Organometallic Chemistry PART 11 =-Bonded Organometallics By A. J. Deeming 1 q2-Alkene Compounds Preparation Structure and Fluxional Behaviow-Routine access to rapid methods of X-ray structural analysis allows many q2-alkene complexes to be studied struc- turally each year and while results taken individually are rarely exciting detailed comparisons are now possible. ,Several structures of complexes relating to [Rh(alkene)J [L = r)’-C5H5 or MeCOCHCOMe] have been determined. The complex [Rh(q’-C5Me5)(PPh3)(C2H4)] has shorter Rh-C(a1kene) bonds than for example [Rh( q5-C,H5)(C2H4)(C2F4)] [2.093 A (mean) compared with 2.1676) A] and a longer CH2-CH2 bond [1.408(16) compared with 1.358(9)A]. This is attributed to a greater r-component to the Rh-C2H4 bonding because of the greater u-basicity and lower w-acidity of PPh3 compared with CZF4.l The 20” twist of the two CH2 planes with respect to each other and the closely tetrahedral geometry of the C atoms are structural details of the PPh3 complex.Rh-C(a1kene) bonds in [Rh(CH3COCHCOCH3)( alkene) (CF3CrCCF3)] (a1 kene = C2& or cyclo-octene) prepared by alkyne addition to the corresponding bis (alkene) complexes are in the range 2.142-2.196 A,’ presumably because CF3C=CCF3 has similar ligating properties to CZF4. More complicated q2-alkene complexes in the same series to be studied structurally are [Rh( q 5-CsH5)(+)-(4S-carvone)]in which the co-ordinated C=C bonds of the diene ligand are far from parallel as in the bis(ethy1ene) complex but rotation about the Rh-alkene bond is not expected to be very energetically demanding.3 Other X-ray structures in this series are [Rh(MeCOCHCOMe)- (CH2:CHCMeOCH2CH:CHMe)I4 and [Rh(PhCOCHCOMe)( 1,6-dichlorocyclo- octa-1,5-diene)].’ Detailed vibrational thermochemical and n.m.r.studies on the effect of varying alkene diketone and metal (Ir or Rh) have shown that the substituent effects are comparable for both metals although the alkene-Ir bonding is 177 K. J. Irwin J. J. Rooney C. D. Stewart M. L. H. Green and R. Mahtab J.C.S. Chem. Comm. 1978,604. W. Porzio and M. Zocchi J. Amer. Chem. Soc. 1978,100,2048. ’J. H. Barlow G. R. Clark M. G. Curl M. E. Howden R. D. W. Kemmitt and D. R. Russell J. Organometallic Chem. 1978,144 C47. W. Winter B. Koppenhofer and V. Schurig.J. Organometallic Chem. 1978,150 145. R. Grigg B. Kongkathip and T. J. King J.C.S. Dalton 1978 333. J. JeEn9 and K. Hulm Acfa Crysf. 1978 B34,2966. A. J. Deeming and J. Evans stronger than for Rh.6 Other alkene complexes of &-metals to be structurally examined are [NEt4][PtC13(CH2:CHOEt)],'which shows a closer approach of the Pt atom to the terminal alkene carbon than to the OEt-substituted one (2.128 compared with 2.208 A) and [PdC12(1,2,5,6-q4-cyclo-octatetraene)].8 A kinetic study of the substitution by alkenes into [PtC1412- is reported' and a 'H and 2H n.m.r. study in liquid crystal solutions of [PtC12(C2H4)(NC5D5)] has established the relative positions of the hydrogen and platinum nuclei. Quadrupole splittings in the 2H spectra have been used to show that the pyridine ring is inclined at an angle to the co-ordination plane with rapid reorientations between symmetry related forms.lo The first reported X-ray structure of a six-co-ordinate ethylene complex [RuCI~(CO)(C~H~)(PM~,P~)~] (1)shows the q2-alkene to be aligned with the C-C bond parallel to the P-Ru-P axis which it could be argued is to prevent competition between the .rr-components of the Ru-C2H4 and Ru-CO bonds for the available metal d-orbitals." However the energy barrier to rotation about the Ru-C2H4 bond is low since rapid rotation occurs down to -40 "C; a single C2H4 'H n.m.r. resonance rather than an AA'BB' spectrum being observed. A similar series of octahedral q2-alkene complexes [W(C0)4L(alkene)] (L=PMe3 or AsMe3) (2) and [W(CO),(PMe,),(alkene)] (alkene =substituted monoene) have been examined spectroscopically.'* The preferred alkene alignment is parallel to the W-L bond as determined from the low-temperature 'frozen-out' n.m.r.spectra. This conformation relates to that for (1)and as with (l) ready rotation about the W-alkene bond occurs and activation parameters are given. Ab initio LCAO-MO-SCF calculations on tr~ns-[MoL~(alkene)~] (L =PH3)(3) have shown that the most stable cQnformation has mutually perpendicular alkene ligands each eclipsing the L-M-L axes.13" The computed alkene rotation barrier of 67kJ mol-' compares with the experimental oc I !.co L I '. value of 64kJ mol-'. The barriers for zerovalent Mo and W complexes (2) and (3) appear to be higher than for the divalent Ru complex (1);this could be explained in terms of differing w-contributions to the alkene-metal bonds lower for Ru" than Moo or Wo.A similar effect probably accounts for the higher barriers for [Ru(arene) (C2H4)2] than for [Rh(C,H,) (C2H4)2]. '3b A. C. Jesse. M. A. M. Meester D. J. Stufkens and K. Vrieze Znorg. Chim. Actu 1978,26 129; A.C. Jesse H. P. Gijben D. J. Stufkens and K. Vrieze ibid. 1978 31 203. 'R. C. Elder and F. Pesa Actu Cryst. 1978 B34 268. N. C.Baenziger C.V. Goebel T. Berg and J. R. Doyle Acta Cryst. 1978 B34 1340. M. Green and C. J. Wilson J. Chem. Res. (S) 1978 175. lo J. W. Emsley and J. Evans J.C.S. Dalfon,1978 1355. L.D. Brown C.F. J. Barnard J. A. Daniels R. J. Mawby and J. A.Ibers Znorg. Chem. 1978,17,2932. U.Koemm C.G. Kreiter and H. Strack J. Orgunometullic Chem. 1978,148 179. l3 (a) C.Bachmann J. Demuynck and A. Veillard 1Amer. Chem. Soc. 1978,100 2366; (6)M. A. Bennett and T. W. Matheson J. Organometallic Chem. 1978 153. C25. Organometallic Chemistry Treatment of [Pt(cod),] with a range of tertiary phosphines or AsPh (L) in ethylene saturated solutions leads to complexes [Pt(C2H4),L] for which alkene rotation has been studied by d.n.m.r.14 The X-ray structure (4) of the mixed C2H4,C2F4 complex has a trigonal planar co-ordination with alkene carbon atoms in the plane. Rotation about the Pt-alkene rather than about the C-C axis is established; in fact this latter process is unknown and Pt-H coupling observed at high temperatures rules out a reversible alkene-displacement mechanism.Replace- ment of one C2H4 in [Pt(C2H,),(PCy3)] by C2F4 lowers the rotation barrier for the remaining C2H4 by 12.6 kJ mol-' and reduced barriers as a result of reduced .rr-back-bonding from platinum are a rationalisation of this. Also as expected for a system where electronic rather than steric effects dominate higher barriers are found with the more basic ligands L. Photochemical displacement of CO by c2H4 leads to complex (3,which gives a C2& 'H n.m.r. singlet at 301 K but an AA'BB' spectrum at 230 K.' Rotational barriers for the W-C2H4 bond are very similar for the corresponding q5-CsH4 and q5-indenyl complexes. Different isomers were observed for the ethylene complex (6) as indicated by two v(C0) absorptions of similar intensity.16 The effect though is probably due to there being different conformations about the Fe-carbene rather than the Fe-ethylene bond.Mixed carbene-alkene complexes are important in alkene metathesis since these are believed to lead reversibly to metallocyclobutane intermediates thus (6) provides a model for this type of compound. Isomers with different alkene conformations (7a) and (7b) are observed for a propene-tantalum complex.l7 Complex (7) relates to the known complex [Ta(C,H,),(H)(C,H,)] and was prepared by treatment of [(Ta(C,H5),Cl2] with PrMgC1. An intermediate propyl complex undergoes &elimination to give propene and otber 2-alkene complexes may be formed similarly. Isomers (7a) and (7b) are interconvertible by alkene rotation but here the barrier is high.The complexes [Ta(C5H5),L(CH,)] (L = CH2 or C2H4) are related in that there is no ready rotation about the Ta-CH2 or Ta-C2H4 bonds.'* The C-C axis in the C2H4 complex is perpendicular to the CH plane of the other compound sothat equivalent metal orbitals are used for ?r-bonding in each case and since there is no suitable metal orbital at 90"no facile ligand rotation occurs. The complex with L = CH converts thermally (50% conversion) to that with L = C2H4 but this is better achieved by treatment with Me3P=CH2. + N.C.Harrison M.Murray J. L. Spencer and F. G. A. Stone J.C.S. Dalton 1978 1337. IS H.G.Ah J. A. Schwkzle and C.G. Kreiter J. Organometallic Chem. 1978,153 C7. l6 W.Priester and M. Rosenblum J.C.S. Chem. Comm. 1978,26. l7 A.H. Klazinga and J. H. Teuben J. Organometallic Chem. 1978,157,413. R. R. Schrock and P. R. Sharp J. Amer. Chem. Soc. 1978,100,2389. A. J. Deeming and J. Evans Treatment of [Nb(C5H5)2C12] with Pr’MgC1 in the presence of cyclo-octatetraene gives [Nb(q’-C,H,)(q2-C8H8)] obtained as a red-brown air-sensitive and paramag- netic solid.” An alternative synthesis of the same compound is to treat NbC15 with K2[C8H8] to give [NbC12(CsH8)](THF) which can then be treated with Na[C,H,]. The evidence for q 2-co-ordination of the cyclo-octatetraene is mainly based on reactivity; it liberates isomers of cyclo-octatriene with HCl (other q2-alkenes behave similarly) and with NaBH gives the diamagnetic q3-allyl complex [Nb(q5- C5H5)2(q3-C8H9)].Nobium(II1) alkene and alkyne complexes are also prepared by direct substitution of CO by C2H4 (80atm) to give [Nb(~s-C,H,)2C1(C2H4)] or by reduction of [Nb(CSH5)2C12] with Na/Hg followed by alkyne addition to give [Nb(C5H5)2Cl(alkyne)] (alkyne =propyne or perfl~orobut-2-yne).