 31P{1H} NMR (C6D,6, ppm): 44.0 (d, 1PRh= 124 Hz).References p.16 1Chapter 4 1604.11.13 {dippp}RhH2(p-H)MgCHPh, 11. In a sealable NMR tube wasweighed 25 mg of compound 12 and 0.25 mL C7D8 added. The sample was degassedthree times, cooled to -196CC and purified dihydrogen introduced. The sample wassealed under H2 and warmed to room temperature. The initially yellow solutiondecolourized on warming. The reaction is quantitative by 31p { 114) NMRspectroscopy. 1H NMR (C7D8,8, ppm): 7.29 (d, Horijo, 2H, 3JH,H = 7.2 Hz); 7.17(t, Hme, 2H, 3JH,H = 7.2 Hz); 6.75 (t, Hpara, 1H, 3JH,H = 7.2 Hz); 2.18 (s, MgCH2Ph,2H); 1.42 (d of sept, PCH(CH3)24H, 2JH,P = 14.2 Hz, 3JH,H = 7.1 Hz); 1.21 (m,PCH2 and PCH2C,6H); 1.02 (dd, PCH(CH3)212H, 3JHP = 13.9 Hz, 3JH,H = 7.1Hz); 0.94 (dd, PCH(CH3)212H, 3H,p = 13.2 Hz, 3JH,H = 7.1 Hz)-9.18 (m, Rh-H,2H); -10.28 (m, Rh-H, 2H). 1H{31P} NMR (C7D8,8, ppm): -9.18 Cd of d of t,Rh-H, 2H, 2JHH = 7 Hz, 1fH,Rh = 21 Hz, 2JH,P = 14 Hz); -10.28 (d of t, Rh-H, 2H,= 7 Hz, 1JH,Rh = 25 Hz). 31P{1H} NMR (C6D,8, ppm): 55.1 (d, 1p,Rh = 94Hz).4.11.14 Synthesis of ZnMe2. To a suspension of ZnC12 (12.8 g, 100 mmol) intoluene (25 mL) was added A1Me3 (100 mL, 2M, 200 mmol) in toluene. The ZnC12was consumed slowly over 6 hours. To this solution was added Et20 (31 mL, 200mmol) in order to complex the A1MeC12 formed in the reaction. The resulting ZnMe2was distilled (b.p. 60CC @ 1 atm) directly from the reaction flask yielding 8.72 g ofZnMe2 (91%). The product contained less the 1% Et20 by 1H NMR spectroscopy.References p.16 1Chapter 4 1614.12 References(1) Burlitch, 3. M. J. Chem. Soc., Chem. Cominun. 1968, 887.(2) Carey, N. A. D.; Noltes, J. G. I. Chem. Soc., Chem. Commun. 1968, 7471.(3) Francis, B. R.; Green, M. L. H.; Luong-thi, T.; Moser, G. A. J. Chem. Soc.,Dalton Trans. 1977, 1339.(4) Heiber, W.; Teller, U. Anorg. Aug. Chem. 1942,249, 43.(5) Burlitch, J. M.; Winterton, R. C. Inorg. Chem. 1979, 18, 2309.(6) Budzelaar, P. H. M.; Boersma, J.; van der Kerk, G. J. M. J. Organomet. Chem.1980, 202, C71.(7) Budzelaar, P. H. M.; Boersma, 3.; van der Kérk, G.J. M. Angew. Chem. 1983,95, 335.(8) St. Denis, 3. N.; Butler, W.; Glick, M. D.; Oliver, 3. P. J. Organomet. Chem.1977, 129, 1.(9) Budzelaar, P. H. M.; Alberts-Jansen, H. J.; Mollema, K.; Boersma, 3.; van derKerk, G. 3. M.; Spek, A. L.; Duisenberg, A. 3. M. J. Organomet. Chem. 1983,243, 137.(10) Tebbe, F. N. J. Am. Chem. Soc. 1973,95, 5412.(11) Budzelaar, P. H. M.; den Haan, K. H.; Boersma, J.; van der Kerk, G. 3. M.;Spek, A. L. Organometallics 1984,3, 156.References p.161Chapter 4 162(12) Budzelaar, P. H. M.; van der Zeijden, A. A. H.; Boersma, 3.; van der Kerk, 0. 3.M.; Spek, A. L.; Duisenberg, A. 3. M. Organometallics 1984,3, 159.(13) Weiss, E. J. Organomet. Chem. 1964,2, 314.(14) Weiss, E. J. Organomet. Chem. 1965,4, 101.(15) Lindsell, W. E. In Comprehensive Organometallic Chemistry; G. Wilkinson, F.G. A. Stone and E. W. Abel, Ed.; Pergamon Press: Oxford, England, 1982; Vol.l;pp2Ol.(16) Kotz, 3. C.; Purcell, K. F. Chemistry & Chemical Reactivity; Second ed.;Saunders College Publishing: Philadelphia, USA, 1991, pp 383.(17) Boersma, J. In Comprehensive Organometallic Chemistry; G. Wilkinson, Ed.;Pergamon Press Oxford, England, 1982; Vol. 2; pp 825.(18) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, Fifth ed.; JohnWiley & Sons: Toronto, Canada, 1988, pp 598.(19) Felkin, H.; Knowles, P. 3.; Meunier, B.; Mitschler, A.; Picard, L.; Weiss, R. J.Chem. Soc., Chem. Commun. 1974, 44.(20) Prout, K.; Forder, R. A. Acta Crystallogr. 1975, B31, 852.(21) Davies, S. G.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1978, 1510.(22) Jonas, K.; Koepe, G.; Krueger, C. Angew. Chem. 1986,98, 901.(23) Reilly, 3. J.; Wiswall Jr., R. H. Inorg. Chem. 1968, 7, 2254.(24) Reilly, 3. J.; Wiswall Jr., R. H. Inorg. Chem. 1967, 6, 2220.References p.161Chapter 4 163(25) Anderson, A. F.; Maeland, A. 3. In Hydrides for Energy Storage. Proceedingsof an International Symposium held in Geilo, Norway, 14-19 August 1977.; D.L. Douglass, Ed.; Pergamon Press: Oxford, England, 1978; pp 151.(26) Schrock, R. R. J. Organomet. Chem. 1976, 122, 209.(27) Fryzuk, M. D.; Piers, W. E.; Rettig, S. 3.; Einstein, F. W. B.; Jones, T.;Aibright, T. A. J. Am. Chem. Soc. 1989,111, 5709.(28) Zerner, M. C. 1991, INDO/1 calculations were perfomed using ZINDO, aprogram developed by Professor M. C. Zerner for the CAChe systemmanufactured by Tektronix, Inc.(29) Burlitch, 3. M. In Comprehensive Organometallic Chemistry; G. Wilkinson, F.G. A. Stone and E. W. Abel, Ed.; Pergamon Press: Oxford, U. K., 1982; Vol. 6;pp 983.(30) CRC Handbook of Chemistry and Physics; Weast, R. C., Ed.; CRC Press, Inc.:Boca Raton, USA, 1984, pp F-181.(31) Fischer, B. Ph. D. Thesis, Rijksuniversiteit van Utrecht, 1989.(32) Budzelaar, P. H. M.; Boersma, 3.; van der Kerk, G. 3. M.; Spek, A. L.;Duisenberg, A. 3. M. Inorg. Chem. 1982,21, 3777.(33) Han, R.; Gorrell, I. B.; Looney, A.; Parkin, G. J. Chem. Soc., Chem. Commun.1991, 717.(34) Fischer, B.; Boersma, 3.; van Koten, G.; Spek, A. L. New J. Chem 1988, 12,613.References p.16 1Chapter 4 164(35) Fischer, B.; Budzelaar, P. H. M.; Boersma, J. Cyclopentadienylzinc-transirionmetal compounds; Elsevier, Amsterdam, 1988; Vol. 4, pp 421.(36) Schrock, R. R.; Cummings, C. C. 1991, personal communication.(37) Brown, H. C.; Racherla, U. S. J. Org. Chem. 1986,51,427.(38) Fryzuk, M. D.; Piers, W. E.; Einstein, F. W. B.; Jones, T. Can. J. Chem. 1989,67,883.(39) Piers, W. E. Ph. D. Thesis, University of British Columbia, 1988.(40) Nixon, J. F.; Pidcock, A. Ann. Rev. NMR Spectrosc. 1969,2, 345.(41) Meek, D. W.; Mazanec, T. J. Acc. Chem. Res. 1981, 14, 266.-(42) Budzelaar, P. H. M.; Boersma, 3.; van der Kerk, G. J. M.; Spek, A. L.;Duisenberg, A. 3. M. Organometallics 1985,4, 680.(43) De Koning, A. 3.; Boersma, J.; van der Kerk, G. 3. M. J. Organomet. Chem.1980, 186, 159.(44) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984, 3, 185.(45) Garrou, P. E. Chem. Rev. 1981, 81, 229.(46) Gorrell, I. B.; Looney, A.; Parkin, G. J. Chem. Soc., Chem. Commun. 1990, 220.(47) Han, R.; Looney, A.; Parkin, G. .1. Am. Chem. Soc. 1989, 111, 7276.(48) Anderson, R. A.; Wilkinson, G. In Inorganic Synthesis; D. F. Shriver, Ed.; JohnWiley & Sons: Toronto, Canada, 1979; Vol. XIX; pp 262.References p.161Chapter 4 165(49) Duff, A. A.; Hitchcock, P. B.; Lappert, M. F.; Taylor, R. G.; Segal, 3. A. J.Organomet. Chem. 1985,293, 271.(50) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; Fifth ed.; JohnWiley & Sons: Toronto, Canada, 1988, pp 159.(51) Green, M. L. H.; Hughes, A. K.; Mountford, P. J. Chem. Soc., Dalton Trans.1991, pp. 1699 and references therein.(52) Doffing, C. 1985, unpublished results.(53) Chatt, J.; Venanzi, L. M. J. Chem. Soc. 1957, 4753.(54) Tani, K.; Tanigawa, E.; Tatsubo, Y.; Otsuka, S. J. Organomet. Chem. 1985,279, 87.(55) Lorberth, 3. J. Organomet. Chem. 1969, 19, 189.(56) Thiele, K. H.; Zdunneck, P. J. Organomer. Chem. 1965,4, 10.(57) Haiduc, I.; Zuckerman, 3. J. Basic Organometallic Chemistry; Walter de Gruyter:Berlin, Germany, 1985, pp 68.References p.161Chapter 5 166CHAPTER 5Synthesis, Structure and Hydrogenation ofq3-BenzylDerivatives of Rhodium and Iridium5.1 IntroductionWhile benzyl complexes of rhodium are suggested to be key intermediates inthe decarbonylation of certain acid chlorides,1 few such complexes have actually beenisolated.2-5 The hapticity of the benzyl ligand can range from i (i) to r2 (u),7 3(ui),8 r4 (iv),9 or iS (v),10 making the benzyl unique as an organometallic ligand(scheme 5.1). Of the rhodium benzyl complexes isolated, the i1,i3 and q5 forms areknown.PEt3OPEt3Cl(i)Me2Me2PhH2C(iv)Scheme 5.10C”ClFe(iii)NO(ii)(iii)References p.196Chapter 5 167In general the synthesis ofr3-benzyl metal complexes can be achieved in severalways, for example: (1) insertion of a substituted styrene into a metal hydride bond?(2) deprotonation of a coordinated, methyl-substituted arene,2 (3) protonation of acoordinated arylalkene,1’(4) metathesis with an appropriate magnesium or lithiumreagent,12 (5) halide abstraction from a benzyl metal halide complex,’3 and (6)oxidative addition of benzylhalide to a metal.14The weak bonding interaction of the phenyl portion of the3-benzyl fragmentleads to a rapid exchange process (suprafacial vs. antarafacial)15 which can beobserved on the NMR time scale by variable temperature 1H NMR (figure 5.1). Theantarafacial exchange process A involves decoordination of the phenyl portion of thebenzyl fragment followed by rotation about the phenyl-benzylic carbon bond andbinding of the opposite face. This process exchanges the ortho protons but does notexchange the syn and anti protons. The antarafacial process B exchanges the syn andanti protons only by simple rotation about the metal-benzylic carbon bond and bindingto the opposite face; this rotation has no effect on the ortho protons. Finally thesuprafacial exchange process C involves migration of the metal fragment to theadjacent face of the benzyl fragment; this has the effect of exchanging the syn and antiprotons as well as the ortho protons.Reports from our laboratory have described the synthesis’6”7of thecoordinatively unsaturated dimers of the general form, [(P-P)Rh]2(i.t-H) (I),incorporating bulky chelating diphosphines. The coordinatively unsaturated nature ofthese dimers has led to a diverse and rich chemistry.’82’References p.196Chapter 5 168Figure 5.1. Exchange processes in3-benzyl complexes. (A) Antarafacialexchange of ortho protons only. (B) Antarafacial exchange of syn and anti protonsonly. (C) Suprafacial exchange of ortho, syn and anti protons.L LHa[Bill.HaHL[cjHHaMLMLReferences p.196Chapter 5 169IThis chapter is concerned with the high yield synthesis of the simple rhodium13-benzyl complex, (COD)Rh(r13- H2Ph) (1), by the reaction of Zn(CH2Ph) orMg(CH2Ph)2(THF)2 with [(COD)Rh]2(J.t-Cl)2. This complex is a useful precursor todiphosphine rhodium3-benzyl derivatives which are formed by simple displacementof the COD ligand. The resultant diphosphine complexes react rapidly with H2 to givehydride dimers of various compositions. The facile formation of a binuclearhexahydride complex, [P2RhH3Jis observed in the case of the bulky, one-carbonbackbone diphosphine complexes incorporating Pr2CH2PPr2 (dippm) orCy2PCHPCy2 (dcypm). The small chelate ring size of these ligands precludes directisolation of the dihydride bridged complexes (I).5.2 Synthesis and Characterization of q3-Benzyl Derivatives ofRhodium and IridiumIn a previous report22 the synthesis ofr3-allylic complexes of rhodium wasachieved by the addition of freshly prepared solutions of simple allyl Grignard reagentsto [(COD)Rh]2(p.