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7 Transition-metal Chemistry By J. R. DILWORTH G. J. LEIGH and R. L. RICHARDS ARC Unit of Nitrogen Fixation University of Sussex Falmer Sussex BN 1 9QJ 1 Groups IV and V Titanium Zirconium and Hafnium;Vanadium Niobium and Tantalum In contrast to the explosion of organometallic and complex chemistry which has been concentrated at the right-hand end of the Transition Series the left-hand end has been somewhat neglected and much of its inorganic chemistry has proceeded along well-tried classical paths involving such areas as phase-studies and formation of polymeric 0x0-species in solution. Of late however there has been greater emphasis on extending to Groups IV and V the techniques and ideas established with for example the platinum metals and consequently new insights are being obtained.The elements of Groups IV and V are electron-deficient in their complexes as judged by the 18-electron rule. Their chemistry which shows a preference for higher rather than lower oxidation states often belies this. Co-ordination number 5 (as in [TiClJ and [TiBrJ) is not usual for titanium(Iv) but has been observed in a dichloromethane solution containing TiC1 or TiBr and the appropriate halide.' In the solid state these ions are dimerized through halogen bridges. Co-ordination number 6 is of course common but is not without surprises. The anion in [AsPh,] [Ta(benzenedithiolate),l exhibits trigonal-prismatic co-ordination,2 but whereas the niobium analogue is regular one of the dithiolates in the tantalum complex is twisted about the two-fold axis by ca.12",and the other two are bent about the S-S axis. No explanation is forthcoming. Co-ordination number 7 has been reported3 in complexes such as [TaCl,L2] (L =NN'-dicyclohexylacetamidinate),which form distorted pentagonal bipyramids with halides in the axial position. However co-ordination number 8 is apparently much more common but several stereochemistries appear possible. The complex K,[Nb(CN),],2H20 is apparently isomorphous with its molyb- denum analogue and thus [Nb(CN),I4- is probably dodecahedral. This is confirmed by the e.s.r. spectrum which also is interpreted as showing that in solution in glycerol the ion takes on an antiprismatic c~nfiguration.~ The antiprismatic structure has now been identified for the first time in a solid of the type [M(LL'),] for M = Nb and LL' =2,2,6,6-tetrame thylheptane-3,5 -dionate .5 Another variant has been recog- nized in the complex [{Nb(C,H,0,),}20(HCl),],MeCN.6The tropolonate ligand is C.S. Creaser and J. A. Creighton J.C.S. Dalton 1975 1402. J. L. Martin and J. Takats Inorg. Chem. 1975 14 1358. M. G. B. Drew and J. D. Wilkins J.C.S. Dalton 1975 261 1. P. M. Kiernan and W. P. Griffith J.C.S. Dalton 1975 2489. T. J. hnnavaia B. L. Barnett G. Podolsky and A. Tulinsky J. Amer. Chem. Soc. 1975,97 2712. 149 J. R.Dilworth G.J. Leigh and R. L. Richards found to have a very short bite [2.43(2) A compared with a previous shortest bite of 2.490(6)A]. This may be associated with the very short interligand distances observed but the 'NbOs' nucleus is best described as 'an irregular bicapped trigonal It is likely however that the dodecahedral structure as evidenced by [NbX,(diarsine),] (X = C1 or Br)7 and [MCl,(diar~ine),]',~ is the most common.It is evident that the various structures available for eight co-ordination are not widely separated in energy so that non-rigidity is common. The complex [Zr(acac),(NO,),] (acac =acetylacetonate) exhibits a distorted dodecahedral co- ordination in the solid state,' and the reasons for the particular stereoisomer which is observed have been discussed. In solution the number of co-ordinating groups does not change but the complex is stereochemically non-rigid on the n.m.r. timescale down to -130 "C with a coalescence temperature of -144 "C.The complex ion [Ta(S,CNMe,),]' is also dodecahedral in the solid state." However in solution the coalescence temperature is -62 "C whereas the isoelectric [M(S2CNEt2),] (M = Ti Zr or Nb) is non-rigid down to at least -140 "C. The reasons for these differences are not evident. There have also been developments in classes of compounds which have been known for some time. Thus tetrahedral titanium has been resolved for the first time in e.g. [(n-CsH4CHMePh)(?r-CSHs)PhTiCI]"and [(?r-CSH4CMe2Ph)-(rr-C5Hs)TiC1(OPh)]12 (see also Chapter 8 p. 192 Scheme 5). The complexes [M(BHJ4] (M =Zr or Hf) can be considered as having the metal in a co-ordination number of 12 since each borohydride ion is bonded to the metal uia a triple- hydrogen bridge.It was suggested some time ago that the borohydride group in these systems can be regarded as a three-electron donor (cf.allyl) and thus the compounds are 16-electron species. However a simple group-theoretical argument has been held to show that the borohydride group is in fact a 3.5-electron donor.13 It is not easy to envisage what this means particularly as there are no geometrical conse- quences (cf.NO) of this assignment. However the arguments are based upon B-H bonding electrons being involved in linkage to the metal and no others. A Raman and i.r. study of [Hf(BH,),] and [Hf(BD,),] suggests that these molecules contain a significant amount of direct Hf-B b~nding.'~ This alone casts doubt on the concept of a ligand donating specific numbers of electrons to an acceptor.A. R. Davis and F. B. Einstein Inorg. Chem. 1975,14 3030. 'D. L. Kepert and K. R. Trigwell J.C.S. Dulron 1975 1903. * J. C. Dewan D. L. Kepert C. L. Raston and A. H. White J.C.S. Dulron 1975 2031. V. W. Day and R. C. Fay J. Amer. Chem. SOC.,1975,97,5136. lo R. C. Fay D. F. Lewis and J. R. Weir J. Amer. Chem. SOC.,1975,97,7179. l1 C. Moise J. C. Leblanc and J. Tirouflet J. Amer. Chem. Soc. 1975,97,6272. 12 A Dormond J. Tironflet and F. Le Moigne J. Orgunometallic Chem. 1975,101 71. 13 A. Davison and S. S. Wreford Znorg. Chem. 1975 14 703. l4 T. A. Keiderling W.T. Wozniak R.S. Gay D. Jarkowitz E. R. Bernstein S. J. Lippard andT. G. Spiro Znorg. Chem. 1975,14 576. Transition -metal Chemistry 151 Complexes such as [(n-C,H,),Zr(BH,),] contain double-hydrogen bridges.However there is a rapid exchange of hydrogens between the B-H bonds and the C5H5 rings. Methylene intermediates such as (1) and (2) have been proposed to explain this e~change.'~ It is likely that this kind of H-transfer from the ring is common in (n-cyclopentadieny1)-complexesof Groups IV and V. An X-ray photoelectron spectroscopic study of volatile vanadium compounds has been reported.'6a It is calculated that even in VF the positive charge on the vanadium is not much greater than one unit and in VCl it is considerably less. In [v(co),] the carbon monoxide is a nett electron acceptor. All this accords with a growing amount of data gathered from other elements. A study of some complexes of pyridine-2,6-dicarboxylicacid17 gave no indication of the formal oxidation state of the vanadium.This also accords with more general experience. A U.V. photoelectron study of [M(NMe,),] (M =Ti Zr Hf V or a typical element of Group IV) as well as of [W(NMe,),] has shown that except for M = V the first band($ arises from MO's which are linear combinations of nitrogen lone-pair AO's.16* StudiesI8 of vanadium tetraphenylporphyrin derivatives have shown that sub- stituents in the phenyl ring have little effect on equilibrium constants or e.s.r. parameters. This is in contrast to the nickel analogues and the reason is not clear. A detailed preparative investigation of vanadium nitrosyls has been reported. l9 This is not a trivial matter because NO tends to attack both metal and certain ligands (such as phosphines) yielding 0x0-complexes and ligand oxides.Van-adium(1v) chloride reacts with NO in carbon tetrachloride at 20°C to yield [V(NO),Cl,] possibly via [V(NO)Cl,]. The tris(nitrosy1) reacts with hard nitrogen- and oxygen-bases L to yield [V(NO)Cl,L,] which have v(N0) at ca. 1650cm-'. Triphenylphosphine oxide in benzene yields [V(NO)(PPh,O),CI]Cl and triphenyl- phosphine in chloroform produces [VOCl,(PPh,O),]. Bis(dipheny1phos-phino)ethane does not react with [V(NO),Cl,] because it is suggested it is too soft. Groups IV and *V show a distinct preference for harder rather than softer ligands and this can even affect reaction mechanisms. Thus in the equilibrium (1)(M=Nb or Ta; X =F C1 or Br) it is found that the mechanism is primarily a dissociative one for L =Me,O or Et,O and associative for L =Me,S Me,Se or Me,Te.,' [Mx,L]+L* * [Mx,L*]+L (1) The compounds MCl (M =Ti or V) and MCl (M =Nb or Ta) form simple adducts with C6HSCN.With acetonitrile however NbCl and TaCl yield amongst other CI 2-I C1/&] Me C=N-Nb-NCMe (3) l5 T. J. Marks and J. R. Kolb J. Amer. Chem. SOC.,1975,97 3397. l6 (a)R. R. Rietz T. F. Schaaf and W. L. Jolly Inorg. Chem. 1975 14 2818; (6) S. G. Gibbins M. F. Lappert J. B. Pedley and G. J. Sharp J.C.S. Dalton 1975 72. D. L. Hoof and R. A. Walton Inorg. Chim. Acta 1975 12 71. 1s F. A. Walker E. Hui and J. M. Walker J. Amer. Chem. SOC.,1975,97 2390. 19 W. Beck H. G. Fick K. Lottes and K. H. Schrnidtner 2.anorg. Chem. 1975,416,97.20 R. Good and E. Merbach Znorg. Chem. 1975,97 1030. 152 J. R. Dilworth G.J. Leigh and R.L. Richards compounds dinuclear complexes (3)., This is presumably a consequence of the strong Lewis acid character of the halides. Methyl isocyanide has been found to insert into the metal-chlorine bonds of MCl (M =V or Ti) and MCl (M =Ti Zr or Hf) to yield derivatives containing the -CCl=NR grouping., Titanium(1v) chloride behaves as a Lewis acid with the base [Pt(PPh,),] which forms [(TiCl,),{TiCl,(PPh,)),Pt] and then this reacts further with triphenylphosphine to yield [(TiCl, PPh,),Pt]. The adduct [(TiCl, PPh,),Pt] was also described., Titanium(1v) nitrate is a strong oxidizing agent which can nitrate aromatics at room temperature. Its electronic structure has been correlated with its observed electron deficiency., Pentakis(NN-dimethylcarbamato)niobium(v) undergoes stepwise and facile exchange with gaseous carbon dioxide.26 The complex itself is eight-co-ordinate with two unidentate and three bidentate dithiocarbamates and it is also formed rapidly from [Nb(NMe,),] and CO,.The COz exchange is believed to be due to the extrusion of CO to form a tetrakis(carbamato)amido-complex which has been detected in solution and which reacts with CO to reform the pentakis(carbamat0)- complex. The mechanisms of rearrangement of chelate complexes have received attention during the past year. Complexes [Ti(dik),(NCO),] and [Ti(dik),(NCS),] (dik = RCOCHCOR; R=Me or But) have been described in considerable detail; they invariably have a cis-c~nfiguration.~~ N.m.r.studies indicate that the alkyl groups of the diketonate are exchanging by a process which does not involve rupture of any of the metal-ligand bonds. A similar exchange has been reported to occur in cis-[Ti(a~etylacetonate),(OPh),].~~ This is consistent with a body of older data. It has now been pointed that because the rates for methyl interchange of the acetylacetonate groups of [Ti(a~etylacetonate)~(OCHMe,),]are the same as those for the methyl interchange of the isopropoxy-groups then the mechanism of interchange must involve inversion of the helicity of the chelate rings. This inference- concerning mechanism is confirmed by another n.m.r. study2” which also agrees with earlier work in suggesting that bond rupture should not be involved in the interchanges.The structures of some compounds have also been determined by less usual methods. Thus comparison of the diffusion coefficients of NbC1 and NbCl and of ZrC1 and NbCl leads to the conclusion that NbCl is a dimer in the gas phase.,’ An n.q.r. study of MX (M =Nb or Ta; X = F C1 or Br) shows that NbF is a tetramer.31 21 J. D. Wilkins J. Organometallic Chem. 1975,92 27. 22 P. A. Finn M. S. King P. A. Kilty and R. E. McCarley J. Amer. Chem. Soc. 1975 97 220. 23 B.Crociani M. Nicolini and R. L. Richards J. Organometallic Chem. 1975,101 c1. 24 J. F. Plummer and E. P. Schram Inorg. Chem. 1975,14 1505. 25 C. D. Garner I. H. Hillier and M. F. Guest J.C.S. Daffon,1975 1934. 26 M. H. Chisholm and M.Extine J. Amer. Chem. Soc. 1975,97 1623. 27 A. F. Lindmark and R. C. Fay Inorg. Chem. 1975,14 282. 28 J. F. Harrod and K. R. Taylor Inorg. Chem. 1975,14 1541. 29 (a)P. Finocchiaro J. Amer. Chem. Soc. 1975 97 4443; (b) N. Baggett D. S. P. Poolton and W. B. Johnson J.CS. Chem. Comm 1975 239. 30 A. D. Westland 2.anorg. Chem 1975,414 284. 31 G. K. Sernin S. L. Kuznetsov I. M. Alimov T. L. Khotsianova E. V. Bryukhova L. A. Nisselson and K. Tretyakova Inorg. aim. Acta 1975 13 181. Transition -metal Chemistry 153 An electron diffraction study of VOC13 shows it to be roughly tetrahedral.32 The penta(thi0cyanates) of niobium and tantalum are dimer~.~~ The structures of metal alkoxides have long been intriguing and a considerable amount of work has been carried out omnew alkoxides.Thus the isopropoxides [MM’(OPr’),] and [MM‘,(OPT~)~~] (M =Nb or Ta; M’ =Ga or Al)have been charac- terized and the structures (4) and (5) A mixed alkoxide containing two different transition elements has been reported for the first time it is “bTa(OMe),ol(6). Me Me Me RR 6 8 OR Me0 0 OMe O O\ ,/OR Ro\ ,/ \I/ \ / \l/\l/ Ro \I/ MM M M M‘ Nb Ta /I\ / \ / \/I\ / \ /!\/I\ ROoO OR RO OR Me0 0 OMe R R Me Me $e The potentially novel allyloxides of titanium niobium and tantalum have been reported but they appear to be normal alkoxide dimer~.~~ Alkoxide dimers such as [Nb,(OMe),,] form adducts [Nb(OMe),L] with a variety of bases L where L can be a primary or secondary amine ammonia an amine oxide or a phosphine ~xide.~’ Compounds L such as tertiary amines ethers sulphides phosphates nitriles or sulphoxides do not form adducts and the overall pattern of behaviour of the various ligands L does not correlate with hard-soft classifications or ideas concerning 7r-bonding.Steric factors may be overriding. The tantalum complexes have higher formation constants than their niobium analogue^.^' There has been considerable activity in the classical areas of 0x0-derivatives and 0x0-polyanions. Vanadium bis(metaphosphate) and tris(metaph0sphate) have been prepared as crystals and their structures inferred.38 The former probably contains vanadium(1v) co-ordinated by oxygen atoms in a distorted octahedron aligned along a crystal axis and with the chains of octahedra linked by metaphosphate chains.The tris(metaphosphate) also has octahedrally co-ordinated vanadium. New polyvana- dates for example Ba,VSi,O, Ba,V,O, Ba6V6014 and Sr6V6011 have been ~haracterized.~~ The preparation and thermal decomposition of Nb3O7Cl have been de~cribed.~’ The constitution and interconversions of the polyvanadates have received considerable attention. The nature of decavanadates in the solid state and in acidic and basic conditions has been studied. The i.r. spectra of solid state and acidic solutions show no sign of hexavanadate formation and are consistent with the presence of [v100~8]6-only or of some protonated species immediately derivable from it. 41 The n.m.r. data can also be rationalized on this basis. Base titration and 32 T.Karakida and K. Kuchitsu Znorg. Chimica Am 1975 13 113. 33 H. Bohland and E. Harke Z. unorg. Chem. 1975 413 102. 34 S.Govil P. N. Kapoor and R. C. Mehrotra Inorg. Chim. Actu 1975,15,43. 3s L.G. Hubert-Pfalzgraf and J. G. Riess Znorg. Chem. 1975,14,2854. P. N. Kapoor S. K. Mehrotra R. B. King and K. C. Nainan Znorg. Chim. Acta 1975 12 273. 37 L. G. Hubert-F’falzgaf,Znorg. Chim. Acta 1975 12 229. 38 B. C.Tofield G. R. Crane G. A. Pasteur and R. C. Sherwood J.C.S. Dalton 1975 1806. 39 A.Feltz S. Schmalfuss H. Langbein and M. Tietz 2. anorg. Chem. 1975,‘417, 125. 40 H. Kodama and M. Goto Z. anorg. Chem. 1975,415 185. 41 F.Corigliani and S. Di Pasquale Inorg. Chim. Acta 1975 12 99. 154 J. R. Dilworth G. J. Leigh and R.L.Richards extraction into non-aqueous solution allowed4' the identification of a series of protonated decavanadates [H3V10028]3- [HzVlo02,]4- and [HVlo028]5- as well as [VloO,,]"-. In basic solution decavanadate decomposes to form [VO,]'- and this decomposition has been shown to proceed via both base-dependent and base- independent paths.43 The base-dependent path involves a reactive alkali-metal cation decavanadate species. Basic solutions of [VO]" have been studied by a variety of techniq~es.~~ The ion [VO(OH),]- of uncertain degree of aquation is predominant and higher oligomers are unimportant. In fact the aquated ion is likely to be [VO(OH),(H,O),]- on the basis of optical and e.s.r. spectra and related to [VO(H,O),]" by simple protonation. 2 Group VI Chromium Molybdenum and Tungsten Complexes with Metal-Metal Bonds.-A recurrent theme in the chemistry of this triad has been the chemistry of derivatives with metal-metal multiple bonds.A comprehensive review of the subject to the end of 1974 has been published.45 Calculations by the SCF scattered-wave Xa method for [Mo2Cls14- ion4" provide striking confirmation for Cotton's original proposals on the nature of the metal- metal quadruple bond. A set of Mo-Mo bonding orbitals of predominantly metal d-character in the order (of increasing energy) a,T,S were found as required for the a,T,and 6 overlap model. An empty 8" orbital lies just above the S orbital and the peak observed at ca. 19 000 cm-' in the electronic spectrum of [Mo,C~,]~- ions can now be assigned to a dipole-allowed S +S" transition.Improved resonance Raman spectra of [Mo~CI,]~-ions with a range of counter-ions have been together with their electronic spectra. The technique involves irradiation with an exciting frequency within the contour of an allowed electronic transition and causes enormous enhancement of bands due to the fundamental metal-metal stretching vibration vl at 346 cm-'. Overtones of up to 11vl are observed for the dicaesium salt. Solution of K4[Mo2Cl,] in O.1M-HSO,CF and addition of K2S04 gives pink K4[Mo,(S04),],2H20 which on attempted recrystallization also forms lavender crystals of K,[Mo,(SO~)~],~.~H,O.~~ Both complexes have the s!me structural skeleton (7) with Mo-Mo bond lengths of 2.1 ll(1) and 2.164(2) A respectively and are related by an ElI2redox potential of 0.22V us.SCE. The complex [Mo,{PhC(NPh),},] prepared by heating [Mo(CO),] with NN'-diphenyl-benzamidine has a structure analogous to the acetates [Mo,(O,CR),] with the amidine groups bridging the two rn01ybdenums.~~ Attempts to prepare the chromium and tungsten analogues gave uncharacterized products appearing to contain arene- tricarbonyl moieties. 42 F. Corigliani and S. Di Pasquale Znorg. Chim. Acta 1975 12 102. 43 D. M. Druskovich and D. L. Kepert J. C. S. Dalton 1975 947. 44 M. M. Iannuzzi and P. H. Rieger Znorg. Chem. 1975,14 2895. 45 F. A. Cotton Chem. SOC.Rev. 1975,4 27. 46 J. G. Norman and H. J. Kolari J. Amer. Chem. SOC.,1975 97 33. 47 R. J. H. Clark and M. L. Franks J. Amer.Chem. SOC.,1975,97 2691. 48 A. R. Bowen and H. Taube Znorg. Chern.,1974,13,2245; F. A. Cotton B. A. Frenz E. Pedersen and T. R. Webb Znorg. Chem. 1975,14,391. 49 F. A. Cotton T. Inglis M. Kilner and T. R. Webb Znorg. Chem. 1975 14 2023. Transition -metal Chemistry Following last year's report" of the preparation of [CrMo(O,CMe),] [MoW(O,CBu'),I]'(8) has been prepared by iodination of benzene solutions of an inseparable mixture of [Mo,(O,CBu'),] and [MOW(O,CBU'),].~~ A crystal structure of an acetonitrile solvate of cation (8)showed that the iodine is bonded exclusively to the tungsten. Reduction with zinc in acetonitrile gave pure samples of the uncharged derivative [MoW(O,CBu'),]. 0' s 'o (7) The reaction between [WCl,(OEt),] and three equivalents of LiNMe gives an inseparable 1:2 mixture of [W(NMe,),] and dimeric [W,(NMe2)6].52 An X-ray crystal structure of this mixture confirmed the presence of a triple bond between the tungstens of the dimer with an W-W bond-length of 2.294 A.The structure and preparation of the molybdenum analogue from MoCl and LiNMe were reported during 1974.53Use of the sterically more demanding LiNEt favours the formation of dimer relative to monomer and permits preparation of pure [W,(NEt2)6],54 which serves as a useful starting point for the synthesis of a range of metal-metal bonded derivatives (Scheme 1). [W,(OSiMe,) J,2Et,NH % [W2(OSiMe3),I Me,SiOHy cs [W(S,CNEt,)3] [W2(NEt2),l ,plOH co [W,(OBu'),] -$ [W,(~B~'),(~,C~BU')~] Scheme 1 Two groups of worker^^^*^^ have studied the interesting equilibrium between a formally triple and a formally single metal-metal bond (see Chapter 8 p.196). A surprising feature of the X-ray crystal structure of [Cp,Mo,(CO),] is the near linearity of the Cp-Mo-Mo-Cp system; the complexes [Cp2M,(CO),] (M = Cr or Mo) have pronounced M-M-Cp angles.57 Nitrogen Fixation and other Reactions of Biological Significance.-Although the role of molybdenum in biological systems is still largely unknown there is great current interest in reactions catalysed by molybdoenzymes particularly nitrogen 50 C. D. Garner and R. G. Senior J.C.S. Chem. Comm. 1974 586. s1 V. Katoric J. L. Templeton R. J. Hexmeier and R. E. McCarley J. Amer. Gem. SOC.,1975,97,5300. 52 F. A. Cotton B.R. Stults J. M. Troup M. H. Chisholm and M. Extine J. Amer. Chem. Soc. 1975,97 1242. 53 F. A. Cotton B. A. Frenz L. Shive M. H. Chisholm and W. Reichert J.C.S. Chem. Comm. 1974,480. 54 M. H. Chisholm and M. Extine J. Amer. Chem. Soc. 1975,97,5625. 55 D. S. Ginley and M. S. Wrighton J. Amer. Chem. Soc. 1975,97 3535. 56 R. J. Klinger W. Butler and M. D. Curtis J. Amer. Chem. Soc. 1975,97 3534. 