~~ The lack of rapid rotation about the Nb-C2H4 bond is shown by the non-equivalence of the ends of the alkene in the ‘H n.m.r. spectrum. The complex previously reported as [R~(styrene)(PPh~)~] formed by treating [RuH,(PPh,),] with styrene has been reformulated as [R~(styrene),(PPh~)~] and appears to be the first fully authentic 16e-ruthenium(0) complex.21 The two styrene ligands in this highly distorted tetrahedral complex (8a; P=PPh3) are quite different one having a normal q2-styrene co-ordination with the a-C further from the metal atom than the B-C.The abnormal styrene has a short phenyl-ruthenium interaction making the a-closer than the p-C to the metal. It may be that the 18e-form (8b) contributes to the ground state structure. Two 31P n.m.r. doublets are consistent with the asymmetric structure being retained in solution but (8) is only stable in styrene solution and even then only in equilibrium with [R~(styrene)~(PPh~)]. Complex (8) reacts with PPh3 to regenerate [RuH2(PPh3)41 (hydrides from PPh3) and is a ready source of other alkene-Ruo complexes.22 Dehydrogenation of tricyclohexylphosphine (PCy3) on reaction with [MCl(cyclo- ~ctene)~] (M=Rh or Ir) leads to complexes [MClL(PCy3)] which contain the isomeric chelating ligands L shown in (9a) and (9b).23 The lost H2is presumably used to form five-co-ordinate metal(II1) dihydrides which are by-products.P H; l9 C. P. Verkade A. Westerhof and H. J. de Leifde Meijer J. Organornetallic Chem. 1978,154,317. 2o S. Fredericks and J. L. Thomas J. Amer. Chem. SOC. 1978,100,350. 21 M. A. A. F. de C. T. Corrondo,B. N. Chaudret D. J. Cole-Hamilton A. C. Skapski and G. Wilkinson J.C.S. Chem. Comm. 1978,463. 22 B. N. Chaudret D. J. Cole-Hamilton and G. Wilkinson J.C.S. Dalton 1978 1739. ” S. Hietkamp D. J. Stufkens and K. Vrieze J. Organometallic Chem. 1978,152,347. 341 Organometallic Chemistry Substituted q2-fulvene complexes are formed replacing one CO ligand in [Mn(r15- C,H,)(CO),] by the fulvene to give [Mn(q5-C,H5)(q2-dimethylfulvene)]and [{Mn( q’-C,Hs)(C0)2}2(p-dime t hylfulvene)].Co-or dination in both cases is through C=C bonds in the five-membered ring.24 A q2-squaric acid complex (10)is derived by displacing ethylene from [Pt(C21&)(PPh3)2] and C-C cleavage in (10) can occur thermally to give the tautomeric product mixture (11) which is isomeric with the original q2-complex.25 The diphenylketen complex [Ni( q2-Ph2C:C:O)(PPh3)2] is formed on treatment of the corresponding C21& complex with the keten and on dissolving this breaks down to [Ni(CO)(PPh3)3];26 a similar reaction occurs on treating [Mn(C,H,)(CO),(THF)] with Ph2C:C:0 except that it is the CO group that is lost giving [Ni(C,H,)(CO),(Ph,C)].Interestingly in this case the keten to carbene conversion may be reversed on treatment with a pressure of CO to give [Ni(C5H5)- (C0),(q2-Ph,C:C:O)] and subsequent hydrogenation gives Ph2CHCH0 and Ph2CHCH20H.27 Metal Atom Derivatives of A1kenes.-The matrix-isolated (C2H4/Ar at 15-25 K) complexes of ethylene [Nin(CzH4),] (n = 1 m = 1 2 or 3; n = 2 rn = 1 2 and possibly species with n > 2)28and [Co,(C2H4),] (n = 1 2 or 4 with rn ~ariable)~’ have been described and their vibrational and electronic spectra discussed. For nickel species such as [Ni(C2HJ] and [Ni2(C21&)] calculations of binding energies and energies of transformation from q2-to di-cr-bonding have been carried OU~.~**~’ In the related reaction between Ni atoms and alkyl- fluoro- and chloro-substituted alkenes similar complexes of type [Ni(alkene),] (n = 1,2 or 3) are formed even for ally1 chloride.Warming the q2-ally1 chloride complexes does not lead by oxidative addition to the q3-allyl nickel complexes reported to be formed by similar treatment of nickel atoms and it was suggested that high-temperature work-up or the prior formation of nickel clusters are required for oxidative addition.,l ’* F. Edelmann K.-J. Jens and U. Behrens Chem. Ber. 1978 111 2895. 2J W.Beck F. Goetzfried and M. W. Chen Chem. Ber. 1978,111,3719. 26 H. Hoberg and J. Korff J. Organometallic Chem. 1978,152,255. 27 W.A.Hermann and J. Plank Angew. Chem. Internat. Edn. 1978,17,525. G. A. Ozin W. J. Power T. H. Upton and W. H. Goddard J. Amer.Chem. Soc. 1978,100,4750. 29 A. J. Lee Hanlan G. A. Ozin and W. J. Power Inorg. Chem. 1978,17 3648. 30 T.H. Upton and W. A. Goddard J. Amer. Chem. SOC.,1978,100,321. 31 G.A.Ozin and W. J. Power Inorg. Chem. 1978,17,2836. A. J..Deeming and J. Evans Reaction of r)*-Alkene Complexes.-Nucleophilic addition at 2-alkenes is an important reaction occurring in the palladium-induced oxidation of ethylene. The idea of co-ordinated OH- migrating to a cis-co-ordinated C2H4 originated from a kinetic analysis of the reaction of [PdCI4l2- with ethylene but must now be discarded on present evidence since a second report confirming trans-addition to C2H has appeared.32 The conclusion depends upon the assumption of CO insertion with retention of configuration at carbon in reaction (1).Nucleophilic addition of Me2NH at [PtC12(PPh3)(C2H4)] leads to a zwitterionic intermediate [&C12(PPh3)-+ (CH2CH2NHMe2)] which readily dehydrochlorinates to give the complex [Pt(CH2CH2NMe2)CI(PPh3)], which appears to be the first chelate of its kind for platinum.33 Nucleophilic addition at q2-allenes may be at the central carbon to give q3-allyl systems but also at a terminal carbon as in reaction (2),the product of which has been fully established by X-ray diffra~tion.~~ Cis- and trans-[PtCI2(amine)- Et NH cis-[PtC12(PPh3)(77 2-CH2:C:CMe2)] [PtC12(PPh3){C(CH2hHEt2): CMe2}] (2) (C2H4)] behave differently with amines (e.g.py).The trans-isomer simply undergoes nucleophilic attack at C2H to give the zwitterionic product (12),but where C1-is trans to C2H4 as in the cis-isomer this is substituted to incorporate two amines giving the product (13).35 CI O C H ,CH I -Pt -py I CI PY (12) (13) Although oxygen- and nitrogen-based nucleophiles do seem to attack q2-alkenes without prior co-ordination the transfer of hydride or alkyl to alkenes may occur intramolecularly and calculations on various possible mechanisms for the insertion of C2€&into Pt-H bonds have been made.36 No facile pathway for hydride migration to C2H4 was found for a five-co-ordinate complex nor for a direct route for a four-co-ordinate complex with trans C2H4 and H.The seemingly most favourable mechanism involves these ligands mutually cis in a four-co-ordinate complex indeed the mechanism with some experimental support.A planar arrangement of the four reacting atoms (M C=C H) seems a requirement and experimental evidence for 32 J. K. Stille and D. Divakaruni J. Amer. Chem. SOC.,1978,100,1303. 33 A.De Renzi A. Panunzi and A. Vitagliano. Gazzetta 1978,108,45. 34 A.De Renzi B. Di Blasio A. Panunzi C. Pedone and A. Vitagliano. J.C.S. Dalton 1978,1392. ” G. Natile J.C.S. Chem. Comm. 1978 654. 36 D.L.Thorn and R. Hoffmann J. Amer. Chem. SOC.,1978,100,2079. Organometallic Chemistry this has come from a study of the hydrogenation of cyclo-octa-1,5-diene (cod) catalysed by [1r(~od)(PPh~)~][PF~].~~ A formation of cyclo-octene (coe) when isomer (14) is in solution is fast but the rate is reduced as this isomerizes to (15) and it has been pointed out that only isomer (14) allows a planar Ir C=C H arrangement.Hydride migration to give a cyclo-octenyl intermediate must be 40 times faster for (14) than (15). Reversible equilibria between metallocyclopentane and bis(ethy1ene) complexes have been reported for complexes [ki(CH2CH2CH2CH2)(PPh3)2] and [h(CH2CH2CH2CH2)(CsHs)2].38 Evidence for this came from an analysis of the mixtures derived by reaction (3) which occurs faster than decomposition with loss of ethylene. No other deuteriated metallocyclopentane rings were observed to be formed. Activation of C-H bonds in ethylene occurs on reaction of but-2-yne with [Rh(qs-indenyl)(C2H4)2]to give complex (16) (X-ray structure; R =Me) as well as a Me (16) (R=H or Me) metallocyclopentadiene complex derived by but-2-yne It seems that an intermedate hydrido(viny1) complex must be formed which can then insert the alkyne into the Rh-H bond.Similar activation of ethylene has only previously been observed in clusters and here the combined involvement of two Rh atoms seems necessary. Displacement of acetate from vinyl acetate occurs when this is reacted with [Ni(PR3),(ethyl methacrylate)] to give [Ni(AcO),(PR,),] (n= 1 where R = cyclohexyl but n = 2 for smaller phosphine substituents) the vinyl group being liberated as eth~lene.