-Cl)2as shown in equation 5.1.1/2 [(COD)Rh](i.i-CI) C3H5MgCICOD = cyclooctadiene I5 I(CH2)n=23,4References p.196Chapter 5 170The use of Zn(CH2Ph) or Mg(CH2Ph)(THF) to prepare (COD)Rh(3- H2Ph)(1)represents an improvement over the previously used synthesis since the alkylatingreagents are solids which can be made on a large scale and stored indefinitely in aglovebox. Mg(CH2Ph)(THF) is the reagent of choice for large scale preparationsdue to the greater insolubility of the byproduct MgC12. Compound 1 is thermallysensitive but can be stored at -40°C under nitrogen for several months with littledecomposition. The COD ligand in 1 can be displaced with the bulky chelatingdiphosphines But2P(CH)3But2 (dtbpp), Pr2(CH3Pr {dippp},Pr2(CH)Pr (dippe),Pr12CHPr (dippm) and CyPCHPCy2 (dcypm),generating the thermally stable3-benzylic compounds 2-6 (scheme 1).1/2 [(COD)Rh](j.t-CI)COD = cyclooctadiene2 R=But,n=33 R=Pr,n=34 R=Pr,n=25 R = Cy, n =16 R=Pr’,n=lIt turns out that the diphosphine3-benzyl derivatives make better startingmaterials than the ally! analogues because the hydrogenolysis of these species ismore facile; for example ( 2P(CH2)3PPr}Rh(13-5)requires 48 hours to go toScheme 5.2Mg(CH2Ph)(THF)or Zn(CH2Ph)1References p.196Chapter 5 171completion, whereas the hydrogenolysis of(Pri2P(CH)3Pr’)Rh(rI-CH2Ph) (3)takes only 2 hours under identical conditions of pressure and concentration. Therhodium benzyl complexes 1-6 are soluble in common organic solvents and crystallizeeasily.The 1H NMR spectrum of 1 shows two resonances for the COD olefinicprotons indicating that the benzylic carbon remains trans to one of the coordinatedolefins of COD. This is consistent with the 13C{1H) NMR spectrum which showstwo resonance for the olefinic carbons of the COD ligand.The 31P(1H} NMR spectra of the rhodium benzyl complexes 2-6 reveal acharacteristic first order AMX pattern that is indicative of mononuclear species. The31P{1H} NMR spectrum of {dippm}Rh(r3CH2Ph) (6) is shown in figure 5.2.Consistent with a mononuclear species is the molecular weight of 450 gmol1 foundfor àomplex {dippm}Rh(3CH2Ph),6 (caic. 442 gmol1). The AMX 31P{1H} NMRpattern for {dippp}Rh(flCH2P ), 3, is maintained from 80°C to -103°C, indicatingthat no exchange process of the phosphines is operative within this temperaturerange. This lack of exchange would rule out the antarafacial exchange process B infigure 5.1, assuming the chelated diphosphine remains intact. The coupling constants1JP,Rh and2Jp,p did not change over this temperature range, in contrast to what hasbeen reported2 for [(PrO)3P]2Rh(ii3-CH26(5(II).H. II(Pr’O)3CH3References p.196A UUuI,..l1IIJIIIII111111111111111111I111111111111111111II4IIIIII11IIIIIIIIII•tII(IIIII••2422201816141210PPMFigure5.2.121.42MHz31P(1H}NMRspectrumoffdippm}Rh(fl3-CH2Ph),6,inC6D.B268Chapter 5 173At high temperature the benzyl ligand in {dippp)Rh(fl3CHPh), 3, may adopt ancoordination but this does not equate the phosphines. This is in agreement withknown three coordinate bis(phosphine) complexes24’5which adopt a bent “T” shapestructure.The 13C{1H} NMR spectra of the rhodium benzyl compounds 1-6 show a shiftto higher field for the ortho and ipso carbons of the benzyl fragment, with respect tothe analogous signals normally observed for i1-CH2Ph complexes, due to theinteraction with the rhodium centre. No change was observed in the 13C(1H) NMRspectrum of (dippp}Rh(i3CH2Ph)down to -90°C. A characteristic doublet for theortho carbon of rhodium benzyl complexes 2-6 is interpreted as coupling to the transphosphine and not to rhodium since this doublet is absent in 1 (COD ligand donor).The benzylic carbon of the diphosphine complexes 2-6 appear as a multiplet with1JCRh on the order of 10 Hz, consistent with the simple doublet of 10.9 Hz observedfor 1. A strong two-bond coupling (—30 Hz) to the trans phosphine is also seen forthe benzylic carbon of the diphosphine complexes 2-6.The 1H NMR spectra of the rhodium benzyl complexes 1-6 are all similar witha characteristic upfield shift for the ortho protons of the benzyl ligand. The 1H NMRspectrum of {dippe}Rh(i3-CH2Ph)(4) is shown in figure 5.3. Both ortho protons areequivalent and appear as a doublet resonance due to coupling to the meta proton of thebenzyl fragment; no ortho proton coupling to rhodium was observed for any of thecomplexes. With the exception of broadening there was no change in the 1H NMR of{dippp}Rh(r3-CH2Ph)down to -70°C. The benzylic protons of the rhodium benzylcomplexes 2-6 appear as doublets with a strong three-bond coupling to thephosphorus trans to the benzylic carbon of about 7 Hz.References p.196IHmH0p I.,’P\)HmH0HbHIIIIII 7(IIIIIIIIII654IIIIIIIII3Figure5.3.299.94MHz1HNMRspectrumof(dippe)Rh(r13-CH2Ph)(4)inC6D(*denotesC6D5H).IIIIIIIIIIIIIIIllIllIllIllIllI21PPM0Chapter 5 175Previously, this has been interpreted as a two-bond proton-rhodium coupling in theanalogous complex [(PrO)3P]2Rh { i3-CH26(CH3)5} ,2 but since the benzylicprotons in (COD)Rh(3- H2Ph) appear as a singlet, it is likely to be transphosphorus-proton coupling. The 1H, 13C{ 1H) and 31P{1H) NMR data abovesuggest that the benzyl ligand in all of the complexes, 1-6, is undergoing a rapidsuprafacial exchange15 which remains fast on the NMR time scale in the temperatureregion studied.The preparation of (COD)fr(i3-CH5)has previously been reported by the lowtemperature addition of Li(C3H5) to [(COD)Ir]2(p-Cl);6due to its thermalinstability this iridium allyl derivative was not isolated but rather used in situ.Anticipating the instability of the analogous complex (COD)Ir(r3- H2Ph , thediphosphines were introduced before incorporation of the benzyl moiety. The additionof two equivalents of a diphosphine ligand to [(COE)21r](p-Cl yields theextremely air-sensitive complexes [P21r](I.t-Cl) (P2 = dtbpp and dippp), as shownin scheme 5.3.Scheme 5.3R1)’R ZCIN[(COE)2Ir](t-CI (H2C) ,Iç (CH2)S4%COE = cyclooctene P CI PR2 R212 R=But,n=313 R=Pr,n=314 R = But, = 315 R= Pr’, n =3Zn(CH2Ph)References p.196Chapter 5 176Only complexes 12 and 13 having diphosphines with three carbon backbone, havebeen prepared in pure form; for the chelating ligands dippe, dcypm and dippm, complexmixtures result. The addition of Zn(CH2Ph) to the diphosphine iridium chlorobridged dimers leads to the desired rj3-benzyl compounds in high yield. The iridiumbenzyl complexes 14 and 15 are quite thermally stable, as they can be storedindefinitely at room temperature under dinitrogen with no detectable decomposition.Similar shifts for the benzyl moiety are observed in the 1H and 13C{1H) NMR spectraas were found for the rhodium analogues. The two doublets at 27.0 and 21.4 ppmobserved in the 31P{1H} NMR spectrum of {dippp}fr(3-CH2Ph)confirm the rigid ri3-coordination of the benzyl ligand.Preliminary studies into the reactivity of the3-benzyl derivatives of iridiumtoward 1,3-butadiene are worth noting. The reaction of isolated (dippp}Ir(3-CH2Ph), 15, with excess 1,3-butadiene leads to the quantitative formation of{dippp)IrBz(fl4-C4H) (16) by 1H and 31P{1H} NMR spectroscopy (equation 5.2).(xs)[ pJ2[5.2]• Pr2• 16The 31P{1H) NMR spectrum of 16 shows two doublets at -2.8 ppm and -17.7 ppmwith a P-P’ coupling of 8 Hz which is indicative of cis-disposed phosphines. The 1HNMR spectrum of 16 is quite complicated; however, the resonances associated withthe3-benzyl moiety do not appear and resonances attributable to an ij1-benzylspecies are apparent. Six resonances associated with the 1 ,3-butadiene fragment areReferences p.196Chapter 5 177also clearly visible at 5.41 (H), 3.91 (H), 2.60 (Ha). 