57 R. D. Adams D. M. Collins andF. A. Cotton Inorg. Chem. 1974,13,1086; J. Amer. Chem. Soc. 1974 96.749. J.R. Dilworth G. J.Leigh and R. L. Richards fixation. This last subject has been exhaustively reviewed in recent and coverage is here restricted to the 1975 literature. A significant advance in abiological nitrogen fixation has been the of the formation of ammonia from dinitrogen terminally co-ordinated to molybdenum or tungsten.The complex trans-[Mo(N,),(dpe),] (dpe =Ph2PCH2CH2PPh2) under- goes up to 37% conversion of one dinitrogen ligand into ammonia when treated with HBr in N-methylpyrollidone (NMP).59 It was proposed that [MoBr,(NNH,) (dpe),] is formed initially and then converted into a nitride via a dinuclear Mo-N-N-Mo system. However protonation of the nitride complexes [MoNX(dpe),] gives the nitrene complexes [MoX,(NH)(dpe),] and no ammonia,61 and it seems possible that the temperatures required to remove the NMP cause partial replacement of the diphosphines by solvent and degradation of the NNH derivative to ammonia. Treatment of the complexes cis-[M(N,),(PMe,Ph),] (M =Moor W) with sulphuric acid in methanol gives ca.36% conversion of one dinitrogen ligand into ammonia for M =Mo and up to 90% conversion for M = W.60,62 In each case ca. 1mole of dinitrogen is evolved. Although no intermediates could be isolated the use of other acids and tertiary phosphines permits the isolation of intermediates containing NNH and NHNH groups bound to the metal [equations (3) and (4)].63 However the mechanism by which these intermediates produce NH is not yet clear. Since base treatment of [MX,(NNH,)(PMe,Ph),] gives 1.6 moles of NH3 for M = W and only half as much for M =Mo there may well be different mechanisms operative for the two metals. These results clearly suggest that the active site of nitrogenase could comprise a single molybdenum binding site for dinitrogen which is then protonated to NH via NNH and NHNH intermediates with little or no hydrazine formation.However the information currently available about the enzyme does not rule out a two-site mechanism (two Mo’s or one Mo and one Fe) with bridged dinitrogen complexes reducing via bridged di-imide and hydrazine intermediates and work continues on the chemistry.of these types of complex ligand prepared by oxidation of bridging hydrazine derivatives. The N-H protons of [p-N2H2{Cr(C0)5}2] undergo rapid H-D exchange and in the presence of catalytic amounts of base rapid and irreversible disproportionation to N2 and [~-N,H,{CT(CO)~}~] occurs.64 A crystal structure of the THF solvate of [p-N2H2{Cr(C0)5}2] shows the di-imide ligand to have a trans configuration with an N-N bond length of 1.25 A.65[Mo(CO),N,H,] is 58 D.Sellmann Angew. Chem. Znternut. Ed. 1974,13,639. A. D. Allen R. 0.Harris B. R. Loescher J. R. Stevens and R. N. Whiteley Chem. Reu. 1973,73 11. 59 C. R. BrQlet and E. E. Van Tamelen J. Amer. Chem. SOC.,1975 Y7 911. 6o J. Chatt A. J. Pearman and R. L. Richards Nature 1975,253 39. 61 J. Chatt and J. R. Dilworth J.C.S. Chem. Comm. 1975 983. 62 J. Chatt J. Orgunometullic Chem. 1975 100 17. J. Chatt A. J. Pearman and R. L. Richards J. Orgunometullic Chem. 1975,101 C45. 64 D. Sellmann A. Brandl and R. Endell J. Orgunometullic Chem. 1975 90 309. G. Muttner W. Gartzke and K. Allinger J. Orgunometullic Chem. 1975,91,47. Transition -metal Chemistry 157 prepared from [MO(co),] and N2H4 and controlled oxidation yields [p-N,H,{Mo(CO),},] which is less stable than its Cr or W analogues and readily disproportionates to the p-hydrazine derivative and N2.66 The formation of nitrogen-carbon bonds directly from dinitrogen is potentially a reaction of industrial importance and continues to be studied.Photochemical reaction of the dinitrogen complexes [M(N2)2(dpe)2] (M=Mo or W) with alkyl halides RX has been independently studied by two groups68769 and shown to give alkyldiazenido (9) and alkylhydrazido(2 -) (10) complexes interconvertible by acid and base. X-Ray crystal structures of (9; R = C6H1,,X =I M =Mo)~~ and (10; R=Me X=Br M=W)68 both show essentially linear M-N-N systems with M-N bond lengths of 1.95(1) and 1.768(14)& respectively.If the alkylation reaction is carried out in tetrahydrofuran as solvent the tetrahydropyridazine complex (11) is formed and can be isolated at its hydrobromide salt.” The four carbons of the pyridazine ring presumably originate from the THF and the role of the methyl bromide is not clear; it may participate in removal of the THF oxygen as an alcohol. R HR + n / \/ v Y I I (9) Efforts continue to be directed towards the simulation of the action of nitrogenase using systems containing a dimeric molybdenum(v) cysteine complex (12) and a reducing agent and the area has been reviewed.71 Such systems reduce acetylene to ethylene and dinitrogen to ammonia in low yields. Ferredoxin model compounds such as [Fe,S,(SR),]”- (n= 2-4) apparently accelerate the transfer of electrons NC 0 CN \II / /YO\ NC 0 CN fS N = -0ZCCHNH2 I \O CH2S-66 D.SelLnann A. Brandl and R. Endell J. Organometallic Chem. 1975,97 229. 67 J. Chatt G. A. Heath and G. J. Leigh J.C.S. Chem. Comm. 1972 444. 68 A. A. Diamantis,J. Chatt G.J. Leigh and G.A. Heath J. Organometallic Chem. 1975,84 C11; F. F. March R. Mason and K. M. Thomas J. Organometallic Chem. 1975,96 C43. 69 V. W. Day T. A. George and S. D. A. Isbe J. Amer. Chem. SOC.,1975,97,4127. ’0 A. A. Diamantis J. Chatt G. A. Heath and G. J. Leigh J.CS. Chem. Comm. 1975 27. 71 G. N.Schrauzer Angew. Chem. Znternat. Edn. 1975 14 514. J. R.Dilworth G.J. Leigh and R. L. Richards from reductant to molybdenum and improve ethylene yields.72 Adenosine-5- triphosphate (ATP) is a requirement for the enzyme and also stimulates the model system.The ATP is postulated to facilitate removal of OH groups from the monomer (13)[formed from (12) in base] as phosphates and thereby increases the concentration of the active reduced Mo'" species (14). Use of the tetracyano-0x0- Mo complex (15) as an alternative to (12) increases the nitrogen-fixing ability of the model system considerably and yields of up to ca. 0.3 moles of ammonia per mole of molybdenum are Electrochemical reduction of the Mo" cysteine dimer shows that it undergoes a single four-electron reduction step to Mo"' products and it is suggested that a monomeric Mo'" species is the catalytically active species.75 A dextran-bound cysteine polymer (1.05 mmol cysteine per g dextran) forms a molybdenum complex analogous to (12) which shows no evidence for alkaline dissociation into monomers analogous to (13).76 However in the presence of borohydride the supposed complex reduces acetylene ca.30 times faster than (12) possibly because the inert support serves to keep apart reduced catalytically-active species analogous to (14),prevent-ing formation of inactive 0x0-bridged dimers. The nitrate ion is+ quantitatively converted into NO and subsequently nit- rogen(m) (probably NO) by reaction with [MoOCl,L,] or [MoOCl,L]- [L = Yh,PO or (Me,N),PO] or [MoOC~,]~- and this has been advanced as a model for the molybdoenzyme nitrate reducta~e.~' The kinetics of the overall reaction were studied by stopped-flow techniques and are consistent with the mechanism in Scheme 2.77 However unlike the enzyme the system is not catalytic and reduces nitrite quantitatively to NO.Since 0-bonding appears to be a prerequisite for the reduction of nitrate or nitrite it is suggested that the protein stabilizes N-bonding of nitrite by hydrogen-bonding with the oxygens preventing its red~ction.~' c1 0 c1 c1 0 c1 c1 0 c1 \II / L i" L c1 0 c1 \II / LL 0 0 0 I 0 0 Scheme 2 Isocyanides nitriles or acetylenes are also substrates for nitrogenase and the chemistry of these ligands bound to molybdenum has been studied. Both dinitrogen ligands of frans-[Mo(N,>,(dpe),] are displaced by methyl isocyanide to give trans-[Mo(MeNC),(dpe),]. One or both of the ligating isocyanides can be protonated at 72 K.Tan0 and G. N. Schrauzer J. Amer. Chem. SOC.,1975,97 3404. 73 G. N. Schrauzer G. W. Kiefer K. Tano and P. R. Robinson J. Amer. Chem. SOC.,1975,97,6088. 74 G. N. Schrauzer P. R. Robinson E. L. Moorehead and T. M. Vickney J. Amer. Chem. SOC.,1975,97 7069. 75 D. A. Ledwith and F. A. Schultz J. Amer. Chem. SOC.,1975 97 6591. 76 H. Susuki S. Meshitsuka T. Tabashima and M. Ichikawa Chem. Letters 1975 4 285. 77 C. D. Garner M. R. Hyde F. E. Mabbs and V. I. Routledge Nature 1974 252 580. 78 C. D. Garner M. R. Hyde and F. E. Mabbs Nature 1975,253,623. Transition -metal Chemistry nitrogen to give complexes containing the carbyne-like ligands -C-NHR.79 Sub-stituted benzonitriles displace only one dinitrogen from [Mo(N,),(dpe),] to give [Mo(N,)(p-XC,H,CN)(dpe),] (X =NH, MeO Me H C1 or COMe) the latter being useful precursors for the synthesis of derivatives such as [MoCl(N,COPh)- (dpe),] with N-C bonds." Acetylene readily displaces the carbonyl ligands from the complexes [Mo(C0),(S2PPri2),] to give [MoCO(C,H,)(S,PP~~,)~]; but reaction with acid gives only ca.20% yields of ethane from the acetylene." 3 Group VII Manganese Technetium and Rhenium Manganese Porphyrin and Related Complexes.-Although the dioxygen-carrying capabilities of iron and cobalt complexes have been extensively investigated (see pp. 162 and 167) analogous manganese derivatives have only recently been studied in detail. Manganese porphyrin complexes were comprehensively reviewed in 1972.* Manganese haemoglobin (MnHb) does not bind dioxygen reversibly and is irrevers- ibly oxidized to Mn"'Hb,83 and the manganese tetraphenylporphyrin (TPP) system also shows significant differences from comparable iron derivatives.Reduction of [Mn"'Cl(TPP)] with [Cr,(acac),] in toluene gives the purple four-co-ordinate species [Mn(TPP),2toluene]( 16).84 A partial X-ray crystal structure and magnetic measure- ments (peR=6.2 BM) suggest a high-spin configuration with the manganese lying out of the plane of the porphyrin ring. [Mn(TPP)] reacts with an excess of a base such as 2-methylimidazole (2-MeIm) to give [Mn(TPP)(2-MeIm)] with no evidence for a six-co-ordinate species.84 In contrast to its iron analogue [Mn(TPP)( 1-MeIm)] does not react with dioxygen except to undergo very slow oxidation.It is suggested that the six co-ordination required for an 0,-adduct cannot occur unless a transition to a low-spin state occurs which is not possible with the porphyrin ligand system. However [Mn(TPP)] does reversibly form an 0,-adduct at -90 "Cin toluene-THF although this has not yet been fully characterized. 79 J. Chatt A. J. L. Pompeiro R. L. Richards G.M. D. Royston K. W. Muir and R. Walser J.C.S. Chem. Comm. 1975,512. 8o T. Tatsumi M. Hidai and Y. Uchida Inorg. Chem. 1975 14 2530. 81 J. W. McDonald J. L. Corben and W. E. Newton J. Amer. Chem. SOC.,1975,97 1970. 82 L. J. Boucher Coordination Chem. Rev. 1972,7 289. 85 C. Ball R. C. Fisher and B. M. Hoffmann Biochern. Biophys. Res. Comm. 1974,59 146. 84 B.Gonzalez J. Kouba S. Yee C. A. Reed J. K. Kirner and W. R. Scheidt J. Amer. Chem. SOC.,1975 97 3247. J. R. Dilworth G.J. Leigh and R. L. Richards Reaction of [Mn(TPP)(py)] in toluene with 0,at -80 "C produces an apparently identical 0,-adduct of stoicheiometry [Mn(TPP)O,] with displacement of ~yridine.~'E.s.r. spectra of the 0 adduct were interpreted in terms of a manganese with three unpaired electrons suggesting that the complex can formally be rep- resented as [Mn'V(TPP)(0,2-)] with a 'sideways bound' 0,2-ligand.85 The structural distortions exhibited by five- or six-co-ordinate high-spin mangan- ese (111) complexes provide the theme for several X-ray crystal structure determina- tions. The structures of [Mn(N,)(TPP)] and [Mn(N,)(MeOH)(TPP)]86 show that the manganese ion is displaced ca.0.18 Afurther out of the plane in the five-co-ordinate derivative. A comparison of the structures of a number of related five-co-ordinate derivatives suggests that manganese(II1) is displaced by ca. 0.25 Afrom the plane in complexes of sterically non-hindered porphyrins. An even larger displacement (0.343A)occurs in the case of (17) with its less constrained quadridentate ligand system.86 The structure of [Mn(acac),N,] shows that the manganese is in fact six co-ordinate as the azide ligands bridge adjacent [Mn(acac),]+ units producing infinite chains of pseudo-octahedral manganese ions.87 The products of oxidation by dioxygen of five-co-ordinate manganese(rI1) Schiff base complexes such as [Mn(salen)(H,O)]' (18; R = H) have not in the past been well characterized p -peroxo di-p -hydroxo and di-p -ox0 structures having been proposed.88 The situation has been clarified by detailed studies of the oxidation of the more soluble [Mn(Busalen)H,O]ClO (18; R = s-b~tyl).~~ In the presence of base and dioxygen this gives a complex formulated as the manganese(1v) [(Busalen)Mn(p-O),Mn(Busalen)]H,O (19).This is dimeric in CHCI and the low magnetic moment (2.5 BM) is attributed to antiferromagnetic exchange between the manganese ions. A characteristic i.r. band in the region 640-4550 cm-'is assigned to the di-p-oxo bridging system. Protonation of (19) with perchloric acid provides further evidence for the structure as hydrogen peroxide is formed via the di-p- hydroxo species [(Busalen]Mn(p -OH),Mn(B~salen)].~~ The preparation of manganese or iron tetraphenvlporphyrin nitrosyl complexes by direct reaction with nitric oxide is dependent on the presence of secondary amine.Thus [(NO)(amine)Mn(TPP)] is prepared in 80% yield by reaction of [ClMn(TPP)] ~35 C. J. Weschler B. M. Hoffmann and F. Basolo J. Amer. Chem. SOC., 1975,97,5278. 86 V. W. Day B. R. Stults E. L. Tasset R. S. Maranelli and L. J. Boucher Inorg. Nuclear Gem. Letters 1975 11 505. 8' B. R. Stults R. S. Maranelli and V. W. Day Inorg. Chem. 1975 14 722. H. S. Maslen and T. N. Wates J.CS. Chem. Comm. 1973 760; T. Matushita T. Yarno I. Masuda T. Shomo and K. Shinra Bull. Chem. SOC.Japan 1973,46 1712. 89 L. J. Boucher and C. G. Coe Inorg. Chem. 1975,14 1289.Transition -metal Chemistry 161 with NO in CHCI with piperidine present." Since it has now been shown that the same reaction can be achieved with the so-called N202 adducts in reality the N-nitrosohydroxylamines [R'R'NNH,][R'R'NNONO] their intermediate forma- tion is advanced as an explanation for the amine specificity of the direct nitrosation reaction." Complexes with Metal-Metal Multiple Bonds.-The chemistry of complexes with metal-metal bonds has also been a feature of the manganese group and as mentioned previously the literature to the end of 1974 has been comprehensively reviewed.45 The electrochemistry of the octahalogenodimetallates [M2C18]"- (M = Tc or Re; n = 2 or 3) has been reported,92 and the processes [Tc2Cls12-+e -+[Tc,C~,]~- and [Re~C18]~-+e -b [Re2C1,]3- shown to be quasi-reversible with El, potentials (rela- tive to SCE) of 0.140 and -0.840 V respectively.Paramagnetic [Tc,C~,]~- has an e.s.r. spectrum corresponding to one unpaired electron coupled to two 99Tc nuclei with I = 9/2; the corresponding [Re2Cl8l3- anion is too unstable for e.s.r. spectra to be However tertiary phosphine derivatives of both [Re2X813- and [Re2Xs14- anions have been prepared.93 Rhenium(II1) chloride or the anions [Re2Xs12- (X = C1 or Br) react with alkyl or mixed alkyl-aryl tertiary phosphines to give species of stoicheiometry [Re,X,(PR,),] or [Re,X,(PR,),] the extent of reduction depending on the degree of alkyl substitution of the phosphine. Thus MePh,P and EtPh,P give [Re,X,(RPh,P),] and PEt gives [Re,X,(PEt,),].The ditertiary phosphine Ph,PCH,CH,PPh (dpe) does not reduce the [Re2C1,]2- ion and [Re,Cl,(dpe),] is formed,94 and shown by a crystal structure det$rminationg5 to have a di-p-chloro bridge with an Re-Re distance of 3.809(1)A7 too large for any metal-metal interaction. The complex [Re,Cl,(PEt,),] is quasi-reversibly oxidizable electrochemically to [Re,Cl,(PEt,),]+ and [Re2C1,(PEt,),l2' and [Re2(PhC0,),l2' can be reduced to [Re2(PhC02),]+.96 The ex. spectra of the monocations can be qualitatively corre- lated with one-electron energy diagrams based on MO and scattered wave Xa calculations. The sulphato-bridged Na,[Re,(SO,),] can be prepared in 90% yield by reaction of [ReCl8I2- with sulphuric acid and sodium sulphate in diglyme.The structure is essentially similar to that of [Mo2(SO4),I4- (7) with an Re-Re bond length of 2.214(1) k9'Partial replacement of halide ions occurs when [Bu,N],[Re,Cl,] is fused with NN'-diphenylbenzamidine with formation of [Re,Cl,(N,CPh,),]. The amidine ligands bridge the two rheniums and the Re-Re bond length of 2.177 A is the shortest yet 9O P. L. Piciulo G. Rupprecht and W. R. Scheidt J. Amer. Chem. Soc. 1974,% 5293. 91 P. L. Piciulo and W. R. Scheidt Znorg. Nuclear Chem. Letters 1975 11 309. 92 F. A. Cotton and E. Pedersen Znorg. Chem. 1975,14 383. 93 J. R. Ebner and R. A. Walton Znorg. Chem. 1975,14 1987. 94 J. A. Jaecker D. P. Murtha and R. A. Walton Znorg. Chem. Acra 1975,13 21. 95 J. A. Jaecker W. R. Robinson and R.A. Walton J.C.S. Dalton 1975 698. 96 F. A. Cotton and E. Pedersen J. Amer. Chem. SOC. 1975,97 303. 97 F. A. Cotton B. A. Frenz and L. W. Shive Inorg. Chem. 1975,14,649. F. A. Cotton and L. W. Shive Znorg. Chem. 1975 14 2027. J. R. Dilworth,G.J. Leigh,and R.L. Richards 4 Group VIIIA, Iron Ruthenium and Osmium Synthetic Dioxygen Carriers.-A feature of the non-organometallic chemistry of iron has been the development of complexes that have dioxygen-carrying capabilities similar to those of haem proteins. Most of the model systems comprise ferrous iron surrounded by four co-planar nitrogens with a variety of nitrogeneous axial ligands and progress to the end of 1974 has been described in two A major problem with the model systems is the irreversible formation of p-0x0- bridged dimers on treatment with dioxygen.This can be avoided by use of bulky Iigands disposed to one side of the N ligand which prevents the irons getting close enough to form a dimer. Thus the ferrous complex of the 'picket-fence' porphyrin [rneso-tetra(aacua -0-pivalamidophenyl)porphyrin,TpivP] (20) adds two molecules of bases such as 1-methylimidazole (1-MeIm) to give diamagnetic six-co-ordinate derivatives which bind 0 reversibly with displacement of one axial ligand."' Although there were disorder problems an X-ray crystal structure of [Fe(O,) TpivP)(l-MeIm)] showed that the 0 is bound 'end-on' with an Fe-0-0 angle of ca. 136O."' The enthalpy of 0,-binding in the solid state has been determined manometrically102 (AH" =-15.6 kcal mol-') and comparison with natural haem proteins (ox myoglobin AW = -15 kcal mol-'; human myoglobin AW = -13.4 kcal mol-') suggests the protein chains in the natural system do not contribute signific- antly to 0,-binding.C Me,I CMe,I NH-CO CO-NH An alternative to the 'picket-fence' approach has been to use substituted haem derivatives such as (21) where the axial base is attached to a pyrrohaem system with a similar geometry to the proximal histidine in rnyogl~bin.'~~~'~~ These systems bind 0,reversibly and the kinetics of oxygenation can be studied as a function of the axial base and solvent polarity which do not interfere. The rates of oxygenation closely resemble those of myoglobin and the dependence of the 0 'on'-rate on the axial base suggests that the natural system could control the rate of binding of 0 by variation of the basicity of the proximal histidine.'@' Not all systems are based on 99 F.Basolo B. M. Hoffmann and J. A. Ibers Accounts Chem. Res. 1975,8,384. loo T.H.Maugh Science 1975,187 154. J. P. Collman R. R. Gagne C. A. Reed T. R. Halbert G. Lang and W. T. Robinson J. Amer. Chem. Soc. 1975,97 1427 and references therein. lo2 J. P. Collman J. I. Brauman and K. S. Suslick J. Amer. Chem. SOC. 1975,97 7185. lo3 C. K.Chang and T. G. Traylor J. Amer. Chem. SOC.,1973,95,5810. 104 C. K. Chang and T. G. Traylor Roc. Naf. Acad. Sci. U.S. A.,1975,72 1166. Transition -metal Chemistry Me porphyrin ligands and the substituted octa-aza[14]annulene complex (22) also undergoes reversible oxygenation at low temperature.The X-ray crystal structure of (22) shows that the iron lies in a 4.5A deep pocket between the 9,lO- dihydroanthracene rings; the octyl groups are directed away from the iron.lo5 0x0-bridge formation can also be inhibited by oxygenation at low temperatures (-50 to -80 "C). [Fe(TPP)(l-MeIm),] is irreversibly oxidized at 25 "C but functions as an 0,-carrier at -80 "C. Oxygenation is almost complete in methylene chloride but minimal in toluene and the stabilization in polar solvents supports the formal representation of the 0,-adduct as [Fe"'(O,-)(TPP)(l-MeIm)]. Studies of the kinetics of oxygenation show that [Fe(TPP)(l-MeIm)] reacts at about the same rate with 0,and 1-MeIm and the stability of the 0,-adduct is dependent on axial base as for complex (20).1°' Attachment of [Fe"(TPP)] to an inert solid support holds the irons apart and prevents dimer formation.The iron perphyrin is bound to silica via 3-imidazoylpropyl groups and binds 0,reversibly at low temperature. However the 0 is only weakly chemisorbed with a pl/ value of 0.4 Torr at -80 "C,compared with an extrapolated value of 0.14 Torr for human myoglobin at 0 0C.99 Cytochrome P450 contains a haem iron prosthetic group but is functionally more complex than haemoglobin acting as a dioxygen and electron-transport agent and as an oxidation catalyst. Four distinct reaction states can be identified correspond- ing to binding of the oxidizable substrate (sub) adjacent to the iron reduction of the ferric cytochrome Fe"'(cyt) binding of 02,and further reduction with loS R.G. Little J. A. Ibers and J. E. Baldwin J. Amer. Chem. SOC.,1975,97,7049. C. J. Weschler D. L. Anderson and F. Basolo J.C.S. Chem. Comm. 1974,757. lo' C. J. Weschler D. L. Anderson and F. Basolo J. Amer. Gem. Soc. 1975 W,6707. lo* I. C. Gunsalus S. G. Sligar and P. G. Debrinner Biochem. SOC.Trans. 1975,3 821; and preceding papers. 164 J. R. Dilworth G.J. Leigh,and R. L.Richards formation of hydroxylated substrate (sub-OH) and water and regeneration of Fe"'(cyt) (Scheme 3). E.s.r. spectra of the biological system suggest axial ligation by sulphur and studies on model systems have accordingly been based on iron complexes with macrocyclic N,-donor and axial thiolate ligands.