~’ 37 R. H. Crabtree H. Felkin. T. Khan and G. E. Morris J. Orgunomefullic Chem. 1978,144 C15. R. H. Grubbs and A. Miyashita J. Amer. Chem. SOC.,1978,100 1300. 39 P. Caddy M. Green L. E. Smart and N.White J.C.S. Chem. Comm. 1978. 839. J. Ishizu T. Yamamoto and A. Yamamoto. Bull. Chem. SOC.Japan 1978,51,2646. 344 A. J. Deeming and J. Evans The high trans-labilising effect of ethylene operates in the aquation of [PtCl4I2- catalysed by [PtC13(C2H4)]- and a kinetic analysis has shown that truns-[PtC12(C2H4)(H20)] is the actual catalyst the rate of the catalysed reaction being proportional to its concentration. Reactions (4) and (5) are the key steps in the proposed mechanism replacement of C1- in the complex [PtC1,(C2H4)] formed in (5) +[PtC14I2-Ft [(C2H,)C1zPt(p-Cl)PtC13]2-~IIZ~S-[P~C~~(C~H~)(H~O)] +H20 (4) [(C2H4)C1zPt(p-Cl)PtC13]2- +H2O * [PtC13(C2H4)]- +[PtCl,(H20)]- (5) being rapid.41 The successive migration of an alkyl group as a polymer chain terminus to a cis-co-ordinated alkene at titanium(II1) (and other metals) is the mechanism generally proposed for Ziegler-Natta polymerization.Noting that alkene metathesis and polymerization catalysts are chemically almost indistinguish- able a new mechanism has been proposed and illustrated for propene in reaction (6) P P Me P Me p. Me Me I I \/ +propene \/ P-CHT CHMe C ___) C -propcne 11. CH, I II Ti-CHMe Ti H-Ti H -TI -11 CHMe H (6) (P= Stereoselective formation of syndiotactic polymer would be controlled by the relative orientations of Me-groups as the metallocyclobutane ring is formed. This mechanism seems to fit the available evidence at least as well as the commonly discussed mechanism. 2 q2-Alkyne Compounds Preparation and Structure.-The X-ray structure of [Fe2(C0),(Ph2PC~CBu')] (17) the first established structure for a compound of type [Fe(CO)4(alkyne)] shows the alkyne to lie in the equatorial plane of a trigonal bipyramid as do alkenes in similar complexes.43 Surprisingly no X-ray structure of a q2-C2H2complex was available prior to (18) being studied although p 2-C2H2 structures have been determined.4 The C-C and C-0 bonds of (18)are approximately parallel.A C2H2 complex of Mo'" has been observed by n.m.r. in the equilibrium (7) and although this was not [MoO(S~CNE~~)~] +alkyne e[M~O(S~CNEt~)~(alkyne)l (7) isolated the related HC=CCO2Me complex was.45 An improved synthesis of [Mo(C5H5),(C2H2)]has been described and the related propyne and but-2-yne complexes also obtained.Acid treatment liberates corresponding alkenes cis- MeCH=CHMe being obtained from [MO(C~H,),(M~CGCM~)].~~ '' M. Green and M. G. Swanwick J.C.S. Dalton 1978 158. 42 K.J. Ivin J. J. Rooney C. D. Stewart M. L. H. Green and R. Mahtab J.C.S. Chem. Comm. 1978,604. 43 A. J. Carty W. F. Smith and N. J. Taylor J. Organometallic Chem. 1978,146 C1. 44 L. Ricard R. Weiss W. E. Newton G. J.-J. Chen and 1. W. McDonald J. Amer. Chem. SOC., 1978,100 1318. 45 E. A. Maatta R. A. D. Wentworth W. E. Newton J. W. McDonald and G. D. Watt I. Amer. Chem. SOC.,1978,100 1320. 46 J. L. Thomas Inorg. Chem. 1978 17 1507. Organometallic Chemistry The dialkynes RC_C-C=CR (R =Me or Ph) react with [Pt(C2H4)k] (L = PPh3 or PMe2Ph) by successive co-ordination through the two multiple C-C bonds to give with an excess of the platinum reagent the complexes [Pt2L4(diyne)] (19).Interestingly a complex of this stoicheiometry but with L = Bu'NC adopts quite a different structure (20) with a Pt-Pt bond.47 Side-on N2co-ordinationis recognized as the counterpart of q2-alkyne co-ordination but no simple isolable mononuclear complexes have been described prior to [Zr(~5-CsHs)2R(N2)] [R =CH(SiMe,),] which gives a 1 :2 :3 :2 :1 e.s.r. quintet (together with 91Zr satellites) showing equivalent coupling to two 14N nuclei and of sufficient magnitude to indicate fairly high spin density at N2. Structure (21) is proposed.48 Reactions.-The titanium(I1) alkyne complex [Ti(C,H,)2(CO)(PhC~CPh)] formed from the dicarbonyl by CO displacement has an alkyne C-C length of 1.285(10)A.Hydrogenation gives [Ti(C,H,),H(CPh=CHPh)] with CO being lost and with cis-addition across the alk~ne.~~ Similar cis-addition occurs in reaction (8) (L= PPh3).,' The oxidative addition product undergoes methyl transfer to the alkyne or (85 '/o ) (15%) the alkyne ligand is lost to give the two respective platinum(I1) products. Presumably oxidative addition of H2is followed by hydrogen atom transfer in the titanium case and in the isomerization of [Pt(PPh3),(Me02CC~CC02Me)] to (22) (X-ray struc- ture) a similar sequence can be envisaged that is oxidative cyclometallation with *'I J. B. B. Heyns and F. G. A. Stone J. Orgqnometallic Chem. 1978,160,337. 48 M. J. S. Gynane J.Jeffery and M. L. Lappert J.C.S. Chem. Comm. 1978,34. 49 G. Fachinetti C.Floriani. F. Marchetti. and M. Mellini J.C.S. Dalton 1978. 1398. T.G.Appleton M. A. Bennett A. Singh and T. Yoshida. J. Organometallic Chem. 1978,154,369. A. J. Deeming and J. Evans ortho-H transfer to platinum followed by its transfer to the alk~ne.~~ The kinetics and mechanism of the internal oxidative addition reaction (9)have been studied the cis-product isomerizing further to the trans-complex in benzene. An intramolecular mechanism is indi~ated.~~ Metal Atom Deivatives.-Copper atoms (0.1 molo/o) trapped in an Ar matrix containing acetylene (0.3 to 10 molo/o) give species with e.s.r. signals attributable to [Cu(C2H2)J (n= 1 or 2) and q2-bonding is proposed rather than u-bonding as in [Al-CH=CH’].53 Nickel or palladium atoms (M) react with CF3C~CCF3 to give compounds which react with CO giving [M(CO)2(alkyne)] which on warming to near room temperature convert to the clusters [M4(C0)4(alkyne)] (known for Ni).54 No CO is taken up by some metals and simple thermally stable alkyne complexes were made for Co Ni Pd Pt Cu and Au.3 q’-Ally1 Compounds Preparation and Structure.-The preparation of [Re2(C3H5)4] was reported earlier and its X-ray structure is now known.” There are four chemically equivalent v3-allyl ligands of normal type with the dimer held together by a triple Re-Re bond (23),whereas in the stoicheiometrically equivalent Cr and Mo compounds (24)which contain quadruple M-M bonds bridging and q3-allyl ligands are both present.The reasons for these differences have not been established. The dimeric complex (23) (24) (M = Cr or Mo) ’’ N. C. Rice and J. D. Oliver J. Organomefallic Chem. 1978 145 121. ’’ J. Burgess M. E. Howden R. D. W. Kemmitt and N. S. Sridhara,J.C.S. Dalton 1978 1577. 53 P. H. Kasai and D. McLeod J. Amer. Chem. SOC.,1978,100,625. K. J. Klabunde T. Groshens M. Brezinski and W. Kennelly J. Amer. Chem. SOC.,1978,100,4437. ” F. A. Cotton and M. W. Extine J. Amer. Chem. SOC.,1978 100 3788. Organometallic Chemistry 347 [Fe2(Co)6(q3-c&)z] also has normal allyl ligand~.'~ The reason for the long Fe-Fe bond [3.138(3) A] probably relates to that put forward for the long bond in [CrZ(co)6( q 5-c5H5)Z1. The very familiar complex [PdzC1z(q3-2-methylallyl)z] reacts with [PdCl,(PhCN),] to insert a PdCl unit between the original two Pd atoms.57 Chloro- bridges hold the three metal atoms together although from the asymmetry of these bridges there appears to be a significant contribution from [(7'-C,H,)Pd]'[PdCl,]'-[Pd( q 3-C4H7)]'.[Pt(q 3-C3H5)(PCy3)2][PF6] (toluene) has a normal structure except that the q3-allyl group adopts two discrete orientations in the crystal with the central allyl carbon above or below the co-ordination plane with occupancy factors of 0.4 and Oh.'