2.57 (Ha), 0.45 (Ha) and 0.11(Ha) ppm along with four isopropyl methine and eight isopropyl methyl resonances.The proposed structure of 16, shown in equation 5.2, is based on the structure of thefive-coordinate amido-diphosphine complex, (fl4-C4H6)Ir { N(SiMe2-CHPPh)},previously prepared in our laboratory.27 No attempt has been made to hydrogenatethis material.5.3 Molecular Structure of {dippp}Rh(3-CH2Ph) (3)The molecular structure of {dippp)Rh(fl-CH2Ph) (3) is shown in figure 5.4,selected bond lengths and bond distances appear in Tables 5.1 and 5.2, respectively.Table 5.1. Selected bond lengths for {dippp}Rh(fl3-CH2P ), 3.Bond Length (A) Bond Length (A) Bond Length (A)Rhl-P1 2.210(1) Rhl-P2 2.255(1) Rhl-C16 2.141(4)Rhl-C17 2.197(3) Rhl-C18 2.362(3) C16-C17 1.426(5)C17-C18 1.419(5) C18-C19 1.398(5) C19-C20 1.360(6)C20-C21 1.389(6) C21-C22 1.351(6)Table 5.2. Selected bond angles for {dippp}Rh(13-CH2P ), 3.Bonds Angles (deg) Bonds Angles (deg)P1-Rhl-P2 96.99(4) P1-Rhl-C16 94.4(1)P1-Rhl-C17 127.4(1) P1-Rhi-Ci 8 160.27(9)P2-Rhl-C16 168.5(1) P2-Rhl-C17 130.71(9)P2-Rhl-C18 102.7(1)References p.196Chapter 5 178Figure 5.4. Chem 3D Plus® representation of the molecular structure of{dippp}Rh(fl3-CH2P ) (3).C21C22 C20C17C8C4C19C6doC5Cl 3ClClC3C14C7C15References p.196Chapter 5 179The diphosphine ligand and thei3-benzy1 moiety adopt a nearly square planararrangement around the rhodium centre using the ortho carbon as the fourth position.The rhodium-phosphorus(P1) bond trans to the benzylic carbon is longer than therhodium-phosphorus(P2) bond cis, by 0.045 A, likely due to a greater stericinteraction with the phenyl portion of the benzyl ligand, as well as a greater a-donation from the benzylic carbon. This is consistent with the higher charge densityon the benzylic carbon compared to the ortho or para carbons.9 The carbon-rhodiumbond lengths in the benzyl fragment increase in the order Rh-C(18) > Rh-C(17) >Rh-C(16) {2.362 A > 2.197 A > 2.141 A), owing to the larger amount of electrondensity on the benzylic carbon and the weak carbon-metal interaction of the phenylportion of the benzyl fragment. The aromaticity of the phenyl ring has been disturbedwith localization of double bonds between C19-C20, and C21-C22. The bond lengthsC16-C17 and C17-C18 are statistically the same due to delocalization of the it-allylicsystem (III).1.360(6) A5.4 Synthesis and Structure of Binuclear Rhodium HydridesifiThe coordinatively unsaturated rhodium benzyl complexes 2-6 all react withhydrogen rapidly at -80°C without the buildup of intermediates as monitored by 31P1.389(6) A1.351 (6) A1.422(5)1.426(5) A1.419(5) A 1.398(6) AReferences p.196Chapter 5 180The binuclear dihydrides 8 and 9 have been reported previously.16”7The binuclearityof hydride 7, having t-Bu substituents at phosphorus, was determined in solution bythe multiplicity of the bridging hydride pattern in the 1H NMR spectrum. The triplet ofpentets pattern is ascribed to coupling to two equivalent rhodium103 nuclei and fourequivalent phosphorus31 nuclei. [{dtbpp}Rh12(p-H)2 (7) is soluble in THF,sparingly soluble in aromatic solvents and insoluble in aliphatic solvents.Attempts to prepare iridium hydrides by hydrogenolysis of the iridium benzylcomplexes 14 and 15 were unsuccessful as only inseparable mixtures of productswere produced as evidenced by 1H and 31P NMR spectroscopy.The rhodium q3-benzyl complexes S and 6 also react with H2 (1 atm) butgenerate hydride complexes having a completely different structure than that indicatedin equation 5.3. This is evident from the 31P{1H} NMR spectra of [{dcypm)RhH3](10) and [(dippm)RhH](11) which show a much reduced phosphorus-rhodiumNMR spectroscopy. Complexes 2-4 give the dihydride dimers, 7-9 as shown inequation 5.3, wherein the diphosphine is chelating on each rhodium center.1. H(1atm)/H% 7P-. [5.3](HC) Rh Rh (CH)NHR2 R2PR212 R=But and n=33 R=Pr and n=34 R=Pr3 and n=2 7 R=But and n=38 R=P and n=39 R=Pr’ and n=2References p.196Chapter 5 181coupling constant (107 Hz vs. typically 160 Hz for formally Rh(I)), indicative of aRh(llI) species.28’9 Furthermore, the 31P(1H} NMR spectra of compounds 10 and11 do not resemble the 31P{1H} NMR spectra of the classic chelating diphosphinedihydride complexes prepared to date.16”7 The hydride derivatives 10 and 11 formdeep red-black solutions in toluene, in contrast to the binuclear dihydride dimers 7-9,which form dark green solutions. In solution complex 10, having cyclohexylsubstituents at phosphorus, loses hydrogen readily under vacuum to yield a singleinsoluble product whose structure is as yet undetermined; however solutions of[{ dippm } RhH3](11) are quite stable in toluene or aliphatic hydrocarbons but doslowly lose hydrogen over many months in benzene. In the solid state 11 isindefinitely stable.Scheme 5.4[(dcypm)RhH3]10[(dippm)RhH3]11The 1H NMR spectrum of 11 shows a septet of virtual triplets30 pattern(3JH,H’ = 7 Hz; [2JH,P +4JH,P’] ÷ 2 = 2 Hz) at 1.88 ppm for the isopropyl methinewhich indicates strongly coupled trans-disposed phosphines. Virtual triplet couplinghas not been observed in any of the chelating diphosphine rhodium complexesprepared in our laboratory. The 1H NMR spectrum of 11 also shows two multiplets inthe hydride region at -10.92 ppm and -14.88 ppm in the ratio of 2:4 with respect to theH2toluene / lhPR25 R = Cy6 R = Pr’References p.196Chapter 5 182ligand resonances (assuming a binuclear structure). In the tetrahydride complex31[{(Me2N)3PRhH](p.- )Rh{P(NMe)(IV), which contains both bridgingand terminal hydrides in the same plane, the bridging hydrides resonate at -10.5 ppmand the terminal at -16.8 ppm.P(NMe2)%S P(NK4e2)H’H”P(NMeP(NMe2)Interestingly, in IV the rhodium centre that contains the trans disposed phosphinesalso exhibits the higher coordination number. Both 1H ( 31P) and selective 1Hhomonuclear decoupling experiments were used to determine how the diphosphineligands in complexes 10 and 11 bind to the rhodium centres (binucleating D vschelating E). The results of the decoupling experiments are shown in figure 5.5.H HP,,, H,, PH HD EIn the1H(31P} NMR spectrum of [{dippm}RhH3](11), the signal at -10.92ppm was reduced to a simple triplet of pentets due to coupling to two equivalentrhodium nuclei and four terminal hydrides, and is assigned to the bridging hydrides; thecoupling to two Rh103 nuclei confirms the binuclear structure of 11. This is in accordwith the molecular weight23 of 722 gmo1 found for [(dippm}RhH3]2 (11) (calcd. 708References p.196Chapter 5 183gmol4). This simple coupling pattern is most easily accommodated by a rigidstructure such as E. Alternatively, if D (binucleating) is assumed to be the structureand it is rigid, a second-order pattern would be expected for the bridging hydrideproviding 2JH,H cis is quite different from2JH,H trans. However, cis and trans hydridecouplings are generally quite small (2-7 Hz) or absent32’3 and therefore it is possiblethat 2JH,H cis 2JH,H trans. The signal for the terminal hydrides at -14.88 ppmremained as a second order pattern in the1H(31P) NMR spectrum, likely due to longrange coupling to rhodium. This is consistent for both structures D and E. The rigidnature of complex 11 is supported by the absence of any exchange between thehydrides from -50°C to +70°C.Differentiation of the two possible structures D and E comes from thephosphorus coupled 1H NMR spectrum. Decoupling of the terminal hydrides at -14.88ppm reduces the bridging-hydrides multiplet at 1D.9L2 ppm to an overlapping triplet ofpentets (1JH,Rh = 24.5 Hz; 2JH,P = 12.2 Hz). Coupling constants in this range arevery common for other rhodium complexes with binucleating phosphines and bridginghydrides.3436 Decoupling of the bridging hydrides at -10.92 ppm reveals a secondorder pattern for the terminal hydrides at -14.88 ppm. A second order pattern wouldbe expected for the terminal hydrides if the phosphines in structure D are all stronglycoupled, whereas structure E would most likely lead to a more simplified pattern.Based on the above data, structure D is the most likely for the hydridecomplexes incorporating the one carbon backbone diphosphines. Although axial-axialinteractions are extensive in binucleating structures, and likely more pronounced withbulky alkyl substituents such as isopropyl or cyclohexyl, we believe this mode ofcoordination is responsible for the observed binuclear hydrides.References p.196Chapter 5 184Rh-Hb-RhII10Hz(a)(C)-10.92 ppm -14.88 ppmFigure 5.5. Results of the decoupling experiments for [{dippm)RhH3]2,11. (a) 1HNMR spectrum of the hydride region. (b) 1 { 31) NMR spectrum of the hydrideregion. (c) homonuclear decoupled ‘H NMR spectrum of the hydride region.Rh-He(b)IReferences p.196Chapter 5 185The trans disposed nature of the phosphines on the octahedrally coordinatedrhodium(Ill) centre in [{(Me2N)3P) RhH](t-H)2[Rh{ P(NMe)3} 2], IV, wouldseem to provide the correct ligand arrangement for the stabilization of a trihydridespecies. Further addition of dihydrogen to IV is not possible since the remaining ciscoordinated phosphines can not move into axial sites due to steric crowding. Indeed,mononuclear trihydride complexes37 such as (But3P)2RhH (V), which contain transdisposed bulky phosphines, have been prepared from (BuP)2RhH and H2.PBUt3H lgjH’H vPBUt3The trihydride complex (BuP)2RhH3, V, readily loses dihydrogen under dinitrogen togive the dinitrogen complex [(But)RhHj1.LN,37which may be a general modeof decomposition for polyhydrides of rhodium bearing trans phosphines.The ligands Pr2PCH2PPr (dippm) and Cy2PCH2PCy2 (dcypm) provide theessential steric bulk and diaxial coordination of the phosphines required for theformation of stable binuclear hexahydride complexes. It is interesting to note theisoelectronic iridium38 analogue, VI, which has two fewer hydrides than thehexahydride structures discussed herein. The difficulty in removing the two remainingcarbonyl ligands has likely rendered hexahydride complexes inaccessible from thisparticular complex.References p.196Chapter 5 186Ph2PPPh“CoIII IS%Ph2P..PPhA mechanism for the formation of the binuclear hexahydride complexes 10 and11 is difficult to substantiate since no intermediates have been observed.Nonetheless