[Fe"'(cyt)] 9[Fe"'(sub)(cyt)] 4; [Fe"(sub)(cyt)] 3 [Fe"(sub) (c yt)(02)] 5 [Fe"'(cyt)] A B C D + Sub-OH + H2O Scheme 3 The five-co-ordinate species [Fe(SPh)(TPP)] can be prepared from [{Fe(TPP)},O] and thiophenol and has an e.s.r. spectrum with g values close to those of species B in Scheme 3.l" In the presence of a base such as methylamine or ammonia at low temperatures an e.s.r. spectrum resembling that of species A is observed. An iron protoporphyrin dimethyl ester (PPDME) system forms the analogous [Fe(SC,H4po- NO,)PPDME)] and the X-ray crystal structure shows the iron displaced ca. 0.43 A out of the plane of the ligating porphyrin. Models for species C afid D in Scheme 3 were synthesized by reaction of benzene solutions of [Fe(PPDME)]"' or [Fe(TpivP)]"' with an excess of crown-ether-solubilized thiol which effects reduc- tion to the ferrous state.Under CO a U.V. band at ca. 450nm appears which corresponds to the anomalous Soret band which gives the cytochrome its name. If mercaptan rather than mercaptide is used the Soret band appears at ca. 420 nm. In combination these studies on model systems while not conclusive do offer confir- mation that the ferric species A and B of cytochrome P450 do contain an axial thiolate ligand. However the nature of the diamagnetic 0,-binding species D is not yet clear. Iron-Sulphur Cluster Systems.-Non-haem iron-sulphur proteins are implicated in biological processes as diverse as photosynthesis and nitrogen fixation. They can be classified according to the number of iron atoms present Fe 2Fe 4Fe and 8Fe proteins.X-Ray crystal structures of the 4Fe protein from Chrumatium and the 8Fe protein from P.aerugenes show them to contain one and two [Fe,S,(S-cys),] clusters (S-cys =cysteinyl sulphur) respectively. Redox and spectral measurements show that the 4Fe proteins are predominantly of two types the high potential protein (HiPIP; Eb -+0.35 V) from photosynthetic bacteria and the non-photosynthetic bacterial ferredoxins (Fd;.Eb- -0.4 V). The complexes [Fe,S4(SR),l2- (R =alkyl or aryl) containing structurally and spectrally analogous clusters were synthesized some time ago and work in this area up to the end of 1974 has been re~iewed."~ The synthetic clusters are prepared in high yields from FeCI, thiol and NaHS in the presence of base and an X-ray crystal structure (23) indicates that they are somewhat distorted from cubic symmetry.' l4 Polarography shows that the [Fe,S4(SR),l2- clusters are members of the electron-transfer series [Fe,S,(SR),]"- lo9 J.P. Collman T. N. Sorrell and B. M. Hoffmann J. Amer. Chem. Soc. 1975,97 913. 110 S. Koch S. C. Tang R. H. Holm R. B. Frankel and J. A. Ibers J. Amer. Chem. Soc. 1975,97 917. C. K. Chang and D. Dolphin J. Amer. Chem. Soc. 1975,97 5948. 11* J. P. Collman and T. N. SorrelldJ. Amer. Chem. Soc. 1975 97,4133. 113 R. H. Holm Endeavour 1975,34,1. 114 B. A. Averill T. Herskovitz R. H. Holm and J. A. Ibers J. Amer. Chem. Soc. 1973,95 3523. Transition -metal Chemistry R where n = 1,2,3 or 4.'15 Magnetic and spectral studies indicate a close similarity between these states and those found in the biological systems as indicated by the columns in Scheme 4.However the 3-+2- reduction step for the synthetic clusters is thermodynamically irreversible with E,,2 values considerably larger than for one-electron reduction of the ferredoxins. The water-soluble cluster [Fe,S,(SCH,CH,CO,),]"-can however be reversibly reduced and the potential associated with the one-electron step (-0.58 V us. hydrogen electrode) is close to that of ferredoxins (Fd)."" [Fe,S4(SR),l4-e[Fe4S4(SR),l3-e[Fe,S4(SR),l2-[Fe,S,(SR),]-2 A Fd, -Fdox -Fds-ox A HiPIP,-,, -HIPIP,, S HIPIP, Scheme 4 The structural unit of the Fe-S moiety of the 2Fe proteins has not been established by X-ray diffraction but the synthetic model (24) prepared according to equation (9 has similar spectroscopic properties to the biological system.The [Fe4S,(SR),I2- clusters undergo facile thiol exchange reactions and this provides the basis of a method for the removal of intact iron-sulphur clusters from the protein^."^ Treatment of a 4:l DMSO:H,O solution of the 8Fe ferredoxin protein from Clostridium pasteurianum with a 35-fold excess of thiophenol gives a 95% recovery of the non-haem iron as [Fe,S4(SPh),12-. The high DMSO content of the solution facilitates reaction by unfolding the protein chains. The Fe,S cores of 2Fe-ferredoxins can be similarly extruded using o-xylylenedithiol. However condi- tions must be carefully controlled as the dinuclear complex readily dimerizes to a four-iron cluster particularly at high pH and in the absence of an excess of thiol."* Although Mossbauer e.s.r.and structural studies indicate that the synthetic clusters are good models for ferredoxins the redox potentials are not comparable. These are clearly dependent on the peripheral groups on the clusters in the model systems and probably on the configuration of the peptide chains in the proteins. The B. V. Pamphilis B. A. Averill T. Herskovitz L. Que and R. H. Holm J. Amer. Chem. SOC. 1974,96 4159. 116 R. G.Job and T. C. Bruice Proc. Nat. Acad. Sci. U.S.A. 1975,72,2478. J. J. Mayerle R. B. Frankel R. H. Holm J. A. Ibers W. D. Phillips and J. F. Weiker Roc. Nat. Acad. Sci. U.S.A. 1973,70 2429. 118 L. Que R. H.Holm and L. E. Mortensen J. Amer. Chem. SOC.,1975,97,463. 166 J. R. Dilworth G.J. Leigh and R. L. Richards latter is certainly suggested by the accessibility of an additional super-reduced state HiPIPs-,d on denaturation of the HiPIP protein with DMSO.'l9 Any subtle distor- tions within the clusters caused by variation of the peripheral ligands should be reflected in the Fe-S stretching frequencies within the cluster. These can be enhanced in intensity by use of resonance Raman spectroscopy and some recent results'20 suggest that the overall symmetry of the biological clusters is lower than that of the models. However these differences are apparently too small to detect by X-ray diffraction as the structures of the biological and synthetic clusters are not significantly different.FeCI3 -+ 2 oCH2SH NaHS NaOMe CH2SH Ruthenium Ammine Complexes.-Ruthenium ammine complexes continue to be a source of unusual and interesting chemistry displacement of the water ligand of [RuA5(H20)I2' (A =NH,) providing a readily accessible co-ordination site. It has been known for some time that [RuA,(H20)I2' reacts with N20 to give [RuA5(N2)I2+ via an unstable N20 complex.12' The latter has now been isolated using high pressures of N20 and isotopic labelling using 15NN0 and ",NO permits assign- ment of anion-dependent i.r. bands in the regions 1945-1975 and 869-880 cm-' to the N20 ligand.122 Force-constant calculations are consistent with an 0-bonded N20 ligand. Nitrogen-metal to carbon-metal bonding isomerization has been observed for imidazole bound to [RuA~]~+.'~~ HCN initially binds via nitrogen and then rapidly isomerizes to the carbon-bound species [RuA,{C(H)N}I2'.In the presence of base a proton is lost generating a cyano-complex which expels an NH ligand to give the product ultimately isolated polymeric [{A,Ru(CN)},]. Xanthine derivatives (25) 124 can also bind to [RuA5I2+ or [RuA,],' via N-7 or C-8 the bonding mode being a function of the substitution pattern of the xanthine and pH; C-bonding is favoured at low pH. 125 Electrochemical studies indicate that both N-and C-bonding stabilize Ru" relative to Ru'" probably because both bonding modes transfer more T-electron density from metal to ligand in the Ru" state. 119 R. Cummack Biochem.Biophys. Res. Comm. 1974,58 974. S.-P. W. Tang T. G. Spiro C. Antaraitis T. H. Moss R. H. Holm T. Herskovitz and L. E. Mortensen Biochem. Biophys. Res. Comm. 1975,62,1. lz1 J. N. Armor and H. Taube J. Amer. Chem. SOC.,1971,93,6476. A. A.Diamantis G. J. Sparrow M. R. Snow and T. R. Norman Austral. J. Chem. 1975,28,1231. 123 R. J. Sundberg R. E. Shepherd and H. Taube J. Amer. Chem. Soc. 1972,94,6558. lZ4 S.S.Isred and H. Taube Znorg. Chem. 1975 14 2561. lZs M. J. Clarke and H. Taube J Amer. Chem. SOC. 1975,97 1397. Transition -metal Chemistry One NH ligand of the Ru"' hexammines [Ru&]"can be deprotonated to NH (pK ca. 12.4) which reacts with dioxygen at pH 13 to give [RuA5(N0)l3+ identified by a strong i.r. band at 1908 cm-' [v(NO)]."~ The NH ligand of [RUA,(NH,)]~' is sufficiently nucleophilic to attack carbonyl carbons and reaction with a-diketones such as diacetyl gives di-imine complexes (26).lZ7Aldehydes RCHO react with [Ru&I3' to give high yields of the nitrile complexes [RuA~(NCR)]~+,~~~ previously prepared from [RUA,(H,O)]~+ and 11itri1e.l~~ The mechanism is not yet known but probably does not involve the Ru'" complexes [RuA,(NCR)I3' as these hydrolyse rapidly in base to amide complexes.13o Treatment of [RuA,(N0)I3' with base produces [RUA,(N,)]~' (25%) and cis-and trans-[Ru(OH)A,(NO)]" (19%);the mechanism is believed to involve nucleophilic attack of an NH ligand on the co-ordinated NO as in Scheme 5.I3l Radiolysis of [RuA,(NO)I3' in Bu'OH generates the Ru" alkylnitroso-complex [RUA,{N(O)CH,C(OH)M~,}]~+; the reaction probably proceeds via attack of the 13' radical CH,C(OH)Me on [RuA,(NO)]*' generated by reaction of H atoms and eiq with the Ru"' nitrosyl complex.133 + [RuA5(N0)13 OH- [RuA4(NH 2)(NO)]z' + [A~Ru{ N(O)NH2)RuA4(NO)] + 4 [RuA5(N2)12++ [RuA4(0H)(NO)l2' Scheme 5 5 Group VIIIB Cobalt Rhodium and Iridium Major areas which have been explored this year are dioxygen complexes new structural properties of chelated complexes and catalytic behaviour.Dioxygen as a Ligand.-An understanding of the binding of dioxygen to cobalt in its complex compounds is of importance with respect to biological dioxygen carriers. 134 Of major interest is the charge distribution within the cobalt-0 moiety. The apportioning of this charge has been the subject of recent controversy but this year Iz6 S.D. Pel1 and J. N. Armor J. Amer. Chem. SOC.,1975,97 5012. lZ7 I. P. Evans G. W. Everett and A. M. Sargeson J.C.S. Chem. Comm. 1975 319. 128 K. Schug and G. P. Guengerich J. Amer. Chem. SOC.,1975,97,4135. Iz9 R. E. Clarke and P. C. Ford Inorg. Chem. 1970,9 227. 130 A. W. Zarella and P. C. Ford Inorg. Chem. 1975,14 42. 13' F. Bottomley E. M. R. Kuremire and S. G. Clarkson J.C.S. Dulron 1975 1909. 132 J. N. Armor R. Furman and M. Z. Hoffman,J. Amer. Chem. SOC.,1975,97 1737. 133 J. N. Armor and M. Z. Hoffman Inorg. Chem. 1975.14.444. 134 F. Basolo B. M. Hoffman and J. A. Ibers Accounts Chem. Res. 1975,8 384. J. R. Dilworth G.J. Leigh and R. L. Richards workers from three independent laboratorie~'~~*'~~ have interpreted e.s.r.spectra of mononuclear dioxygen adducts from Schiff -base or amine complexes of cobalt(I1) in terms of almost complete transfer of an electron from cobalt to dioxygen giving a formally Co"'-O,-linkage. These results convincingly reinforce earlier similar interpretations of such charge transfer in substituted porphyrin complexes of cobalt. An X-ray photoelectron spectroscopic study of dioxygen adducts of Schiff base complexes of cobalt showed that the Co2p3, binding energies increase by 0.9- 1.9 eV when the Co" complexes take up dioxygen again indicating considerable electron transfer to dioxygen.136 0 [L5-cO-0 / 3 [L5Co-0 /0-coL5 1 (271 (28) The reaction of O2with low-spin cobalt(I1) complexes commonly gives terminally- bonded mononuclear (27) or dioxygen-bridged dinuclear (28) adducts and physical studies on both classes of compound have been carried out.The Co-0-0 bond angle of 153.4' for (NEt4)3[Co(CN)5(02)]137 is interpreted in terms of the Col"-superoxide linkage (27). The structure of the dinuclear analogue [(CN)5$02Co(CN)5]5- shows the 'staggered' structure (28) with an 0-0 distance of 1.26 A typical of p-superoxide binding.138 Examination of the electronic spectra of this Complex and its ammine analogue [(NH3)5Co02Co(NH3)5]5+ has established low-spin d6 Co"' centres for both compounds and ligand field ligand-to-metal charge transfer and superoxide-localized transitions have been identified.'39 In particular the bands due to metal-to-ligand charge transfer terminating in the out- of-plane .rr(02-) orbital have been assigned (486 and 672 nm respectively) and a resonance Raman study confirms these assignments the electronic transitions being coupled to the 02-bands (at 1104 and 1135 cm-' respectively) in the Raman spectra.14' The structure of the five-co-ordinate precursor of the above dioxygen compounds [Co(CN),I3+ shows that the yellow solid form of this complex is a truly five-co- ordinate square-pyramidal compound but possibly the green form observed in aqueous solution may have an apical H20 molecule completing octahedral co- ~rdination.'~~ If tertiary phosphines replace cyanide as ligands to cobalt a different mode of co-ordination of dioxygen results.Thus reaction of [Co(CN),(PMe,Ph),] with dioxygen gives the unsymmetrical dinuclear complex [Co2(CN),(PMe2Ph),(02)] (29).14* While this mode of binding of dioxygen is unusual for dinuclear cobalt complexes the 0-0 distance (1.44 A)is in the range of such distances in analogous 135 R.F. Howe and J. H. Lunsford J. Amer. Chem. Soc. 1975,97,5156;D. Getz E. Melamud B. L. Silver and Z. Dori ibid. p. 3847. 136 J. H.Burness J. G. Dillard and L. T. Taylor J. Amer. Chem. SOC.,1975,97,6080. 137 L. D. Brown and K. N. Raymond Znorg. Chem. 1975,14,2595. 138 F. R. Franczek W. P. Schaefer and R. E. Marsh Znorg. Chem. 1975,14 611. 139 V. M. Miskowski J. L. Robbins I. M. Treitel and H. B. Gray Znorg. Chem. 1975,14 2318. 140 T. C. StrekasandT. G. Spiro Znorg.Chem. 1975,14 1421. 141 L.D. Brown and K. N. Raymond Znorg. Chem. 1975,14 2590. 14* J. Halpern B. L. Goodall G. P. Khane H. S. Lin and J. J. Pluth J. Amer. Chem.SOC.,1975,97,2301. Transition -metal Chemistry PhMe,P c PMe,Ph N mononuclear complexes e.g. [IrC1(CO)(02)(PPh3)2] (1.51A) and (Co(Ph,PCH=CHPPh,),(O,)]+ (1.42 A). It is suggested that in (29) both cobalt atoms are formally Co"' two electrons being transferred to the dioxygen via a ligand- bridged inner-sphere mechanism. The complex oxidizes PMe,Ph in methanol solution [equation (6)]. +3PMe2Ph +~[CO(CN)~(PM~,P~)~] [CO,(CN)~(PM~~P~)=,(O,)] +2Me2PhP0 (6) The dioxygen adducts of iridium [IrX(O,)(CO)(PPh,),] (X =C1 Br or I) although quite stable under normal conditions lose dioxygen on irradiation even at 77 K.It is suggested that the photoinitiation process is triggered in an electronic state possessing iridium-to-phosphine charge-transfer chara~ter.'~~ The X-ray structure of one such adduct [Iro2{Ph2PCH2P~h2}2]PF6, has been re-determined.'44 The 0-0 bond distance now found (1.52A) is cpsiderably shorter than that previously obtained and in the range (1.41-1.52A) found in a variety of such complexes of cobalt rhodium and iridium; thus an apparent anomaly is resolved. Dioxygen adducts of a number of other cobalt complexes have been prepared and investigated. Equilibrium studies on some chelating polyamine complexes of cobalt which give w-peroxo-w-hydroxo-complexes with dioxygen and act as reversible dioxygen carriers have shown a linear relationship between the logarithm of the stability constant of the dioxygen adduct and the sum of the pK's of the atoms ligating the cobalt This relationship allows prediction of the tendency of cobalt complexes to form stable dioxygen adducts.In particular it shows that the symmetrical and unsymmetrical ethylenediaminediacetic acids form quite stable dioxygen complexes in an appropriate pH range although they contain only two basic nitrogen atoms rather than the three which had previously been considered necessary. Chelate Complexes of Biological Relevance. In a study of the interactions of metal ions and nucleotides cytosine 5'-monophosphate (CMP) gave a polynuclear cobalt complex [Co(CMP)(H,O)],H,O which has tetrahedral Co" bound to two oxygen atoms of a bridging phosphate group and N-3 of the ~yrimidine.'~~ Cobalt(II1) complexes of azophenols have been prepared and their relevance to azotyrosine- modified enzymes which may form exchange-inert Co"' complexes is noted.14' The X-ray structure of [Co(tren)(gly)]'+ [tren = tris-(2-aminoethyl)amine,gly =glycine] formed by the hydrolysis of a glycine ester with [Co(tren)(OH)(H20)]2' shows that 143 G. L. Geoffroy G. S. Hammond and H. B. Gray J. Amer. Chem. SOC. 1975,97,3933. w4 M. Laing M. J. Nolte and E. Singleton J. Amer. Chem. Soc. 1975,97 6396. 145 G. McLendon and A. E. Martell J.C.S. Chem. Comm. 1975 223. 146 G. R. Clark and J. D. Orbell J.C.S. Chem. Comm. 1975 697. 147 W. I. White and J. I. Legg J. Amer. Chem. SOC. 1975,97 3937.J. R. Dilworth G.J. Leigh and R. L. Richards the glycine is co-ordinated with its nitrogen atom trans to the tertiary amine of tren and the tren ligand forms three diamine rings with two K and one K' conformations. This structure relates to specific hydrolysis of peptides by cobalt(II1) complexes. '48 In a cobalt(Iz1) carboxypeptidase A complex the magnetic moment (p,* =4.77 BM) and intensity of the principal visible absorption band (555.5nm E = 150) are considered compatible with a five-co-ordinate cobalt centre.14' Cobalt complexes containing the corrin inner ring structure have been obtained by abstraction of hydride with a quinone or other reagents from bis(p-iminoamine)cobalt(II) com-plexes containing 14- 15 or 16-membered rings.'" Complexes of Sulphur Ligands.-Some novel polynuclear cobalt complexes with bridging sulphur groups have been characterized.The tetrameric cluster compound (30)has a Co4S10 framework of effectively 7'' symmetry with bridging angles at S of 113".15' A monosulphur-bridged dinuclear complex [(CN),CoSCo(CN)J- which is easily hydrolysed has been prepared from [Co(CN),I3- and sulphur. 152 Dinuclear thio- bridged complexes with di thiocarbamato- or NN'-e thylene-bis(thiosalicyla1diminato)-ligands have been prepared and structural spec-troscopic and magnetic properties determined. 153 Oxidation of the complex [Co(en),(CH,CH,NH,)]'' with Npv' gives a novel cobalt(II1) disulphide complex [CO(~~)~(S(SCH,CH,NH,)CH~CH,NH,}]~'. A radical dimer intermediate is pro- posed.154 Ph A novel terdentate ligand is formed by the condensation of two benzoyl isothiocyanate molecules in the presence of [RhCI(PPh,),] (3l).15 The triply-bridged p-chloro-p-phenylthio-complex [Ir,H,Cl(SPh),(PPh,),] has been prepared by reaction of [IrHCI(SPh)(PPh,),] with AgCIO in acetone.156 Thioformato-complexes [Ir(S,CH)X(PPh,),](X = C1 or Br) have been prepared and the diagnostic spectral properties of this ligand attached to various metals given.15' 148 Y.Mitsui J. Watanabe Y. Iitaka and E. Kimura J.C.S. Chem. Comm. 1975 280. 149 R. C. Rosenberg C. A. Root and H. B. Gray J. Amer. Chem. SOC. 1975,97,21. 150 S. C. Tang and R. H. Holm J. Amer. Chem. Soc. 197.5,97,3359. 151 1. G. Dance and J. C. Calabrese J.C.S. Chem. Comm. 1975,762. Is* P.S. Poskozim J. Znorg. Nuclear Chem. 1975,37 2342. 153 A. R. Hendrickson R. L. Martin and D. Taylor J.C.S. Dalton 197.5 2182; M. F. Corrigan K. S. Murray R. M. Sheahan B. 0.West G. D. Fallon and B. M. Gatehouse Znorg. Nuclear Chem. Letters 1975,11,62.5. lS4 M. Woods J. C. Sullivan and E. Deutsch J.C.S. Chem. Comm. 1975 749. 155 C. M. Lowie J. A. Ibers Y. Ishii K. Itoh I. Matsuda and F. Ueda J. Amer. Chem. Soc. 1975,95,4748. 156 P. J. Roberts G. Ferguson and C. V. Senoff J. Organometallic Chem. 1975,94 C26. 157 S. D. Robinson and A. Sahajpal J. Organometallic Chem. 1975 99 665. 15' conformational properties of the rings are discussed. Transition -metal Chemistry 171 Chelating Phosphine Complexes.-This work involves primarily rhodium and iridium.Large-ring co-ordination complexes with trans-chelate phosphine ligands have recently been synthesized and structural parameters have now been determined for trans-[IrCl(CO){Bu',P(CH,),,PBu',}] and [RhCl(CO){Bu',P(CH,),,PBu'~}]~. The former has a 13-atom ring and the latter two pdiphosphines forming a 26-membered ring; the phosphorus atoms are trans at the metal centres. The Some o-metallated complexes [~r(~~){~~u',(~6~4~}{~~u'~(~~~~~-~}] (X = H or Me) give (X =H) a blood-red paramagnetic (peR= 1.73 BM) iridium@) complex trUnS-[rr(pBUt2(c6H4o)),l on exposure to air. A hydrido-complex [irH{PBu',(C6H46)},] is formed from this and dihydrogen. which reverts to its congener on exposure to air. A benzene solution of trans-[fr{PBu',(c6H40)}~] slowly gives in air the purple C-metallated compound [~~{PBu'~(C~H~O)}{PBU'(C~H~O)(CM~,~H,}].'~~ Another paramagnetic IrI' com- plex [Ir(0,CR),(AsPh,)(CNC6H4Me-p)] (/lefi= 1.67 BM e.s.r.g values at 2.039 and 2.015) has been prepared by treatment of [IrH,(AsPh3),(CNC6H4Me-p)] with p-chlorobenzoic acid. 160 Reactions of Co-ordinated Ligands and Catalysis.-When co-ordinated to [M(NH3),I3+(M=Co Rh or Ir) organic nitriles are activated towards nucleophilic attack. Thus reduction of nitriles by BH4- Michael addition of carbanions to acrylonitrile (M =Co) or base hydrolysis of acetonitrile of benzonitrile (M =Co Rh or Ir) are all greatly accelerated by co-ordination to these metal centres.'61 The complex [Co(NHJnNO]'+ bound within a Y-type zeolite is a catalyst for the conversion of NO and NH into N2and H,O at temperatures above 50 0C.162 This effect relates to the catalysed reduction of oxides of nitrogen from effluent gas streams by ammonia.The compounds [IrC1X(NO)(CO)(PPh,)2] undergo an appar- ent electrophilic attack on the 'NO-' ligand by dioxygen to give nitrato-complexes [IrClX(N0,)(CO)(PPh,)2]; the rate of oxidation decreases with X in the order X = I >Br >C1> NCS >NCO >N3.163 Asymmetric hydrogenation using rhodium complex catalysts continue to receive attention. The catalyst [Rh(cyclo-octa-1,5-diene){1,2-bis[o-anisyl(phenyl)phosphino}ethane)]+ induced optical purity in excess of 95-96'/0 in the reduction of a-acylamidoacrylic acids. 