* The X-ray structures of [PdzC12(l-3-q3-6-chlorocyclo-octatrienyl)2] derived from [PdC1z(PhCN)z] and cyclo-octatetraene" and of [RU(~~-C~H~)(NO)(PP~~)~]~' have been described. A detailed analysis of a standard synthetic route to q3-allyl palladium complexes as applied to a wide range of alkenes has been made and mechanisms including oxidative addition to give hydridopalladium(1v) intermediates discussed.61 There is of course precedence for oxidative addition of alkenes as in the addition of propene to [Ru(qZ-MeCN)(PPh3),] to give [RuH(PPh3)(q3-C3HS)(MeCN)], and tauto- merism involving a hydrido (q3-allyl) and a q2-propene complex was considered to account for some reaction products of the q3-C3H5 complex.62 Ally1 complexes are also generated from allylic halides and from a kinetic study of the oxidative addition of allyl bromide to [Mo(CO),(phen)] in 1,2-dichloroethane this seems to involve the rate-determining loss of CO (probably solvent-assisted) prior to oxidative addi- ti~n.~~ In tetrahydrofuran solution a small second order kinetic term is also observed.The phenalenium ion (X') displaces ethylene from [Pt(CZH4)(PPh3),] to give [Pt(X)(PPh3)z]' and both n.m.r. and diffraction methods have established the q3-allyl mode of bonding in (25).64 Another example has been reported of carbenium ion stabilization by metal atoms modifying their bonding to the ligand. The q2-to q3-ligand transformation in reaction (10) allows a ready loss of OH-56 C. F. Putnik J. J. Welter G. D. Stucky M. J. D'Aniello B. A. Sosinsky J. F. Kirner and E. L. Muetterties J. Amer. Chem. SOC. 1978,100,4107. 57 P. M. Bailey E. A. Kelley and P. M. Maitlis J. Organometallic Chem. 1978 144 C52. 58 J. D. Smith and J. D.Oliver Znorg. Chem. 1978,17 2585. s9 N. C. Baenziger C. V. Goebel B. A. Foster and J. R. Doyle Actu Cryst. 1978 B34 1681. " M. W. Schoonover C. P. Kubiak and R. Eisenberg Znorg. Chem. 1978,17,3050. 61 B. M. Trost P. E. Strege;L. Weber T. J. Fullerton andT. J. Dietsche J. Amer. Chem. SOC. 1978,100 3407. '' E. 0.Sherman and P. R. Schreiner J.C.S. Chem. Comm. 1978,223. 63 J.-C. Rousche and G. R. Dobson J. Organometallic Chem. 1978 150 239. 64 A. Keasey P. M. Bailey and P. M. Maitlis J.C.S. Chem. Comm. 1978 142. A. J. Deeming and J. Evans R = H or Me; M = Rh(C5H5)or Fe(C0)3 in solution with the ready formation of the stable cationic complex.65 Electrophilic attack of BF3 at the ketonic oxygen atom of [Fe(C0)4-(q2-PhCH:CHCOPh)] leads to [Fe(C0)4(PhCH:CH-kPh-OBF3)] which could be easily formulated as a q3-allyl complex.66 Reaction of this product with cyclo- hexylamine (RNH2) gives complex (26) (X-ray structure) the amine adding as a nucleophile both at the carbon atom of a metal carbonyl to give the carbamoyl group as well as formally displacing the group [OBF3I2-.Twoproducts from the reaction of [Co(CO),]- and CH,:C(CH,Cl) have been shown by X-ray diffraction to be the q3-allyl complexes (27) and (28);crystals of (27) but a P(OMe) derivative of (28) being chosen for st~dy.~' \ /NR (CO),Fe-C \O (26) .A, (CO),Co-, -Co( CO) (27) (28) q 3-Allyl complexes are formed from the metallocyclopentane complex f I (diphos = Ph2PCH2CH2PPh2) [Pt(CH2CH2CH2CH2)(diphos)] by the abstraction of hydride ion by [Ph3C]+ in dichloromethane.68 The intermediate [Pt(CH,CH,CH=CH,)(diphos)]* is proposed but the isomeric q3-~rotyl complex is isolated.Displacement of C1- from the cyclopropyl complex [PtCI(C3H5)L2] (L =PMe2Ph) allows a very specific C2-C3 bond cleavage with no hydrogen atom transfer as shown by deuteriation; reaction (1l).69q3-Allylic complexes are also " I. T. Chizhevsky and A. A. Koridze J. Organometallic Chem. 1978,153 C28. 66 A. N. Nesmeyanov M. I. Rybinskaya L. V. Rybin N. T. Gubenko N. G. Bokii A. S. Batsanov and Yu. T. Struchkov J. Organometallic Chem. 1978 149 177. 67 K. Cann P. E. Riley R. E. Davis and R. Pettit Znorg. Chem. 1978 17 1421. P. Diversi G. Ingrosso and A. Lucherini J.C.S. Chem. Comm. 1978 735. 69 R.L. Phillips and R. J. Puddephatt J.C.S. Dalton. 1978 1732. Organometallic Chemistry 349 formed by opening C rings in the reaction of [PtD(N03)L2] (L = PEt or PPh3) with methylenecyclopropane and when L = PEt3 the product contains D specifically in the 2-position that is [Pt(q3-MeCHCDCH2)L2]+ is formed as the exclusive product. Me 4+ D-Pt + Pt D When L = PPh3 both q3-1-methyl- and -2-methyl-ally1 complexes are formed. Pathway (12) is proposed although attempts of corroborating this by isolating cyclopropylmethyl complexes by other routes were U~SUCC~SS~U~.~~ Phenyl-cyclopropane reacts with [IrCl(N2)(PPh3)2] to give [IrHC1(v3- PhCH-CH.CH,)- (PPh3)2] which is apparently the first structurally characterised hydrido (q3-allyl) complex,” but unlike [MoH(~~-C~H,)(P~~PCH~CH~PP~~)~], there is no rapid transfer of hydrogen atoms between the q3-allyl and the metal atom.q3-Acryloyl ligands relating to simple q3-allyl are present in the 1 1 adduct (29) formed between [FeH(C0)4]- and MeO2CC-CCO2Mp. Bond lengths in this molecule indicate a greater contribution of (29a) than (29b).72 Protonation with C0,Me 1-CF3C02H gives [Fe(CO),( q2-trans-Me02CCH=CHC02Me)]whereas Me’ addi- tion (using [Me30]’) gives what could be described as a prop-2-en-1-ylidene complex and its X-ray structure has been illustrated as in (30).73 Another q3-ligand is derived from an alkyne by treating [Mo(C,H,)(CO),Me)] with but-2-yne. The intermediate [Mo(C,H,)(CO),(CMe=CMeCOMe)] reacts with various ligands L(Bu‘NC CO or PPh,) to give [Mo(C,H,)(C0)(L)(q3-CMeCMeCO2)]; CO is incorporated into a lactone ring which acts as a q3-allyl.The X-ray structure is known where L = Bu‘NC.’~ The dynamic behaviour of pseudo-octahedral Mo and W complexes can be interpreted in terms of interchange between configurations such as (31a) and (31 b). Complexes such as [MO(~’-C~H,)(CO)~(P~~PCH,CH~PP~~)]+~~ 70 R. L. Phillips and R. J. Puddephatt J.C.S. Dalton 1978 1736. 71 T. H. Tulip and J. A. Ibers J. Amer. Chem. SOC. 1978,100 3252. 72 K. Nakatsu Y. Inai T. Mitsudo Y. Watanabe H. Nakanishi. and Y. Takegami J. Organometallic Chem. 1978,159. 11 1. 73 T. Mitsudo Y. Watanabe H. Nakanishi I. Morishima T. Inubushi and Y. Takegarni J.C.S. Dalton 1978 1298. 74 M. Green J. Z.Nyathi C. Scott F. G. A. Stone A. J. Welch and P. Woodward J.C.S. Dalton 1978 1067. ’’ J. W. Faller and D. A. Haitko J. Organometallic Chem. 1978 149 C19. A. J. Deeming and J. Evans and [M~(q~-C~H~)(CO)~(acac)(py)]'" have been studied. No evidence for dynamic behaviour was obtained from the 13C n.m.r. spectra of [Mn(q3-C3H,)(CO)4].77 Considerable twisting of the C ring brings HA (endo) close to the metal atom [Fe-H = 1.879(9)A; neutron diffraction] in the 16e-q3-allyl complex [Fe(q3-cyclo- octenyl)L3]' [L = P(OMe)3](32),which was formed by protonating the correspond- ing q4-diene comple~.~~*~~ Thus there is a bonding C-H-Fe interaction. 31P n.m.r. signals in ratio 1 :2 are obtained even down to -140 "C (AB spectrum) so that very + rapid site exchange between HA and HB must occur in solution.However cyclo- hexenyl and cycloheptenyl analogues give ABC 31P n.m.r. spectra at low tempera- tures consistent with an asymmetric structure. Sodium amalgam reduction of this cation gives the corresponding 17e-complex which gives a variable temperature e.s.r. spectrum with 31Pnuclei in ratio 1 1 :1at -140 "C. A fast process (10" s-'; 25 "C) leads to exchange of two 31P nuclei while a slower process (-2 X lo's-'; 25 "C) exchanges all 31P nuclei." The X-ray structure of a norbornene copper(1) complex contains a short Cu-HC distance of 2.01(15)8 but the true nature of this inter- action is unknown." q '-q 1nterconversions.-Thermal decarbonylation of [Mn(CO)5( q '-cis or fruns-crotyl)] gives only [Mn(C0)4( q 3-syn-crotyl)] but using [Ir(Ph2PCH2CH2PPh2)2]C1 as a CO-acceptor under mild conditions there is complete retention of configuration; reactions (13a) and (13b).** Slow q1-q3 interconversions are found for complexes [PtCltq '-allyl)(PPh3)(RNC)] (R = Me or Ar)83*84 which give q3-allyl complexes by 76 B.J. Brisdon and A. A. Woolf J.C.S.Dalton 1978,291,and G.Doyle J. Organometallic Chem. 1978 150,67. 77 A. Oudeman and T. S. Sorensen J. Organometallic Chem. 1978 156 259. " S.D. Ittel F. A. Van-Catledge C. A. Tolman and J. P. Jesson J. Amer. Chem. Soc. 1978,100 1317. 79 J. M.Williams R. K. Brown A. J. Schultz G. D. Stucky and S. D. Ittel J. Amer. Chem. Soc. 1978,100 7407. S. D. Ittel P. J. Krusic and P. Meakin J. Amer. Chem. Soc. 1978,100 3264.M. Pasquali C. Floriani A. Gaetani-Manfredotti and A. Chiesi-Villa J. Amer. Chem. SOC., 1978,100 4918. " N. N. Druz V. I. Klepikova M. I. Lobach and V. A. Kormer J. Organometallic Chem. 1978,162,343. 83 G.Carturan A. Scrivanti U. Belluco and F. Morandini Znorg. Chim. Acta 1978,27 37. '* G.Carturan A. Scrivanti U. Belluco and F. Morandini Znorg. Chim. Acta 1978 26 1. Organometallic Chemistry 351 -co ( trans *Mn(CO)5 + :,-Mn(CO) syn loss of C1- PPh3 or RNC and where R =2,6-Me2C6H3a CHZClz solution contains five different species containing q or q3-allyl ligands. A study has been made of the more dynamic system [PdCl(q 1-CH2Ph)(PEt3)z]+; and for the optically active 77 CHDPh complex no loss of activity occurs in these inter conversion^.