several important features are worth noting (scheme 5.5). Thehydrogenolysis of the mononuclear complexesP2Rh(i3-CH) (P2 = dcypm 5 anddippm 6) proceeds cleanly to give only one phosphorus containing compound by3lp1H) NMR spectroscopy. Furthermore, the four membered chelate ring is likely tobe labile due to ring strain which may facilitate phosphine dissociation39 at some keystep in the hydrogenation. The bridging coo ntion geometry of the diphosphinecertainly relieves this ring strain and likely leads to the much more stable binuclearhexahydride structure D.10 R = Cy11 R=Pr’Scheme 5.5R2 T<:H ,,,, •jØ%” H,,01,[BF4]2 VIRhR2P)PR5R = CyR = Pr’R2 H<VP,,,,’R2 H2 H2- CH3Phdimerization1/2References p.196Chapter 5 1875.5 Summary and Future ConsiderationsThe straightforward synthesis and characterization of the above mentionedcomplexes have provided a facile route for the production of diphosphine3-benzylderivatives of rhodium and iridium. For the mononuclear complexes of the generalformulaP2Rh(3-CH) (P2 = dtbpp, dippp and dippe), binuclear dihydridederivatives, [PRh]2(.t-H) are formed. New binuclear hexahydride complexes[RhH2](J.t- )t-P2)2, incorporating a binucleating diphosphine, are formed whenthe mononuclear compoundsP2Rh(rj3-CH) (P2 = dippm and dcypm) arehydrogenated. A single crystal analysis of the hexahydride derivatives would be ofinterest to substantiate the proposed structures. Changing the isopropyl substituentson phosphorus to cyclopentyl may yield more crystalline material.Initial reactivity studies on the hexahydride complex [RhH2](i-H)t-dippm)2 suggest that the reaction with ethylene and butadiene is rather complicated,confirming that the structural differences that exist for chelating versus binucleatingdiphosphine complexes carry over to the reactivity patterns of these species.5.6 Experimental Section5.6.1 General Information. See section 2.7.1 (chapter 2) for details.5.6.2 Starting Reagents. RhC13.xH2O and IrCl3.xH2O were obtained fromJohnson-Matthey and used as received to prepare [(COD)Rh](j.t-Cl) (COD = 1,5-cyclooctadiene)4°and [(COE)21r]2(1’-Cl)2 (COE = cyclooctene)41,respectively.Dibenzylzinc Zn(CH2Ph) and bis(tetrahydrofuran)dibenzylmagnesiumMg(CH2Ph)THF),42 I ,3-bis(ditertiarybutylphosphino)propane (dtbpp) and 1,3 -bis(diisopropylphosphino)propane (dippp), 1 ,2-bis(diisopropylphosphino)ethane(dippe),17 and bis(diisopropylphosphino)methane (dippm)” were prepared accordingReferences p.196Chapter 5 188to the literature. Bis(dicyclohexylphosphino)methane (dcypm) was prepared fromC12PCH1”and cyclohexyl Grignard, a detailed preparation of which is shownbelow. The hydride dimers [{dippp)Rh]2(t-H)216and [(dippe)Rh]2(j.i-H)217wereidentified spectroscopically by comparison to authentic samples prepared by publishedroutes.5.6.3 Synthesis of (COD)Rh(3- H2Ph) (1). Using Zn(CH2Ph).To asolution containing [(COD)Rh](ji-Cl) (250 mg, 0.507 mmol) in toluene (50 mL)was added dropwise a solution of Zn(CH2Ph) (126 mg, 0.509 mmol) in toluene (10mL) over 1 minute. The initially yellow solution turned dark orange as ZnC12precipitated. The mixture was stirred for 4 hours followed by removal of the tolueneunder vacuum and the solid taken up in pentane (50 mL). The mixture was stirred for20 minutes then filtered through a medium porosity fit. Concentration of the solutionin vacuo to 10 mL followed by cooling to -40°C yielded 245 mg (80%) of orangecrystalline 1. Larger scale reactions gave lower yields using Zn(CH2Ph). Thecomplex can be stored for several months at -40°C. Anal calcd. forC15H9Rh: C,59.61; H, 6.34. Found: C, 59.46; H, 6.36%. 1H NMR (C6D,, ppm): 7.08 Ct, H ofphenyl, 2H, 3JH,H = 7 Hz); 6.72 (t, Hp of phenyl, lH, 3H,H = 7 Hz); 5.71 (d, H0 ofphenyl, 2H, 3JH,H = 7 Hz); 4.68 (s, =CH, 2H); 3.77 (s, =CH, 2H); 2.12 (s, CH2Ph,2H); 2.0-1.7 (m, CH2 of COD, 8H). 13C{H} NMR (C6D,, ppm): 132.4 (C ofPh); 123.1 of Ph); 121.8 (C of Ph); 109.7 (C0 of Ph); 87.3 (d, =CH, ‘Jc,i.i = 9.6Hz); 73.0 (d, =CH, 1JC,Ri = 15.2 Hz); 38.4 (d, CH2Ph,1JC,ih = 10.9 Hz); 32.2 (CH2 ofCOD); 30.6 (CH2 of COD).Using Mg(CHPh)(THF) To a suspension containing [(COD)Rh]2(p.-Cl)(1.103 g, 2.23 mmol) in THF (100 mL) was added dropwise a solution ofMg(CH2Ph)2(THF) (0.785 g, 2.24 mmol) in THF (10 mL). The initially yellowsolution turned dark orange as MgC12 precipitated. After 4 hours the THF wasReferences p.196Chapter 5 189removed under vacuum and the solid taken up in pentane (75 mL). The mixture wasstirred for 20 minutes and then filtered through a medium porosity fit. Removal of thesolvent yielded 1.240 g (92%) of 1.5.6.4 {dtbpp}Rh(3-CH2Ph) (2). To a solution containing 1 (142 mg, 0.469mmol) in hexanes (10 mL) was added dropwise a solution of dtbpp (156 mg, 0.469mmol) in hexanes (5 mL). The solution turned deep red from the initial orange colour.The solution was stirred for 1 hour followed by filtration. The volume was reduced invacuo to 10 mL and cooled to -40°C to yield 175 mg (7 1%) of red crystalline 2. Anal.Calcd. forC26H49PRh: C, 59.31; H, 9.38. Found: C, 59.58; H, 9.49%. 1H NMR(C6D,3, ppm): 7.21 (t, Nm of phenyl, 2H, 3JH,H = 7 Hz); 6.84 (t, H of phenyl, 1H,=7 Hz); 6.04 (d, H0 of phenyl, 2H, 3JH,H = 7 Hz); 2.31 (d, CH2Ph, 2H, 3JH,P =6.2 Hz); 1.68 (m, CR2 ligand, 2H); 1.36 (m, CH2 ligand, 4H); 1.26 (ci, CH3 of ligand,18H); 1.03 (d, CTh of ligand, 18H). 31P{1H-} NMR (C6D,3, ppm): 61.5 (dd, A,1P,Rh = 266 Hz; 2Jp,p’ = 29 Hz); 51.4 (dd, PB, 1Jph = 173 Hz; 2Jp’,p = 29 Hz).13C{H) NMR(6D,3, ppm): 132.3 (C of Ph); 121.4 (C0 of Ph); 120.9 (C ofPh); 109.2 (d, C0 of Ph, 2Jp = 7.2 Hz); 38.4 (C(CH3);38.6 (C(CH3);37.0 (d,CH2Ph,1C,Rh = 9.5 Hz); 31.1 (d, CH3 of ligand); 30.6 (d, CH3 of ligand); 24.1 (ligand);23.4 (ligand); 22.8 (ligand).5.6.5 {dippp}Rh(-CHPh) (3). The preparation of 3 is identical to that for 2.Compound 3 was obtained as red crystals in 85% yield. Anal. Calcd. for22H41PRh: C, 56.17; H, 8.78. Found: C, 56.08; H, 8.77%. 1H NMR (C6D,3,ppm): 7.24 (t, Hm of phenyl, 2H, 3JHH = 7 Hz); 6.63 (t, H of phenyl, 1H, 3JH,H = 7Hz); 5.87 (d, H0 of phenyl, 2H, 3JHH = 7 Hz); 2.25 (d, CH2Ph, 2H, 3JH,P = 7.1 Hz);1.92 (d of sept, CH(CH3)22H); 1.68 (m, PCH2 2H); 1.64 (d of sept, CH(CH3)22H);1.26 (m, PCH2 2H); 1.23 (m, PCH2C 2H); 1.12 (dci, CH(CH3)26H); 1.04 (dd,CH(CH3)2,6H); 0.96 (dd, CH(CH3)26H); 0.85 (dd, CH(CH3)2611). 31P{1H}References p.196Chapter 5 190NMR (C6D,6, ppm): 48.3 (dd, A,1Jp,pj = 242 Hz; 2Jp,p = 40.8 Hz); 33.9 (dd, B,1JP,1h = 172 Hz; 2Jp,p = 40.8 Hz). 13C{H} NMR (C6D,8, ppm): 132.2 (Cm ofPh); 119.1 (C0 of Ph); 117.8 (C of Ph); 105.1 (d, C0 of Ph, 2J,p = 7.7 Hz); 34.8(ddd, CH2Ph,1JCh = 9.1 Hz; 2Jc,p = 32.1 Hz; 2J,p = 2.5 Hz); 29.8 (d, CH(CH3));25.6 (d, CH(CH3)); 23.9 (d, ligand backbone); 21.1 (d, CH(CH3)); 20.9 (d, CH(CH3));20.5 (d, ligand backbone); 20.2 (d, ligand backbone); 20.0 (dd, CH(CH3)); 19.3 (d,CH(CH3)).5.6.6 {dippe}Rh(q-CH2Ph) (4). See preparation of 2 for experimental details.4 was obtained in 80% yield as deep orange crystals. Anal. Calcd. forC21H39PRh:C, 55.27; H, 8.61. Found: C, 55.35; H, 8.76%. 1H NMR (C6D,8, ppm): 7.29 (t, Hmof phenyl, 2H, 3H,H = 7 Hz); 6.57 (t, Hp of phenyl, 1H,3JH,H = 7 Hz); 5.91 (d, H0 ofphenyi, 2H, 3JH,H = 7 Hz); 2.47 (d, CH2Ph, 2H, 3JH,P = 7.5 Hz); 1.88 (d of sept,CH(CH3)2,211); 1.69 (d of sept, CH(CH3)2, 211); 1.19 (rn, PCH2 2H); 1.07 (dd,CH(CH3)2,6H); 1.02 (m, PCH2 2H); 0.92-0.77 (m, CH(CH3)218H). 31P{1H}NMR (C6D,6, ppm): 97.9 (dd, A,1Jp,pj = 245 Hz; 2Jp,p = 20.5 Hz); 91.0 (dd, B,1Jp,pj = 177 Hz; 2Jp,p 20.5 Hz). 13C{H} NMR (C6D,8, ppm): 132.5 (Cm ofPh); 119.1 (C0of Ph); 118.1 (C of Ph); 105.6 (d, C0 of Ph, 2C,P = 8.7 Hz); 32.5 (dd,CH2Ph; ‘fc,im = 8.7 Hz; = 33.9 Hz); 28.0 (dd, CH(CH3)2;25.7 (d, CH(CH3)2;23.7 (ddd, PCH2); 21.7 (ddd, PCH2); 20.1 (d, CH(CH3)2;19.8 (d, CH(CH3)2;19.1 (d,CH(CH3)2;18.9 (d, CH(CH3)2.5.6.7 {dcypm}Rh(T-CHPh) (5). The preparation of S is identical to that for 2.Compound S was isolated as orange plates in 92% yield. Anal. Calcd. for32H53P2Rh: C, 63.78; H, 8.86. Found: C, 64.03; H, 9.08%. 1H NMR (C6D,6,ppm): 7.41 (t, Hm of phenyl, 2H, 3H,H = 7 Hz); 6.54 (t, Hp of phenyl, 1H, 3JHH 7Hz); 5.96 (d, H0 of phenyl, 2H, 3JH,H = 7 Hz); 2.61 (t, PCH2, 2H); 2.41 (d, CH2Ph,2H, 3JH,P = 6.6 Hz); 2.1-1.1 (br m, ligand resonances, 44H). 31P{1H} NMR (C6!),References p.196Chapter 5 1916, ppm): 13.7 (dd, PA,1Jp,pj = 221 Hz; 2Jp,p =77 Hz); 1.0 (dd, B,1Jp, = 148 Hz;2Jp’,p = 77 Hz). 13C{H) NMR (C6D,3, ppm): 132.8 (Cm of Ph); 120.1 (C10 ofPh); 118.0 (C of Ph); 106.3 (d, C0 of Ph,2J,p = 9.5 Hz); 37.5 (dd, PCH2); 36.7 (dd,CH2Ph, ‘cj1= 4.1 Hz; 2c,p = 13.2 Hz); 30.3; 30.2; 29.9; 29.8; 27.7; 27.6; 27.5; 27.4;26.7 (overlapping cyclohexyl carbons).5.6.8 {dippm}Rh(q3-CHPh) (6). See preparation of 2 for experimental details.6 was obtained in 77% yield as deep red-orange crystals. Anal. Calcd forC20H37PRh: C, 54.30; 8.43. Found: C, 54.46; H, 8.41%. 1H NMR (C6D,6, ppm):7.35 (t, Nm of phenyl, 2H, 3JH,H = 7 Hz); 6.55 (t, H, of phenyl, 1H, 3JH,H = 7 Hz);5.90 (d, H0 of phenyl, 2H, 3JH,H =7 Hz); 2.38 (d t, PCH2, 2H); 2.36 (d, CH2Ph, 2H,3JH,P = 6.9 Hz); 1.77 (d of sept, CH(CH3)22H); 1.64 (d of sept, CH(CH3)22H);1.11 (d d, CH(CH3)26H); 1.08 (d d, CH(CH3)26H); 0.95 (d d, CH(CH3)26H); 0.91(d d, CH(CH3)26H). MP{tH} NMR (C6D,3, ppm): 23.4 (dd, A, -Jp = 222Hz; 2Jp,p’ = 77 Hz); 10.8 (dd, B,1Jp,rn = 149 Hz; 2Jp’,p = 77 Hz). 