164 Similarly high optical yields have been obtained in the reduction of a-ethylstyrene and N-acetamidoacrylic acid derivatives with a rhodium complex of trans-1,2-bis(diphenylphosphinoxy)cyclohexane,and related reductions occur using isopropylidene- 2,3-di hydroxy- 1,4-bis(dipheny1phosphino)butane as a ligand.165 F. C. March R. Mason B. L. Shaw and K. M. Thomas J.CS. Chem. Comm. 1975,584. 159 H. D. Empsall E. M. Hyde and B. L. Shaw J.C.S. Dalton 1975 1690. 160 A. Araneo F. Morazzoni and T. Napoletano J.C.S. Dalton 1975,2039. I. I. Creaser and A. M. Sargeson J.C.S. Chem. Comm. 1975,974;A. W.Zanella and P. C. Ford Inorg. Chem. 1975,1442,700. 162 K. A. Windhorst and J. H. Lunsford J.C.S. Chem. Comm. 1975,852. 163 M. Kubota and D. A. Philips J. Amer. Chem. SOC. 1975 97 5638. W. S. Knowles M. J. Sabachy B.D. Vineyard and J. Weinkauf J. Amer. Chem. SOC. 1975,97,2567. 165 M. Tanaka and I. Ogata J.C.S. Chem. Comm. 1975,735;T. P. Dang J. C. Poulin and H. B. Kagan J. Organometallic Chem. 1975,91 105. J. R.Dilworth G.J. Leigh and R.L.Richards Rhodium(II1) chloride acts as a homogeneous catalyst for isotopic hydrogen exchange in deuteriation of aromatic compounds or alkanes. "' Reduction of dinitrogen to ammonia has been catalysed by aqueous acidic solutions of rhodium(II1) or iridium(II1) chloride. The reaction of a 1:3mixture of dinitrogen and dihydrogen in presence of a reducing agent (TiCI or SnCI in 10molar excess) gives yields of ammonia in the range 0.1-0.4 moles per mole of 6 Group VIIIC Nickel Palladium and Platinum Complexes of polydentate often macrocyclic ligands continue to be a feature of the chemistry of nickel.Complexes of Multidentate Ligands.-Square-pyramidal complexes with for the first time nickel-bismuth bonds have been prepared from tris-(0-dimethylarsinopheny1)bismuthine (bitas) [NiX(bitas)] (X = halide) and [Ni,(bifa~)~]~+. In the latter complex bitas functions as a terdentate and a quadri- dentate ligand (32). 1,3-Bis(dimethyIstibino)propane (dmsp) gives square-pyramidal complexes [NiX(dmsp),]ClO,. '" Trigonal-bipyramidal stereochemistry is shown by [NiI(NCH2CH2NMe2)3]I.'69 The complex [NiI(nas)JBPh [nas = tris-(2-diphenylarsinoethyl)amine] reacts with NaBH in ethanol to give a dimeric com- pound of nickel(1) (33) with a linear Ni-I-Ni bridge. This unit allows antifer- romagnetic interaction between metal atoms.''O A novel linear Ni-S-Ni system occurs in (34) prepared by reaction of [Ni(H2O)6l2+ H2S and 1 1,1-tris(diphenylphosphinomethy1)ethane. The short Ni-S (2.034A) distance indicates a high r-component in the Ni-S bonds in keeping with the linear Ni-S-Ni system and diamagnetism of the ~omplex.'~' Five-co-ordinate complexes particularly of nickel can have square-pyramidal or trigonal-bipyramidal structure depending on the ligating atoms. The ligand (Ph,PCH,CH,),N however having the NP3 donor set appears to confer exclusively 166 M. R. Blake J. L. Garnett I. K. Gregor W. Hannan K. Hoa and M. A. Long J.C.S. Chem. Comm. 1975,930. 167 M. T. Khan and A. E. Martell Inorg. Chem. 1975 14 938. W. Levason C. A. McAuliffe and S.G. Murray J.C.S. Chem. Comm. 1975,164;R. J. Dickenson W. Levason C. A. McAuliffe and R. V. Parish ibid.,p. 272. 169 P. L. Orioli and N. Nardi J.C.S. Chem. Comm. 1975 229. 170 L. Sacconi P. Dapporto and P. Stoppioni J. Amer. Chem.Soc. 1975,97 5595. 171 c.Mealli S. Midollini and L. Sacconi J.C.S. Chem. Comm. 1975 765. Transition -metal Chemistry trigonal-pyramidal geometry upon nickel(11). 172 This geometry is assigned to the complexes [Ni(CN),L,] and [NiLJ2+ (L =tertiary phosphine or phosphite) which in common with many five-co-ordinate complexes are labile in solution giving an equilibrium of the type (7). The factors determining the equilibrium position are discussed in terms of the electronic spectra of the complexes.173 The ligand tetars ms-Me2As(CH2)3As(Ph)CH,As(Ph)(CH2)3AsMe,, gives square-pyramidal com- plexes of type [MX(tetars)]' (M =Ni" Pd" or Pt") whose absorption and circular dichroism spectra are interpreted in terms of the orbital energy ordering dxy>d, > d, >d,2 >dX2- ,2.174 [NiX2Lgln+ $ [NiX2LJ"* +L (X =CN n =0; X =L n =2) (7) Synthesis of macrocyclic-ligand complexes of ten involves a condensation reaction between a carbonyl compound and an amine function in the presence of or in the co-ordination sphere of the metal. Many further examples of this type of system have appeared this year.'75 A Schiff-base complex of this type with a planar N3 donor set (39 also has both uni- and bi-dentate nitrato-gro~ps.'~~ Some new examples of dimeric Schiff-base complexes of nickel(I1) have been prepared (36) and show intermolecular anti-ferromagnetic beha~i0ur.l~~ I+ Ph\ Me C1 (35) + 172 M.D. Vaira and L. Sacconi J.C.S. Dalton 1975 493. '73 E. J. Lukosius and K. J. Coskran Znorg. Chem. 1975,14 1922. izB. Bosnich W. G. Jackson and S. T. D. Lo,Inorg. Chem. 1975,14 2998. D. B. Bonfoey and G. A. Melson Znorg. Chem. 1975,14,304; N. F. Curtis,J.C.S. Dalton 1975,87.91; R. Cheney L. E. Heyman and E. L. Blinn Znorg. Gem. 1975,14,441; P. Domiano A. Musatti and N. Nardelli,J. C.S. Dalton 1975,295;J. C. DabrowiakandD. H. Busch Znorg. Chem. l975,14,1881;M. J. Mocella F. Wagner E. K. Barefield and I. C. Paul J. Amer. Chem. Soc. 1975,97 192. 1'6 E. C. Alyen G. Ferguson and R. J. Restivo Znorg. em. 1975,14,2491; P.H. Merrell J. C. S. Chem. Comm. 1975,269. 177 R. J. Butcher and E. Sinn J.C.S. Chem. Comm. 1975,832. 174 J.R. Dilworth G. J.Leigh and R. L. Richards Macrocyclic bis( p-iminoamine) complexes of nickel(I1) (see also copper and cobalt) containing 14-membered rings are converted into the delocalized radical cation (37) by oxidative dehydr~genation.'~' This has an e.s.r. signal of more than 80 lines which has been analysed in terms of a 2Bluground state with an essentially Nil'-L-(15m) system; that is extensive ligand delocalization of the unpaired electron. This formalism is similar to that used to describe certain porphyrin cation radicals one of which [Ni"(TPP)]' undergoes reversible electron transfer to give [Ni"'(TPP)]'. This process has been likened to a suggested mechanism of electron transfer in cytochromes [equation @)I."' [Fe"'(cyt)] +[Fe"(cyt)]' $[Fe"'(cyt)]+ (8) The above oxidative dehydrogenation method has been used extensively to convert other larger ring complexes into less saturated derivatives.17' The base- promoted reduction of nickel(I1) complexes of macrocyclic ligands gives nickel- macrocycle radical species which undergo a number of other reactions and are suggested as intermediates in macrocyclic amine-complex reactions. Zerovalent Complexes.-Complexes of nickel palladium and platinum in the zero oxidation state particularly with tertiary phosphine ligands continue to be prepared and their reactions studied. New examples are [Pt{P(CF,)Ph,},],'81 bis-[ 1,2- bis(difluorophosphino)cyclohexane]nickel(0),182 and [Pt(MeC(CH,PPh,),}(PR,)] R =alkyl aryl F NMe, or OPh).lS3 Heating [Pt(PPh,),] in benzene gives the cluster compounds (38) and (39).lS4The reactions of ethane- 1,2-di t hiol 2-(methyl t hio)e t hane thiol and 2-(methy1thio)ethane disulphide with [M(PPh,),] (M =Ni Pt or Pd) have been studied and [Pt(SCH2CH2S),(PPh3),] [Pd,(SCH,CH,S),(PPh,),] and [Ni(SCH,CH,S)(Ph,PCH2CH2PPh2)] prepared.By using an excess of halogen and short reaction times the addition of halogens to [Pt(PPh,),] has been shown to give exclusively trans-[PtX,(PPh,),] (X =C1 Br or I) as the initially formed The commonly observed products from such reactions are the cis- complexes formed by isomerization in the presence of free phosphine avoided by the p2 pPh2 /\ PhP Pt-/ \pt/PPh3 Ph3P -Pt -Pt-PPh I\ /I \/ Ph? P-Pt-PPhz P I Ph 2 Ph (38) (39) 178 M.Millar and R. H. Holm J.C.S. Chem. Comm. 1975,169; S. C. Tang and R. H. Holm J. Amer. Chem SOC.,1975,97 3351. 179 D. Dolphin and R. H. Felton Accounts Chem. Res. 1974,7,26; T. Nien and I. Fujita J. Amer. Chem. Soc.,1975,M 5288. 180 E. K. Barefield and M. T. Mocella J. Amer. Chem. SOC.,1975,97 4238. 181 T. G. Attig M. A. A. Beg and H. C. Clark Znorg. Chem. 1975,14 2986. 18* N. R. Zack K. W. Morse and J. G. Morse Inorg. Chem. 1975,14 3131. J. Chatt R. Mason. and D. W. Meek J. Amer. Chem. SOC.,1975,97 3826. N. J. Taylor P. C. Chieh and A. J. Carty J.C.S. Chem. Comm. 1975,448. 185 (a) B. Ranchfuss and D. M. Roundhill J.Amer. Chem. SOC.,1975,97,3386; (b)R. C. Stonfer ibid. p. 195; (c) K. B. Dillon T. C. Waddington and D. Younger J.C.S. Dalton 1975,790; (d)J. F. Plummer and E. P. Schram Znorg. Chem. 1975 14 1505; (e) K. Maeda 1. Moritani Y. Hosokawa and S. I. Murakashi J.C.S. Chem. Comm 1975,689; (f)M. Foa and L. Cassar J.C.S. Dalton 1975 2572. Transition -metal Chemistry 175 above reaction conditions. [M(PPh,),] (M =Ni Pt or Pd) react with liquid HCl to give cis-[MC1,(PPh,),],'85c with TiCl (M =Pt) to give an adduct with Pt-Ti bonds,"5d and with ketoximes in the presence of dioxygen (M =Pd) to give nitriles and a1deh~des.l'~~ The mechanism of oxidative addition of aryl halides to [Ni(PPh3)4] has been in~estigated."~~ Oxidation StateOne.-Examples of platinum(1) and palladium(1) complexes are still rare (see Chapter 8 p.207).186n*b Electrochemical and e.s.r. studies of dithiolene complexes of palladium and platinum indicate that paramagnetic and presumably monomeric complexes of Pd' and Pt' are formed with these ligand~."~ Nudear Magnetic Resonance Studies.-N.m.r. spectroscopy continues to be a powerful tool in the study of palladium and platinum complexes. The platinum(0) complexes [Pt(triphos)(PR,)] [triphos =MeC(CH,PPh,),] mentioned above have 1fi'"Pt3''Y(R3)] values larger than corresponding values in truns-platinum(11) (twice) and cis-platinum(I1) (ca. 55% greater) complexes. J(31P,31P) values are also higher than in platinum(r1) complexes. These differences are considered to be caused by the steric constraint of the triphos ligand which confers relatively low s-character in the Pt-triphos bonds and correspondingly high s-character in the Pt-PR bonds.lg3 The 1J('95Pt31P) values for cis-[PtCl,(R,PCH,CH,PPh,)] (R = CF or Ph) show a strong dependence on substituents at phosphorus.'s8a The values of J('95Pt 13C)and J(195Pt,'9F) for platinum complexes of carbon monoxide188b or SCF3188C have been discussed in terms of trans -influence of hydride and halide co-ligands. The first values of J('95Pt,77Se) and J('95Pt,125Te) have been reported. They decrease markedly in the order C1> Br >I in the compounds [PtX,(SeMe,)]- [PtX,(SeMe,)]-and [PtX,(TeMe,)]- (X =C1 Br or I).'88d Values of 2J(195Pt 195Pt) have been determined for the complexes [PtCI,(PBu,),] and [Pt214(PBu3),].The mode of bonding of SCN groups (whether Nor Sligation) has been a subject of interest and controversy for many years. Recently n.m.r. spectroscopy and X-ray crystallography has been used to determine the binding of the SCN group to platinum and palladium. In the platinum case the linkage isomers of [Pt(CNS),(SMe,),] (no implied N or S bonding) have been identified from coupling patterns of the 'H_(195pt}INDOR spectra and it is thought likely that 195Pt chemical shifts will provide a means of distinguishing isomers.'89a The ,'Pn.m.r. spectra of cis-[PtX,{P(OPh),},] (X = CNS or C"NS) show the independent existence of linkage isomers in solution. lS9' An X-ray study of the complexes [Pd(CNS),{Ph,P- (CH,),PPh,)] has shown that in the solid state the thiocyanate co-ordination changes from S (n = 1)to SN (n = 2) and N2(n= 3).It is concluded that the bonding mode is controlled primarily by steric effects.lS9' 186 (a) A. Modinos and P. Woodward J.C.S. Dalton 1975 1516; (b)D. J. Doonan A. L. Balch S. Z. Goldberg R. Eisenberg and J. S. Miller J. Amer. Chem. Soc. 1975,97 1961. lS7 F. C. Seuftleber and W. E. Geiger J. Amer. Chem. SOC. 1975,97 5018. 188 (a)T. McLeod Lj. Manojlovit-Muir D. Millington K. W. Muir D. W. A. Sharp and R. Walker J. Organometulfic Chem. 1975,97 C7;(6)W. J. Chewinski B. F. G. Johnson J. Lewis and J. R. Norton J.C.S. Dalton 1975 1156; (c) K. R. Dixon K. L. Moss and M. A. R. Smith ibid. p. 990. (d)P. L. Goggin R. J Goodfellow and S. R. Haddock J.C.S. Chem. Comm 1975 176; (e)A.A. Kiffer C. Masters and J. P. Visser J.C.S. Dalton 1975 1311. lE9 (a)S. J. Anderson and R. J. Goodfellow J.C.S. Chem. Comm. 1975 443; (6) A. J. arty and S. E. Jacobson ibid. p. 175; (c) G. J. Palenik M. Mathew W. L. Stiffen and G. Berau J. Amer. Chem. SOC. 1975,97 1059. J.R. Dilworth G. J.Leigh and R. L. Richards Hydrocarbon Activation.-Important in the search for a catalyst for activation of saturated hydrocarbons is the observation of hydrogen-deuterium exchange in alkanes catalysed by platinum complexes.'90a Further work has shown that by use of H,PtCl in aqueous trifluoroacetic acid at 120"C benzene has been oxidized to chlorobenzene and hexane to chlorohexanes. 1906 Hydrogen-deuterium exchange at alkyl groups of L moieties occurs in the complexes [Pt,Cl,L,] (L=PPr, PBu, PBu'Pr, PBu',Pr PPrPh, PPr,Ph or PBu'Ph,) in aqueous (D,O) acetic acid (CH,COOD) medium.Exchange also occurs at the saturated (C-5) carbon of RCMe,CH=CH (R =Et Pr or Bu) under similar conditions. It may occur through dimeric complexes of the type [Pt,Cl,(RCMe,CH=CH,)] isolated from the reac- tion medium or related dimeric compounds. 19' Diazene Ligands.-Understanding of the properties of diazene (N,R) ligands has progressed from study of their platinum complexes. The bridging diazenido-ligand N,H occurs in the complexes [Pt(N2H)2(PR3)2]22+ [PR = PPh, PPh,Me or P(C,H,Me),] 192 prepared by hydrazine reduction of cis-[PtCl,(PR,),]. In the complex [PtCl(N,C,H,F)(PEt,),] the diazenido-group has the 'doubly-bent' struc- N-/ ture -N and is readily protonated at both nitrogen atoms.193 7 Group IB Copper Silver and Gold Principal activity this year has involved study of structural and magnetic properties of polynuclear complexes and biologically relevant copper complexes.Structural and Magnetic Studies.-The tetrameric species [MXPEt,],(M = Cu or Ag; X =C1 Br or I) have a distorted 'cubane' structure with p,-halide bridges. Only for large halogens (Br or I) together with bulky phosphines (PPh,) does the structure change to 'step-like'. The complex [(CuI),(Ph,PCH,PPh,),] has a triangle of copper atoms connected by iodide and diphosphine bridges (40).194 Polynuclear copper complexes bridged by a variety of groups show magnetic interaction of the antiferromagnetic type and a number of further examples have been investigated this year.An unusual example is the trinuclear complex (41) the first example of a linear array of three oxygen-bridged copper(I1) atoms. Magnetic l90 (a)M. B. Typbin A. E. Shilov and A. A. Shteinman Doklady Akad. Nauk S.S.S.R. 1971,198,380;R. J. Hodges D. E. Webster and P. B. Wells J. Chem. SOC(A),1971 3230; (b)J. R. Sanders D. E. Webster and P. B. Wells J. C. S. Dalton 1975 1191. 191 A. A. Kiffen C. Masters and L. Raymond J.C.S. Dalton 1975 853; P. A. Kramer and C. Masters ibid. p. 849. 192 M. Kembler S. Cenini F. Conti and R. Ugo J.C.S. Dalton 1975 1081. 193 S. D. Ittel and J. A. Ibers Znorg. Chem. 1975 14 636; S. Krogsrund and J. A. Ibers ibid. p. 2298. 194 M. R. Churchill and B.G. DeBoer Znorg. Chem. 1975,14,2402;with S. J. Merdak ibid.,pp. 2041,2496. Transition-metal Chemistry studies show that only two of the three electrons of the trimer are paired only the spin-doublet state being pop~lated.'~~ Antiferromagnetic behaviour has been studied in the complexes diquinoline tetra-p -trifluoroacetate( O,O)-dicopper(~~),'~~ [Cu(tren),X,l2' (tren = 2,2',2"-triaminotriethylamine X = C1 NCO or NCS),19' [{CuLX,},,] (X =C1 or Br L = nicotinamide or is~nicotinamide),'~~ and bis(nicotinato)silver(~r).'~~A correlation between metal environment and antiferromagnetic interaction in oxygen-bridged copper(I1) dimers has been demonstratedzo0 and the magnetic properties of ternary oxides of copper in oxidation states (I) to (IV) have been investigated.,Oi Unusual Valence States and Biologically Related Complexes.-A mixed-valence cluster compound [Cu,(S,CNEt,),Cl,] consists of elongated square-pyramidal Cu" linked by chloride and sulphur bridges to a tetrahedral Cu' unit.It is formed by reduction of polynuclear chloride-bridged [Cu2(S2CNEt2)C12] and is associated with [Cu2(S2NEt2),C12] dimers in the The mixed Ad1'-Au' compounds [Au(mnt)][Au(MPh,),J (mnt =maleonitrile dithiolate M =P or As) are converted into the Au" anion [Au(mnt),12- on treatment with Na,(mnt) probably by an electron-transfer mechanism.203 A Cu"' complex [Cu(G,)]- (G2-=deprotonated tetraglycine) is unusual in that it is reasonably stable in aqueous solution in contrast to the few other examples of Cu"' complexes.The Cu"'-Cu" potential 0.140 V is low enough to suggest that further similar compounds should be obtainable. [Cu(G,)]- is formed by reaction of dioxygen with Cu" tetraglycine complex pro- vided that photochemical inhibition of the reaction is avoided. It is suggested that Cd-Cu"' couples could occur in biological systems such as galactose oxidase thus avoiding high-energy free-radical intermediate^."^ Study of copper-sulphur interactions in relation to copper-containing proteins such as oxidases has been an active field this year. The results of a X-ray photoelec- tron spectroscopic study of bean plastocyanin has been interpreted in terms of delocalized Cu"-cysteine-sulphur binding.205 Comparison has been made between copper-sulphur binding in various complexes and the environment of copper in 195 W.A. Baker and F. T. Helm J. Amer. Chem. SOC. 1975,97 2295 references therein. 196 J. A. Moneland and R. J. Doedens J. Amer. Chem. SOC.,1975,97 508. 19' E. J. Laskowski D. M. Duggan and D. N. Hendrickson Znorg. Chem. 1975,14 2449. 198 R. P. Eckberg and W. E. Hatfield J.C.S. Dalton 1975 1364. 199 R. P. Eckberg and W. E. Hatfield Znorg. Chem. 1975 14 1205. 2oo E. Sinn J.CS. Chem. Comm. 1975,665. 201 M. Arjomand and D. J. Machin J.C.S. Dalton 1975,14 1205. 202 A. R. Hendrickson R. C. Martin and D. Taylor J.C.S. Chem. Comm. 1975,843. 203 T. J. Bergendahl and J. H. Waters Znorg. Chem. 1975,14 2556. 204 F. P. Bossu G. L. Burce K. L. Chellappa and D. W. Margerum J. Amer. Chem. SOC., 1975,97,68%;G.L. Burce D. W. Margerum and E. B. Paningo J.C.S. Chem. Comm. 1975,261. 205 P. J. Clendening H. B. Gray F. J. Grunthaner and E. I. Solomon J.Amer. Chem. SOC.,1975,97,3878. 178 J. R. Dilworth,G.J. Leigh,and R.L.Richards 'blue' proteins as is shown by its spectral parameters. In [bis-(2-pyridyl)disulphide]copper(~)perchlorate the copper selects N3S co-ordination pos- sibly its environment in natural systems.206 A dinuclear complex of copper(r1) with oxidized glutathione is considered to be dimeric with Cu" bridged by a disulphide unit. The Cu" atoms interact as shown by e.s.r. measurements and the compound provides the basis for a scheme to account for the properties of the Cu pair in 'blue' oxidases which accepts two Copper complexes of cyclic or linear poly-thioethers show an absorption (600nm) similar to that of 'blue' proteins assigned in both complexes and proteins to an S+Cu" charge-transfer band.Of this group the complex of the ligand (42) has a planar arrangement about copper suggesting that distorted symmetry about copper need not occur in the proteins. A further extrapolation from this work is that thioether sulphurs of methionine groups could be the copper-binding site of 'blue' proteins.208 Thee.s.r. and visible spectra of a Cur' a,-mercaptopropionylglycine complex are similar to the corresponding parameters for 'blue' A kinetic study of the reduction of 'blue' proteins by [Fe(edta)12- has been discussed in terms of an outer-sphere mechanism for all such proteins but laccase which requires a specific protein activation to accept reductant.,lo In other studies of biological relevance comparison of e.s.r.and electronic spectra of Cu" carboxypeptidase A and model Cu" complexes suggests a protein co-ordination significantly distorted from planar to tetrahedral symmetry.211 Other ligands of the amino-acid type whose interactions with copper have been studied include ace tyl histamine ace tyl his tidine [with Cu'] ;L-hist idine gl y cylgl ycerine and D-penicillamine histidine peptides simple dipeptides epinephrine ~-3,4-dihydroxyphenylalanine and other catechols [with CU"].~~~ Steric and electronic effects in copper Schiff -base complexes have been reviewed.213 Interaction of hydrazines and triazenes with copper have been studied.1,l-Dimethylhydrazine reacts with copper(r1) chloride to give a purple complex of 1,l-dimethyldiazene [Cu3Cl,{Me,N=N},]. Copper(I1) bromide gives the salt [Cu,Br,][Me,N,CHNMe,] in which the central carbon of the cation appears to be derived from formaldehyde formed by hydrolysis of 1 l-dimethyldia~ene.,~~ The metal-metal bonded compounds [L,(CO)MCu(RNNNR)X] (M = Rh' or 18; L =AsR or PR,; R = Me or aryl; and X = C1 Br or I) have been prepared and contain an M'+Cu' donor bond bridged by the triazenido group.215 M. M. Kadooka L. G. Warner and K. Seff J.C.S. Chem. Comm. 1975,990 and references therein. 207 P. Kroneck J. Amer. Chem. SOC.,1975,97 3840. 208 T. E. Jones D. B. Rorabacker and L. A. Schrymowycz J. Amer. Chem. SOC.,1975,97 7485; L. C. Zimmer and L.L. Diaddario ibid. 7163 and references therein. 209 V. Sugiura Y. Hirayama H. Tamaka and K. Ishizu J. Amer. Chem. SOC.,1975,97,5577. 210 S. Wherland R. A. Holmerda R. C. Rosenberg and H. B. Gray J. Amer. Chem. SOC.,1975,97,5260. 211 R. C. Rosenberg C. A. Rost P. K. Bernstein and H. B. Gray J. Amer. Chem. SOC.,1975,97,2092. z12 P. A. Terinissi and A. Vitagliano J. Amer. Chem. SOC.,1975,97 1572; S. H. Laurie T.Lund and J. B. Brynor. LCS. Dalton 1975 1389; R. P. Agarwal and D. D. Perrin ibid. p. 268; G. Brookes and L. D. Pettit ibid. p. 2302; R. K. Boggess and R. B. Martin J. Amer. Chem. SOC.,1975,97 3076. 213 H. S. Moslea and T. N. Waters Coordination Chem. Rev. 1975 17 137. 214 J. R. Boehm A. L. Balch K. F. Bizot and J. H. Enemark J. Amer. Chem. SOC.,1975,97,501.215 J. Kyper P. I. Van Wet and K. Vrieze J. Organometallic Chem. 1975,96 289.