^^ Exchange between ql-and q3-benzyl complexes in nitrile solutions is rapid enough at elevated temperatures to give n.m.r.line broadening. Reactions.-Reversible ring opening of q3-cyclobutenyl complexes [reaction (14)]86-88 occurs and with certain substituents and for L = acac both species may be RR R R=Ar; X=Ar' or OMe present in The ring-opening is stereospecific and conrotatory for L = acac but isomeric products are obtained when L = dithiocarbamate. The q3-allyl complex [Mn(C0)4( 1-3-q3-cyclo-octenyl)] is formed by isomerization of the 1,2,6-q3-isomer on standing in hexane solution but reverts to the 1,2,6-q3-mode of bonding in the PPh3 substituted form.89 Only a few of the many examples of the use or intermediacy of q3-allyls in organic synthesis will be given.COz-insertion into [Ni( q3-2-methylallyl)z] in the presence of PMe for example gives complex (33)and several more complex examples are given 0 It I PMe (33) 13' Y. Becker and J. K.Stille J. Amer. Chem. SOC.,1978,100,845. 86 S.H.Taylor and P. M.'Maitlis J. Amer. Chem. SOC.,1978,100 4700. 87 J. R.Jack C. J. May and J. Powell J. Amer. Chem. SOC.,1978,100 5057. 88 P. M.Bailey S. H. Taylor and P. M. Maitlis J. Amer. Chem. SOC.,1978 100,4711. 89 P.J. Harris S. A. R. Knox,and F. G. A. Stone J. Organometallic Chem. 1978,148 327. A. J. Deeming and J. Evans for C0,-insertion into q3-allyl bonds in the intermediate Ni complexes in butadiene oligomerization and in all cases organic carboxylato-complexes are formed.” Organic products of nucleophilic addition of [MeCOCHCOMeI-or [MeS02CHC02Me]- at (q3-allyl) palladium complexes have been studied all involving the nucleophile adding at a terminal allylic It is claimed that the electrophilicity of the ally1 ligand increases on incorporating tertiary phosphines or phosphites into the complex.q3-Allyls of Mn93 and C094 have been studied as hydrogenation catalysts for alkenes or arenes with emphasis on the range of applicability of these catalysts. 4 q4-Cyclobutadiene Compounds Preparation and Structure.-The nickel(0) cyclobutadiene complex [Ni( 7‘-C4Me4)(bipy)]was prepared by Na reduction of the long known nickel(I1) complex [NiC12(q4-C4Me4)],in the presence of bipy and isolated as very stable copper- coloured platelets giving intense blue The state of oligomerization in these phases is not known.The complex [Ni(q4-C4Ph4),] is the first simple bis (cyclobutadiene) metal and the electronic structure of the parent C4H4 complex based on INDO SCF MO calculations has been de~cribed.~’ The complex synthesized by the photochemical reactions (15) as bright orange moderately air-sensitive crystals is apparently the first unsubstituted C4H4early transition metal complex,98 and the X-ray structure of the closely related complex [M0(q4- C4Ph4),(C0),] is reported.99 The annellation of cyclobutadiene has been achieved by the double Wittig reaction (16; X=CH2 or CO) and where X=CO the X-ray structure is established. loo 72-Cyclobutadiene has been recognized in the complex 90 P.W. Jolly S. Stobbe G. Wilke R. Goddard C. Kriiger J. C. Sekutowski and Y.-H. Tsay Angew. Chem. Internat. Edn. 1978,17 124. 91 W. R. Jackson and J. U. Strauss Aust. J. Chem. 1978,31,1073. 92 B. M. Trost L. Weber P. E. Strege T. J. Fullerton andT. J. Dietsche J. Amer. Chem. SOC. 1978,100. 3416. 93 L. S. Stuhl and E. L. Muetterties Znorg. Chem. 1978 17 2148. 94 L. S. Stuhl M. Rakowski DuBois F. J. Hirsekorn J. R. Bleeke A. E. Stevens and E. L. Muetterties J. Amer. Chem. SOC.,1978,100,2405. ” U. Griebsch and H. Hoberg Angew. Chem. Internat. Edn. 1978,17,950. 96 H. Hoberg R. Krause-Going and R. Mynott Angew. Chem. Internat. Edn. 1978.17 123. 97 D. W. Clack and K. D. Warren J. Organometallic Chem. 1978 161 C55. 98 M. D. Rausch and A.V. Grossi J.C.S. Chem. Comm. 1978,401. 99 A. Efraty J. A. Potenza L. Zyontz J. Daily M. H. A. Huang and B. Toby I.Organometallic Chem. 1978,145,315. Organometallic Chemistry 353 (34)which has a localized C=C bond (bond lengths a 1.51; b 1.52; c 1.34 A) and interestingly this has an isomeric form in which the seven-membered ring is folded so that the P atom does not approach the metal; as a consequence q4-co-ordination is then required."' + PhP-RhL Reactions.-Cyclodimerization of alkynes is a general route to q4-cyclobutadiene complexes and conjugated diynes can give complexes such as (35a). Vacuum sublimation (lop4torr) through a hot tube (525 "C) converts (35a) into a 1:1mixture with (35b) but it was established that (35c) was not formed.This is evidence against a mechanism involving reversible cyclodimerizations with diyne intermediates and for one with a transient intermediate such as (35d).'02 5 q4-Diene Compounds Preparation Structure and Dynamic Behaviour.-The displacement of q4-enones (e.g. benzylideneacetone) from [Fe(q4-enone)(C0)2L] (L =tertiary phosphine phosphite or CO) by dienes etc. is a useful route to q4-diene complexes and the synthetic ~sefulness'~~ and the kinetics of displacementlo4 have been examined. Competing associative and dissociative pathways have been identified. A novel synthesis of q4-diene complexes is the treatment of [Co(CsH5)(PPh3)(q2-PhC-CPh)] with N2CHR (R=COzMe etc.) which at room temperature gives [Co(C,H5)(q4-RCH:CPhCPh:CHR)] (isomers) as well as products with coupled alkynes that have been studied by X-ray diffracti~n."~ The X-ray structures of (36) formed from MeCGC-CECMe and [Fe(C0)5],'06 of [RuH(q4-butadiene)-loo M.B. Stringer and D. Wege Aust. J. Chem. 1978,31,1607. lo' W. Winter and J. Strahle Angew. Chem. Internat. Edn. 1978,17 128. lo' J. R.Fritch and K. P. C. Vollhardt J. Amer. Chem. Soc. 1978,100,3643. lo' B.F. G. Johnson J. Lewis,G.R. Stephenson and E. J. S. Vichi J.C.S. Dalton 1978,369. J. A. S. Howell and P. M. Burkinshaw J. Organometallic Chem. 1978,152,C5. lo' P. Hong K. Aoki and H. Yamazaki J. Organometallic Chem. 1978,150,279. '06 G. G.Cash and R. C. Pettersen Znorg. Chem. 1978,17,650. 354 A. J. Deeming and J. Evans (PMe2Ph),][PF6],lo' and of the fluxional molecule [Fe(q4-cyc1ohexadiene)-(CO)z(EtNC)]'08 have been reported.One cyclo-octatetraene is readily displaced from [Fe(q4-C8H8)(q6-C8H8)] by monodentate phosphines or phosphites (L) to give [Fe( q4-C8H8)L3] but by Ph2PCH2CH2PPhz under N2to give [Fe(q4-C8H8)(diphOS)- (N2)][v(N2) = 2105 ~m-'].'~~ Interestingly,N2 co-ordination rather than a q4to q6 conversion of the C8H8 ligand takes place but as expected the Nzis readily displaced by CO. Lanthanide metal atoms react at -196°C with buta-1,3-diene to give after work-up brown solids of type [M(C4H6),] (M = Er Nb or Sm).'" These may contain bonding as in (37b) with an unco-ordinated double bond rather than the q4-bonding as in (37a). Clear evidence for (37b) type bonding was obtained for [Pt(q4-cod)(1,4-q2-CH2CR=CRCH2)] (R = Me or Ph) which was formed by treat- ing [Pt(cod),] with the appropriate diene."' This is of course an oxidative addition of 1,3-diene.Three separate X-ray structures have been determined for q4-complexes of type (38) prepared by reaction of [Fe2(CO),] with substituted cyclopropenes or by reaction of a complex of type (30)with PPh3 or CO. The q4-vinylketen description (38a) has been preferred by some"2 but the q3-allyl/acyl description (38b) by others,' 13*'14 partly on the basis of the CAC bond lengths as found in the appropriate molecules. R3 R4 R3 R4 R' R2 R3 R4 C"C/A Ref. \/ \/ CTC Rz \ 1 \* H Ph Ph Ph 1.494 114 C C \ C=O H H COzMe OMe 1.48 112 *O R< Fe' Me Me H H 1.442 113 (COh The dynamic behaviour of q4-diene complexes of iron continues to be of interest.[Fe(C0)3(q4-cycloheptatriene)] shows no n.m.r. line broadening up to about 100"C but by spin saturation transfer techniques the transfer of spin between ring positions lo' T. V. Ashworth E. Singleton M. Laing and L. Pope J.C.S. Dalton 1978 1032. H. Behrens G. Thiele A. Piirzer P. Wiirstl and M. Moll J. Organometallic Chem. 1978 160 255. H. Felkin P. W. Lednor J.-M. Normant and R. A. J. Smith J. Organometallic Chem. 1978,157.C64. 'lo W. J. Evans S. C. Engerer. and A. C. Neville J. Amer. Chem. Soc. 1978,100,331. '11 G.K.Barker. M. Green J. A. K. Howard J. L. Spencer andF. G. A. Stone J.C.S. Dalton 1978,1839. T. Mitsudo. T. Sasaki Y. Watanabe Y. Takegami S. Nishigaki and K. Nakatsu J.C.S.Chem. Comm. 1978,252. '13 P. Binger B. Cetinkaya and C. Kriiger J. Organometallic Chem. 1978,159,63. 11' G.Dettlaf U. Behrens and E. Weiss Chem. Ber. 1978 111 3019. 