13C{H} NMR(C6D,6, ppm): 132.8 (Cm of Ph); 120.2 (C1of Ph); 117.9 (C of Ph); 106.5 (d, C0 ofPh, 2JC,P = 9.6 Hz); 35.1 (dd, PCH2); 29.1 (dd, CH2Ph,1JC,RII = 9.2 Hz; 2p= 36.9Hz); 26.8 (ddd, CH(CH3)2;26.4 (dd, CH(CH3)); 19.9 (d, CH( CH3)2; 19.8 (d, CH(CH3)2; 19.5 (d, CH( CH3)2; 19.3 (d, CH( CH3)2. Mol. wt. (cryoscopic in benzene):found 450, calcd.: 442.5.6.9 [{dtbpp}Rh]2(i-H)(7). To a 350 mL reactor bomb equipped with a stirbar was added 2 (176 mg, 0.334 mmol) in toluene (50 mL). The solution wasdegassed three times and the vessel cooled to -196C. Hydrogen was then added to 1atmosphere and the inlet valve closed. The solution was warmed to room temperatureand stirred for 24 hours. The toluene was removed under vacuum and the productextracted with 30 mL THF. The deep green solution was filtered, concentrated to 15mL and cooled to -40°C to yield 78 mg (54%) of green crystalline 7. Anal. Calcd forReferences p.196Chapter 5 192C38H86P4Rh: C, 60.94; H, 11.57. Found: C, 61.21; H, 11.69%. 1H NMR (C6D,8,ppm): 1.81 (m, PCH2 8H); 1.48 (m, PCH2C 4H); 1.39 (d, PC(C113)72H); -8.79(t of pentet, RhHRh, 2H, 1JH,Rh = 9.6 Hz; 2H,P = 22.2 Hz). 31P{1H) NMR (C6D,8, ppm): 69.8 (br d, 1Jp,pj = 145 Hz).5.6.10 [{dippp}Rh]2(j.t-H) (8). The preparation of 8 is analogous to that for 7with the exception that the product was isolated from toluene/hexanes. 8 wasisolated in 84% yield as green crystals. 1H NMR (C6D,6, ppm): 1.82 (d of sept,CH(CH3)2,8H); 1.60 (dd, CH(CH3)224H); 1.21 (dd, CH(CH3)224H); 0.95 (m,ligand backbone, 12H); -6.61 (t of pentet, RhHRh, 2H). 31P{1H} NMR (C6D,6,ppm): 50.2 (d of m, 1Jp,Rh = 160 Hz).5.6.11 [{dippe}Rh](.L-H)2 (9). The preparation of 9 is analogous to that for 7with the exception that the product was isolated from toluene/hexanes. 9 wasisolated as green crystals in 66% yield. 1H NMR (C6D,6, ppm): 1.83 (d of sept,CH(CH3)2,8H); 1.40 (dd, CH(CH3)224H); 1.11 (dd, CH(CH3)224H); 1.04 (br d,ligand backbone, 8H); -4.81 (t of pentet, RhHRh, 2H). 31P{1H} NMR (C6D,8,ppm): 104.7 (d of m, ‘Jp,im = 160 Hz).5.6.12 [RhH](t-H){. -dcypm} (10). In a sealable NMR tube wasdissolved 5 (30 mg, 0.049 mmol) in C7D8 (0.4 mL). The tube was cooled to -196°Cand hydrogen introduced to 1 atmosphere. The tube was sealed and the solutionwarmed to RT as the deep red-black hydride formed. Only one compound is formed by31P{1H) NMR. 1H NMR (C6D,8, ppm): 2.21 (br in, PCH2 4H); 1.80, 1.62, 1.41(m, ligand resonances, 88H); -10.90 (m, RhHRh, 2H); -14.73 (in, R1IH, 4H).31P{1H) NMR (C6D,6, ppm): 65.8 (d of m, 1JP,Rh = 107 Hz).5.6.13 [RhH2]2(.t-H)2{J.L-dippm} (11). To a 350 mL reactor bomb equippedwith a stir bar was added 6 (75 mg, 0.169 mmol) in 25 niL pentane. The solution wasReferences p.196Chapter 5 193degassed three times and the vessel cooled to - 196°C. Hydrogen was then added to1 atmosphere and the inlet valve closed. The solution was warmed to roomtemperature and stirred for 4 hours. The colour of the solution turned deep red-blackinstantly. The reaction is quantitative by 31P{1H} NMR. 11 can be recrystallizedfrom pentane at -40C and is stable in the solid state. Anal. Calcd forC38H86P4Rh:C, 44.08; H, 9.39. Found: C, 44.41; H, 9.5 1%. 1H NMR (C6D,6, ppm): 1.91 (br m,PCH2, 4H); 1.88 (d of sept, CH(CH3)28H); 1.25 (dd, CH(CH3)224H); 1.20 (dd,CH(CH3)2,24H); -10.92 (m, RhHRh, 2H); -14.88 (m, RhH, 4H). 31P{1H} NMR(C6D,6, ppm): 74.3 (d of m, 1Jp,Rh = 107 Hz). 1H{31P) NMR (C6D,6, ppm):1.91 (s, PCH2 4H); 1.88 (sept, CH(CH3)28H); 1.25 (d, CH(CH3)224H); 1.20 (d,CH(CH3)2,24H); -10.92 (t of pentet, RhHRh, 2H,2JH,H’ = 4.5 Hz; 1JH,im = 24.5 Hz);-14.88 (m, RhH, 4H). Mol. wt. (cryoscopic in benzene): found 722; calcd. 708.56.14 [{dtbpp)ir]2(.t-Cl) (12). To a stirred suspension of [(COE)2Ir]2(I.L-Cl)2 (389 mg, 0.434 mmol) in hexanes (25 mL) was added slowly a solution of dtbpp(289 mg, 0.869 mmol) in 10 mL hexanes. The colour of the solution changed instantlyfrom orange to deep red as the solution became homogeneous. After a few secondsthe solution began to precipitate a red powder. The volume was reduced to 10 mLhexanes and the mixture cooled to -40CC for 24 hours. The red powder was collectedon a fme porosity flit and washed with 5 niL cold hexanes to yield 447 mg (92%) of 12.The product was dried under vacuum for 6 hours on a vacuum line to remove residualCOE. The product is extremely oxygen sensitive and should be stored under nitrogenat -40°C. This sensitivity thwarted all attempts to obtain accurate microanalysis ofthis product. The powder was sufficiently pure for metathetical reactions. 1H NMR(C6D,6, ppm): 1.51 (d, PC(CH3); 1.35 (m, PCH2); 1.21 (m, PCH2C).31P{1H} NMR (C6D,6, ppm): 14.69 (s).References p.196Chapter 5 1945.6.15 [{dippp)Ir]2(p.-C1) (13). See preparation of 12 for experimentaldetails. 13 was obtained in 90% yield as an orange powder. Again 13 is extremelyoxygen sensitive and should be stored under nitrogen at -40°C. 1H NMR (C6D,6,ppm): 2.13 (d of sept, PCH(CH3)2;1.54 (dd, PCH(CH3)2;1.18 (dd, PCH(CH3)2;0.96 (m, PCH2 and PCH2C). 31P{1H) NMR (C6D,6, ppm): 11.37 (s).5.6.16 {dtbpp)Ir(r3-CHPh) (14). To a stirred suspension of 12 (184 mg,0.164 mmol) in toluene (25 mL) was added dropwise a solution of Zn(CH2Ph) (41mg, 0.166 mmol) in hexanes (10 mL). The colour of the solution changed from red toorange as ZnC12 precipitated. The stirring was continued for 24 hours after which timethe mixture was filtered through a medium porosity fit. Concentration of the solutionto 10 mL and cooling to -40°C overnight yielded 145 mg of orange crystalline 14(72%). Anal. Calcd forC26H.49P1r: C, 50.71; H, 8.02. Found: C,50.31; H, 7.59%.1H NMR (C6D,6, ppm): 7.15 (t, Hm of phenyl, 2H, 3JH,H = 7 Hz); 6.68 (t, Hp ofphenyl, 1H, 3JHH = 7 Hz); 6.03 (d, H0 of phenyl, 2H, 3JH,H = 7 Hz); 2.49 (t, CH2Ph,2H, 3JHP = 2.3 Hz); 1.70 (m, CH2 ligand, 2H); 1.48 (m, CH2 ligand, 4H); 1.25 (br s,CH3 of ligand, 18H); 1.15 (br s, CH3 of ligand, 18H). 31P{1H) NMR (C6D,6,ppm): 39.8 (br s, PA); 36.4 (br s, PB). 13C{H} NMR (C6D,8, ppm): 132.4 (Cof Ph); 120.9 (C0of Ph); 120.7 (C of Ph); 109.2 (d, C0 of Ph, = 7.2 Hz); 38.6(C(CH3);38.4 (C(CH3);37.1 (d, CH2Ph,1JC,Rh = 9.2 Hz); 31.1 (d, CH3 of ligand);30.6 (d, CH3 of ligand); 24.2 (ligand); 23.4 (ligand); 22.9 (ligand).5.6.17 {dippp}Ir(-CH2Ph) (15). The preparation of 15 is identical to that for14. Compound 15 was obtained as red crystals in 70% yield. Anal. Calcd forC22H41PRh: C, 56.17; H, 8.78. Found: C, 56.08; H, 8.77%. 1H NMR (C6D,3,ppm): 7.18 (t, Hm of phenyl, 2H); 6.54 (t, Hp of phenyl, 1H); 5.84 (d, H0 of phenyl,2H); 2.38 (d, CH2Ph, 2H, 3H,p = 7.0 Hz); 2.04 (d of sept, CH(CH3)22H); 1.82 (d ofReferences p.196Chapter 5 195sept, CH(CH3)22H); 1.69 (m, PCH2 2H); 1.82 (d of sept, CH(CH3)2, 2H); 1.51 (m,PCH2,2H); 1.21 (m, PCH2C 2H); 1.11 (dd, CH(CH3)26H); 1.05 (dd, CH(CH3)26H); 0.98 (dd, CH(CH3)26H); 0.87 (dd, CH(CH3)26H). 31P{1H) NMR (C6D,6,ppm): 27.0 (d, A,2Jp,p = 11.2 Hz); 21.4 (d, B,2Jpçp = 11.2 Hz). 13C{H) NMR(C6D,6, ppm): 132.2 (Cm of Ph); 119.1 (C1of Ph); 117.8 (C of Ph); 105.1 (d, C0 ofPh, 2J,p = 7.7 Hz); 34.8 (ddd, CH2Ph,1JCh = 9.1 Hz; 2cp = 32.1 Hz; 2Jc = 2.5Hz); 29.8 (d, CH(CH3)); 25.6 (d, CH(CH3)); 23.9 (d, ligand backbone); 21.1 (d,CH(CH3)); 20.9 (d, CH(CH3)); 20.5 (d, ligand backbone); 20.2 (d, ligand backbone);20.0 (dd, CH(CH3)); 19.3 (d, CH(CH3)).5.6.18 {dippp}Ir(CHPh)(4-),16. 50 mg of 15 was weighed into areactor bomb and 10 mL hexanes added. The solution was degassed three times andexcess 1 ,3-butadiene added. The colour of the solution turned pale yellow instantly.111 NMR (C6t7,6, ppm): 7.26 (t, Hm, 2H); 7.20 (d, H0, 2H); 6.99 (t, H, 1H); 5.41(m, 111); 3.91 (m, Hcentrai, 1H); 2.68 (d oft, 1H); 2.57 (d oft, 1H);2.35 (d of sept, CH(CH3)21H); 2.21 (d of sept, CH(CH3)21H); 2.11 (s, CH2Ph,2H); 1.98 (d of sept, CH(CH3)21H); 1.92 (m, PCH2 2H); 1.90 (d of sept,CH(CH3)2,1H); 1.52 (m, PCH2 2H); 1.31 (m, PCH2C 2H); 1.27 (d of d,CH(CH3)2,3H); 1.13 (d of d, CH(CH3)23H); 1.11 (d of d, CH(CH3)23H); 1.09 (d ofd, CH(CH3)23H); 1.01 (d of d, CH(CH3)23H); 0.98 (d of d, CH(CH3)23H); 0.93 (dof d, CH(CH3)23H); 0.89 (d of d, CH(CH3)23H); 0.45 (m, Hj, 1H); 0.11 (m,114). 31P{lH} NMR (C6D,6, ppm): -2.8 (d, A,2Jp,p’ = 8.0 Hz); -17.7 (d, B,2Jp’,p 8.0 Hz).5.6.19 Preparation of Cy2PCHy. To a mechanically stirred solution ofC6H11MgC1 (429 mL, 1 M) in Et20 (500 mL) at 0°C in a 1 L, 3-necked flask wasadded dropwise an ether (100 mL) solution ofC12PCH1 (15.00 g, 53.6 mmol) over2 hours (cyclohexyl Grignard was prepared from cyclohexyichioride and excessReferences p.196Chapter 5 196magnesium in ether at 0°C). The mixture was stirred for an additional 2 hours. Theexcess Grignard was destroyed by adding 500 mL of degassed H20 (saturated withNH4C1) dropwise at 0°C. The ethereal layer was separated from the aqueous layerand dried with sodium sulfate (10 g Na2SO4). The ether was removed under vacuumto yield 13.2 g crude Cy2PCH2PCy2 (61%). The product can be recrystallized fromether at -40°C. 31P{1H} NMR (C6D,3, ppm): -11.1 (s). The 31P{1H} NMRspectrum compares well to the spectrum of material prepared by a different route.455.7 References(1) Lau, K. S. Y.; Becker, Y.; Huang, F.; Baenziger, N.; Stifle, 3. K. J. Am. Chem.Soc. 1977, 99, 5664.(2) Burch, R. R.; Muetterties, E. 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Chem. Soc. 1969, 91, 1339.(16) Fryzuk, M. D.; Piers, W. E.; Einstein, F. W. B.; Jones, T. Can. J. Chem. 1989,67,883.(17) Fryzuk, M. D.; Jones, T.; Einstein, F. W. B. Organometallics 1984,3, 185.(18) Fryzuk, M. D.; Rosenberg, L.; Rettig, S. J. Organometallics 1991, 10, 2537.(19) Fryzuk, M. D. Organometallics 1990,9, 1359.(20) Fryzuk, M. D.; Piers, W. E.; Rettig, S. 3.; Jones, T.; Einstein, F. W. B.;Aibright, T. S. J. Am. Chem. Soc. 1989, 111, 5709.(21) Fryzuk, M. D.; Piers, W. E. Polyhedron 1988, 7, 1001.