ISSN:0308-6003    

DOI:10.1039/PR9757200149

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

8 Organometallic Compounds By D. J. CARDIN Department of Chemistry Trinity College Dublin University Dublin 2 K. R. DIXON Department of Chemistry University of Victoria Victoria 6.C. Canada 1 Introduction This chapter deals first with main-group and early transition-metal (Groups 111-VI) compounds (D.J.C.) followed by metal carbonyls and the later transition-metal derivatives (K.R.D.). The first part contains a section of shorter topics which were felt to be of wide general interest (in which the order of presentation is by the Group of the periodic table to which the appropriate metal belongs) and a selection of review articles and books. In the main the coverage is for the year 1975 but the second part covers specifically November 1974 to early November 1975.2 Reactions of Metal Atoms Conceptually one of the simplest and most attractive methods for the synthesis of organometallic compounds is the direct reaction of metal atoms with appropriate ligands (see Chapter 6 p. 120). This subject has received much attention recently and various aspects have been reviewed by Skell,'" Timms,lb Koerner von Gustorf,* and Klabunde3 (for matrix-isolation work with metal carbonyls see Section 20). At present all the transition metals can be used in this type of synthesis many in gram quantities. Sandwich complexes have been made for chromium,44 titanium,' and even tungsten.4b The use of halogen-substituted arenes leads to some unexpected effect^.^**^ Thus for vanadium whereas monosubstitution by chloro- fluoro- or trifluoromethyl-groups gives greater yields than with non-substituted benzene disubstitution by the same groups gives reduced or zero yields.Yields were not so (a) P. S. Skell and M. J. McGlinchey Angew. Chem. Internat. Edn. 1975,14 195; (b) P. L. Timms ibid. p. 273. * E. A. Koerner von Gustorf 0.Jaenicke 0.Wolfbeis and C. R. Eady Angew. Chem. Internat. Edn. 197514 278. K. J. Klabunde Angew. Chem. Internat. Edn. 1975 14 287. (a)P. S. Skell D. L. Williams-Smith and M. J. McGlinchey J. Amer. Chem. SOC.,1973,95,3337;(b)M. P.Silvon E. M. Van Dam and P. S. Skell ibid. 1974,96,1945;(c)P. S. Skell and L. K. Wolf ibid. 1972 94 7919. R. Middleton J. R. Hull S. K. Simpson,C. H.Tomlinson andP. L.Timms J.C.S. Dalton 1973,120. V. Graves and J.J. Lagowski Abstracts 165th A.C.S. Meeting Dallas Texas 1973(Paper No. INOR 52). F. W. J. Benfield M. L. H. Green J. S. Ogden and D. Young J.C.S. Chem. Comm. 1973,866. (a) K. J. Klabunde and H. F. Efner J. Fluorine Chem. 1974 4 115; (b) K. J. Klabunde and H. F. Efner Inorg. Chem. 1975 14 789. 179 D.J. Cardin and K. R. Dixon sensitive with chromium and the bis(trifluoromethyl)benzenechromium(O) com-plexes are remarkably air stable.8b Interest also continues in the reactions of the vapours of main-group metals with organic molecules. Lithium vapour is known to react with chloro~arbons~” giving polylithio-organic and with carbon va~our,~’ compounds. The reaction of excess lithium vapour with alkenes has been studied and the products characterized by hydrolysis (H20and D20),affording alkenes and alkanes identified by n.m.r.g.l.c. and mass spectrometry or by conversion into poly(trimethylsily1) derivatives. Poly-lithioalkenes predominate in the products and addition across the double bonds is relatively uncommon.9c Although the reactions of aluminium vapour with olefins afforded no isolable aluminium D20 hydrolysis products were interpreted in terms of intermediate a-bonded alkylaluminiums. More recently the reaction with ethylene has provided evidence of a complex involving donation from the n-orbitals of the olefin based on e.s.r. spectra of the matrix-isolated complex. lo Complexes are also formed with gallium and indium atoms. The equilibrium between the carbene and ‘carbenoid’ species produced by reaction of lithium atoms with carbon tetrachloride is known to lie well to the left of C1,CLi $ CCI + LiCl (1) equation (l).’la Careful analysis of i.r.data of the matrix products with the metals ‘Li Na K or Cs has revealed a further type of carbenoid species (1).’lb 3 Carbene and Carbyne Complexes In spite of the preparation of numerous carbene complexes of the transition metals,12 until recently no methylene complexes had been obtained although they had been postulated as reaction intermediate^'^"-' and complexes of secondary carbenes (CHR)are well The synthesis of the first methylene complex is shown in equation (2).14” The bis(cyclopentadieny1)methylene complex decomposes slowly in WCP) (Cp’)Me Ph,C + BF,-[Ta(Cp)(Cp’)Me,I+BF,-*Ta(Cp)(Cp’)Me(CH,) (2) Cp = q5-CsH5;Cp’ = q5-CsH4R R = H or Me; base = Me,PCH, LiN(SiMe,), or NaOMe (a)C.Chung and R. J. Lagow J.C.S. Chem. Comm. 1972 1078; (b)L. A. Shimp and R. J. Lagow J. Amer. Gem. SOC.,1973,95,1343;(c)J.A. Morrison C. Chung and R. J. Lagow ibid. 1975,97,5015. lo P. H. Kasai and D. McLeod J Amer. Chem. Soc.,1975,97 5607. l1 (a)D. F. Hoeg D. 1. Lusk and A. L. Crumbliss J. Amer. Chem. SOC.,1965,87,4147,and refs. therein; (b)D. A. Hatzenbuhler L. Andrews and F. A. Casey ibid. 1975,97 187. l2 D. J. Cardin B. Qtinkaya M. J. Doyle and M. F. Lappert Chem. SOC.Reu. 1973,2,99;M. F. Lappert J. OrganometallicChem. 1975 100 139. l3 (a)M. L. H. Green M. Ishaq and R. N. Whiteley J. Chem.Soc. (A),1967,1508; (b)M.R. Collier B. M. Kingston and M.F. Lappert Chem. Comm. 1970,1498;(c) N. J. Cooper and M. L. H. Green J.C.S. Chem. Comm. 1974,761; (d)B. Cetinkaya M. F. Lappert G. M. McLaughlin and K. Turner J.C.S. Dalton 1974 1591; (e)R. R. Schrock J. Amer. Chem. SOC.,1974 % 6796. 1 (a)R. R. Schrock J. Amer. Chem. SOC.,1975,97,6577;(b)L. J. Guggenberger and R. R. Schrock ibid. p. 6578; (c)L. J. Guggenberger and R. R. Schrock ibid. p. 2935. OrganometaI I ic Compounds deuteriobenzene solution forming 0.5 mol of Ta(Cp),Me(CH,CH,) and presumably Ta(Cp),Me which can be trapped as Ta(Cp),Me(CO) under carbon monoxide. With CD31 the methylene complex yields CH,D and the two isomers of Ta(Cp),(CH2CD2)I presumably uia Ta(Cp),Me(CH,CD,)I. This and other reac- tions show nucleophilic properties for the co-ordinated methylene group.The crystal structure of the complex reveals two eclipsed cyclopentadienyl rings related by a mirror plane containing the C-Ta-C bonds of the CH,-Ta-CH sy~tem.'~' By contrast with the majority of carbene complexes,12 the methylene group can n-bond only with the metal atom and the Ta-CH distance [2.206(10)A] is considerably shorter than the Ta-CH (ca. 2.25A) of the same compound but longer than the formal triple bond [1.76(2) A] of Ta(CH,CMe,),CCMe,,Li(NN'-dimethylpiperazine). 14c This 7r-bonding is supported for the cyclopen-tadienyl(methylcyclopentadieny1)methyleneanalogue for which n.m.r. measure-ments indicate a rotational barrier about the Ta-CH bond in excess of 2 1kcal mol-' . Insertion reactions into M-Ccarb bonds are not common and few have been reported since the curious reaction of PhSeH with carbenes of the Group VIA metals was rep~rted."~ The insertion of aminoacetylenes equation (3) has now been described.15' ,*7NEt2 (OC),CrC(OMe)Me + HC_CNEt,-(OC),Cr -c (3) \ CH II C(0Me)Me Carbyne complexes which were originally prepared from carbene species using boron halidesl5" have now been obtained by a variety of routes. {A number of C-chlorocarbene complexes such as [Cr(CO),(CClNMe,)] [Mn(CO),-(CClNMe),)]' or [Rh(CO)Cl,(CClNMe,)] which may be intermediates in the carbyne synthesis have been prepared from (Me,NCCl,)'Cl-and Na',[Cr(C0),I2- Na'[Mn(CO)5]- or Rh' ~pecies."~}. Thus whereas chromium carbenes with hydroxyl substituents react with carbodi-imide forming new carbene complexes [equation (4)],'5e tungsten analogues give dinuclear carbyne derivatives [equation (5)].Whereas it has been known for some time that electron-rich olefins such as [:CN(Me)CH,CH,NMe], are sources of metal carbene complexes,12 it has now been shown that under milder conditions this olefin and [Cr(CO),(nor- bornadiene)] give the N,N-bonded [Cr(CO) (olefin)] complex.'5f The effect on structure and bonding of heteroatom substituents on the Ccarb atom of carbene complexes has been well documented but corresponding information on 1s (a)E. 0.Fischer and V. Kiener Angew. Chem. Internat. Edn. 1967,6,961; (b)K. H. Dotz and C. G. Kreiter J. Organornetallic Chem. 1975,99,309; (c)E. 0.Fischer C. G. Kreiter J. Miiller G. Huttner and H.Lorenz Agnew. Gem. Infernat. Edn. 1973,12,564;(d) A. J. Hartshorn M. F. Lappert and K. Turner J.C.S. Chem. Comm. 1975 929; (e) E. 0.Fischer K. Weiss and C. G. Kreiter Chem. Ber. 1975,107,3554; cf) B. atinkaya P. B. Hitchcock M. F. Lappert and P. L. he J.C.S. Chem. Comm. 1975 683; (g)E. 0.Fischer G. Kreis F. R. Kreissl W. Kalbfus and E. Winkler J. Organometallic Chem. 1974,65,113; (h)E. 0.Fischer G. Huttner W. Kleine and A. Frank Angew. Chem. Internat. Edn. 1975,14 760; (i) E. 0.Fischer and V. Schubert J. Organometallic Chem. 1975,100 59. D.J. Cardin and K.R.Dixon carbyne derivatives is new. Diethylaminocarbyne complexes of tungstenlSg and chromium have been obtained and the crystal structure of the latter has been While the Cr=C distance of trans-[Et,NC=Cr(Br)(CO),]-[1.720(10) A] is not significantly greater than that found in the analogous methylcar- byne c~mplex,'~' the C-N distance [1.294(12) A] is indicative of considerable double-bond character.4 a-and f3-Eliminations Of the various elimination processes involved in the decomposition of metal alkyls the a-process is relatively little documented and was not established for homoleptic derivatives of the early transition elements. 16" However evidence had been obtained for such a mechanism occurring in tungsten alkyl~,'~" supported by D-labelling experiments. The a-abstraction process has now also been demon- strated in a homoleptic species [equation (6)],also supported by labelling studies.16b Ta(CH,CMe,),Cl + 2LiCH,CMe -+ [Ta(CH,CMe,),] -+Ta(CH,CMe,),CHCMe (not (6) isolated) It appears from data so far available'," that intramolecular a-abstraction will occur most easily when the metal atom is sterically crowded.The isolation of stable Pr',Cr shows that neither this last impression nor the view that alkyls with p-hydrogen atoms will be unstable has general validity. The mechanism proposed'6C [equations (7) and (S)] was suggested by the increase of yield observed upon irradiation. Analogous compounds replacing isopropyl with methyl ethyl or t-butyl CrCl + 3Pr'MgBr -P [CrPr',] !% Pr'. + [CrPr',] (7) (not isolated) Pr'. + CrPri3 + ~r~r' (8) groups could not be obtained and the stability of the isopropyl species was attributed to the stability of the radicals as well as to steric crowding.l6 (a)P. J. Davidson M. F. Lappert and R. Pearce Accounts Chem. Res. 1974,7,209;(b) R. R. Schrock J. Amer. Chem. SOC.,1974 96 6796; (c)J. Miiller and W. Holzinger Angew. Chem. Znternat. Edn. 1975 14 760. Organometallic Compounds 183 5 Organo-lanthanides and -actinides An area which attracted much attention during 1975 is that of organo-lanthanide and -actinide species. Several review articles a~peared,'~+~ and a number of interesting publications will be described. The allyl compounds Cp2MC3H5 appear to be n-bonded when M is a lanthanide (Sm Er or H0),17= whereas a crystal structure of Cp,UCH,C(Me)CH shows that the 2-methylallyl group is c+-bonded;17' cr-bonding had previously been suggested for the allyl analogue17g on the basis of i.r.spectroscopy and indeed the new lanthanide species show a band at 1533cm-' associated with the C-C stretching mode of .rr-ally1 groups. The organometallic chemistry of the lanthanides has been mainly restricted to wbonding ligand~,'~~" but alkyl and aryl derivatives have now been prepared by the organolithium route for Gd Er and Yb [equation (9)]. Although air- and moisture-sensitive the new Cp2LnC1 + RLi + Cp2LnR + LiCl (R = Ph or Me) (9) compounds show thermal stability decomposing only above 130"C under Ar.l7" The unusual temperature dependence of magnetic susceptibility might provide evidence for considerable covalency in the new species and is not observed for example in the v-bonded complexes. The reaction of trimethylsilylmethyl-lithium with uranium tetrachloride afforded solvates of Li,U(CH,SiMe,), the first uranium compound with more than a single metal-carbon u-bond.17' Vibrational spectra of the product of the exchange reaction shown in equation (10) indicate a triple hydrogen bridge. The "B decoupled 'H n.m.r. spectrum of Cp,UBH exhibits at Cp,UBH + R,B + Cp,UH,BR + RzBH (R = Et or Ph) (10) low temperatures collapse of the BH multiplet although the slow exchange limit could not be This is the first time for any metal borohydride species that slowing of the bridge/ terminal hydrogen rearrangement could be observed. Bis(cyc1o-octatetraeny1)uraniumand related molecules are highly air-sensitive. An air-stable 'uranocene' derivative has been obtained by using 1,3,5,7-tetraphenylcyclo-octatetraene dianion and uranium tetrach10ride.l~" The stability is presumably the result of steric blocking of the metal atom and consequently suggests that oxidative attack (0,)takes place at U and not at the ring.6 Cyclopentadienyl and Cyclo-octatetraenyl Compounds Current interest in the bis(cyclopentadieny1)metal derivatives of the Group VIA metals undoubtedly springs from the discovery of the remarkable reactions with 17 (a)M. Tsutsui N. Ely and A. E. Gebala Ann. New York Acad. Sci. 1974,239,160;(b)M. Tsutsui U.S. Ntis AD-A Rep. 1975 No. 008871 [Govt. Report Announce. Index (U.S.) 1975 75 631; (c) T. J. Marks J. Orgunometullic Chem. 1975 95 301; (d) N. S. Vyazankin R. N. Shchelokov and 0.A. Kruglaya Metody Elem.-Org. Khim.1974,2,905[Nauka Moscow]; (e)M. Tsutsui and N. Ely J. Amer. Chem. Soc. 1975,97,3551; v) G. W. Halstead E. C. Baker and K. N. Raymond ibid. p. 3049; (g)F. A. Cotton J. W. Faller and A. Musco Znorg. Chem. 1967,6,179,and refs. therein; (h)See for example K. 0.Hodgson F. Mares D. F. Starks and A. Streitwieser J.Amer. Chem. Soc. 1973,95,8650;(j)H. Gysling and M. Tsutsui Adv. Organometallic Chem. 1970 9 361; (k) M. Tsutsui and N. M. Ely J. Amer. Chem. Soc. 1975 97 1280; (I) R. Anderson E. Carnowa-Guzman K. Mertis E. Sigurdson and G. Wilkinson J. Organometallic Chem. 1975,99 C19; (m)T. J. Marks and J. R. Kolb J.Amer. Chem.Soc. 1975,97,27;(n)A. Streitwieser and R. Walker,J. Organometallic Chem. 1975,97,C41. D.J. Cardin and K.R.Dixon C-H bonds.'8a The Mo and W compounds are relatively reactive compared with the Cr but only the W species inserts into aromatic C-H bonds.Reactivity with CO also varies and the adduct Cp,Cr(CO) is formed reversibly under carbon monoxide in contrast to the known stable Mo and W analogues.'8b Not surprisingly the com- plexes (C,H,)(C,H,)M(CO) are stable for all three metals but tungsten is unique in forming CP~W(CO)~ a 20-electron complex. The carbonyl i.r. stretches exhibit no variations attributable to 'back-bonding' effects which are presumably not significant in determining reactivity differences. These are discussed subsequently in terms of structure and bonding. 18' New q2-nitrile complexes of molybdenocene have been obtained some of which can be reduced to yield ammonia uia isolable iminium intermediates [equation (11)].18d These adducts differ from earlier related r NH2 1' Cp,Mo(CF,CN) HC'-Hzo k2M0(C1)C (1 1) II CF CliNaBH,-OH ~ 1 NH + Cp2MoH + unidentified hydrocarbons molecules which either proved to be a-bonded'8e or had labile nitrile molecules.'8f (Details of aza-ally1 derivatives of Mo and W are described in Section 22.) The dicarbonyl derivative of titanocene is now more easily accessible,18g and its crystal structure has been reported.lsh By contrast with titanocene dichloride the cyclo- pentadienyl rings are eclipsed.The Ti-C(0) bond length [2.030(11) A] is the first structural information available for a Group IVA metal carbonyl. Cyclo-octatetraene (cot) complexes of titanium have been prepared by a new route and (Reproduced by permission from J.Organometallic Chem. 1975,92 329) l8 (a)K. Elmitt M. L. H. Green R. A. Forder I. Jefferson and K. Prout J.C.S. Chem. Comm. 1974,747; (b) K. L. Tang Wong and H. H. Brintzinger J. Amer. Chem. SOC.,1975,97,5143; (c)H. H. Brintzinger L. L. Lohr and K. L. Tang Wong ibid. p. 5146; (d)J. L. Thomas ibid. p. 5943; (e)J. G. Dunn and D. Edwards Chem. Comm. 1971 482 and refs. therein; (f) W. J. Bland R. D. W. Kemmitt and R. D. Moore J.C.S. Dalton 1972 1292; (g) H. Alt and M. D. Rausch J. Amer. Chem. Soc. 1974,96,5936; (h)J. L. Atwood K. Stone H. G. Alt D. C. Hrncir and M. D. Rausch J. Organometallic Chem. 1975 96 C4;0')H. R. Van der Wal F. Overzet H. 0.Van Oven J. L. de Boer H. J. De Liefde-Meijer and F.Jellinek J. Organometallic Chem. 1975,92,329;(k)J. Knol A. Westerhof H. 0.Van Oven and H. J. De Liefde-Meijer J. Organometallic Chem. 1975,% 257. Organometallic Compounds their structures determined [(2) and (3)].'*j The cot ligands in (2) lie approximately perpendicular to the body diagonals of the hexahedron (distorted cube). In both structures the cot rings assume an umbrella-like shape with the hydrogen atoms bent in towards the titanium atoms. Related cyclo-octatetraenetitanium derivatives undergo formal oxidation with iodine [equations (12) and (13)] forming iodides whose crystals are both thermally- and air-stable (although they decompose rapidly with water).lgk (q8-cot)(qS-Cp)Ti+ +I2 (q8-cot)(qS-Cp)TiI (q8-cot)(q5-Cp)Ti+ +I2 -P (q8-cot)(qS-Cp)TiI 7 Hydrometallations Insertion reactions involving zirconium-carbon and -hydrogen (hydrozirconation) bonds not only provide potentially useful synthetic procedures but are mechanisti- cally unusual.Thus the hydrozirconation of olefins by contrast with e.g. hydrofor-mylation gives an alkylzirconium species having the metal attached to the least -or + -P Cp,(Cl)Zr (14) -or hindered carbon atom even if internal olefins are used1'= [equation (14)]. The alkyls thus formed undergo carbon monoxide insertion even faster than their titanium analogues 19b although dibenzylzirconocene fails to react with CO under forcing conditions.19c The resulting acyl compounds can be cleaved to yield the correspond- ing aldehyde acid or ester.These cleavage reactions are of mechanistic interest since the protic cleavage of many transition metal-carbon bonds is believed to occur by oxidative addition followed by reduction involving the loss of R,C-H species a process clearly not likely with docomplexes. This has been examined with optically active carbon substituents and found to occur with retention of configuration at C Cp,(CI)ZrCHDCHDBu' + Br2 benzene BrCHDCHDBu' (15) for the reaction in equation ( 15).19d (Halogen cleavage of alkyl-iron'" and -cobaltlgf complexes has been studied and found to occur with inversion at the C-centre.) The structure of the transition state remains in doubt but it is possible that the electronic configuration (16-electron) may favour a frontside attack at the Zr-C bond.'9d Sulphur dioxide also inserts into the C-Zr c+-bond (of the same asymmetric compound) with retention of configuration whereas reaction with CpFe(CO),CHDCHDBu' took place with > 95% inversion.19g Insertion into the l9 (a)C. A. Bertelo and J. Schwartz J. Amer. Chem. Sac. 1975,97,228; (6)G. Fachinetti and C. Floriani J. Orgunometaflic Chem. 1974,71 C5;(c)G. Fachinetti and C. Floriani J.C.S. Chem. Comm. 1972 654; (d)J. A. Labinger D. W. Hart W. E. Seibert and J. Schwartz J. Amer. Chem. Soc. 1975,97,3851; (e)P. L. Bock D. J. Baschetto J. R. Rasmussen J. P. Demers and G. M. Whitesides ibid. 1974 96 2814; (f) F. R. Jensen V. Madan and D. H. Buchanan ibid. 1971,93,5283; (g)See G. M. Whitesides and D. J. Boschetto ibid. 1971,93,1529; (h)D.W. Hart T. F. Blackburn and J. Schwartz ibid.,1975 97 679. 186 D.J. Cardin and K. R. Dixon Zr-H bond of Cp,ClZrH also occurs with disubstituted acetylenes. When unsym- metrical acetylenes are employed a mixture of products is obtained initially [equa- tion (16)] dependent on the bulk of the s~bstit~enfs.~~" The initial product mixture c1 / Cp,(Cl)ZrH + R'CECR' +Cp2Zr / R' (16). H 'R2 + slowly (at room temperature) rearranges to a composition of higher regioselectivity a process catalysed by the initial zirconium hydride. Since pure vinylzirconium derivatives undergo no such rearrangement whereas it is known to occur for the alkyls the process is envisaged as taking place through the alkyl species ZrR'CH-CHR'Zr formed by double hydrozirconation of the acetylene.8 Sixteen-electron Compounds It has often been remarked that in their organometallic compounds the transition elements 'obey' the effective atomic number rule (especially in the middle of the series) with surprising frequency sometimes adopting unexpected structures. Two recent examples are shown in (4)20a and (5).20b Perhaps more surprising are the * ._-/Mo\\PPhMe, PhMe2PMe2PhP (4) (5) well-known pyrazolylborato-complexes of molybdenum. Sixteen-electron com- plexes of Mo or W were prepared from CpM(Cl)(CO) and acetylenes RC,R (R =Me CF, or C0,Me) in which the (three) carbonyl groups were displaced by two acetylene The complex [Ph,B(pz),](CO),MoC,H,Me unlike related compounds,21 has 3-2-methylallyl carbonyl and pyrazolyl N-atoms as Mo ligands without additional metal co-ordination making it a 16-electron species.9 Silacyclopropanes Silacyclopropanes have long been known as intermediates in thermolyses and photolyses of organosilicon compounds. For example the photolysis of 2-phenyl-heptamethyltrisilane afforded a silacyclopropane which was trapped with 20 (a)J. Muller and H. Menig J. Orgunometullic Chem. 1975,96,83;(b)R.Mason K. M. Thomas and G. A. Heath J. Orgunometullic Chem. 1975,90 195; (c)J. L. Davidson M. Green D. W. A. Sharp F. G. A. Stone and A. J. Welch J.C.S. Chem. Comnt. 1974 706. 21 F. A. Cotton T. LaCour and A. G. Stannislowski J. Amer. Chem. SOC. 1974,% 754. Organometallic Compounds 187 methano1.22a*b The products of photolysis of the same trisilane with dimethyl- butadiene (Scheme 1) provide evidence for the formation of a 1,2-adduct (silacyclo- propane) (6),which undergoes further rearrangement either to give (7) which could have resulted from direct 1,4 attack or to give (8).The isolation of (8) is best 1. .Me r6 1 MePhHSiH,C \SZ w / Me-Si-Ph (8) Ph I (7) OMe (9) Scheme 1 explained by further reaction of (6),whose existence is also supported by trapping with methanol after irradiation affording (9).’” The thermolysis of phenyl- trimethylsilyldiazomethane which affords a benzosilacyclopentene had previously been reported to proceed via a silacyclopropane intermediate but this route has now been ruled out and it seems likely that the intermediates are the phenylcarbene and the cycloheptatrienylidene derived therefrom.22d The first stable silacyclopropanes were isolated in 1972 and proved to be highly reactive compared with larger rings containing silicon.22e Hexamethylsilacyclopropane has been synthesized [equation (17)] and is also stable under inert atmosphere but reacts with the protic species H20,NH3,or alcohols giving ring-opened products having Si-0 or Si-N bonds.*” Me,Si(CMe,Br) + Mg-THF +! / Si (17) ‘3 The new compound provides a low-temperature route to dimethylsilene.The latter has been identified by several techniques including trapping by a number of silanes. The previously prepared silacyclopropanes did not afford silenes on thermolysis but gave dimeric and polymeric species.22e.g MO calculations on 7-siladispiro[2,0,2 llheptane suggest increased Si-C bond strength due to hypercon- jugative effects and further that d-o-hyperconjugation may also contribute sig- nificantly to the strengthening of the Si-C bond in the (unknown) cyclopropylidenesilanes.’’h The tetraphenyl-substituted boracyclopropenyl anion has been proposed in reactions following the photolysis of sodium tetraphenylborate in the presence of tolan.22i 22 (a)M.Ishikawa M. Ishigino and M. Kumada J. Orgunomefullic Chem. 1973,49 C71; (b)M. Ishikawa and M. Kumada ibid. 1974,81 C3; (c)M. Ishikawa F. Ohi and M. Kumada ibid. 1975,85 C23; (d)J. J. Barton J. A. Kilgour R. R. Gallici A. J. Rothschild J. Slutsky A. D. Wolf and M. Jones J. Amer. Chem.Soc. 1975,97,658; (e)R. L. Labert and D.Seyferth ibid. 1972,94,9246;(f)D. Seyferth and D. C. Annarelli ibid. 1975,97,2273;(g) D. Seyferth and D. C. Annarelli ibid. 1975,97,7162; (h)P. D. Mollere and K. Hoffman ibid. 1975,97 3680; (j)J. J. Eisch K. Tameo and R. J. Wilcsek ibid. 1975 97. 895. D.J. Cardin and K. R. Dixon 10 Main-group Organometallic Ions Although siliconium ions (five-co-ordinate) have been described as intermediates and attempts have been made to trap silicenium ions (three-co-ordinate) the existence of the latter had not been established prior to 1975. The ion (10;M = Si) has now been trapped following reaction between the silepin (10; M = SiH) and an equimolar quantity of triphenylcarbenium perchlorate in CH,Cl at ca. -50 0C.230 The reaction produces a coloured solution which reacts with NaBD,-diglyme or NaBH,-H,O-dioxan to yield the silepin (Si-D) or a mixture of this (Si-H) and the silanol respectively.The substituted ferrocenylsilicenium ion has also been n N Me2 (10) Another interesting group of organometallic ions consists of boron-substituted carbanions. These have been suggested as intermediates in a number of reactions including the base-induced deboronation of gem-diboryl species which has been employed in the synthesis of C=C compounds from C=O ones. The ion (11) [equation (IS)] has been isolated and characterized (including n.m.r. data) and shown to react with a variety of carbonyl compounds affording substituted ethylene~.,~' 11 Double-bonded Silicon The pyrolysis of silacyclobutanes and production of intermediates containing double bonds to silicon were reported by Gusel'nikov and colleagues in 1966,24" and a short review of this area has now been published by the same group.24b The subject continues to excite interest concerning both the mechanistic details and reactivity and the identification of new Si=E bonds.TWOgroups have reported studies on 23 (a) J. Y. Corey J. Amer. Chem. SOC.,1975 97 3237; (b) J. Y. Corey D. Gust and K. Mislow J. Organometallic Chem. 1975 101,C7; (c) D. S. Matteson and L. A. Magelee ibid. 1975,93 21. 