355 Organometallic Chemistry 1and 6 was detected for X =CH2 consistent with process (17)."' Where X =CO process (16) must be slow since by selectively destroying one of the two enantiomers illustrated using circularly polarised light (380-500 nm) a specific rotation of 0.012 f0.002"was measured.'16 Since this only corresponded to about 3% destruc- tion the estimated rotation for the pure enantiomer is about 700". The method of spin saturation transfer has been applied to a study of [Fe(q"-c~H~)(rl"-c~H~)l (CsH8 = cyclo-octatetraene)."' Whizzing of the q4-ring could not be frozen out (AGs< 23 kJ mol-') while there is no evidence for shifts in the other ring.The transition state for the exchange of the two rings as deduced from spin saturation transfer must have the four types of CH in the q6-rhg distinguishable. Dynamic 'H and 13Cn.m.r. studies on (Cr(CO),(q"-butadiene)] and [M~(CO),(q~-butadiene)~] have shown these to undergo polytopal rearrangements possibly via trigonal pris- matic transition states.'18 The complexes [CoL3(q4-diene)]' (L =tertiary phos- phine; diene =butadiene or isoprene) are square pyramidal from limiting low- temperature 'H and 31Pn.m.r. spectra but are fluxional at higher temperatures.'" Reactions.-q"-Diene complexes may be protonated to give q 3-allyl complexes. [RuH(q6-C6Me6)( q4-cyclohexa-1,3-diene)]+ was obtained by protonation and although the q3-allyl complex is not formed it is involved in a rapid equilibrium with the hydrido(q4-diene) complex.This is necessary to account for the three-proton n.m.r. signal (8 -2.90 p.p.m.) which is the average for RuH and two endo ring hydrogen atoms. 13' Another example of electrophilic addition is the formation of [Fe(CO)3(CsHsCOMe)]+ by treatment of the cyclo-octatetraene complex [Fe(CO)3(CsHs)] with the Friedel-Crafts acylating reagent (MeCOCl and AlC13). A [5,l,O]bicyclic system had been proposed for this as for the protonated q4-CsHs complex but the X-ray structure establishes a [3,2,1]-bicyclic ligand containing q 3-allyl and q2-monoene groups.'2o Oxidation of [Fe(CO)3(CsHs)] with AgPF6 for example gives the coupled product [(C0)3Fe(~5-C8H8-C8H8-~ 5)Fe(CO)3]2+and while a C-C bovd is formed between the two Cs rings each forms a [5,1,0]-bicyclic system.12' A1Cl3 induces carbonylation of [Fe(C0)3(q4-C6HS)] (C6H8 = cyclohexa-1,3-diene) to give the ring-expanded q4-1,3,5-cycloheptadien-2-onecomplex [Fe(CO),(C,H80)] CO being incorporated into the c6 ring.Thermal treatment of this under CO pressure gives further (transannular) carbonylation to give bicyclo [3,2,l]oct-2-ene-4,8-dione(CSHs02).'22 K. J. Kavel and M. Brookhart J. Amer. Chem. SOC.,1978,100,1619. S. Litman A. Gedanken Z. Goldschmidt and Y.Bakal J.C.S. Chem. Comm. 1978,983. 11' B.E.Mann J.C.S. Dalton 1978 1761. 11* C.G. Kreiter and S. bkar J. Organometallic Chem. 1978,152 C13.M. Bressan R. Ettorre and P. Rigo J. Organometallic Chem. 1978 144 215. 120 A. V. Rivera and G. M. Sheldrick Acta Cryst. 1978,B34,1716. lZ1 N.G.Connelly,M. D. Kitchen R. F. D. Stansfield S. M. Whiting and P. Woodward J. Organometallic Chem. 1978,155 C34. lZ2 B.F. G. Johnson,K. D. Karlin and J. Lewis J. Orgartometallic Chem. 1978,145 C23. A. J. Deeming and J. Evans Important 1,3-diene coupling reactions occur with [Pt(cod),] or [Pt(C,H,),(PMe,>] although it is unlikely that q4-co-ordination is involved at any stage Scheme 18. These products of course relate to intermediates in butadiene oligomerizations at nickel. The trans- arrangement of the vinyl groups in the divinylmetallocyclopentane is significant in that cis-divinylcyclobutane is obtained as a nickel-catalysed product.Since divinyl-metallocyclobutane isomers should be interconvertable by q 1-73-allyl interconversions it is not clear whether the cis- organic product is formed because reductive elimination is favoured for this arrangement or whether for nickel the cis-metallocycle is the stable form."' -[Pt(C2H4),(PMe3)] Scheme 1 *X-ray structure 6 qs-Diene Compounds Preparation and Structure.-Treatment of [W(C5H5)(C0),Cl3] with sodium cyclo- pentadienyl in THF gave a product of apparent formula [W(C,H,),(CO),] the yields of which are increased by addition of NaBH,. The X-ray structure (39) shows that two C,H groups have been added to a C ring to generate the substituted q3-cyclopentenyl ligand.'23 Treatment with sodium and then FeCI; gives a ferrocene derivative by introducing a Fe atom between the two unco-ordinated C5 rings.', Complex (39)is an 18e-system as is [W(C5H5),(C0),] by virtue of one q3-and one q5-ligand.The X-ray structures of and the corresponding indenyl complex'26 prepared in low yield by the reaction of W(CO) with indene are reported. Rapid interchange between the q3-and q5-ligands occurs. An improved synthesis of [M2(C0)6(q5-CsH4R),] (M = Cr Mo or W) by a classical route using Na[C5H4R] has been described. 127 More specialized routes to cyclopentadienyl complexes are reported. Diazocyclopentadiene C5H4N2 reacts with various metal halo complexes to give q5-C51-L,X (X = halide) and this has been applied to Fe and Re.128 Fulvenes 123 J. L. Atwood R.D. Rogers W. E. Hunter I. Bernal H. Brunner R. Lukas and W. Schwarz J.C.S. Chem. Comm. 1978,451. 124 H. Brunner R.Lukas and A. Woditsch J. Organometallic Chem. 1978 161 C49. 125 G.Huttner H. H. Brintzinger L. G. Bell P. Friedrich V. Bejenke and D. Neugebauer J. Organo-metallic Chem. 1978,145 329. 126 A. N. Nesmeyanov N. A. Ustynyuk L. G. Makarova V. G. Andrianov Yu. T. Struchkov and S. Andrae J. Organometallic Chem. 1978,159 189. 127 R. Birdwhistell P.Hackett and A. R. Manning J. Organometallic Chem. 1978,157 239. 128 W. A. Hermann and M. Huber Chem. Ber. 1978,111,3124. Organometallic Chemistry 357 are reduced with LiAlH4 to give substituted cyclopentadienyl anions that may be used to make q5-C5H,R c~mplexes,'~~ and by reacting [(EtO)SiMe2(C5H5)] or [(EtO),Si(C5H5)] with silica gel cyclopentadiene groups may be attached to the surface and metal atoms co-ordinated to these.One such silica-bound complex (40) has been applied to alkene hydroformylation. There is no tendency in these complexes to form binuclear or polynuclear complexes as with unsupported spe- cies.130 The structure of [Fe2(C0)4(q 5-C,H5)2] has been accurately redetermined at 74 K by X-ray and neutron diffraction and calculated electron deformation maps do not reveal electron accumulation between the metal atoms.13' 3,5-Dimethyl-aceheptylene reacts with Mn2(CO)lo to give complex (41) containing two Mn(CO) units bonded either side of the ligand each to a C5 group.'32 Manganocene is high spin (6Alg ground state) and shows cyclopentadienide-type chemistry.The 1,l'-dimethyl substituted compound shows cross-over between high and low spin forms and now the electron diffraction structures of both forms have been measured. The Mn-C distances are greater in the 6Al than in the 2E2 ground state form [2.433(8) compared with 2.144(12) A]. The mol fraction of high spin form [0.62(4)] at 100 "C in the gas phase compares well with that in toluene at 98 0C.'33 Complete methyl-substitution favours low spin and for [Mn(C5Me5)2] there is no evidence for thermal population of the high spin state. This complex undergoes reversible reduction to the diamagnetic complex [Mn(C5Me5),]- iso- electronic with decamethylferrocene.. 34 The first 13C n.m.r. isotope shifts in paramagnetic compounds have been measured for the metallocenes [M(C,R,),] (R = H or D; M = Co Fe+ Cr or V).These are discussed using ferrocene and perdeuterioferrocene as references. '35 The 13C and 'H n.m.r. spectra of the paramagnetic compounds [V(C5H4R),X] (R = Me or Et; X = halide) are well resolved and electron spin delocalizations as determined from n.m.r. shifts have been discussed. These complexes show no tendency to dimerise as does [Ti(C5H5),Cl]. with EtLi or Me3SiCHzLi (RLi) 136 Treatment of [V(C5H5),ClZ] gives solutions of the complexes [V(C5H5),R2]; these were characterized by their e.s.r. spectra which were compared with that of the parent dichloride and treated theoretically. lZ9 P. Renaut G. Tainturier and B. Gautheron J. Organometallic Chem.1978,148,35. 130 F.R. W. P. Wild G. Gubitosa. and H. H. Brintzinger J. Organometallic Chem. 1978,148 73. 13' A. Mitschler B. Rees and M. S. Lehmann I.Amer. Chem. SOC. 1978,100,3390. 13' M.R. Churchill and S.A. Julius Inorg. Chem. 1978,17 2951. 133 A. Almenninger A. Haaland and S. Samdal J. Organometallic Chem. 1978,149. 219. 134 J. C. Smart and J. L. Robbins J. Amer. Chem. SOC.,1978,100,3936. 135 F.H.Kohler and W. Prossdorf J. Amer. Chem. SOC. 1978,100 5970. F. H. Kohler and W. Prossdorf Chem. Ber. 1978,111,3464. 