(22) Fryzuk, M. D.; Piers, W. E. Organomet. Synth. 1986,3, 128.(23) Clark, E. P. Indust. Eng. Chem., Anal. Chem. 1941, 13, 820.References p.196Chapter 5 198(24) Van Gaal, H. L. M.; Van Den Bekerom, F. L. A. J. Organomet. Chem. 1977,134,237.(25) Yosbida, T.; Okano, T.; Otsuka, S. J. Organomet. Chem. 1978, 134, 237.(26) Muetterties, E. L.; Tau, K. D.; Kirner, 3. F.; Harris, T. V.; Stark, 3.; Thompson,M. R.; Day, V. W. Organometallics 1982, 1, 1562.(27) Fryzuk, M. D.; Joshi, K.; Rettig, S. 3. Polyhedron 1989,8, 2291.(28) Nixon, J. F.; Pidcock, A. Ann. Rev. NMR Spectrosc. 1969,2, 345.(29) Meek, D. W.; Mazanec, T. 3. Acc. Chem. Res. 1981, 14, 266.(30) Brookes, P. R.; Shaw, B. L. J. Chem. Soc. (A) 1967, 1079.(31) Meier, E. C.; Burch, R. R.; Muetterties, E. L.; Day, V. W. J. Am. Chem. Soc.1982, 104, 2661.(32) Fryzuk, M. D.; MacNeil, P. A. Organometallics 1983,2, 682.(33) Mann, B. E.; Masters, C.; Shaw, B. L. J. Chem. Soc., Chem. Commun. 1970,846.(34) Antonelli, D. M.; Cowie, M. Inorg. Chem. 1990,29, 4039.(35) McDonald, R.; Cowie, M. Inorg. Chem. 1990,29, 1564.(36) Woodcock, C.; Eisenberg, R. Inorg. Chem. 1984,23, 4207.(37) Oshida, T.; Okano, T.; Thorn, D. L.; Tulip, T. H.; Otsuka, S.; Ibers, 3. A. J.Organomet. Chem. 1979, 181, 183.References p.196Chapter 5 199(38) McDonald, R.; Sutherland, B. R.; Cowie, M. Inorg. Chem. 1987,26, 3333.(39) Antonelli, D. M.; Cowie, M. Organometallics 1990, 9, 1818.(40) Chatt, 3.; Venanzi, L. M. J. Chem. Soc. 1957, 4753.(41) Van Der Ent, A.; Onderlinden, A. L. Inorg. Synth. 1973, 14, 94.(42) Schrock, R. R. J. Organomet. Chem. 1976, 122, 209.(43) Tani, K.; Tanigawa, E.; Tatsubo, Y.; Otsuka, S. J. Organomet. Chem. 1985,279, 87.(44) Novikova, Z. S.; Prishchenko, A. A.; Lutsenko, I. F. J. Gen. Chem. USSR 1977,707.(45) Priemer, H. Ph. D. Dissertation Thesis, Universität Bochum, 1987.References p.196Appendix 200AppendixA.1 Details of the Molecular Orbital AnalysesA.1.1 Extended Hückel Parameters.Orbital H1, eV C2 C1 C2H is -13.60 1.30C2s -21.40 1.625C2p -11.40 1.625N 2s -26.00 1.95N2p -13.40 1.95P 3s -18.60 1.60P3p -14.00 1.60Cl 3s -26.30 2.183C13p -14.20 1.733Zr 5s -9.87 1.817Zr 5p -6.76 1.776Zr4d -11.18 3.8350 1.5050 0.6210 0.5769Ta 6s -10.10 2.280Ta6p -6.86 2.241Ta 5c1 - -12.10 4.7620 1.9380 0.6815 0.5774A.1.2 Labelled model of [(H3P)2TaH2}2(1.L-H),2’, showing connectivity.H16H7HiSHlOHi iH24P6H8Hi 2Hi9H9Hi 4 H20Appendix 201A.1.3 Cartesian Coordinates for [(H3P)2TaH2](p.-H),2’AtomType X Y ZTa(1) -1.275 -0.002 0.004Ta(2) 1.275 0.002 -0.005P(3) -3.007 -0.984 1.677P(4) -3.022 0.973 -1.655P(5) 3.022 -0.973 1.655P(6) 3.007 0.984 -1.677H(7) -1.664 1.512 0.896H(8) -1.665 -1.518 -0.884H(9) 1.664 -1.512 -0.896H(10) 1.665 1.518 0.884H(11) -0.004 1.311 -0.341H(12) 0.004 -1.311 0.341H(13) -2.828 -0.406 2.917H(14) -2.828 -2.349 1.775H(15) -4.284 -0.71 1225H(16) -2.850 2.339 -1.755H(17) -2.850 0.395 -2.897H(18) -4.295 0.703 -1.195H(19) 4.295 -0.703 1.195H(20) 2.850 -2.338 1.755H(21) 2.850 -0.395 2.897H(22) 4.284 0.719 -1.225H(23) 2.828 0.406 -2.917H(24) 2.828 2.349 -1.775Appendix 202A.1.4 INDOI1 eigenvalues and symmetries for[(H3P)2ZrC1(NH)]2(t-N2).Energy (eV) Symmetry Energy (eV) Symmetry0.267 l3ag-14.792 7ag-0.142 8a -16.217 5a-0.427 9a -16.231 4bg-6.937 8bg 16.954 4a-8.483 12b -17.028 5b-8.746 l2ag-17.029 6ag-9.052 7a -17.080 4b-9.059 11b -17.090 3bg9.103 7bg-17.524 Sag-9.140 hag-18.628 3a9.453 10b -18.644 2bg.9.779 lOag-21.393 2au-10.329 6bg-21.877 4ag-11.164 9b -21.898 3b=11.829 9ag-26.662 2b-12.540 6a -26.759 3ag12.553 5bg-27.093 lbg-12.602 8b -27.523 1a-12.629 8ag-33.591 2ag-13.111 7b -33.655 1b-13.381 6b -38.747 lagThe HOMO is 8bg (-6.937 eV), the LUMO is 9a (-0.427 eV).Appendix 203A.1.5 Labelled model of[(H3P)2ZrCl(NH)](i- showing connectivity.H13Hi 1H25H20H17A.1.6 Cartesian coordinates for[(H3P)2ZrC1(NH)](Ii-N2).Atom Type X Y ZZr(1) -1.870 0.003 -0.004Zr(2) 1.870 -0.003 0.004P(3) -2.816 2.458 0.862P(4) -2.819 -2.450 -0.874P(5) 2.816 -2.458 -0.862P(6) 2.819 2.450 0.874N(7) -2.607 0.684 -1.928N(8) 2.607 -0.684 1.928N(9) 0.000 0.730 0.258N(10) 0.000 -0.730 -0.258H(1 1) -3.779 2.264 1.83 1H(12) -1.773 3.192 1.390H(13)-3.365 3.141 -0.204H(14) -3.369 -2.310 -2.132H(15) -1.778 -3.354 -0.925Hi 2 H21H24H23CI 27H22N9C128H26HN1ONBH16 H15H19H18continuedAppendix 204A.1.6 continued______________________________________________H(16) -3.783 -2.907 0.002H(17) 3.365 -3.141 0.204H(18) 1.773 -3.192 -1.390H(19) 3.779 -2.264 -1.831H(20) 3.783 2.907 -0.002H(21) 1.778 3.354 0.925H(22) 3.369 2.311 2.132H(23) -2.790 -0.022 -2.711H(24) -2.788 1.725 -2.093H(25) 2.788 -1.725 2.093H(26) 2.790 0.022 2.711C1(27) -2.727 -0.776 2.200C1(28) 2.727 0.776 -2.200A.1.7 Labelled model of (H3P)2ZrC1(NH2) showing connectivity.H13N4Hi 2H8P2Hi iPH7H9H1OC15Appendix 205A.1.8 Cartesian coordinates for(H3P)2ZrC1(NH).AtomType X Y ZZr(1) -0.252 0.485 0.718P(2) -2.870 -0.120 0.044P(3) 2.336 -0.167 -0.025N(4) -0.268 1.521 -1.194Cl(5) -0.261 -1.834 1.634H(6) -3.169 0.437 -1.183H(7) -3.023 -1.490 -0.024H(8) -3.721 0.392 1.002H(9) 3.222 0.329 0.910H(10) 2.462 -1.539 -0.096H(11) 2.613 0.385 -1.259H(12) 0.655 1.767 -1.677H(13) -1.198 1.784 -1.652A.1.9 Labelled model of(H3P)2Ta(=CH)(NH showing connectivity.Hi 1C5H14H7H6HiOH8p3H 9tN4Hi 2 H13Appendix 206A.1.1O Cartesian coordinates for(H3P)2Ta(=CH)(NH.AtomType X Y ZTa(1) -0.218 -0.267 0.542P(2) -2.312 -0.218 -1.270P(3) 2.551 -0.272 0.585N(4) 0.044 -2.293 -0.204C(5) 0.020 1.561 -0.028H(6) -3.495 0.017 -0.600H(7) -2.100 0.785 -2.193H(8) -2.386 -1.433 -1.921H(9) 3.016 -1.493 0.140H(10) 3.026 0.729 -0.238H(1 1) 2.992 -0.055 1.875H(12) -0.757 -2.782 -0.718H(13) 0.975 -2.800 -0.058H(14) 0.403 1.775 -1.026H(15) -0.229 2.3-79 0.647A.2 X-ray Crystallographic Analysis of [{dippp}TaClH](p.-H)-SC7 CI SC3C13Appendix 207Table 1 Crystallographic ParametersFormulaCryst color, forma(A)b(A)c(A)P (deg)Cryst systSpace groupVol (As)Density (gcni3)calcd.zCryst dimens (mm)Abs coeff, Il (cmi)Rediation ,Temp (C)Scan speed (deg/min)Scan range (deg)Bkgd/scan time ratioData collectedDataF02>3o(F)No. of variablesR (%)R1,, (%)Largest 8/ in finalleast squares cycleMax.. res id - electron density (e/A3)Atom associatedC3OB7C12P4STa2black blocks10.730(2)15.653(2)13.402(3)110.78(2)monocl in IcP21/c2104.6(7)1.6120.54 x 0.50 x 0.4252.85Mo ICc (0.71069)242.0—7. 0(O/2Oscan)1.0 below ICc11.0 above 1Ca20.5303923651816.146.650.0062.2TaAppendix 208Table 2 Positional Parameters88multiplied by 10’Atom x y z Atom x y zTa 80(0) 5143(0) 1010(0) Cl—164(3) —1137(2) 2972(2)S —2117(6) 6(4) 4527(5) P1 —2003(3) 856(2) 2422(2)P2 1681(3) 843(2) 3302(3) Cl —1523(16) 1548(8) 1535(10)C2 —284(17) 1292(12) 1308(11) C3 1059(14) 1529(9) 2151(11)C4 —3108(17) 1571(10) 2922(17) C5 —2304(18) 2234(10> 3644(16)C6 —4145(16) 2019(12) 1879(22) C7 —3253(18) 141(10) 1402(22)C8 —2782(24) —341(14) 688(15) C9 —3836(19) —478(13) 2067(23)ClO 2787(25) 89(13) 2827(33) Cli 2162(35) —387(18) 1871(29)C12 3436(22) —558(14) 3832(30) C13 2923(16) 1562(12) 4338(22)C14 2191(19) 2215(10) 4780(17) C15 3845(22) 1983(13) 3810(27)Table 3: Selected Bond Distances and AnglesDistances (A)Ta—Ta 2689(1) Ta—Cl 2. 409(3) Ta—Pi 2.616(3)Ta—P2 2.613(3) Ta—S 2.537(5) Ta—S’ 2.541(5)P1—Cl 1.81(1) C1—C2 1.52(2) P2—C3 1.80(1)C2—C3 1.53(2) Pl—C4 192(2) C4—C5 1.47(2)C4—C6 1.61(2) P1—C7 1.90(2) C7—C8 1.44(3)C7—C9 1.59(3) P2—dO 1.94(2) ClO—Cil 1.43(4)C10—C12 1.63(4) P2—C13 1.91(1) C13—C14 1.53(3)C13—C15 1.54(3)Appendix 209Angles (deg)P1—Ta-ClS-Ta-ClS-Ta—P1Ta-S-TaTa—P1—C4Ta—P2—C3Ta—P2—C 13C7-P1—C1C10-P2-C3C13—P2-C10C3 -C2 -ClC5—C4-P1C6—C4-C5C9-C7—P1Cl 1—C1O—P2C12—C10--C11C15—C1 3—P292.1(1)103.0(2)75.5(1)64.1(2)113.2(6)116.8(4)112.9(8)100 (1)100 (1)104 (1)117 (1)111 (1)109 (1)106 (2)118 (2)110 (2)111 (1)P2 -Ta-ClP2 -Ta-PiS-Ta-P2Ta—Pi-CiTa—Fl -C7Ta—P2-C 10Cl—P 1—C4C7—P1—C4C13—P2—C3C2—C1—P1C2—C3-P2C6-C4-P1C8-C7-P1C9-C7-C8C12—C10—P2C14-C13—P2C14—C13—C1592.1(1)90.1(1)159.4(1)117.1(5)119.6(5)116.8(4)103.6(7)103.2 (9)102.8 (8)116.5 (9)117 (1)106 (1)117 (2)•111 (2)104 (2)111 (1)113 (2)Appendix 210A.3 X-ray Crystallographic Analysis of [{dippp}TaClH]2(p-H)Appendix 211EXPERIMENTAL DETAILSA. Crystal DataEmpirical FormulaFormula WeightCrystal Color, HabitCrystal Dimensions (mm)Crystal SystemNo. Reflections Used for UnitCell Determination (2 range)Omega Scan Peak Widthat Half—heightLattice Parameters:F00011(MoKa)DiffractometerRadiationTemperatureTake—off AngleDetector ApertureC30H7212P4Ta989.60green, prism0.070 X 0.200 X 0.250mono c 1 in i c25 ( 32.9 — 41.5°)0.35a — 11.576 (2)Ab — 12.434 (3)Ac — 14.913 (3)A— 107.49 (1)°V = 2047 (1)A3P21/c (*14)21.605 g/cm398421°CSpace GroupZ value55.82 cmB. Intensity MeasurementsRigaku AFC6SMoKa (X — 0.71069 A)6.0°6.0 mm horizontal6.0 mm verticalAppendixScan WidthNo. of Reflections MeasuredCorrections285 mmco— 288.0°/mm (in omega)(8 rescans)(1.31 + 0.35 tane)°60.2°Total: 6478Unique: 6200 (Rt — .054)Lorentz—polarizationAbsorption(trans. factors: 0.45 — 1.00)Decay (—11.00% decline)Secondary Extinction(coefficient: 0.98057E—07)RefinementPatterson MethodFull—matrix least—squaresE w (Fo1 — lFcI)24F02/ci(F02)0.02All non—hydrogen atoms352017320.350.027; 0.0261.190.005076 e/A3—0.64 e/A3Crystal to Detector DistanceScan TypeScan Rate212C. Structure Solution andStructure SolutionRefinementFunction MinimizedLeast—squares Weightsp—factorAnomalous DispersionNo. Observations (I>3.00(I))No. VariablesReflection/Parameter RatioResiduals: R; RGoodness of Fit IndicatorMax Shift/Error in Final CycleMaximum Peak in Final Diff. flapMinimum Peak in Final Diff. MapAppendix 213Table . Final atomic coordinates (fractional) and Beq 2)*Ta ( 1)Cl(1)P(1)P(2)C(1)C(2)C(3)C(4)C(S)C(6)C(7)C(8)C(9)C(10)C(1l)C(12)C(13)C(14)C(15)H(1)H(2)0.49681(2)0.4972(1)0.6687(1)0.3166(1)0.6064(4)0.4880(5)0.3732(5)0.7740(5)0.7671(5)0.2079(5)0.2217(5)0.8626(5)0.7054(6)0.8162(5)0.8701(6)0.2723(6)0.1201(6)0.1830(5)0.1136(6)0. 