24 (a)N. S. Nametkin. V. M. Vdovin L. E. Gusel'nikov and V. I. Zav'yalov Zzvest. Akad. Nauk S.S.S.R. Ser. khim. 1966,589; (b)L. E. Gusel'nikov N. S. Nametkin and V. M. Vdovin Accounts Chem. Res. 1975,8 18; (c)T.J. Barton G. Marquardt and J. A. Kilgour J. Organornetulfic Chem. 1975,85,317; (d)C. M. Golino R. D. Bush P. On and L. H. Sommer J. Amer. Chem. SOC.,1975,97 1957; (e)C. M. Golino R. D. Bush and L. H. Sommer ibid. 1975 97 7371; (f) L. H. Sommer and J. McLick J. Organometallic Chem. 1975 101 171; (g) Yu. A. Ustynyuk P. I. Zakharov A. A. Azizov G. A. Shchembelov and I. P. Gloviozov ibid. 1975 96 195. Organometallic Compounds thermolysis of 2-substituted 1,l-dimethylsilacyclobutanes and conclude that C-C rather than Si-C bond cleavage OCCUTS.~~~,~ The products from both cleavage mechanisms are shown in Scheme 2 and the predominance of products formed via path b shows C-C rupture while the magnitude of the substituent effect makes the alternative (Si-C) bond breakage an unlikely initial RCH + Me,% -II II a CH CH2 RCH +CH *I 11 II \ R bSiMe -3 SiMe CH Scheme 2 The unsubstituted silaethene appears to be generated in the pyrolysis (560 "C N2 flow system) of silacyclobutane.It polymerizes in the absence of traps; reactions with a number of reagents are presented in Scheme 3.24e HZSi3 + H,Si=CH + high mol. wt. polymer /2sio)3 1 \ SiH2 -CH2 Ph2Co \N CISiH,CH,SiCI \ SiMe Ph,C=CH + Ph2CH2 ? I I I SiMe /0 49 % '% CH,SiH,CH,CN \ O-SiMe 3% 18 % Scheme 3 Evidence for the first Si=S intermediate comes from the reaction of thioben-zophenone with pyrolysis products of 1,l-disubstituted silacyclobutanes the prop- osed reaction sequence is given in Scheme 4.24f Me2Si3-+[CH =SiMe2] Ph2C=S b [Ph,C!-; CH,-SiMe 1 -I CH J/ S Me,S/ 'SiMe, p,A,h + [Me,Si=S] -+ \/ S Scheme 4 No isolable Si=C species has yet been described but the synthetic chemist is challenged by the suggestion based on CND0/2 calculations that 6,6-dimethyl-6- silafulvene is potentially such a stable 12 Silatranes and Stannatranes The discovery of neurophysiological effects in tricyclic esters having the structure (12; M =Si) has provided impetus for further chemical studies.Numerous syntheses D.J.Cardin and K.R. Dixon of substituted derivatives of the silicon ('silatrane') compounds have been pub- li~hed,~~",~ as has a new route equation (19) to the tin analogues ('~tannatranes').~~~ The tin compounds also have five-co-ordinate metal although n.m.r.evidence has been interpreted in terms of equilibrium between four- and five-co-ordinate species in s01ution.~~~ RSn(OEt) + N(CH,CH,OH) + RSn(OCH,CH,),N + 3EtOH (19) The acid-catalysed solvolysis of 1-organosilatranes has been studied. It is first- order in silatrane and probably goes by initial protonation of the nitrogen with breaking of the Si-N bond but the protonation is almost complete at the transition state.25d &>O'M-0 "IOR (1 2) 13 YIides The chemistry of ylides in an inorganic context has been developed over the past few years and the chemistry of P As and S ylides and in particular the work of Schmidbaur's group has been reviewed.26" Relatively few arsonium ylides have been isolated and the first example which is not stabilized by carbonyl groups was recently prepared [equation (20)].26b This thermally unstable compound gives on (Ph,AsMe)Br + NaNH Ph,As=CH f NaBr + NH3 (20) decomposition triphenylarsine polymethylene and ethylene among the products.The 'J(CH) coupling (compared with the arsonium cation) suggests that little rehybridization occurs on the CH -+CH2 change i.e. that the carbon atom in the methylide has pseudo-tetrahedral geometry. The same ylide has also been obtained using NaH and found to react with a number of acyl halides with transylidation.26c3d Interest in [Ph3P=N=PPh3]+X- and in the di-ylide Ph,P=C=PPh, stemmed from the unusual physical properties the PNP angle is dependent on the anion and the ylide is triboluminescent probably as a result of a delicate balance of energy levels associated with the angular deformation.The methyl analogue can be prepared as shown in equations (21)-(23).26' The di-ylide is a very air-sensitive material a strong base and a stronger nucleophile than mono-ylides.26' 25 (a)M. G. Voronkov V. M. D'yakov and L. I. Gubanova Zhur. obshcheiKhim. 1975,45,1901,1902 1903 1904 1905; (b) E. Popowski M. Michalik and H. Kelling J. Orgunomefulfic Chem. 1975 88 157; (c)M. Zeldin and J. Ochs ibid. 1975,86,369;(d)A. Daneshrad C. Eaborn R. Eidenschenk and D. R. M. Walton ibid. 1975,90 139. 26 (a)H. Schmidbaur Accounts Chem. Res. 1975,8 62; (b)Y. Yamamoto and H. Schmidbaur J.C.S. Chem. Comm. 1975,668; (c)P. S. Kendurkar and R. S. Tewari J.OrganometallicChem. 1975,102 141; (d)P. S. Kendurkar and R. S. Tewari ibid. p. 173; (e)0.Gasser and H. Schmidbaur J. Amer. Chem. SOC.,1975,97,6281; ('j) H. Schmidbaur,H. J. Fuller and F. H. Kohler J. Orgunometullic Chem. 1975,99,353;(g) H. Schmidbaur and R. Franke Znorg. Chim. Actu 1975,13,85; (h)H. Schmidbaur and R. Wolfgang Chem. Ber. 1975,108,2659; 6)E. Kurras U. Rosenthal H. Mennenger G. Oehme and G. Engelhardt 2.Chem. 1974,14 160; (k) E. Kurras H. Mennenger G. Oehme U. Rosenthal and G. Engelhardt J. Organometallic Chem. 1975,84 C13. Organometallic Compounds 2Me,P=CH + Me,PF2 -+ Me,P=CHPMe,F + (Me,P)F (21) or Me,P=CHSiMe + Me,PF + Me,P=CHPMe,F + Me,SiF (22) Me,P=CHPMe,F + NaH + Me,P=C=PMe + H + NaF (23) Reaction of phosphorus ylides with trialkyl derivatives of Ga In or Tl,has been found to yield phosphonium betaine structures e.g.Me3P'-CH,-GaMe3.26f The use of ylides in the preparation of metal alkyls is well known. Recent examples are shown in equations (24)-(26) including extension to the relatively novel arsenic ylides.L6g*h rAU -7 Me,PAuCl + Me,P=CH + Me,P PMe LAuJ Me,As=CHSiMe + CuCl -+ CU I -+ Me,AsAgCl + Me,As=CH Ag/-AsMe,\ I Me As An interesting related reaction is the synthesis of homoleptic alkyls of chromium26i and using phosphonium salts and alkyl metal anions [equation (27)]. The molybdenum species are less air-sensitive and reactive and react with Li,Mo,Me + 4(Me,P)CI + Mo,[(CH,),PMe,] + 8MeH + 4LiCl (27) acetic acid to give molybdenum(r1) acetate.The probable structure involves bridging alkyl ligands in an arrangement similar to the acetate. 14 Chiral Metal Centres The synthesis of organometallic compounds with chiral metal centres continues to receive attention particularly for main-group elements. Many of the syntheses use classical methods involving separation of diastereomeric pairs but the hydrosilyla- tion of (-)-menthone or (+)-camphor using Wilkinson's catalyst or an analogue having optically active phosphine ligands has been reported.27" The alkoxysilanes are obtained in up to 82% optical purity and can be converted into alkyl silanes using 27 (a)R. J. P. Corriu and J. J. E. Moreau J. Organometaffic Chem. 1975,91 C27; (b)R. J. P. Corriu F. Larcher and G. Royl J. Organometaffic Chem.1975 102 C25; (c) J. Tirouflet A. Dormond J. C. Leblanc and F. Le Moigne Tetrahedron Letters 1373 257; (d) F. Le Moigne A. Dormond J. C. Leblanc C. Moise and J. Tirouflet J. Organometuffic Chem. 1973,54 C13; (e)C. Moise J. C. Leblanc and J. Tirouflet J. Amer. Chem. Soc. 1975,97,6272; (f) J. C. Leblanc C. Moise and T. Bounthakna Compt. rend. 1974,278,973; (g) G. Simonneaux,A. Meyer and G. Jaouen J.C.S. Chern. Comm. 1975 69. 192 D.J. Cardin and K. R. Dixon Grignard reagents with retention of configuration. The first optically active bifunctional silanes in which the Si atom is the only chiral centre a-naphthylferrocenylfluorosilane and a-naphthylferrocenylchlorofluorosilane,have been prepared. Fluorine was introduced by reaction of menthoxysilanes with BF3 which goes with inversion of configuration; chlorine was attached with retention using PdC1 and ~ilanes.~~’ Relatively few early transition-metal compounds with chirality at the metal have been reported partly because the mechanism and steric course of reactions are not always straightforward particularly at octahedral metals.Full details are now available of the first resolved titanocene derivative of which preliminary reports have a~peared.,~‘,~ The preparation is outlined in Scheme 5,27eand is based on the separation of diastereoisomers. The second chiral centre was removed by HC1 cleavage which has been establishedz7’ to be selective and stereospecific. CpTiC1 + Cp’ + CpCp’TiC1 C6F5MgBr + ( f)-CpCp’Ti(C6F,)C1 ( -)-S-2-phenyl-propan-1-01 CP\ ,C& I HCI-benzene CpCp’Ti(C,F,)OCH,CHMePh /Ti\ CP‘ CI Scheme 5 The first optically active chromium(0) species enantiomeric at Cr have been prepared from optically pure 1-S-[l-CO2Me-2-Me-(q6-C,H,)]Cr(CO), by sub- stitution of carbonyl by CS and (PhO),P followed by removal of the initial chirality by reduction with LiAlH,-AlCl,.The preparation of chiral arenechromium tricar- bonyls offers the possibility of catalytic asymmetric 15 Metal-Carbon Bond Strength Data Thermochemical data on alkyl and aryl derivatives of transition metals and derived strengths of v-C bonds do not in general support the once widely held view that such bonds are weak and $an only be sustained by suitable ligand combinations. Mean bond-energy terms for the bonds M-C in homoleptic metal alkyls (M =Ti Zr or Hf) with bulky ligands R range from 44 kcal mol-’ for Ti R =neopentyl to 75 kcal mol-’ for Zr R = CH,SiMe,.Zr forms stronger bonds with C (by ca. 15%) than Ti.28a It is interesting (i) that whereas bond strengths decrease upon descending a group of typical elements (e.g. Ge>Sn>Pb) the reverse trend is found in a transition-metal group (e.g.,Ti<< Zr <Hf) and (ii) that steric effects influence bond strengths (Me3CCH2 <Me,SiCH,). Microcalorimetric measurements have been 28 (a)M. F. Lappert D. S. Patil and J. B. Pedley 3.C.S.Chem. Comm. 1975,830; (b)F. A. Adedigi D. L. S. Brown J. A. Connor M. L. hung I. M. Paz-Andrade and H. A. Skinner J. Organometallic Chem. 1975,97,221; (c)J.Tamas G.Czira A. Mal’tsev andO. M. Nefedov MagyarKim. FolyWrat 1974,80 439 (Chem. Abs. 1975,82,24 962j); (d) R. A. Burnham and S. R. Stobart J. Organometallic Chem. 1975,86 C45. Organometallic Compounds 193 made on arenechromium tricarbonyl compounds and bond enthalpy contributions derived.286 These decrease as the donor power of the arene decreases from 55(4) kcal mol-' for the arene-metal bond of the hexamethylbenzene complex to 38(5)kcal mol-' for the corresponding bond of the chlorobenzene derivative. Mass spectrometric data were used to determine the dissociation energy of the Ge-C bond in Cl,GeMe which was found to be 66 kcal mo1-'.28c Metal-metal bond dissociation energies have also been obtained by the mass spectrometer technique for the species Me3M'M2(CO), as follows D(M'-M2)/kcal mol-' Ge-Co 73.8; Si-Co 64.6; Si-Re 71.5; Ge-Re 73.8; and Sn-Re 85.3.28d 16 Oleh Metathesis The remarkable catalytic disproportionation of olefins continues to attract consider- able attention and two reviews of the process have ap~eared.~~~'~ The question of mechanism in this process is one of the most fascinating aspects and several have been advanced including cyclobutane-metal complexes and metallocyclic species in the transition In 1972 a mechanism for the dismutation of electron-rich olefins was advanced which involved one-carbon transfers and a metal-carbene was identified as an intermediate.29c However the unusual nature of the olefins and the low activation energy of the process for other olefins left it an open question as to whether the mechanism would have wider connotation.Two groups have reported findings which do lend support to this type of mechanism. The distribution of deuterium in the products of metathesis of [1,l,8,8-2H,]octa- 1,7-diene with octa- l,7-diene using the catalyst systems WC1,-BunLi-benzene and PhWC1,-AlC1 is consistent (agreement is particularly good for the latter catalyst) with the single-C transfer idea.29d Similar conclusions have also been reached from determination of product ratios with time in an experiment in which cyclo-octene trans -but-2-ene and trans-oct-4-ene disproportionated with a Mo-A1 catalyst.29' The authors also point out that the formation of catenanes in the disproportionation reaction can be simply accounted for by cyclization of a terminal carbene with an internal double bond.Further experimental data will be needed before it is possible to say whether the dismutation of alkynes is likely to occur through carbyne intermediates. The photochemical generation of an olefin dismutation catalyst requiring no co-catalyst has been Now photolysis of W(CO) in CCI has been found to give Cl,W(CO), which catalyses the reaction upon thermal or photochemical activati01-1.~~~ A brief description of the olefin metathesis reaction interpreted as a synchronous process has been given.29i 17 Metal-Metal Bonds and Clusters The chemistry of compounds containing intermetallic bonds is once again an area of great activity. (For metal carbonyl clusters see Section 20; see also Chapter 7 29 (a)R.J. Haines and G. J. Leigh Chem. SOC.Rev. 1975,4 155; (b)J. C. Mol and J. A. Moulijn Adu. Catalysis 1975,24 131; (c)D. J. Cardin M. J. Doyle and M. F. Lappert J.C.S. Chem. Comm. 1972 927; (d)R. H. Grubbs P.L. Burk and D. D. Carr J. Amer. Chem. SOC.,1975,97,3265; (e)T. J. Katz and J. McGinnis ibid. 1975,1592; cf) A. A. Agapiou and E. McNelis J.C.S. Chem. Comm. 1975 187; (g) P.Krausz F. Gamier and J. E. Dubois J.Amer. Chem. SOC., 1975,97,437 (h)A. A. Agapiou and E. McNelis,J. Organometallic Chem. 1976,99 C47; (j)F. D. Mango Coordination Chem. Rev. 1975,15 142. D.J. Cardin and K.R.Dixon pp. 154 and 161.) The chemistry of systems having quadruple and and other metal- metal bonds of high order has been re~iewed.~'" A number of bimetallic and metal cluster compounds particularly with metals of Main Groups I1and I11 have bridging carbonyls of novel geometry.The crystallographic identification of a carbonyl group bridging two Mn atoms with both C and 0interacting with one of the metal centres was noted for the first time (for details see In certain situations the spectroscopic identification of bridging carbonyls may not be simple. Reaction of trimethylaluminium or dimethylaluminium hydride with CpW(CO),H gives [CpW(CO),AlMe212. This compound contains rings of 12 atoms (WCOAIOC), each aluminium having two methyl substituents and the tungsten atoms an additional carbonyl and the cyclopentadienyl group. The rings are easily cleaved by protic species HX affording the tungsten hydride and (Me,AlX), while donors trimethylamine and diethyl ether yield the adducts of the AlW monomer The structure of the ring compound is unusual in that two of the carbonyl bridges are very close to hear (173-176").In the reaction of trimethylgallium with the same tungsten h ydride the compound CpW(CO),GaMe is formed,30d and this has been shown to have a Ga-W bond.30' In hot hydrocarbon solution decomposition to yield [CpW(CO),],GaMe and [CpW(CO),],Ga occurs neither of which like [CpW(CO),],In,30f shows i.r. bands due to bridging carbonyl ligands. The four-metal gallium system has three Ga-W bonds lying in a plane the molecule (apart from the cyclopentadienyl rings) having roughly C3h Magnesium resembles aluminium in forming several compounds linked to a transition metal via a Mg-0-C-M bridge and e.g.the crystal structure of (py)4Mg[Mo(CO)3Cp]2 has established this type of bonding in a trans-arrangement about approximately octahedral magnesium.3og The conditions favourable for the formation of M-C-0-Mg bonds have now been examined and several useful synthetic approaches described.,Oh The solubility of the magnesium compounds in hydrocar- bon solvents makes them potentially very useful in metallation reactions where polar solvents are not suitable. It has been remarked that lithium is capable of stabilizing unusual transition- metal compounds notable among which are polynuclear species such as Li,Cr2Me,,4THF,30' Li6Ni2N2(C6&)2,2Et20,30k and L~,MO,C,~H,,.~~' In such structures the interactions of the organic groups with the lithium atoms may be more significant than the base-lithium and it is noteworthy that in a neutron and X-ray diffraction study of LiBMe the bridging of lithium atoms by both linear Li-CH,-B and double and triple H-bridges is found.30m The authors note the well-known reactivity of C-H when p to early main-group or transition metals and point out that electron-deficient structures can become co-ordinatively saturated by the interaction of alkyl H atoms with metals.In this respect lithium shows strong Lewis 30 (a)F. A. Cotton Chem. SOC.Rev. 1975,4,27;(b)R. Colton C. J. Commons and A. F. Hoskins J.C.S. Chem. Comm. 1975 363; (c) A. J. Conway G. J. Gainsford R. R. Schrieke and J. D. Smith J.C.S. Dalton 1975 2499; (d) A.J. Conway P. B. Hitchcock and J. D. Smith ibid. p. 1945; (e) Personal communication to the authors of ref. 30d by J. P. Oliver; (f) A. T. T. Hsieh and M. J. Mays J Orgunometallic Chem. 1972,37,9; (g)S. W. Ulmer P. M. Sharstad J. M. Burlitch and R. E. Hughes J. Amer. Chem. SOC.,1973,95,4469;(h)G. B. McVicker Inorg. Chem.,1975,142087;(j)F. Mein and K. Schmiedenknecht J. Organometuffic Chem. 1966,6,45,and refs. therein; (k)K. Jonas Angew. Chem. Zntemat.Edn. 1973,12,997171)C. Prout and M. L. H. Green J.C.S. Chem. Comm. 1973,259; (m)W. E. Rhine G. Stucky and S. W. Pederson J. Amer. Chem. SOC. 1975 97 6401; (n) F. Armitage 'Inorganic Rings and Cages' E. Arnold London 1972 and refs. therein. Organometallic Compounds 195 acidity towards the weakly basic hydrogen atoms of hydrocarbon chains and in the structure investigated each lithium atom has 10 hydrogen atoms within its first co-ordination sphere [6 at 2.234(10) A and 4 at 2.115(8) A]?0m The tetrahedral P can be substituted by various groups affording cluster com- pounds of which those structurally examined are edge-substituted species (see Chapter 6 p.121).30" 18 Shorter Topics The structure of the dilithium derivative of the hexatriene dianion involves a planar geometry for four hydrogens and carbons of the anion and lithium interactions with four of the C atoms.31 Two structural studies of bis(cyclopentadieny1)magnesium have appeared; the gas-phase electron diffraction data indicate eclipsed cyclopen- tadienyl rings but do not completely exclude the staggered while X-ray data for the crystal at least show a staggered ring a~rangement.~~' Mic-rowave examination of CpBeH and isotopically labelled species shows a dipole moment of 2.08(1) D and a Be-H distance of 1.32(1) A the molecule having the expected CSu The existence of Grignard analogues for strontium and barium has been suggested in the literature and THF adducts have now been reported obtained from the finely divided metal and alkyl iodides at -78 "C.The compounds have low solubility and thermal stability but are solvolysed with pro- duction of alkane using protic solvents and afford low yields of tertiary alcohols on treatment with The reaction of indene with calcium bis(tetraethy1)ala- nate gives an indenylaluminium compound (LAlEt,)Ca(AlEt,) (L= indenyl) which disproportionates easily losing Et3A1.336 Perfluoroalkyl iodides react with calcium amalgam to give the perfluoroalkylcalcium iodides as evidenced by their reactions with carbonyl compounds which in some cases proceed in good yield suggesting that the reagents may have potential value as perfluoroalkylating species.33c When the Grignard reagents RMgX (R = 3-phenyl-1-propyl or 1-phenyl-2-propyl) are irradiated in the Mg-C chromophore region (ca.254 nm) terminal olefins and HMgX are formed the latter disproportionating. The elimination reaction is 99% (or more) a p-elimination process established by D-labelling Several structural studies of tin(r1) compounds appeared during 1975 mostly of compounds with co-ordination number for Sn of 4 or more.An interesting com- pound is (C61-&)Sn(AlC1,),C6H, in which the tin atom has approximate pentagonal- bipyramidal co-ordination one axial position being the centre of a benzene ring making appropriate the description 'r-benzene complex of tin(11)'.~~ N.m.r. studies of the dynamic equilibrium in Cp,M(BH,) (M = Zr or Hf) and Cp,Zr(H)BH have revealed a new type of borohydride exchange in which hyd- rogens of the cyclopentadienyl ring exchange with those of the BH4 group. The 31 S. K. Akora R. B. Bates W. A. Beavers and R. S. Cutler J. Amer. Chem. SOC. 1975,97,6271. 32 (a)A. Haaland J. Lusztyk J. Brunvon and K. B. Starowieyski J. Orgunometullic Chem. 1975,85,279; (b) W. Biinder and E. Weiss ibid. 1975 92 1; (c) T.C. Bartke A. Bjoerseth A. Haaland K. M. Marstokk and H. Moelendal ibid. 1975 85 271. 33 (a)B. G. Gowenlock W. E. Lindsell and B. Singh J. Orgunometullic Chem. 1975,101 C37 (b)L. I. Zakharkin Y. S. Zavizion and L. L. Ivanov Zhur. obshchei Khim. 1975,45,1900;(c)G.Santini M. Le Blanc and J. G. Riess J.C.S.Chem. Comm. 1975 678; (d) B. 0.Wagner and G. S. Hammond J. Organometallic Chem. 1975 85 1. 34 P. F. Rodesiler T. Auel and E. L. Amma J. Amer. Chem. Soc. 1975,97 7405. 196 D.J. Cardin and K. R. Dixon predominantly unimolecular process is thought to occur via q '-C,H,M carbene (or ylide) intermediates. It also occurs but more slowly in the solid phase for Cp2Zr(BD,),.35" Reactions between Cp2ZrC12 and Et3A1 have been reported to yield a range of alkyl aluminium and zirconium species including one with a 16-membered ring containing four Al and two Zr atoms.Structural evidence based on n.m.r. spectra is Monomeric paramagnetic carbonyls of vanadium are a unique group and to date no dimeric carbonyl derivatives can be regarded as established. However the chemistry of these species has been little studied owing to the lack of a reactive and suitable starting material. Photosubstitution of the carbonyl anion [v(co)6]-by o-phenylenebis(dimethylarsine) (diars) affords the thermally stable anion [V(CO),(diars)]- which affords the first alkyl or 3-allyl carbonyl derivatives of V on treatment with methyl iodide or ally1 chloride re~pectively.~~" The ion Cp2V+ which is isoelectronic with the monomeric form of titanocene has been isolated from aqueous media in the form of adducts [VCp2L]' (L= H20 acetone or pyridine).The .rr-basicity of these species is shown by their ready conversion into the known cation [CP~V(CO)~]+ and also into isocyanide or phosphine complexes.366 The preparation of phenylvanadium dichloride by reaction of diphenyl-lithium with vanadium(1v) chloride has been reported but the solid appears to be a co-ordination p01ymer.~~~ Niobium(v) chloride reacts with the cyclo-octatetraene anion to yield M'[Nb(cot),]- the first cyclo-octatetraene complex of the Group VA metals. A crystal study shows a trigonal arrangement of the ligands with two q3-bonded and one q4-bonded although the molecule is fluxional in solution. Reactions with phosphines and hydrogen afforded no characterizable vanadium compounds although with CO salts of the [V(CO),]- anion were is~lated.~'" A new low- pressure synthesis of Cp,NbH from Cp,NbCI has been reported to give yields up to 55% after hydrolysis with aqueous NaOH.The insertion of acetylenes into the Nb-H bond and the reactions of the vinyls so formed are described.37b The reversible addition of carbon monoxide (2 mol) across a Mo-Mo bond is the first reported example of this type of process [equation (28)]. The forward reaction (C,Me5)(CO),Mo~Mo(CO),(C,Me,)+ 2CO -+ (C,Me,)(CO),Mo-Mo(CO),(C5Me5) (28) can be induced by visible light or thermall~,~~" while there is precedent for the The reverse reaction which is also photochemical probably involves cleavage of the Mo-Mo bond and photolysis of the hexacarbonyl species in carbon tetrachloride yields the species (q5-C5Me5)Mo(CO)3CI.38Q Phosphines or phos- phites also react with the tetracarbonyl complex (with C,HJ contrary to earlier 35 (a)T.J. Marks and J. R. Kolb J. Amer. Chem. SOC. 1975 97 2397; (b)W. Kaminsky and H. Sinn Annalen 1975 429; (c)W. Kaminsky and H. J. Vollmer ibid.,p. 438. 36 (a)J. E. Ellis and R. A. Faltynek J. Orgunometallic Chem. 1975 93 205; (b)G. Fachinetti and C. Floriani J.C.S. Chem. Comm. 1975,578; (c)S. Schroeder A. Lachowitz and K. H. Thiele Z. anorg. Chem. 1975,415 104. 3' (a)L. J. Guggenberger and R. R. Schrock J. Amer. Chem. SOC. 1975,97,6693; (b)J. A. Labinger and J. Schwartz ibid. p. 1596. 38 (a)D. S. Ginley and M.S. Wrighton J. Amer. Chem. SOC.,1975,97,3533;(b)P. Hackett P. S. O'Neill and A. R. Manning J.C.S. Dalton 1974 1625; (c)R. J. Klinger W. Butler and M. D. Curtis J. Amer. Chem. SOC.,1975,97,3535;(d)T. Ito and A. Yamamoto J.C.S. Dalton 1975,1398;(e)D. L. Lewis and S. J. Lippard J. Amer. Chem. SOC. 1975,97 2697. Organometallic Compounds 197 Acetylenes react forming bridged dimolybdenum derivatives. The X-ray structure determination of the tetracarbonyl compound with unsubstituted cyclopentadienes confirms the triple-bonded formulation MorMo = 2.448( 1)A.38c (For further photochemistry of metal carbonyls see Section 20.) The reactions of Mo(C,H,)(dppe) with a number of reagents have been examined among which the contrasting thermal {to give cis-[Mo(CO,(dppe),]} and photochemical (to give an uncharacterized CO adduct) behaviour with carbon dioxide is The structure of [(Bu'NC),Mo]+PF,- shows the same co-ordination polyhedron as had been established for the iodohexakis(iso-cyanide)molybdenum(iI) cation i.e.a monocapped trigonal There is much evidence to suggest that tungstenocene is an intermediate in the reactions (both thermal and photochemical) of a number of species Cp2WX (X includes H2 CO and Cl,) and is highly reactive for example inserting into the C-H bonds of mesitylene or p-~ylene.