137 A. G. Evans J. C. Evans D. J. C. Espley P. H. Morgan and J. Mortimer J.C.S. Dalton 1978,57. A. J. Deeming and J. Evans Interchange between q3-and q5-C5H5 rings has been menti~ned'~~"~~ and 77'-and q5-rings commonly interchange as in a recent example [Mo(q'-C,H,)(q '-CsHs)(NO)(S2CNR2)] which also undergoes 1,2-shifts of the q '-ring and rotation about the C-N bond as independent fluxional proce~ses.'~~ Energy changes have been calculated for the cyclopentadienyl compounds C5H5X [X =H Me SiH, Mn(CO), Li CUR efc.] as the group X slides across the face of the C5 ring passing from a q'-arrangement through q3,q5,and finally to q2.The relative contributions of the acceptor orbitals of X of a and e symmetry control the preferred geometries and the lowering of the energy of the e orbital going down the group (X = CH, SiH3 GeH, or SnH3) is responsible for the decreasing barrier to sigmatropic shifts.13' Various calculations on q-carbon ring complexes have been carried out relating the influence of ring size to the metal-ligand interactions 'H n.m.r.shifts et~.'~' Reactions.-CF,C~CCF reacts with [MO(C~H~)~I(NO)] adding in a Diels-Alder fashion to one of the cyclopentadienyl ligands to give a bicylo-ligand and this appears to characterize cyclopentadienyl ligands that are less than pentuhaptu or where a greater than 18e-configuration occurs as with nickelocene. 14' Nickelocene also undergoes a strange reaction with bis(dipheny1phosphino)maleic anhydride Ph2PC4O3PPh2,to give a 70% yield of the complex (42) with one C5H5 ligand having inserted into the bidentate ligand. (42) is diamagnetic and a formal localization of a positive charge on nickel and a negative charge on the chelating ligand would account for Unusual behaviour of q5-ligands is also found in the thermal decom- position of [Zr(C5Me5),(H)(CH2CHMe2)]to give 2-methylpropane.143 There is no kinetic isotope effect on deuteriation at the metal-hydride site but surprisingly only on replacing CH by CD3 at the q5-rings. The hydrogen atom transferred to CH2CHMe2 is derived from a CH group not from ZrH and it is proposed that the reductive elimination occurs for the intermediate (43)and not the original complex. H-H M. M. Hunt W. G. Kita B. E. Mann and J. A. McCleverty J.C.S. Dalton 1978,467. N. T. Anh M. Elian and R. Hoffmann J. Amer. Chem. SOC. 1978,100 110. 140 D. W. Clack and K. D. Warren Inorg. Chim. Acta 1978,30,251; J. Organometallic Chem. 1978,157 421 and 1978,162,83. 14' M. M. Hunt and J. A. McCleverty J.C.S.Dalton 1978,480. 14' W. Bensmann and D. Fenske Angew. Chem. Internat. Edn. 1978 17,462. 143 D. R. McAlister D. K. Erwin and J. E. Bercaw J. Amer. Chem. Soc. 1978 100 5966. 144 S. Dzierzgowski R. Giezynski M. Jarosz and S. Pasynkiewicz J. Organometallic Chem. 1978 152 281. 13' 359 Organometallic Chemistry 7 q6-Arene Compounds Preparation and Structure.-The black paramagnetic arene complex [TiC12(C6Me6)][A1C14] is formed by reducing [TiCl,] with Et2AlCl in the presence of he~amethylbenzene,'~~ and Nb atoms react with benzene to give [Nb(C6H6)2] as deep red-purple very air-sensitive crystals. The corresponding toluene and mesity- lene compounds have also been described and their e.s.r. spectra re~0rded.l~~ [W(arene)2] has been prepared previously in low yields by reduction methods or on a small scale using W atoms from a hot filament but now using W atoms formed with an electron gun 1.4 g is obtained in 2.5 h.The compound is much more basic than Moor Cr analogues being protonated in dilute aqueous HCl.146 The preparations of various Moo and Mo" arene compounds including [Mo( q6-arene)(PR,),] are described.147 X-Ray structure determinations of [Mo(q7- C7H7)(BPh4)] and [NEt,][Mo(CO),(BPh,)] have established q6-C6HsBPh3in both'48 and the structure of [Fe(qs-CsHs)(q6-C24H12)]+ has shown that Fe is co-ordinated to one of the outer coronene c6 rings as expected from calculations.149 Using the complexes [RuC12(arene)12 the hydrogenation catalyst [RUHCl(C&k6)(PPh,)] has been ~ynthesized,"~ and reduction with sodium naphthenide in the presence of ligands leads to [Ru(C6H6)LL'] (L and L'are different tertiary phosphines or pho~phites)."~ Complexes of type [Ru(q4-arene)( q6-arene)] have been synthesised by cyclo- trimerization of alkynes with [R~(C~H~)(diene)]l~~ or from Ru atoms and arenes.15 The benezene complex was prepared from Ru atoms and its limiting low-temperature n.m.r.spectrum is consistent with the formulation [~u(q"-C~~~)(q'-C~Hg)l. Simul-taneous broadening of the n.m.r. Me-signals (intensity ratio 2 6 2 :2) of the dynamic complex [Ru(q4-C6Me6)(q6-C6Me6)] occurs and the most likely process involves [R~(q~-c~Me~)~]. Addition of AlMe dramatically affects the d.n.m.r. spectra by accelerating preferentially a localized exchange in the q4-ligand this being too slow for the pure complex to affect the spectra n0ticeab1y.l~~ The metal atom method has been applied to the synthesis of [Ni(C6F5)2(q6-toluene)], which is isostructural with the Co analogue already re~0rted.l~~ Reactions.-There is a nearly quantitative formation of the complexes [Cr(C0)3(fulvene)] by photochemical substitution of arene by dimethyl- or diphenyl-fulvene at the complexes [Cr(CO),(arene)].156 An interesting loss of N2 and HPF6 occurs on heating crystals of [Mn(Co),(q6-c6H,N,)][PF6] to give ring contraction to [Mn(C0)3(q5-C5H4CN)].157 Both benzyl anions and cations may be stabilized by co-ordination. Complete exchange of toluene methyl hydrogen atoms 14' F. G. N. Cloke M.L. H. Green and D. H. Price J.C.S. Chem. Comm. 1978,431. F. G. N.Cloke M. L. H. Green and G. E. Morris J.C.S. Chem. Comm. 1978,72. 147 E. Carmona-Guzman and G. Wilkinson J.C.S. Dalton 1978 1139. M. B. Hossain and D. van der Helm Inorg. Chem. 1978,17,2893. 149 G. Schmitt W. Keim J. Fleischhauer and U. Walbergs J. Organometallic Chem. 1978 152 315. Is" M. A. Bennett T.-N. Huang A. K. Smith and T. W. Turney J.C.S. Chem. Comm. 1978,582. H. Werner and R. Werner Angew. Chem. Internat. Edn. 1978,17,683. A. Lucherini and L. Porri J. Organometallic Chem. 1978,155 C45. 153 P. L. Timms and R. B. King J.C.S. Chem. Comm. 1978 898. M. Y. Darensbourg and E. L. Muetterties J. Amer. Chem. SOC.,1978,100 7425. K. J. Klabunde B. B. Anderson M. Bader andL.J. Rabonovich J. Amer. Chem. SOC., 1978,100,1313. F. Edelmann D. Wormsbacher. and U. Behrens Chem. Ber. 1978,111,817. G. A. M. Munro and P. L. Pauson J. Organometallic Chem. 1978,160 177. A. J. Deeming and J. Evans occurs for solutions of [M~~(pSMe>~(toluene)~] in D20-Na,P04 buffer (pD = 11) presumably via the co-ordinated benzyl anion,'58 whereas many examples of benzyl cation stabilization are known as in a recent Calculations for benzyl cations free and co-ordinated to Cr(C0)3 show an increased .rr-electron density in the C-C bond to the exocyclic carbon and indicate that the bend of 40"of this bond out of the arene plane towards the metal atom gives a stabilization of about 150 kJ mol-' .16' The fluorene complex [Cr(CO)3(q6-C13Hlo)] deprotonates with KOBu' to give an intermediate q6-species with a negative charge formally on the C ring which isomerizes with ti of several minutes to the q5-species reaction (19).This product methylates at Cr with Me1 but the methyl migrates to the C ring and Cr from this to the c6 ring back to its original position.l6* An e.s.r. and 'H n.m.r. study has shown that electron transfer between [Cr(arene)2] and [Cr(arene)2]' approaches the diffusion-control limit (kexch-3 x 10' mol-' dm3 s-') the rate being only slightly affected by methyl substitution at the arene.I6* 8 Nucleophilic Addition at Co-ordinated Carbocycles exo-Nucleophilic addition at [Fe(C0)3(q5-cyclohexadienyl)]+ has been confirmed for F-addition which only occurs with 'bare' F-(KF/18-crown-6 ether/CH3CN),'63 and for CN- addition.'64 exo-Addition of Pr'S- at a q3-allyl group co-ordinated at Fe also occurs.'65 The reaction of [M(C5Me,)(q4-C7H8)]2' (M= Rh or Ir; C7H8 = cycloheptatriene) with acetone gives the exo-isomer of [M(C5Me5)(q'-C7H8CH2COMe)]'.'66 Nucleophiles do not always add at the carbocycle of course and transient intermediates in the reaction of [M(C0)3(q7-C7H7)]' (M =Mo or W) with I- have been studied by flow 'H n.m.r.and stopped-flow spectrophotometric methods.'67 An intermediate with a M-I bond is rapidly formed but this then isomerizes by I- transfer from M to C7H7 not necessarily intramolecularly to give [M(CO),(C,H,I)] and finally CO is lost to give [M(C0)21(C7H7)]. This is ample demonstration that isolated products do not necessarily indicate the initial site of attack.The nucleophilic addition of tertiary phosphines at q4-and q6-cyclic IS8 W. E. Silverthorn C. Couldwell and K. Prout J.C.S. Chem. Comm. 1978 1009. IS9 D. Seyferth J. C. Merola and C. S. Eschbach J. Amer. Chem. Soc. 1978,100 4124. 