48760. 58530.40067(2)0.2645(1)0.2842(1)0.2896(1)0.1743(5)0.1216(4)0.1799(5)0.3470(5)0.2079(5)0.3547(5)0.2134(5)0.4232(5)0.4063(6)0.2758(5)0.1447(6)0.4152(6)0.4294(6)0.2797(6)0.1532(6)0. 39240.50970.47755(1)0.5979(1)0.44792(9)0.37077(9)0.3658(4)0.3717 ( 4)0.3128(4)0.3906(4)0.5498(4)0.2677(4)0.4301(4)0.4548(5)0.2998(4)0.6393(4)0.5303(5)0.2070(4)0.2963(5)0.5021(4)0.3653(5)0. 37540. 4663Beq2.233(7)3.65(6)2.57(5)2.66(5)3.5(2)3.8(2)3.7(2)3.3(2)3.7(2)3.4(2)3.6(2)4.6(3)4.4(3)4.3(3)5.8(4)4.8(3)4.9(3)4.2(3)5.3(3)2.72.7*8— (8/3)nEEUjjai*a*(aj.aj)eqatom x y zAppendixTable . Bond angles (deg) with estimated standard deviations.214atom atom - atom angle atom atom atom angleTa(l)* Ta(1) Cl(l) 118.65(4) C(l) P(1) C(4) 100.7(3)Ta(1)* Ta(1) PCi) 128.24(3) C(l) P(1) C(5) 100.8(3)Ta(i)*Ta(1) P(2) 128.84(3) C(4) PCi) C(5) 105.3(2)Ta(1)* Ta(l) H(i) 109 Ta(1) P(2Y C(3) 110.3(2)Ta(l)* Ta(1) H(2) 46 Ta(l) P(2) C(6) 119.6(2)Ta(1)* Ta(1) H(2)* 43 Ta(1) P(2) CU) 117.2(2)C1(l) Ta(1) PCi) 84.68(5) C(3) P(2) C(6) 100.5(3)Cl(l) Ta(1) P(2) 84.66(5) C(3) P(2) C(7) 101.0(3)Cl(i) Ta(1) 11(1) 133 C(6) P(2) C(7) 105.4(2)Cl(1) Ta(1) 11(2) 137 P(1) C(i) C(2) 117.1(4)C1(1) Ta(1) H(2)* 88 C(l) C(2) C(3) 113.3(5)P(i) Ta(1) P(2) 96.S2(4) P(2) C(3) C(2) 116.8(4)P(l) Ta(1) 11(1) 67 P(l) C(4) C(8) 112.8(4)P(1) Ta(1) H(2)* 85 P(l) C(4) C(9) ii1.(4)P(1) Ta(1) 11(2) 161 C(8) C(4) C(9) 109.3(5)P(2) Ta(1) 11(1) 63 PCi) C(S) C(10) 113.9(4)P(2) Ta(1) 11(2) 138 P(1) C(5) C(11) 115.3(4)P(2) Ta(1) H(2)* 100 C(10) C(S) C(i1) 110.0(5)H(i) Ta(i) 11(2) 80 P(2) C(6) C(12) 112.0(4)11(1) Ta(1) B(2)* 128 P(2) C(6) C(13) 112.1(4)11(2) Ta(1) H(2)* 88 C(12) C(6) C(13) 110.4(5)Ta(1) P(1) C(i) 111.2(2) P(2) C(7) C(14) 113.5(4)Ta(1) P(1) C(4) 119.0(2) P(2) C(7) C(15) 115.8(4)Ta(1) P(1) C(S) 117.2(2) C(14) C(7) C(15) 110.7(5)Appendix 215Table. Bond lengths (A) with estimated standard deviations.atom distanceC(7) 1.863(5)C(2) 1.546(7)C(3) 1.537(8)C(S) 1.509(8)C(9) 1.537(8)C(l0) 1.537(8)C(11) 1.528(8)C(12) 1.531(8)C(13) 1.530(8)C(14) 1.525(8)C(lS) 1.528(8)atom atom distance atomTa(1) Ta(1)* 2.5547(7) P(2)Ta(1) C1(1) 2.466(2) C(1)Ta(1) P(1) 2.603(1) C(2)Ta(1) P(2) 2.608(1) C(4)Ta(1) H(1) 1.50 C(4)Ta(1) H(2) 1.74 C(S)Ta(1) H(2)* 1.82 C(S)P(1) C(1) 1.832(6) C(6)P(1) C(4) 1.858(5) C(6)P(1) C(5) 1.863(6) C(7)P(2) C(3) 1.838(6) C(7)P(2) C(6) 1.855(5)* Refers to symmetry operation: 1—x,1—,1—zA.4 X-ray(here and elsewhere).C’sezoC9Cli C4ciCaCi4Ci5Appendix 216EXPERIMENTAL DETAILSA. Crystal DataEmpirical FormulaFormula WeightCrystal Color, HabitCrystal Dimensions (mm)Crystal SystemNo. Reflections Used for UnitCell Determination (2 range)Omega Scan Peak Widthat Half—heightLattice Parameters:Space GroupZ value‘‘(MoKcc)DiffractometerRadiationTemperatureTake—off AngleDetector ApertureC44H8PRh2Zn1073.61brown, prism0.250 X 0.300 x 0.340monoclinic25 ( 20.1 — 27.00)0.39a 19.608 (7)Ab = 12.891 (6)Ac = 22.847 (6)AS = 120.02 (2)°V — 5001 (3)AC2/c (*15)41.426 g/cnt3223217.65 cmB. Intensity MeasurementsRigaku AFC6SMoK (X — 0.71069 A)21°C6.006.0 nun horizontal6.0 mm verticalAppendix 217Scan Width2emaxNo. of Reflections MeasuredCorrectionsStructure SolutionRefinementFunction MinimizedLeast—squares Weightsp—factorAnomalous DispersionNo. Observations (I>3.00(I))No. VariablesReflection/Parameter RatioResiduals: R; RGoodness of Fit Indicator‘1ax Shift/Error in Final CycleMaximum Peak in Final Diff. MapMinimum Peak in Final Diff. Map32.0°/mm (in omega)(8 rescans)(1.05 + 0.35 tan8)°55.00Total: 6185Unique: 6009 (Rmt = .071Lorentz—polarizationAbsorption(trans. factors: 0.84 — 1RefinementPatterson MethodFull—matrix least—squaresL w (IFol— jFcI)24Fo2/u(Fo2)0.03All non—hydrogen atoms277323911.600.044; 0.0481.640.031.46 e/A3—1.19Crystal to Detector DistanceScan TypeScan Rate285 mmc— 2 eC. Structure Solution andAppendix 218Table . Final atomic coordinates (fractional) and B(eq)z B(eq)Rh(1) 0.42356(3) 3.03(2)Zn(l) 0.46718(5) 4.60(4)PCi) 0.3368(1) 3.56(7)P(2) 0.3415(1) 3.53(7)C(1) 0.2417(4) 5.4(3)C(2) 0.2039(5) 7.8(5)C(3) 0.2423(4) 4.8(3)C(4) 0.3025(4) 4.4(3)C(S) 0.3729(4) 4.6(3)C(6) 0.3178(4) 4.8(4)C(7) 0.3822(4) 4.8(3)C(8) 0.2581(5) 6.3(4)C(9) 0.3683(5) 5.9(4)C(l0) 0.4024(6) 7.0(5)C(11) 0.3157(6) 7.2(5)C(12) 0.2751(5) 5.9(4)C(13) 0.3905(5) 6.5(5)C(14) 0.4023(5) 6.5(4)C(15) 0.3331(6) 7.4(5)C(16) 0.4117(5) 6.9(5)C(17) 0.4467(4) 4.6(4)C(18) 0.4400(5) 6.7(5)C(19) 0.4723(7) 8.5(6)C(20) 0.5137(7) 8.2(6)C(21) 0.5229(6) 7.4(5)C(22) 0.4878(5) 6.3(5)H(1) 0.528(6) 12(3)atom x y0.55656(4) 0.19637(3)0.44026(7) 0.29722(5)0.4812(1) 0.0977(1)0.6827(2) 0.1928(1)0.5461(7) 0.0452(4)0.5976(8) 0.0805(5)0.6955(6) 0.1179(4)0.3469(6) 0.0990(4)0.4678(6) 0.0364(4)0.6905(6) 0.2615(4)0.8133(6) 0.1953(4)0.3416(7) 0.1370(5)0.2675(6) 0.1257(5)0.5709(8) 0.0262(4)0.4164(8) —0.0317(4)0.5933(7) 0.2630(5)0.7107(8) 0.3302(4)0.8259(7) 0.1399(5)0.9051(7) 0.1960(6)0.3575(7) 0.3362(5)0.2574(7) 0.3695(5)0.1720(9) 0.3334(5)0.0808(9) 0.3621(7)0.071(1) 0.4293(7)0.150(1) 0.4706(5)0.2472(8) 0.4401(5)0.594(7) 0.237(6)Appendix 219Table . Bond angles (deg) with estimatedparentheses.standard deviations inatom atom atom angle atom atom atom angleRh(1)* Rh(1) Zn(1) 57.76(3) Rh(1) P(1) C(5) 114.2(2)Rh(1)*Rh(1) Zn(1)* 56.19(3) C(1) P(1) C(4) 100.2(4)Rh(1)* Rh(1) P(1) 145.85(6) C(l) P(1) C(5) 101.2(4)Rh(1)*Rh(1) P(2) 117.95(5) C(4) P(1) C(5) 101.6(3)Rh(1)* Rh(1) 11(1) 27(3) Rh(1) P(2) C(3) 119.9(3)Rh(1)*Rh(1) li(1)* 37(4) Rh(l) P(2) C(6) 119.1(3)Zn(1) Rh(1) Zn(1)* 72.94(4) Rh(l) P(2) C(7) 111.3(3)Zn(1) Rh(1) P(1) 113.58(6) C(3) P(2) C(6) 100.7(4)Zn(1) Rh(1) P(2) 111.82(6) C(3) P(2) C(7) 100.7(3)Zn(1) Rh(1) 11(1) 85(3) C(6) P(2) C(7) 102.3(4)Zn(1) Rh(1) R(1)* 59(4) P(1) C(1) C(2) 117.8(6)Zn(1)* Rh(1) P(1) 89.77(6) C(1) C(2) C(3) 116.0(8)Zn(1)* Rh(1) P(2) 169.86(6) P(2) C(3) C(2) 116.7(5)Zn(1)* Rh(1) H(1) 56(3) P(1) C(4) C(8) 111.6(6)Zn(1)* Rh(1) H(1)* 92(4) P(1) C(4) C(9) 113.1(5)P(1) Rh(1) P(2) 96.12(7) C(8) C(4) C(9) 111.0(7)P(1) Rh(1) H(1) 136(3) P(1) C(5) C(10) 110.6(5)P(1) Rh(1) H(1)* 171(3) P(1) C(S) C(11) 116.1(6)P(2) Rh(1) H(1) 115(3) C(10) C(S) C(11) 111.3(7)P(2) Rh(1) H(1)* 83(4) P(2) C(6) C(12) 110.5(6)11(1) Rh(1) H(1)* 52(6) P(2) C(6) C(13) 112.4(5)Rh(1) Zn(1) Rh(1)* 66.05(4) C(12) C(6) C(13) 111.0(7)Rh(1) Zn(1) C(16) 135.0(3) P(2) C(7) C(14) 111.2(6)Rh(1)* Zn(1) C(16) 1S4.7(3) P(2) C(7) C(15) 116.0(6)Rh(1) P(1) C(1) 117.9(3) C(14) C(7) C(15) 110.7(7)Rh(1) P(1) C(4) 118.9(3) Zn(1) C(16) C(17) 118.3(6)Appendix 220Table . (continued)atom atom atom angle atom atom atom angleC(16) C(17) c(18) 121(1) C(19) C(20) C(21) 121(1)c(16) C(17) C(22) 122(1) c(20) C(21) C(22) 118(1)C(18) C(17) C(22) 116.9(8) c(17) C(22) C(21) 120(1)C(17) C(18) c(19) 123(1) Rh(1) H(1) Rh(l)* 116(5)C(1B) C(19) C(20) 121(1)Table . Bond lengths (A)in parentheses.with estimated standard deviationsatom atom distance atomRh(1) Rh(1)* 2.764(1) C(4)Rh(1) Zn(1) 2.513(1) C(4)Rh(1) Zn(1)* 2.558(1) C(S)Rh(1) PCi) 2.255(2) C(5)Rh(1) P(2) 2.261(2) C(6)Rh(1) H(1) 1.8(1) C(6)Rh(1) H(1)* 1.4(1) C(7)Zn(1) C(16) 2.020(8) C(7)P(1) C(1) 1.838(8) C(16)P(1) C(4) 1.862(8) C(17)P(1) C(5) 1.867(8) C(17)P(2) C(3) 1.846(7) C(18)P(2) C(6) 1.847(8) C(19)P(2) C(7) 1.852(8) C(20)C(1) C(2) 1.49(1) C(21)C(2) C(3) 1.50(1)atomC(8)C(9)C(10)C(11)C(12)C(13)C(14)C(15)C(17)C(18)C(22)C(19)C(20)C(21)C(22)distance1.51(1)1.52(1)1.51(1)1 .54( 1)1.52(1)I tfI •.4.._,.,1.51(1)1.53(1)1.48(1)1.34(1)1.40(1)1.34(1)1.34(1)1.35(2)1.43(1)* Symmetry operation: 1—xy1/2—z.AppendixA.5 X-ray Crystallographic Analysis of [{dippp)Rh]2(j.i.-H) 2( L- Zn C p ) 2cliCA. Crystal Data221Empirical FormulaFormula WeightCrystal Color, HabitCrystal Dimensions (mm)Crystal SystemNo. Reflections Used for UnitCell Determination (28 range)Omega Scan Peak Widthat Half—heightC47H88PRh2Zn1113.68orange, prism0.200 x 0.300 x 0.400monoclini c25 ( 30.0 — 35.8°)C13C6ciaC15EXPERIMENTAL DETAILS0.38Appendix 222Lattice Parameters:a 12.050 (6)Ab = 35.230 (4)Ac = 12.414 (2)A= 97.84 (3)°V = 5221 (3)ASpace Group P21/n (#14)Z value 4Dcalc 1.417 g/cm3F000 232011(MoKcx) 16.93 cm’B. Intensity MeasurementsDiffractometer Rigaku AFC6SRadiation MoKa (X = 0.71069 A)Temperature 21°CTake—off Angle 6.00Detector Aperture 6.0 mm horizontal6.0 mm verticalCrystal to Detector Distance 285 mmScan TypeScan Rate 16.0°/mm (in omega>(8 rescans)Scan Width (1.13 + 0.35 tane)°2emax 55.0°No. of Reflections Measured Total: 12761Unique: 12197 (Rmt .03Corrections Lorentz—polari zationAbsorption(trans. factors: 0.90 — 1Decay ( —2.40% decline)Appendix 223C. Structure Solution andStructure SolutionRefinementFunction MinimizedLeast—squares Weightsp—factorAnomalous DispersionNo. Observations (I>3.OOG(I))No. VariablesReflection/Parameter RatioResiduals: R; RGoodness of Fit IndicatorMax Shift/Error ifl Final CycleMaximum Peak in Final Diff. MapMinimum Peak in Final Diff. 1’lapRefinementPatterson MethodFull—matrix least—squaresE w (IFol — IFCI)24Fo2/()0.01All non—hydrogen atoms614350512.160.032; 0.0291.520.050.48 e/A3—0.53 e43Table. Final atomic coordinates (fractional) and Beq 2)*0CC.atom x z BeqRh(1) 0.49163(3) 0.154958(9) 0.32386(3) 3.14(1)Rh(2) 0.63513(3) 0.110973(9) 0.19497(3) 2.93(1)Zn(1) 0.49790(5) 0.15914(1) 0.11474(4) 4.33(3)Zn(2) 0.44451(4) 0.09205(1) 0.22042(4) 3.76(2)PCi) 0.3473(1) 0.18077(3) 0.3956(1) 4.05(6)P(2) 