~~" The photo-induced insertion of tungsten into methanol has been shown to give both Cp,W(H)OMe and Cp,WMe(OMe) probably via the insertion of tungstenocene into the 0-H and C-H bonds of methanol re~pectively.~~" Alkyl- and acyl-pentacarbonyltungsten anions have been obtained by two routes treatment of the corresponding halide anions with organolithium reagent and photolysis of the appropriate neutral species (OC),WCOR.39b Reactions with HCl trityl tetrafluoroborate CO or PPh are reported for some of the anions.The reaction of dibenzylmagnesium with tungsten tetrachloride affords tetrabenzyltung~ten.~~" Other reports on homoleptic metal alkyls and organometal- lic compounds in high oxidation states (including tungsten) are covered in Section 22. 19 Books and Reviews Main-Group and Early Transition Elements Among many review articles on the subject matter of this Chapter the following are among the most directly relevant. Matteson's book on organometallic reaction mechanisms of the non-transition elements presents a critical review of its subject including the elements B and Si but not P.40 Other books include works on organometallic reaction^,^^ and organometallic compounds of the transition ele- ments and related aspects of catalysis.42A new edition of 'Baiant' has appeared reviewing the Si literature since 196 1.43 The organometallic chemistry of the main-group elements has been reviewed,44 and articles dealing with aspects of this area cover synthesis and reactions of organo-lithium reagents derived from weakly acidic C-H and 3y (a)L.Farrugia and M. L. H. Green J.C.S. Chem. Comm. 1975,416 and refs. therein; (6)C. P. Casey S. W. Polichnowski and R. L. Anderson J. Amer. Chem. Soc. 1975,97,7375; (c) K.H. Thiele A. Russek R. Opitz B. Mohai and W. Brueser Z. anorg. Chem. 1975,412 11. 40 D. S. Matteson 'Organometallic Reaction Mechanisms of Non-transition Elements' Academic Press New York 1974. 41 'Organometallic Reactions' ed. E. I. Becker and M. Tsutsui Wiley New York 1975. 42 B. L. Shaw and N. L. Tucker 'Organo-transition Metal Compounds and Related Aspects of Catalysis' Pergamon New York 1975. 43 V. Baiant J. Hetflejs V. Chvalovsky J. Joklik 0.Kruchna J. Rathousky and J. Schraml 'Handbookof Organo-silicon Compounds. Advances since 1961' Vol. 1 Dekker New York 1975. 44 J. D. Smith and D. R. M. Walton Adu. Organornetallic Chem. 1975,13,453. 45 D. Ivanov G. Vasilev and I. Panaiotiev Synthesis 1975 83. 198 D.J. Cardin and K.R. Dixon cy~lopolyarsines.~~ In the series edited by Nesmayanov and Kocheskov the organic chemistry of Tc,~’ Ta,48 lanthanides,”‘ Nb,49 Hf,” V,’ and ZrS2 has been described. The Journal of Organometallic Chemistry annual review series continues. Organometallic compounds with bonds between transition metals and elements of Group IIIB have also been s~rveyed.’~ 20 Metal Carbonyls Matrix Isolation of Radical Species other Metal Carbonyl Transients.-Interest in paramagnetic carbonyl complexes and in unstable carbonyls in general has acceler- ated in recent years with the development of methods for treating metal atoms with various substrates (see also Section 2) and also with the development of carbonyl photochemistry. Mn(CO) in particular has been of interest to many research groups.54 Originally suggested as a precursor of [Mn(CO),]’ in the mass spectrum of pyrolysed Mn,(CO),, Mn(CO) had been proposed as an intermediate in a number of chemical reactions of Mn,(CO),, and an e.s.r.spectrum obtained from 350 nm photolysis of Mn,(CO), in THF had been assigned to the pentacarbonyl. A report this year5’= disputes this e.s.r. assignment and suggests that the six-line spectrum is actually due to an Mn“ species [MII(THF)~],+. The spectrum is remarkable because of its very narrow hyperfine lines. An alternati~e~~’ approach to the problem via homolysis of the M-C bond of [RMn(CO),] (R =Me or PhCH,) has yielded e.s.r. evidence for the generation of Mn(CO),. U.V. irradiation in the presence of the spin trap nitrosodurene gives e.s.r.spectra of the nitroxides ArN(O)Mn(CO) and ArN(0)R (Ar =2,3,5,6-Me4C,H) but the spectrum of the free Mn(CO) radical has still not been [Similarly photolysis of vitamin BI2 coenzyme 5’-deoxyadenosylcobalamin or ethylcobalamin in aqueous medium in presence of Bu‘NO as spin trap has afforded the 5’-deoxyadenosyl(Bu‘)NO or Et(Bu‘)NO re~pectively.~~‘] The characterization of Mn(CO) has now been achieved by matrix-isolation technique~.’~ Using an Mn:CO ratio of 1:lo4or less condensed in an argon matrix the principal species is Mn(CO), and at higher Mn:Co ratios the dinuclear Mn,(CO) species are obtained. 1.r. spectra of the pentacarbonyl indicate a square-pyramidal structure and this observation completes the characterization of the series of pentacarbonyls of the first transition series from vanadium to iron (see Table I p.220).54An alternative trigonal-bipyramidal fcrm of Cr(CO) has been claimed to exist but it now seems likely that this is in~orrect.’~ Thus there is a clear 46 L. R. Smith and J. L. Mills J. Organometallic Chem. 1975 84 1. 47 A. A. Ioganson K. N. Anisimov and N.E. Kolobova Metody. Elem.-Org. Khim. 1974 2,851. 48 A. A. Pasinskii Metody Elem.-Org. Khim. 1974 1,453. 49 A. A. Pasinskii Metody Elem.-Org. Khim. 1974 1 434. so E. M. Brainina Metody Elem.-Org. Khim. 1974,1 373. s1 A. A. Pasinskii Metody Elem.-Org. Khim. 1974,1 389. 52 E. M. Brainina Metody E1em.-Org. Khim. 1974 1 320. 53 A. T. T. Hsieh Znorg. Chim. Acta 1975 14 87. 54 H. Huber E.P. Kundig G. A. Ozin and A. J. Poe J. Amer. Chem. SOC.,1975,97,308,and references therein. 5s (a)A. Hudson M. F. Lappert and B. K. Nicholson J. Organometallic Chem. 1975,92 C11; (b) A. Hudson M. F. Lappert P. W. Lednor and B. K. Nicholson J.C.S.Chem. Comm. 1974,966; (c)K. N. Joblin A. W. Johnson M. F. Lappert and B. K. Nicholson ibid. p. 441. 56 J. D. Black and P. S. Braterman J. Amer. Chem. Soc. 1975,97 2908. Organometallic Compounds 199 correlation of stereochemistry with electron configuration and this is expected in terms of the generally accepted MO sequences for trigonal-bipyramidal and square- pyramidal complaes. Assuming low-spin configurations the 15-and 17-electron trigonal-bipyramidal forms should be subject to first-order Jahn-Tdler distortion towards a square-pyramidal form and the 16-electron complexes are stable to second-order Jahn-Teller distortions only in the square-pyramidal configuration.The 18-electron species should exhibit second-order instability in both D3hand C, forms and this is considered to account for the well-known facile interchange of axial and equatorial CO groups.54 Similar conclusions regarding the relationship between electron configuration and geometry in M(CO) species have been reached as part of a wide-ranging theoretical study of M(CO), M(CO), and M(CO) carbonyl frag- ments using extended Huckel calculation^.^^ Among the many topics covered by this study is a rationalization of the preferences of Fe(CO) and Cr(CO) fragments for bonding with conjugated and non-conjugated dienes respectively.In other matrix-isolation studies the range of binary carbonyls has been extended along the transition series to copper the species characterized being Cu(CO),- and cu,(co)6. The latter is the dinuclear carbonyl which would be predicted to follow Ni( CO),. 58 Photochemistry.-Metal-centred radicals of the Mn(CO) and related types may also be generated in photochemical processes. Of the large amount of reported work on photochemistry of metal carbonyl~,'~ relatively little is concerned with homolysis of metal-metal bonds to yield metal-centred radicals. For example previous studies on photolytic reactions of M2(CO), species (M=Mn or Re) have yielded both simple substitution products such as Mn,(CO),(PPh,) from Mn,(CO), and PPh3 and mononuclear products resulting from cleavage of the M-M bond such as ReCl(CO) from Re,(CO), and CCl,.These reports were qualitative in nature and quantitative studies giving definitive evidence for the primary photochemical proces- ses were not available. A series of studies reported this year6' presents evidence that the primary process in photochemical reactions of M,(CO), (M =Mn or Re) Mn2(CO)9(PPh3) MnZ(CO)8(PPh3)2 MnRe(CO)lO [(q5-C5HS)M(Co)312 (M =Mo or W) and (OC),M'M2(CO),(v5-C5H5) (M'=Mn or Re and M2=Mo or W) is homolytic cleavage of the metal-metal bond. Results for the [(~5-C,H,)M(CO)3] complexes are typical. These molecules have an intense fairly narrow near-u.v. absorption (ca. 20 000 cm-') which has no analogue in (q5-C,H,)M(CO),C1 com-plexes and is assigned to a one-electron transition which is essentially u +u*with respect to the M-M bond.Photolysis results in excitation of this transition with consequent bond homolysis. The principal evidence is (i) photolysis in CCl solution proceeds according to equation (29) where n is very near 2.0 and the chloride is the hv CCI (T 5-C~H5)2M2(C0)6-+ n (T '-C5HS)M(CQ3C1 (29) sole photoproduct; (ii) photolysis in the presence of Ph3CC1 gives e.s.r. evidence for formation of Ph3C* and in the presence of PhCH,Cl the products are PhCH,CH,Ph and (qS-C,H,)M(CO),C1; and (iii) photolysis of mixtures of [(r)5-C5Hs)M1(CO)3]2 57 M. Elian and R. Hoffmann Znorg. Chem. 1975 14 1058. 5R H. Huber E. P. Kundig M. Moskovits and G. A. Ozin J.Amer. Chem. Soc. 1975,97 2097. 59 M. Wrighton Chem. Rev. 1974,74 401 and references therein. 6o M. S. Wrighton and D. S. Ginley J. Amer. Chem. Soc. 1975,97 2065 4246 4908. D.J. Cardin and K. R.Dixon with Mi(CO), (M’ =Mo or W M’ = Mn or Re) gives all four M’-M2 species (q5-C5H5)M’(CO),-M’(CO)5 in high yields based on the disappearance of homonuclear species. The 17-electron intermediates generated in these photolytic reactions may be compared with the well-known and important catalytic species [Co(CN),I3-. Reac- tions of the latter with alkyl halides (RX) are known to proceed by radical pathways giving both [Co(CN),RI3- and [Co(CN),XI3-. The difference between this process and the reactions of M(CO) (M = Mn or Re) or (q5-C,H5)M(CO) (M = Mo or W) with PhCH2Cl to yield PhCH,CH,Ph and M(CO),Cl or (q5-C,H,)M(CO),Cl is attributed to the very low steady-state concentration of metal radicals in the latter experiments.This renders coupling of metal and organic radicals an unlikely process.6o The comparison with [Co(CN),]’- is strengthened by the discovery that Re(CO), generated by irradiation of Re,(CO), at 311nm is capable of activating molecular hydrogen. The proposed mechanism involves dissociation of CO from Re(CO), oxidative addition of H to the resulting Re(CO), species and subsequent reaction to ReH(CO), H,Re,(CO), and H,Re3(C0)l,.61 The apparent conflict between the above processes requiring M-M bond homolysis as the primary photochemical process and previous reports of heterolysis and substitution reactions is considered to be due to the possibility of secondary thermal reactions.For example Scheme 6 is proposed6’ to account for photosub- stitution in Mn,(CO)lo. An independent flash photolysis study6’ of [(q5-C,H,)Mo(CO),] is slightly at variance with these suggestions in that two inter- mediates were detected both of which react by independent thermal processes to ::32[Mn(CO),]%Mn,(CO), * 2[Mn(CO),PPh,] + 2CO Mn(CO) +‘Mn(C p3\ ),PPh3 r/A Mn2(C0)8(PPh3)2 Mn,(CO),PPh Scheme 6 regenerate the starting complex. One of these is assigned as (q’-C,H,)Mo(CO) and the other as (q5-C,H,),Mo,(CO), but it is not certain that the latter is a primary photoproduct.62 However the possibility of substitution via homolysis has been further supported by studies of the reactions of [Mn(CO),(PPh,)] with P(OPh) and of ReH(CO) with PPh3.63 Both reactions proceed by initial generation of radicals M(CO),L (M = Re L = CO; M = Mn L =PPh,) followed by associative ligand exchange at the reactive intermediate.This type of process was previously unknown for simple substitution reactions which had been considered to proceed by straightforward dissociative or associative pathways involving the substrate species and no radical intermediate^.^^ Fluxional Processes.-The possibility of ‘carbonyl scrambling’ as an important class of fluxional process was first pointed out in 1972 by Bullitt Cotton and Marks as a 61 J. L. Hughey C. R. Bock and T. J. Meyer J. Amer. Chem. Soc. 1975,97,4440. 62 B.H. Byers and T. L. Brown J. Amer. Chem. Soc. 1975,97,3260. 63 J. P. Fawcett R. A. Jackson and A. J. P& J.C.S. Chem. Comm. 1975 733; B. H. Byers and T. L. Brown J. Amer. Chem. SOC.,1975,97 947. Organometallic Compounds 20 1 result of studies on the carbonyl-bridged complex (q5-CSH5)2Fe2(C0)4. Since that time the ready availability of I3C n.m.r. has led to a rapid expansion of knowledge in this area the majority of studies being devoted to bridge-terminal interchanges involving migration of CO groups from one metal atom to another particularly in dinuclear species. Typical of these studies are the observations for (77’-CSHS)2Fe,(CO)3[P(OPh)3](13) and the similar results obtained by an independent group on the analogous triethyl phosphite complex.64 In the solid state the triphenvl phosphite complex has structure (13) but in solution i.r.and ‘H and 13C n.m.r. spectra show rapid interconversion between isomers having cis and trans arrangements of the cyclopentadienyl groups and simultaneous exchange of car- bonyls between bridging and terminal sites. The generally accepted mechanism for processes of this type involves two essential steps (i) concerted opening and closing of pairs of ligand bridges and (ii) hindered internal rotations in the non-bridged tautomers. If the above mechanism is correct then cis-trans isomer interconversion and bridge-terminal CO exchange in (13) should occur at the same rate. This is observed experimentally and the above mechanism is thus well established although no rationalization for the necessity of concerted pairwise bridge opening and closing has been pre~ented.~~ A survey of the stereochemistry of the compounds [Fe(q’- C,H,)(CO),Y] where Y can be a univalent group or may be a group capable of bridging to the iron has now shown that the geometry in these species is consistently close to octahedral.This observation implies a rigidity in the local stereochemistry at iron and one consequence of this is that the tautomer interconversion mechanism for [Fe($-C,H5)(CO)2]2 and related species must involve simultaneous making or breaking of two carbonyl bridge ~ystems.~’ The mechanism of CO transfer in systems such as (q5-CSH5)zRh2(C0)3 which involve only a single carbonyl bridge is less well established. Intermediates involving a triple CO bridge have been prop- osed but the facile CO site exchange in [(q5-C5H5)2Rh2(C0)2{P(OPh)3}], where such an intermediate requires a phosphite bridge renders this process unlikely.Moreover the 31P n.m.r. spectrum of the phosphite complex is temperature invariant indicating that the phosphite remains co-ordinated to one rhodium atom. The authors favour a mechanism involving formation of a new CO bridge synchron- ous with the breaking of the existing bridge.66 A fundamentally different type of carbonyl scrambling process has been demon- strated by a I3C n.m.r. study of (14).67Several previous experiments had indicated that in species having non-equivalent CO groups within M(CO) sets site exchange 64 F. A. Cotton L. Kruczynski and A.J. White Inorg. Chem. 1974,13,1402 and references therein; D. C. Harris E. Rosenberg and J. D. Roberts J.C.S. Dalton 1974 2398. 6s J. R. Miller and F. S. Stephens J.C.S. Dalton 1975 833. 66 J. Evans B. F. G. Johnson J. Lewis and T. W. Matheson J.C.S. Chem. Comm. 1975,576. 67 F. A. Cotton D. L. Hunter and P. Lahuerta Inorg. Chem. 1975 14 511 and references therein. D.J. Cardin and K. R.Dixon (14) by a process equivalent to rotation of the M(CO) fragment was a possibility. For the acenapthylene complex (14) this process may be unambiguously demonstrated even though no other fluxional process (e.g.‘ring whizzing’) is occurring. Between -60 and +45”C 13C n.m.r. spectra show that three CO groups a b and b’ are interchanging but there is no interchange with the groups c and c’.The process is essentially rotation of the Fe(CO) unit and the more normal bridge-terminal mechanism is prevented by the unusually long Fe-Fe bond (2.77 A). The complex Fe,(CO),(cycloheptatriene) also has an exceptionally long Fe-Fe bond (2.87 A) and is believed to represent another example of the same type of process although in this case definite proof is lacking.67 As noted above the majority of the CO scrambling processes studied in detail have involved dinuclear complexes. Observations on trinuclear complexes were limited to the prediction and confirmation that the barrier to total CO scrambling in Fe,(CO), is <5 kcal mol-l i.e. the system is still fluxional at -150 0C.68 Variable- temperature 13C n.m.r.of M3(CO)12 (M = Fe Ru,or 0s) and related complexes has now shown that several different scrambling processes can Fe,(CO), has the solid-state structure (15) and it is therefore probable that scrambling occurs via pair-wise bridge-terminal interchange of the type discussed above. This type of mechanism is also required for [HFe,(CO),,]- (16) since the unique bridging CO is not involved in the interchange. However an alternative 0 OCGCO p\ oc&c:o oc co OC -M ICO\,Lco oc /-\ oc co co (15) 68 F. A. Cotton and D. L. Hunter Inorg. Chim. Acta 1974 11,L9. Organometallic Compounds mechanism which is essentially a rotation of an M(CO) group similar to that discussed above for M(CO) groups is required by evidence on [Ru,(C~),,(N~),] (17).This species exhibits three I3C n.m.r. signals with relative intensity 4:4:2 indicating that localized exchange of axial and equatorial CO is occurring at the Ru(CO) group. Since the Ru(CO) groups are rigid CO-bridged intermediates are clearly not co OC\ / Similar fluxional processes have been observed for tetranuclear species. For example in H,FeRu,(CO), (18)at least three carbonyl exchange processes can be distinguished the most rapid (ca. -70 "C) localized at Fe the next (ca. -45 "C) localized at the three Ru atoms and the last general over all metal centres at +95 0C.70 13C N.m.r. studies have also prompted a re-opening of the long-standing argument as to the solution structure of Co,(CO),,. At -100°C three equal- intensity resonances corresponding to one bridging and two terminal environments are observed suggesting a structure with DZdsymmetry rather than the accepted structure with C3 In contrast the 13C n.m.r.spectrum of Co,(CO),,[P(OMe),] at -82 "C shows bridging terminal CO groups in a ratio of 3:8 as expected for a C, structure with one of the basal terminal CO groups replaced by phosphite. The differences are most probably due to the difficulties of interpreting the. relative intensities of n.m.r. lines affected by rapid s9Coquadiupolar re~axation.'~~ Work on CO scrambling in larger clusters has also been reported this year.' R~~(CO)~~ undergoes rapid is not fluxional at +70 "C whereas [R~~(CO),S]~- complete carbonyl scrambling even at -70 "C. The structure of the anion is derived from the neutral species by removal of one face-bridging carbonyl and this change is considered to make available intermediates involving minimal changes in symmetry and bonding.Another anion [Rh7(CO),,l3- is intermediate between the other two species being rigid at -70 "C but undergoing partial CO exchange at +25 0C.72 BridgingCarbonyl Structures.-The fundamental terminal and symmetrically bridg- ing modes of carbonyl bonding have been known for a very long time and more 69 A. Forster B. F. G. Johnson J. Lewis T. W. Matheson B. H. Robinson and W. G. Jackson J.C.S. Chem. Comm. 1974,1042. 70 L. Milone S. &me E. W. Randall and E. Rosenberg J.C.S. Chem. Comm. 1975,452. 71 (a)J. Evans B. F. G. Johnson J. Lewis and T. W. Matheson J.Amer. Chem. SOC.,1975,97 1245; (6) M. A. Cohen D. R. Kidd and T. L. Brown J. Amer. Gem. Soc. 1975,97,4408. 72 B.T. Heaton A. D. C. Towl P. Chini A. Fumagelli D. J. A. McCaffrey and S. Martinengo J.C.S. Chem. Comm. 1975,523. D.J. Cardin and K. R. Dixon h Ph recently two additional types of co-ordination have been shown to be relatively common. Co-ordinated carbonyls may form bridges to main-group or other transi- tion elements via oxygen bonding. Moreover as reported last year there exists a complete range of carbon-bridged types varying from the normal symmetrical bridge to the very unsymmetrical bridges exemplified by (19). There are also examples where only one of a pair of bridging carbonyls is asymmetric and others where a single asymmetrical carbonyl is the only bridging group.73 The product of reaction of Mn,(CO), with Ph,PCH,PPh (dpm) has the molecular formula Mn,(CO),(dpm), and appears to represent an important new type of carbonyl bridging stru~ture.'~ The manganese atoms are bridged by the dpm groups so that the two manganese and four phosphorus atoms are almost coplanar.Approximately perpendicular to this plane is a plane containing the carbonyl groups [see (20)]. The Mn-Mn bond is 2.934A comparable with that in Mn,(CO)l, and the bridging carbonyl is apparently bound by a rather long u-bond to Mn( 1) [Mn(l)-C is 1.93 compared with an average 1.69 A for the terminal Mn-C bonds] and via its .rr-electrons to Mn(2) [Mn(2)-C is 2.01 8 and Mn(2)-0 is 2.20 A].'" Bonding to Mn(2) is thus similar to olefin or acetylene bonding and may be compared to structures such as (21).75 Cluster Carbonyl Structures.-One of the interesting features of cluster chemistry is the intermediate position which these complexes occupy between molecular species and metal lattices.In the long term this relation could lead to important results in the field of catalysis. However most of the clusters studied to date have an essential difference from metallic lattices in that the metal atoms are arranged in one or other of the common co-ordination polyhedra and the centre of the polyhedron is unoccupied i.e. there is no metal atom co-ordinated solely by other metals. Exceptions to this statement such as the [Pt(SnCl3),l3- ion are fairly normal co-ordination complexes and the environment of the central metal ion bears little relation to that of a metal in a metallic lattice.However in recent years X-ray diffraction studies on gold clusters have been reported in which a polyhedron of gold atoms has another gold atom at its centre.76 The geometries of both [Au,{P(p- MeC,H,),},][PF,] and [Au l13{P(p-Fc6H4)3}] are derived from a centred icosahed- ron in the former case by removal of four atoms constituting an equatorial rectangle 73 F. A. Cotton and J. M. Troup J. Amer. Chem. Soc. 1974,96 1233 5070 and references therein. 74 R. Colton C. J. Commons and B. J. Hoskins J.C.S. Chem. Comm. 1975,363; C.J. Commons and B. J. Hoskins Austral. J. Chem. 1975,28 1663; R. Colton and C. J. Commons Austral. J. Chem. 1975,28 1673.75 €3. A. Patel R. G.Fischer,A. J. Carty D. V. Naik and G. J. Palenik,J. Olganometallic Chem.,1973,60 c49. Organometallic Compounds 205 and in the latter by replacement of one triangular face by a single gold atom.76 [Rh6(CO),,C]2- is the first metal cluster with a trigonal-prismatic arrangement of metal atoms and its oxidation with Fe3+ has yielded several interesting produ~ts.~' [Rh,(CO),,C] is related to the trigonal prism by capping one rectangular face and bridging one base edge. [Rh15(C0)&]- has the more complex geometry (22) in which the metal atoms form a centred tetracapped pentagonal prism and is the first example apart from the gold clusters above of a completely encapsulated metal atom. The mean distance from the central Rh to its 12 near neighbors is 2.908,.The analogy between this complex and a metal lattice is spoiled by the two carbide carbons which lie at 2.06 A from the centre Rh.77 However in the structure (23) of the [Rh13(C0)24H3]2- ion derived from reaction of [Rh12(C0)30]2- with hydrogen and studied by X-ray diffraction7' of its [(Ph,P),N]' salt the arrangement of rhodium atoms is essentially that found in hexagonal close-packing. The 13rhodium atoms are located in three nearly parallel layers making a cluster of D3,, idealized symmetry and the central metal atom is surrounded by 12 metal atoms at mean distances of 2.81 8,. Comparison with the cubic close-packed distance of 2.69 8 in Rh metal indicates that the electron density is higher in the (22) (23) The first example of a homonuclear trigonal-bipyramidal metal cluster has been Reduction of Ni(CO) by alkali metals in THF gives [Ni6(C0),,]'- and [Ni,(C0)12]2- and X-ray diffraction study of the latter as its [(Ph,P),N]' salt reveals a trigonal-bipyramidal cluster of Ni atoms with three bridging and three terminal carbonyls symmetrically disposed in the equatorial plane and three terminal carbonyls on each axial Ni.79 Platinum(1) and Palladium(i).