160 D. W. Clack and L. A. P. Kane-Maguire J. Organometallic Chem. 1978 145 201. 161 A. N. Nesmeyanov N. A. Ustynyuk L. G. Makarova S. Andre Yu. A. Ustynyuk L. N. Novikova and Yu. N. Luzikov J. Organometallic Chem. 1978,154,45. 162 Ch. Elschenbroich and U. Zenneck J. Organometallic Chem. 1978 160 125. 163 B. F. G. Johnson K. D. Karlin J. Lewis and D. G. Parker J. Organometallic Chem. 1978,157,C67. 164 B. F. G. Johnson J. Lewis D. G. Parker P.R. Raithby and G. M. Sheldrick J. Organometallic Chem. 1978,150,115. 165 A. V. Rivera and G. M. Sheldrick Acta Cryst. 1978 B34 3374. 166 C. White S. J. Thompson and P. M. Maitlis J.C.S. Dalton 1978 1305. 167 P. Powell L. J. Russell E. Styles A. J. Brown 0.W. Howarth and P. Moore J. Organometallic Chem. 1978,149 C1. Organometallic Chemistry polyenes has also been studied mechanistically.'68 A theoretical study of the problem has indicated that attack at metal or CO in the series [M(CO),L] (M = Ni L = C2H4;M =Co L = CJHs etc. through to Cr) should occur since calculated 'frontier electron density parameters' favour attack at one or other of these sites depending upon M but that attack at alkene carbon should not occur initially.'69 9 Dinuclear and Polynuclear Compounds The range of hydrocarbon bridges between metal atoms is enormous.For example several papers have appeared describing bridging cyclo-octatetraene as in Scheme 2. [Ti2(CgH&] was known previously to have a p-CsHs as in (A) but reduction Scheme 2 Some M2(C8H8) arrangements (0= CH) gives the green diamagnetic complex [Ti2(C8H8)3]2- believed to contain the bridge as in (B); only one 'H n.m.r. singlet is observed so accidental coincidence or exchange behaviour is necessa~y.'~~ contains p-C,H8 type (c)but the [CO~(C~H~)~(C~H~)] structure of the oxidation product [CO,(C~H,)~(C,H,)]~' is ~nknown.'~' In the salt [Nd(C8H8)(THF)2] [Nd(C,H&] the anion and cation are linked by a bridge of type (D),'72while [MO2(CgHg)3] contains two q4-CgHg rings and a p-C8Hs as in (E).173 [Cr(C,H,),] reacts with [C,H8]2- to give [Cr2(CsH,),(CsH8)] in which the C ring has opened as in (F).174 On treatment of this Cr compound with CO [Cr2(C,H,),(CO),] and cyclo-octatetraene are formed.The C8Hs bridge in (F) is rather like similar bridges formed by alkyne oligomerization with [M2(C5Hs),(CO),] (M = Cr or Mo); D. M. Birney A. M. Crane and D. A. Sweigart J. Organometallic Chem. 1978 152 187. D.A.Brown J. P. Chester and N. J. Fitzpatrick J. Orgunometallic Chem. 1978,155 C21. 170 S. P. Kolesnikov J. E. Dobson and P. S. Skell J. Amer. Chem. SOC. 1978 100,999. 17' J. Moraczewski and W. E. Geiger J. Amer. Chem. SOC. 1978,100,7429. 172 C. W.DeKock S. R. Ely T. E. Hopkins and M. A.Brault Inorg. Chem. 1978 17 625. F. A. Cotton S. A. Kock A. J. Schultz and J. M. Williams Inorg. Chem. 1978 17 2093. "* W. Geibel G. Wilke R. Goddard C. Kriiger and R. Mynott J. Organometallic Chem. 1978,160,139. 362 A. J. Deeming and J. Evans the X-ray structure of [MO(CSH~)~{CSH~(COZM~)~}] shows an open CS chain but with different attachment at the Mo atoms to that in (F).17’ [M Reactions of alkenes and alkynes with [M2(C5H5)2(CO)4] =Cr (X-ray structure rep~rted’~~) and a11ene’79 Mo or W] have been studied and the a~etylene’~~”~~ adducts examined and crystal structures determined. In the alkyne adducts the C-C axis is perpendicular to the M-M axis and such systems have been studied theoretically.180~181Terminal q2-co-ordination of alkenes and alkynes in clusters is rare because of the strong tendency towards oxidative addition (C-H cleavage) or oligomerization but two T2-C2H4 complexes are reported [OS~(CCJ),~(C~H~)]’~~ and [HOs3(SMe)(CO),(CzH4)].ls3 The X-ray structure of the latter has been deter- mined. These were available because readily displaceable groups were present in the clusters used to make them. Oxidative addition of alkenes can give vinyl complexes and these are obtained from the above compounds. Three structures of vinyl compounds of type [HOS,(CO)~,(CRCHR’)] are reported. Where R = R’ = H the U-T arrangement (44a) is present (full neutron and X-ray studyiB4) but a p3-arrangement is adopted when R = R’= CF3.18’ In contrast the zwitterionic form (44c) occurs when R=H and R‘=NEt2.186 In the iridium clusters It ’a,\ 1 CH=NEt2 05 [I~,(C~)~(C,H~Z)Z(CSH~~)]’~~ derived from and [I~~(CO)~Z(C~H~~)(CSH~~)(C~H~O)~~~~ [Ir4(CO)12] and cyclo-octa-1,5-diene (CsH12) both p-vinyl and p-alkyne ligands derived by oxidative addition are present.The p3-indyne ligand in [H20S3(C0)9(p3-CgH6)] also derived by oxidative .addition (of indene) has been shown to contain dynamic co-ordination; evidence for concerted rotation and 175 S. A. R. Knox R. F. D. Stansfield,F. G. A. Stone M. J. Winter and P. Woodward J.C.S. Chem. Comm. 1978 221. 176 M. D.Curtis and W. M. Butler J. Organometallic Chem. 1978,155 131. 177 D.S.Ginley C. R. Bock M. S. Wrighton B. Fischer D. L. Tipton and R. Bau J. Orgunometallic Chem. 1978,157,41.178 W. I. Bailey M. H. Chisholm F. A. Cotton and L. A. Rankel J. Amer. Chem. SOC.,1978,100 5764. 179 W. I. Bailey M. H.Chisholm F. A. Cotton C. A. Murillo and L. A. Rankel J. Amer. Chem. SOC.,1978 100,802. 180 A. B. Anderson J. Amer. Chem. SOC.,1978,100 1153. 181 D.L.Thorn and R. Hoffmann Inorg. Chem. 1978,17,126. 182 B. F.G.Johnson J. Lewis and D. Pippard J. Organometallic Chem. 1978,145 C4. 183 B. F.G.Johnson J. Lewis D. Pippard and P. R. Raithby J.C.S. Chem. Comm. 1978,551. 184 A. G. Orpen D. Pippard G. M. Sheldrick. and K.D. Rouse Acru Cryst. 1978 B34,2466. 185 M. Laing P. Sommerville Z. Dawoodi M. J. Mays and P. J. Wheatley J.C.S. Chem. Comm. 1978 1035. 186 J. R.Shapley M. Tachikawa M. R. Churchill and R. A. A. Lashewysz J.Orgunometallic Chem. 1978 162,C39. 187 G. F.Stuntz J. R. Shapley and C. G. Pierpont Znorg. Chem. 1978,17 2596. 188 C. G. Pierpont G. F. Stuntz and J. R. Shapley J. Amer. Chem. SOC.,1978 100 616. Organometallic Chemistry 363 flipping of the indyne ligand comes from d.n.m.r. The related ortho-phenylene (benzyne) complex [H,OS~(C~)~(C,H~)] originally prepared directly from benzene and [OS~(CO)~~] may also be prepared from benzaldehyde or benzyl Alkynes react with metal clusters in many ways. They may be bisected as in the reaction of PhCGCPh with [os6(co)18] to give [os,(c~),,(~~-cP~)(~~-cP~)].'~~ p3-Co-ordination of alkynes is common but MeO,CC~CCO,Me (L) reacts with [Ir4(co)12] to give [Ir4(Co)8(p2-L)2(p4-L)2] containing a rectangular Ir4 geometry and a new form of alkyne to cluster bonding.'92 Oligomerization is however the dominant behaviour as in the formation of compounds of apparent formulae [Fe3(C0)6(EtC~CH)4],193[R~3(C0)7(B~tC~CH)4],194and[Os3(CO),(EtC~CH)2] (x = 9 or Alkyne ligands are not present in these compounds because new ligands are formed by C-C cleavage or formation hydrogen atom transfer from C to M or from C to C and CO incorporation into the organic ligand.Three separate reports of the formation of p2-CR-CR-CR bridges between nickel,196 palladi~m'~' or platinum198 have appeared. In asymmetric bridged compounds u-bonds from the terminal carbons to one metal atom and a q3-allyl bond to the other can be envisaged but for symmetrical bridges this description is inappropriate.The complex [H30s3(C0)9(CCR2)]' has been shown to have a non-centred probably tilted arrangement of the CCR ligand (n.m.r. evidence) while the related complex [Co3(C0),(CCR2)]' has been discussed in terms of a centred vertical arrangement. A theoretical treatment favours an arrangement for cobalt as for osmium.199 In9 A. J. Deeming J. Organometallic Chem. 1978 150 123. 19' K. A. Azam C. Choo Yin and A. J. Deeming J.C.S. Dalton 1978 1201. 191 J. M. Fernandez B. F. G. Johnson J. Lewis and P. R. Raithby Acta Cryst. 1978 B34,3086. P. F. Heveldt B. F. G. Johnson J. Lewis P. R. Raithby and G. M. Sheldrick J.C.S. Chem. Comm. 1978 340. 193 E. Sappa A Tiripicchio and A. M. M. Lanfredi J.C.S. Dalton 1978 552. 194 S. Aime G.Gervasio L. Milone E. Sappa and M. Franchini-Angela Inorg. Chim. Acta 1978,27 145. 195 M. R. Churchill and R. A. Lashewycz Znorg. Chem. 1978,17 1291. 196 P. D. Frisch R. G. Posey and G. P. Khare Znorg. Chem. 1978 17,402. P. bL Bailey A. Keasey and P. M. Maitlis J.C.S.Dalton 1978 1825. 19' 19' W. E. Carroll M. Green J. A. K. Howard M. Pfeffer and F. G. A. Stone J.C.S. Dalton 1978 1472. 199 B. E. R. Schilling and R. Hoffmann J. Amer. Chem. SOC.,1978,100,6274.