0.6220(1) 0.19856(3) 0.3953(1) 3.87(6)P(3) 0.6751(1) 0.09406(3) 0.0264(1) 3.58(5)P(4) 0.7361(1) 0.06290(3) 0.2900(1) 3.46(5)C(i) 0.3793(4) 0.2182(1) 0.4981(4) 5.8(3)C(2) 0.4582(5) 0.2483(2) 0.4674(5) 7.3(3)C(3) 0.5805(4) 0.2369(1) 0.4841(4) 5.4(3)Appendix 224Table . Final atomic coordinates (fractional) and Beg 2)*atom x y z Beg 0CC.0.640.36C(4) 0.2731(4) 0.1453(1) 0.4701(4) 4.9(3)c(5) 0.2365(5) 0.2032(2) 0.2979(6) 7.5(4)C(6) 0.7020(5) 0.2275(1) 0.3060(4) 5.7(3)C(7) 0.7337(4) 0.1749(1) 0.4898(4) 4.8(2)C(8) 0.3574(5) 0.1219(2) 0.5452(4) 6.9(3)c(9) 0.1824(5) 0.1605(2) 0.5338(5) 8.7(4)C(10) 0.1691(5) 0.1741(2) 0.2248(5) 7.1(3)C(11) 0.167(1) 0.2344(3) 0.325(1) 8.1(7)C(11A) 0.242(2) 0.2380(6) 0.272(1) 8(1)C(12) 0.7773(5) 0.2036(2) 0.2454(5) 7.6(3)C(13) 0.6203(6) 0.2514(2) 0.2288(5) 8.3(4)C(14) 0.6835(5) 0.1537(2) 0.5771(4) 6.4(3)c(15) 0.8315(5) 0.2000(2) 0.5390(5) 7.5(3)C(16) 0.7373(4) 0.0467(1) 0.0111(4) 4.6(2)C(17) 0.7290(4) 0.0187(1) 0.1029(4) 4.9(2)C(18) 0.8037(4) 0.0294(1) 0.2078(4) 4.7(2)c(19) 0.5618(4) 0.0935(1) —0.0913(3) 4.4(2)c(20) 0.7829(4) 0.1238(1) —0.0261(4) 4.4(2)C(21) 0.6484(4) 0.0311(1) 0.3650(4) 5.4(3)C(22) 0.8555(4) 0.0767(1) 0.3947(4) 4.3(2)C(23) 0.4703(5) 0.0653(2) —0.0724(4) 6.5(3)C(24) 0.5974(5) 0.0860(2) —0.2028(4) 6.6(3)C(25) 0.7395(5) 0.1632(2) —0.0632(4) 6.2(3)C(26) 0.8874(4) 0.1280(1) 0.0573(4) 5.7(3)C(27) 0.9280(4) 0.1064(2) 0.3502(4) 6.1(3)C(28) 0.9292(5) 0.0445(2) 0.4459(4) 6.9(3)C(29) 0.6195(4) 0.0498(1) 0.4678(4) 5.7(3)Appendix 225Table. Final atomic coordinates (fractional) and Beg 2)*atom x*Beg —y z Beg 0CC.C(30) 0.6740(6) —0.0101(2) 0.3771(5) 9.0(4)C(31) 0.3871(6) 0.1984(2) 0.0247(4) 6.4(3)C(32) 0.3176(6) 0.1709(2)—0.0300(6) 7.7(4)c(33) 0.3485(7) 0.1655(3)—0.1309(6) 9.2(5)C(34) 0.4347(7) 0.1898(3) —0.1408(6) 8.9(5)C(35) 0.4604(6) 0.2107(2)—0.0478(6) 7.5(4)C(36) 0.3580(4) 0.0397(1) 0.1904(4) 4.5(2)C(37) 0.2712(4) 0.0615(1) 0.1317(4) 4.8(2)C(38) 0.1950(4) 0.0701(2) 0.2015(5) 5.7(3)C(39) 0.2319(5) 0.0547(2) 0.3021(5) 6.1(3)C(40) 0.3302(5) 0.0359(1) 0.2971(4) 5.5(3)C(41) 1.0040(7) 0.1007(3) 0.7976(7) 8.4(5)C(42) 1.0560(5) 0.0814(3) 0.8835(6) 7.9(4)C(43) 1.0285(7) 0.0452(3) 0.9008(7) 9.2(5)C(44) 0.9473(8) 0.0274(2) 0.8282(9) 9.7(6)C(45) 0.8983(7) 0.0459(4) 0.7421(8) 10.8(6)C(46) 0.9257(8) 0.0841(3) 0.7256(6) 9.3(5)C(47) 1.0284(8) 0.1412(3) 0.7813(7) 12.7(6)Appendix 226Table . Selected bond lengths (A) and angles (deg) withestimated standard deviations.atom atom distance atom atom distanceRh(1) Rh(2) 2.9507(9) Zn(2) C(36) 2.127(4)Rh(1) Zn(1) 2.6115(8) Zn(2) C(37) 2.471(5)Rh(1) Zn(2) 2.5854(7) Zn(2) C(40) 2.659(5)Rh(1) P(1) 2.251(2) C(31) C(32) 1.396(8)Rh(1) P(2) 2.288(1) C(31) C(35) 1.411(8)Rh(2) Zn(1) 2.4812(9) C(32) C(33) 1.368(9)Rh(2) Zn(2) 2.453(1) C(33) C(34) 1.36(1)Rh(2) P(3) 2.290(1) C(34) C(35) 1.369(9)Rh(2) P(4) 2.313(1) C(36) C(37) 1.418(6)Zn(1) Zn(2) 2.8200(8) C(36) C(40) 1.416(6)Zn(1) C(31) 2.131(5) C(37) C(38) 1.379(6)Zn(1) C(32) 2.656(7) C(38) C(39) 1.380(7)Zn(1) C(35) 2.706(6)- C(39) C(40) 1.365(7)Rh(1) 11(1) 1.72 Rh(2) H(1) 1.74Rh(1) H(2) 1.57 Za(2) H(2) 1.66atom atom atom angle atom atom atom angleRh(2) Rh(1) Zn(1) 52.56(2) Rh(2) Zn(1) Zn(2) 54.68(3)Rh(2) Rh(1) Zn(2) 52.10(2) Rh(2) Zn(1) C(31) 172.0(2)Rh(2) Rh(1) P(1) 165.52(4) Zn(2) Zn(1) C(31) 128.5(2)Rh(2) Rh(1) P(2) 98.08(4) Rh(1) Zn(2) Rh(2) 71.64(2)Zn(1) Rh(1) Zn(2) 65.72(2) Rh(1) Zn(2) Zn(1) 57.58(2)Zn(1) Rh(1) P(1) 119.95(4) Rh(1) Zn(2) C(36) 154.1(1)Zn(1) Rh(1) P(2) 103.65(4) Rh(2) Zn(2) Zn(1) 55.61(2)Zn(2) Rh(1) PCi) 114.44(4) Rh(2) Zn(2) C(36) 131.2(1)Zn(2) Rh(1) P(2) 149.40(4) Zn(1) Zn(2) C(36) 141.5(1)P(1) Rh(1) P(2) 95.86(5) Zn(1) C(31) C(32) 95.4(4)Rh(1) Rh(2) Zn(1) 56.68(2) Zn(1) C(31) C(35) 97.6(4)Rh(1) Rh(2) Zn(2) 56.26(2) C(32) C(31) C(35) 106.8(6)Appendix 227atom atom atom angle atom atom atom angleRh(2) Rh(1) 11(1) 31.6 Rh(l) Rh(2) H(1) 31.2Rh(2) Rh(1) H(2) 89.6 Zn(1) Rh(2) H(1) 86.3Zn(l) Rh(1) H(1) 82.7 Zn(2) Rh(2) H(1) 72.4Zn(1) Rh(1) H(2) 80.9 P(3) Rh(2) B(1) 174.5Zn(2) Rh(1) B(l) 69.1 P(4) Rh(2) H(1) 86.5Zn(2) Rh(1) H(2) 38.2 Rh(1) Zn(2) H(2) 35.7p(l) Rh(1) H(l) 157.0 Rh(2) Zn(2) 11(2) 106.6P(l) Rh(1) 11(2) 76.5 Zn(1) Zn(2) 11(2) 73.1P(2) Rh(1) 11(1) 81.4 C(36) Zn(2) 11(2) 122.0P(2) Rh(1) 11(2) 172.3 Rh(1) 11(1) Rh(2) 117.211(1) Rh(1) 11(2) 105.5 Rh(1) 11(2) Zn(2) 106.1Rh(1) Rh(2) P(3) 147.59(4) C(31) C(32) C(33) 108.7(7)Rh(1) Rh(2) P(4) 114.49(3) C(32) C(33) C(34) 107.6(7)Zn(1) Rh(2) Zn(2) 69.71(3) C(33) C(34) C(35) 110.4(7)Zn(1) Rh(2) P(3) 91.31(4) C(31) C(35) C(34) 106.5(7)Zn(l) Rh(2) P(4) 168.82(3) Zn(2) C(36) C(37) 85.9(3)Zn(2) Rh(2) P(3) 111.37(4) Zn(2) C(36) C(40) 95.2(3)Zn(2) Rh(2) P(4) 99.91(4) C(37) C(36) C(40) 106.2(4)P(3) Rh(2) P(4) 96.55(5) C(36) C(37) C(38) 107.7(4)Rh(1) Zn(1) Rh(2) 70.76(3) C(37) C(38) C(39) 108.8(5)Rh(1) Zn(l) Zn(2) 56.69(2) C(38) C(39) C(40) 108.9(5)Rh(l) Zn(1) C(31) 117.2(2) C(36) C(40) C(39) 108.4(5)Appendix 228A.6 X-ray Crystallographic Analysis of {dippp}Rh(3-CH2Ph)C9C5docli C8C16Ci?C3C?digC6CzoC13Appendix 229EXPERIMENTAL DETAILSA. Crystal DataEmpirical FormulaFormula weightCrystal Color, HabitCrystal Dimensions (mm)Crystal SystemNo. Reflections Used for UnitCell Determination (28 range)Omega Scan Peak Widthat Half—heightLattice Parameters:a — 10.540 (3)Ab — 15.030 (9)Ac 14.858 (5)A0 — 92.91 (3)°V 2351 (2)A3Space Group P21/n (114)Z value 4Dcalc 1.329 g/cm3992M(NoK)DiffractometerRadiationTemperatureTake—off AngleDetector ApertureC22H41P2Rh470.42orange, prism0.250 x 0.400 x 0.450monoclinic25 ( 29.3 — 37.0°)0.388.52 cm1B. Intensity MeasurementsRigaku AFC6SMoKa (X — 0.71069 A)21°C6.0°6.0 mm horizontal6.0 mm verticalAppendix 230Crystal to Detector DistanceScan TypeScan RateScan Width2ema xNo. of Reflections MeasuredCorrectionsC. Structure Solution andStructure SolutionRefinementFunction MinimizedLeast—squares Weightsp—factorAnomalous DispersionNa. Observations (I>3.OOa(I))No. VariablesReflection/Parameter RatioResiduals: R; RGoodness of Fit Indicator?lax Shift/Error in Final CycleMaximum Peak in Final Diff. MapMinimum Peak in Final Diff. Map285 mmw—2 832.0°/mm (in omega)(8 rescans)(1.35 + 0.35 tan8)°60.0°Total: 7325Unique: 7084 (Rt — .028Lorentz—poiarizationAbsorption(trans. factors: 0.73 — 1Decay ( —6.80% decline)RefinementPatterson MethodFull—matrix least—squaresE w (IFol — IFcI)24Fo2/a()0.04All non—hydrogen atoms415223817.450.036; 0.0431.330.061.20 e7A3—0.74 e/A3Appendix 231Table . Final atomic coordinates (fractional) and B(eq).z B(eg)Rh (1)P(1)P(2)C(1)C(2)C(3)C(4)C(5)C(6)C(7)C(8)C(9)C(10)C(ll)C(12)C(13)C(14)C(15)C(16)C(17)C(18)C(19)C(20)C(21)C(22)0.42648(1)0.61338(8)0.3887(1)0.6854(4)0.6501(4)0.5158(4)0.7396(4)0.6275(4)0.3494(4)0.2552(4)0.7562(5)0.8682(4)0.6129(5)0.5320(5)0.4523(5)0.3155(6)0.1271(5)0.2743(5)0.4289(4)0.3533(3)0.2407(3)0.1682(4)0.2081(5)0.3231(5)0.3937(4)0.23824(2)0.29422(6)0.16739(6)0.2621(3)0.1706(3)0.1647(3)0.2639(3)0.4171(3)0.0480(3)0.2095(3)0.1631(3)0.3106(4)0.4629(3)0.4538(3)0.0018(3)—0.0054(4)0.1948(4)0.3089(4)0.2919(3)0.2132(2)0.2083(2)0.1304(3)0.0564(3)0.0575(3)0.1324(3)0.16881(2)0.21265(6)0.29851(6)0.3233(3)0.3571(3)0.3892(3)0.1350(3)0.2212(3)0.2819(3)0.3629(3)0.1334(3)0.1517(4)0.1300(4)0.2846(3)0.2319(3)0.3649(4)0.3134(3)0.3815(4)0.0354(3)0.0300(2)0.0783(2)0.0773(3)0.0342(3)—0.0074(3)—0.0093(2)2.95(1)3.66(4)3.79(4)5.0(2)5.4(2)5.3(2)4.7(2)5.0(2)5.1(2)5.2(2)6.5(3)7.6(3)6.7(3)6.3(2)6.5(2)8.1(3)7.0(3)7.1(3)4.2(2)3.5(1)3.7(1)4.7(2)5.4(2)5.5(2)4.5(2)atom x yAppendix 232Table . Bond angles (deg) with estimatedin parentheses.standard deviationsatom atom atom angle atom atom atom angleP(1) Rh(1) p(2) 96.99(4) P(1) C(4) C(9) 116.1(3)P(l) Rh(1) C(16) 94.4(1) C(8) C(4) C(9) 110.8(4)P(1) Rh(1) C(17) 127.4(1) PCi) C(S) c(l0) 112.7(3)P(1) Rh(i) C(18) 160.27(9) P(1) C(5) C(ll) 110.5(3)P(2) Rh(1) C(16) 168.5(1) C(10) C(5) C(11) 110.4(4)P(2) Rh(1) C(17) 130.71(9) P(2) C(6) C(12) 110.4(3)P(2) Rh(1) C(18) 102.7(1) P(2) C(6) c(13) 117.3(3)C(16) Rh(i) C(17) 38.4(1) C(12) C(6) C(13) 111.0(4)C(16) Rh(1) C(18) 66.0(1) P(2) C(7) C(14) 112.2(3)C(17) Rh(1) C(18) 36.0(1) P(2) C(7) C(1S) 109.3(3)Rh(1) PCi) C(1) 119.0(1) C(14) C(7) C(15) 109.6(4)Rh(1) P(1) C(4) 112.2(1) Rh(1) C(16) C(17) 73.0(2)Rh(1) P(i) C(S) 117.8(1) Rh(i) C(17) C(16) 68.7(2)C(i.) P(1) C(4) 102.4(2) Rh(1) C(17) C(18) 78.3(2)C(1) PCi) C(5) 99.9(2) Rh(i) C(17) C(22) 115.7(2)C(4) P(1) C(S) 103.2(2) C(16) C(17) C(18) 119.6(3)Rh(i) P(2) C(3) 118.6(2) C(16) C(17) C(22) 123.6(4)Rh(1) P(2) C(6) 113.0(1) C(18) C(17) C(22) 116.1(3)Rh(1) P(2) C(7) 116.9(1) Rh(1) C(18) C(17) 65.6(2)C(3) P(2) C(6) 103.0(2) Rh(1) C(18) C(19) 127.0(3)C(3) P(2) C(7) 99.9(2) C(17) C(18) C(19) 120.6(3)C(6) P(2) C(7) 103.3(2) C(18) C(19) C(20) 120.6(4)PCi) C(1) C(2) 115.9(3) C(19) C(20) C(21) 119.9(4)C(1) C(2) C(3) 113.9(3) C(20) C(21) C(22) 120.8(4)P(2) C(3) C(2) 115.0(3) C(17) C(22) C(21) 121.8(4)P(i) C(4) C(B) 109.8(3)Appendix 2330Table . Bond lengths (A)in parentheses.with estimated standard deviationsatom atom distance atom atom distanceRh(1) P(1) 2.210(1) C(4) C(9) 1.535(6)Rh(1) P(2) 2.255(1) C(5) C(10) 1.520(6)Rh(1) C(16) 2.141(4) C(5) C(11) 1.516(6)Rh(1) C(17) 2.197(3) C(6) C(12) 1.514(7)Rh(1) C(18) 2.362(3) C(6) C(13) 1.529(6)P(l) C(1) 1.840(4) C(7) C(14) 1.521(7)P(1) C(4) 1.862(4) C(7) C(15) 1.531(7)P(1) C(5) 1.857(4) C(16) C(17) 1.426(5)P(2) C(3) 1.852(4) C(17) C(18) 1.419(5)P(2) C(6) 1.856(4) C(17) C(22) 1.422(5)P(2) C(7) 1.853(4) C(18) C(19) 1.398(5)CC1) C(2) 1.516(6) C(19) C(20) 1.36G(6C(2) C(3) 1.518(6) C(20) C(21) 1.389(6)C(4) C(8) 1.525(6) C(21) C(22) 1.351(6)

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