-These are rare oxidation states the former being previously represented only bJ' JPtcl(PPh3)2], [Pt2C14(C0)zI2- [Pt,C12(Ph2PCH2PPh,)2] and [(Ph3P)2 t.S.Pt(CO)(PPh,)] and the latter by [Pd,Cl,(Bu'NC),] [Pd2Cl,(C0)2]2- an ill defined species [Pd(C6&)(H,0)(C10,)], and some very unusual organo- bridged compounds [Pd,(C,H,)(PPh,),I] (A) and 76 P.L. Bellon M. Manassero and M. Sansoni J.C.S. Dalton 1972 1481; P. L. Bellon F. Cariati M. Manassero L. Naldini and M. Sansoni J.C.S. Chem. Comm. 1971 1423. 77 V. G. Albano M. Sansoni P. Chini S. Martinengo and D. Strumolo J.C.S. Dalton 1975 305 and references therein. 78 V. G. Albano A. Ceriotti P. Chini G. Ciani S. Martinengo and W. J. Anker J.C.S. Chem. Comm. 1975,859. 79 G. Longini P. Chini L. D. Lower and L. F. Dahl J. Amer. Chem. Soc. 1975,97 5034. 206 D.J Cardin and K. R. Dixon ,c-c w' CC 0 CI cI t CI-Pt -Pt -Cl I I Pd - c 0 CI Br (25) [Pd~,C17(C6H6)],(B). X-Ray structure studies were available only on the sulphur- bridged platinum compound and the organo-bridged palladium compounds the latter having structures analogous to (24) except for the replacement of the C,H and Br bridges by allyl and iodide in (A) and by two benzene bridges in (B).Moreover all of the known compounds appear to be ligand bridged with the observed diamagnetism indicating some metal-metal bonding.80*8' An X-ray struc- ture determination carried out this year has confirmed the original suggestions (made in 1973 by Goggin and Goodfellow and based mainly on vibrational spectra) that the [Pt2C14(C0)2]2-ion contains an unsupported Pt -Pt bond and can exhibit an unusual form of isomerism. The anion was studied as its [NPr,]+ salt and is of the basic structural type shown in (25). Co-ordination about each platinum is distorted square-planar and the two planes are twisted about the Pt-Pt bond to give a transoid configuration with the dihedral angle between the two Pt-Cl groups being 120".The complex studied was one of the two isomers originally isolated; the other is thought to have the related cisoid structure. The 120"angle is considered to be a compromise between repulsions due to filled interaxial d -orbitals (optimum angle 135") and interligand repulsions (optimum angle 90°).80 The closely related pal- ladium(1) ion [Pd2(CNCH3)6]2+ has a similar structure and is thus the first Pd' dimer without bridging ligands in the solid state. Unlike the platinum complex the two square planes are almost perpendicular (dihedral angle 86.2"),a situation akin to the Ni' complex [Ni,(CN),l2- (dihedral angle 82").*' The metal-metal bonds in both palladium and platinum complexes are among the shortest known (2.531 A and 2.584 A respectively).X-Ray structure determinations of [Pd2(p-Br)(p-CSHS)(PPri)2] (24)82 and [Pd,(p-C,H,)(p-C,H,)(PPh,),l (C)"' demonstrate that the unusual type of bridging discussed above for allyl groups or benzene in complexes (A) and (B) can be extended to the cyclopentadienyl group. Both structures are of the type (24)except that in (C) the bridging bromide is replaced by a bridging methallyl group. The Pd-Pd bond lengths are 2.609 % and 2.679 % for (24) and (C) respectively which may be compared with the values of 2.686 A and 2.58 A reported for (A) and (B) respectively. In (24) the cyclopentadienyl ring has four C-C distances approxi- mately equal (1.46-1.52 A) but the bond parallel to the Pd-Pd axis is much shorter (1.33 A) and the ring may be regarded as an allyl plus alkene group.SO A. Modinos and P. Woodward J.C.S.Dalton 1975 1516 and references therein. D. J. Doonan A. L. Balch S. Z. Goldberg R. Eisenberg and J. S. Miller J. Amer. Cfwm. Soc. 1975,97 1961. 82 A. Ducruix H. Felkin C. Pascard and C. K. Turner J.C.S. Chem. Comm. 1975 615. 83 H. Werner D. Tune G. Parker C. Kruger and D. J. Brauer Angew. Chem. Infernat. Edn. 1975,14 185. Organometallic Compounds 207 21 Metal Hydrides Paramagnetic hydrido-complexes are still very unusual species. [ReHX,(PPh,),(acac)] (X=C1 or I) has been isolated from reaction of [ReH,(PPh,),(acac)] with CCl or I, and several salts of the type [CoHL,]X [L =P(OEt),Ph P(OMe),Ph or P(OPh),; X =PF or BF,] have been obtained by reaction of trityl salts with CoHL,.Details of the preparation and characterization of the first paramagnetic hydrides of Fe' and Fe'" have now been rep~rted.~ Mild oxidation of [FeHCl(diphos),] (diphos =Ph,PCH,CH,PPh,) with AgClO or a trityl salt yields [FeHCl(diphos),]X (X =ClO or BF,) and reduction of the same substrate by powdered sodium in benzene gives [FeH(diphos),]. The Fe' species may also be obtained by a similar reduction of [FeH(diphos),]BPh,. The Fe' and Fe"' species have magnetic moments 1.8 and 2.16 BM respectively consistent with a low-spin configuration and a single unpaired electron as found in the [CoHL,]+ ions. Presence of hydride is confirmed by evolution of hydrogen in reactions with HC1 and by oxidation and reduction reactions to known Fe" hydride complexes.Although they deteriorate rapidly in solution the new hydride complexes are stable to air for several hours in the solid state and are thus considerably more stable than the [CoHL,]' Although Fe' is a well-established oxidation state in organometal- lic complexes such as [Fe,(C0),(q'-C5H5),] it is still rare in derivatives of nitrogen and oxygen donors. The macrocyclic ligand (26) forms iron complexes which can be reduced by controlled-potential electrolysis to purple Fe' derivative^.^^ Electrolysis in MeCN solution on the first reduction plateau (-1.2 V) gives [Fe'(tetraene-N,)]+ [tetraene-N =(26)] isolated as its [CF,SO,]- salt and repeated scanning of the second reduction plateau (-1.6 V) gives [Fe'H(tetraene-N,)(MeCN)] v(Fe-H) = 1890 cm-' via hydrogen abstraction from the supporting electrolyte Bu",NBF,; reaction with CCl yields CHCl,.In addition to this unusual hydride stable alkyl or aryl derivatives of Fe' are isolated by reduction of [Fe"(tetraene-NJCl]' by lithium alkyls or aryls to yield [FeR(tetraene-N,)] R =Me or Ph. All of these Fe' species have magnetic moments 2.1-2.3 BM and their e.s.r. spectra are typical of low-spin d7 ~ysterns.~' A hydrido-complex of Fe' is. also formed when FeC1 is reduced by NaBH in butan-1-01 in the presence of the triphosphine ligand MeC(CH,PPh,) (P,). Addi-tion of [Bu",N]PF permits isolation of the complex [Fe2H3(P3),]PF6 which has been studied by X-ray diffraction on the CH,Cl solvate.The structure is as shown in (27) 84 M. Gargano P. Giannoccaro M. Rossi G. Vasapollo and A. Sacco J.C.S. Dalton 1975 9 and references therein. 85 M. C. Rakowski and D. H. Busch J. Arner. Chern. Soc. 1975,97,2570. D.J. Cardin and K. R. Dixon and differs from the Fe' species discussed above in being diamagnetic due to a metal-metal interaction.86 The other interesting structural feature is the trihydrido bridge; only two examples seem to have been reported previously namely [Ir2H3(q5- C5H.J2]+ and [Re,H3(C0)6]-.87 The product of reaction of Co(BF,) with the arsenic analogue (A,) of P under similar conditions has also been studied by X-ray diffraction. [Co,H,(A,),]BPh has the same structure as (27) but is paramagnetic with peff=3.17 BM for the dimeric entity.The metal-metal bond lengths are very similar (Fe-Fe = 2.332 82 and Co-Co =2.377 82) and unusually short. Both this fact and the magnetic differences can be rationalized using an MO scheme proposed previously for confacial bioctahedral complexes. This predicts a bond order of three for the Fe complex and two for the Co complex with two unpaired electrons in degenerate anti-bonding orbitals in the latter case.86 The bulky ligand tricyclohexylphosphine has been used to stabilize a number of unusual hydrido species. An addition this year is the paramagnetic hydride [~H(B~){P(C6Hl1),},], formed by reaction ofCoC1 and P(C6Hll) with NaBH in toluene-ethanol solution. Magnetic susceptibility (pea=2.15 BM) and e.s.r.meas- urements are typical of low-spin Co" with v(Co-H) = 1797 cm-'. X-Ray diffrac- tion shows structure (28) with co-ordinated BH completing a distorted square- pyramidal geometry about cobalt. The Co-H length (1.34 & appears unusually short but this conclusion is tentative in view of the high standard deviation (0.09 A). The complex is an active catalyst for hydrogenation and isomerization of olefins.88 22 Organometallic Compounds One-carbonLigands.-Alkyls (see ref. 16a). A brief report suggests that reaction of manganese(I1) chloride with a trimethylsilylmethyl-metal derivative or a related reagent gives the crystalline alkyls Mn(CH,R) (R =SiMe, CMe, or CMe,Ph) which are thermally stable to over 100°C in contrast to the ready detonation of MnMe, the only previously known binary alkyl for this oxidation state.Oxidation of the new alkyls by molecular oxygen gives green products which may be Mn(CH,R) species analogous to the tetranorbornyl Mn'" compounds reported previously. Lithium salts of the alkylate anions [MnMe,12- [COR,]~- (R =Me or CH,SiMe,) and [U(CH2SiMe3)6]2- have also been ~btained.~' Alkyls of rhenium are even more difficult to obtain than those of manganese except of course for carbonyls and 86 P. Dapporto S. Midollini and L. Sacconi Inorg. Chem. 1975,14 1643. 87 C. White A. J. Oliver and P. M. Maitlis J.C.S. Dulton 1973 1901 and references therein. M. Nakajima H. Moriyama A. Kobayashi T. Saito and Y. Sasaki J.C.S. Chem. Comm. 1975 80. 89 R. Andersen E.Carmona-Guzman K. Mertis E. Sigurdson and G. Wilkinson J. Organometallic Chem. 1975,99 C19. Organometallic Compounds 209 related species. [ReOMe,] was reported only last year and the full papers have now been p~blished.'~ Reactions of [ReOCl,(PPh,),] or [ReOCl,] with LiMe in diethyl ether both give [ReOMe,] the former in 70% and the latter in 20% yield. In the former case traces of 0 are necessary for high yields; 0,does not affect the yield in the latter reaction but it is evident that both processes are more complex than simple methylation. [ReO(CH,SiMe,),] and [Re2O3(CH2SiMe3),] have also been prepared by reaction of Me,SiCH,MgCl with [ReOCl,(PPh,),]; the former is air stable in contrast to [ReOMe,]. Both oxotetra-alkyl species are paramagnetic and e.s.r.electronic absorption and i.r. spectra are consistent with a square-pyramidal ~tructure.~~ WMe was first prepared in 1972 and as reported last year TaMe is (with ReMe, vide infra) the only other example of a homoleptic methyl in an oxidation state greater than four. Preparation of WMe by interaction of LiMe and WCl is a rather complex reaction and it now appears that some of the difficulties are due to the fact that adventitious oxygen is required." Reaction of WCl with trimethylaluminium at -70 "C is a better procedure for preparing WMe, and it is important to note that the compound is potentially explosive. The analogous reaction of AlEt with [ReOMe,] yields the new green paramagnetic ReMe, which is reasonably stable at 25 "C. A stable methyl of an even higher oxidation state [Rev1IO2Me3] is obtained by oxidation of [ReOMe,] with nitric oxide," a reaction which must finally dispel the idea that alkyls are stabilized only in low oxidation states.Insertion Reactions.-The importance of the /3 -hydride elimination process as a factor in destabilizing transition-metal alkyl complexes has been noted.'6n There is still very little information available on the intimate mechanism of the reaction but the reverse process hydride insertion has been studied in more detail especially for platinum complexes. For the general reaction (30) two principal mechanisms have trans-[PtHXQ,]"' + alkene trans-[PtX(alkyl)Q,]"+ (30) been discussed and a paper this year9* summarizes the existing data and proposes a unified reaction scheme (Scheme 7).Originally the reaction was assumed to involve insertion insert ion ?l 11 trans-Q,PtHX + un [Q,PtHX(un)] E [Q,PtHX(un)] etc. (29) (294 11 11 X-+ [trans-Q,PtH(un)]+ X-+ [cis-Q,PtH(un)]+ 11 (30a) insertion un = unsaturated ligand Scheme7 90 K. Mertis D. H. Williamson and G. Wilkinson J.C.S. Dalton 1975,607;J. F. Gibson K. Mertis and G. Wilkinson J.C.S. Dalton 1975 1093. 91 L. Galyer K. Mertis and G. Wilkinson J. Organomefallic Chem. 1975,88 C37. D.J. Cardin and K. R. Dixon associative alkene co-ordination to give a five-co-ordinate intermediate (29) followed by rearrangement to the square-planar insertion product. Complexes similar to (29) have been isolated e.g. [PtH(CN){C2(CN)4}(PEt3)2] and [PtClMe(C,(CF,),}(AsMe,Ph)] but only the methyl complex has been shown to undergo a subsequent insertion reaction.Recent kinetic data have tended to favour four-co-ordinate intermediates (30) and trans-[PtH(GH,)(PEt,),]+ has been observed by n.m.r. spectroscopy in the reaction of trun~-[PtH(acetone)(PEt,)~]+with C2H4 and isolated as its [BPh,]- salt from the reaction of trans-[PtH(NO,)(PEt,),] with C2H4. In the unified reaction Scheme 7 the five-co-ordinate intermediate (29) may be either a transition state or a bona fide intermediate. Weak ligands (NO3- acetone MeOH etc.) favour (30) [i.e. (29) is then a transition state] and stronger ligands (29) although in the latter case definition of the necessary ligand properties is not clear-cut.The intermediates (29a) and (30a) represent changes of stereochemistry which may be necessary before insertion can occur.92 For (29) this presents little difficulty since stereochemical interchange is facile in five-co-ordinate systems but in (30) there is a problem presented by the observed trans geometry of the intermediates and the necessity for adjacent hydride and C,H positions prior to insertion. This could be resolved either by an X-assisted trans +cis isomerization (Scheme 7) or by an associative process involving an additional C;H4 The trans -B cis isomerization route is suggested by the analogous reaction of truns-[PtHX(PEt,),] with alkynes which always results in a vinyl with Pt and H in mutually cis positions.94 However this mechanism is clearly not possible for ethylene insertion into the Pt-H bond of trans-[PtHCI(P-P)L where P-P is the diphosphine (31) which spans puns positions in square-planar complexes (32).95 The problem has also been discussed regarding the insertion (31) reactions of trans-[PtMe(q-allene)(PMe,Ph),]+ to cis-[Pt(~-2-methylallyl)-(PMe,Ph),]'.The relation to the above insertions is clear and the reaction shows first-order kinetics. A five-co-ordinate transition state is considered unlikely since addition of anionic or neutral donors or excess allene suppresses the insertion. A slight dependence of AH+ on the counter-ion SbF6- -BF,-> PF6- suggests that the reactive species is a tight ion pair but it seems that the chief role of cationic intermediates in promoting Pt-H and Pt-C insertions is activation of the unsatu- rated hydrocarbon rather than stabilization of five-co-ordinate intermediate^.^^ The 92 H.C. Clark C. R. Jablonski and C. W. Wong Znorg. Chem. 1975,14 1332 and references therein. 93 H. C. Clark C. R. Jablonski J. Halpern,A. Mantovani,andT. A. Wed Znorg. Chem. 1974,13,1541. g4 H. C. Clark and C. S. Wong J. Organometallic Chem. 1975,92 C31. 95 G. Bracher P. S. Pregosin and L. M. Venanzi Angew. Chem. Internat. Edn.,1975,14,563. 96 M. H. Chisholm and W. S. Johns Inorg. Chem. 1975,14 1189. Organometallic Compounds 211 possibility of achieving adjacent hydride and ethylene positions via tetrahedral intermediates remains essentially unexplored. Oxidative Addition.-This is another reaction of central importance in organometallic mechanisrn~.~~ As reported last year use of the spin trap Bu'NO has provided evidence for a non-chain radical process in the oxidative addition of alkyl halides to [Pt(PPh,),] and stereochemical studies on similar reactions of [Pd(PPh,),] have suggested an SN2type of attack by the metal at the carbon centre.The latter work also indicated a need for caution in that addition of Bu'NO to the reaction of PhMeCHBr with [Pd(PPh,),] produced Bu'(PhCH,)NO* even though the reaction probably does not normally proceed by a radical mechanism (this is because Pd" alkyls are significantly less stable than Pt" analogues and react with Bu'NO). However CIDNP evidence has now confirmed that radicals are involved in oxidative - SN2 Pto + RX R-Pt"-X % 7 Pt'-XR.1 PtI-X + R' R2 q0, RX X-Pt"-X + R' chain process R-Pt"-X H-PP-X Scheme 8 addition of isopropyl iodide to [Pt(PEt3),]. Moreover this reaction in common with several others involving reactive alkyl halides is more complex than a simple addition to form trans-[Pt(Pri)I(PEt,)J; other products are trans-[PtHI(PEt,),] trans-[PtI,(PEt,),] propene propane and 2,3-dimethylbutane. Scheme 8 is prop- osed to unify these and other observations. The initially formed radical pair (Pt'-X R.)can collapse to the regular adduct or diffusively separate. Subsequent reaction of the separated radicals depends on the reactivity of the alkyl halide; very reactive ones form dihalide and organic radicals and less reactive ones initiate a chain process.97 The initial radical pair formation may be preceded by one-electron transfer.The reaction of M(PEt,) (M = Pt or Ni) with tetracyanoethylene (TCNE) generates the TCNE radical anion detected by e.s.r. but the corresponding M' species is not In contrast reductive elimination reactions in two cases studied this year appear to occur by concerted intramolecular processes. Ther- molysis of cis-[PtAr,L,] {Ar= Ph or 4-MeC6H,) = (PPh3)* [P(4-MeC6HJ3], Ph2PGH4PPh2 or Ph,PCH,PPh,} generated Ar2 quantitatively and without isomerization whereas radical pathways or ortho-metallation should produce ArH or isomerized aryk9' Moreover kinetic studies on reductive elimination of ethane 97 A. V. Kramer and J. A. Osborn J. Amer. Chem. Soc.1974,96,7832 and references therein. 98 I. H. Elson D. G. Morrell and J. K. Kochi J. OrganometallicChem. 1975,84 C7. 99 P. S. Braterman R. J. Cross and G. B. Young J.C.S. Chern. Cornrn. 1975,627. 212 D.J.Cardin and K. R. Dixon from fac-[PtClMe,(PMe,Ph),] suggest a concerted elimination process from a five- co-ordinate intermediate formed by dissociation of tertiary phosphine. The inter- mediate resembles an ethane complex of platinum(I1) and the process is similar to that previously proposed for reductive elimination from Au'" species.'oo Dialkylaminomethyl and Dialkylphosphinomethyi Ligands.-The ligating proper- ties of unsaturated species containing heteroatoms are a potentially rich field of chemistry. A structure containing q2-bonded [Me,N=CH,]' a formal three- electron donor was first suggested in 197 1 for the complex [CuCl(Me,NCH,)]Br.pis type of co-ordination has been confirmed by X-ray study of (CH2CH2NCH2)Mn(CO), which has Mn-N = 1.98 A Mn-C= 2.09 A and C-N = 1.45 A the last being an essentially typical single bond length. A wide range of (q2-R,CNH,)M(CO) (M = Mn or Re) complexes has now been reported from elimination of RiSnBr between R;NCH2SnR and M(CO),Br."' A more direct approachlo2 uses reaction of [Me,NCH,]I with Na[M(C0),(q5-C,H,)] (M = Mo or W) to synthesize the 0-bonded derivatives M(CO),(q'-C,H,)(q '-CH,NMe,). Wheo M = Mo the 0-bonded complex transforms under reflux in light petrol to the n-bonded derivative Mo(C0),(q5-C,H,)(q2-CH2NMe2), a reaction reminiscenf of the familiar CT -P T ally1 interchange.The change is from one- to three-electron donor in both cases. Curiously the expected magnetic inequivalence of N-methyl groups and methylene protons is not observed in the n.m.r. spectrum and this situation is also found for the seven-co-ordinate derivatives MI(CO),(NCMe)( q2-CH,NMe,) obtained by reaction of [Me,NCH,]I with M(CO),(NCMe)j. In addition to the q ' and q2derivatives an unusual reaction of [Me,NCH2]I with [Fe(C0),I2- or [Cr(CO),]'-yields the known carbene complexes Fe(CO),(CHNMe,) and Cr(CO),(CHNMe,) presumably by hydrogen abstraction from one MCH,NMe group to give NMe3.'02 Analogous phosphino-derivatives have also been reported. '03 Reaction of CoCl(PMe,) with the ylide Me,PCH2 gives a very air-sensitive red product formu- lated as Co(q2-CH2PMe2)(PMe3) on the basis of 'H and 31P n.m.r.Interestingly in view of the above observations on q2-CH,NMe, the compound is fluxional and assignment of definite phosphorus positions in the co-ordination sphere is not possible. The q2-CH2PMe2 system can also arise by an unusual oxidative addition reaction. Treatment of FeCl,(PMe,) with Mg and PMe in THF yields FeH(q2- CH,PMe,)(PMe,) from oxidative addition of a trimethylphosphine to the Fe centre. It is suggested that equilibrium formation of Fe(PMe,) may be involved in reactions of this species. lo3 X-Ray confirmation of the q2-CR,PR possibility has come from a rather unexpected quarter. trans-[PtCl,(PPr",),] reacts with 1-lithium 2-phenyl-1,2-dicarbaclosododecaborane to give a product containing a 0-carbaboranyl ligand and an internally metallated q 2-P(Pr"2)CHEt ligand (cited in ref.103). Two Carbon Ligands.-Aza-allyl Complexes and Related Species. Continuing the theme of ligating properties of hetero-unsaturated ligands we note that 2-aza-ally1 100 M. P. Brown R. J. Puddephatt and C. E. E. Upton J.C.S. Dalton 1974 2457. 101 E. W. Abel and R. J. Rowley J.C.S. Dalton 1975 1096 and references therein. 102 C. W. Fong and G. Wilkinson J.C.S. Dalton 1975 1100. 103 H. H. Karsch H. F. Klein and H. Schmidbaur Angew. Chem. Znternat. Edn. 1975 14 637 and references therein. Organometallic Compounds complexes have been known for several years. An unusual reaction of LiNCR2 (R =Ph or p-tolyl) with MC1(C0),(q5-C5H5) (M =Mo or W) yields M(CO),($- C5H5)(R2CNCR2) complexes by elimination of cyanate.An X-ray study of the complex with M =Mo and R =p-tolyl shows a bent (128") aza-allene structure with the CR2 planes mutually perpendicular but low-temperature n.m.r. studies suggest an asymmetric ?r-aza-ally1 structure in Extension of this work to 1,3- diaza-ally1 compounds has been achieved by reactions of RNC(R)NRLi with MC1(C0),(q5-C5H5) or with MnX(CO) (X =Cl,Br or I). In the latter case the initial product is a carbamoyl complex Mn(CO),{CO.NRC(R)=NR} which decar- boxylates under U.V. irradiation to Mn(CO),{RNC(R)=NR}. Co-ordination of the hetero-ligand is probably of a a,a-type analogous to a carboxylate rather than an ally1 group. lo4 Reactions of an cy -chloroenamine Me2C=C(NR,)C1 =Me or CH3\ /NRZ CH3\ /NRZ R R -c1-A /c=c\ ___) c=c -\N/ I CH3 c1 CH3/\M(CO),(CsHs)x CH3\ /c\ M(Co)y- 1(C5H5)x + 1 /c\c/ (C5H5)xM(CO),-CH3 II RR 0 \/ I-co .C' II 0 1-2co 4+H' H R H I CH3 R C=C=N +/ Scheme 9 2R =(CH,),] with a carbonyl anion [M(CO),J- (M =Mn or Re) [M(CO),(q'- C,H,)]-(M =Mo or W) [Co(CO),]- or [Fe(CO),(r]5-C,H,)]- reveal an exception- ally varied co-ordination chemistry (Scheme 9).Seven different modes of co-ordination are established by spectroscopic data including the first examples of 1-aza-ally1 and 2-azabutadiene complexes the former being an Mo species isolated as 104 T. Inglis and M. Kilner J.C.S. Dalton 1975 924 930 and references therein. D.J.Cardin and K. R. Dixon its PF6- salt and the latter an Mn compound formed by hydrogen migration in the ligand Phosphonium Betaine Complexes. (See also Section 13.) Reaction of (21) with triethyl phosphite results in nucleophilic attack at the a-carbon of the acetylide to yield a new type of two-carbon three-electron ligand. X-Ray diffraction studies of the product Fe2(PPh2)(Co),C{P(oEt),}CPh,show a structure with C-C and P-C bond lengths in the bridging group 1.34 and 1.74 A respectively. This indicates considerable multiple character in both bonds and a formulation intermediate between (33) and (34).lo6 (EtO),P\' Ph / Ph (33) (34) Tris(ethylene)plutinurn and Related Species. The synthetic potential and catalytic activity of labile olefin-substituted Mo complexes are well established.The many elegant studies using bis(cyc10-octa- 1,5-diene)nickel and cyclo-dodeca- 1,5,9- trienenickel are of particular interest and the tremendous potential of correspond- ing platinum complexes is obvious. Although bis(cyc1o-octa- 1,5-diene)platinum (35) has been obtained previously by U.V. irradiation of PtPr\(1,5-C8H,,) in the presence of 1,5-C8H12,a convenient and reliable synthesis was lacking. Moreover the other known Pto species such as Pt(PPh,) or Pt(C,H,)(PPh,) contain relatively non-labile tertiary phosphines. Thus the preparation of (35) in good yield by the treatment of Li2C8H8with PtC12(1,5-C,H12) in the presence of excess 1,5-C8H12 is an important advance and has already led to much novel chemistry (Scheme 10).lo7 The structure of Pt(C2H4)3 and related species is of especial interest since a theoretical study of Ni(C,H,) has predicted a trigonal-planar structure rather than one having alkene ligands perpendicular to the co-ordination plane.The only X-ray structure confirming this prediction was that of tris(bicyclo[2,2,l]heptene)nickel. This type of structure has now been confirmed for Pt(C,H,),(C,F,) easily derived from Pt(eH,) by a simple displacement reaction and also for tris-(bicyclo[2,2,l]heptene)palladium (D) and the corresponding platinum compound and Pt(GHJ2(PMe3). The last example was characterized by 13C n.m.r. studies (the others by X-ray diffraction) which show rotation of the co-ordinated ethylene at ambient temperature and a trigonal-planar structure at low temperatures.Bis(cyc1o- octa-1,s-diene)palladium (E)has also been obtained by a reaction analogous to the synthesis of (33 and reacts with C2H4 to produce a complex which is probably Pd(C.J34),.'07 Preparation of (D)and (E)on a gram scale has also been achieved by condensation of palladium atoms with the appropriate ligand at low temperatures (-196 and -120 "C respectively)."' lo5 R. B. King and K. C. Hodges J. Amer. Chem. Soc.,1975,97,2702. Io6 Y. S. Wong H. N. Paik P. C. Chieh and A. J. Carty J.C.S. Chem. Comm. 1975 309. lo' M. Green J. A. Howard J. L. Spencer and F. G. A. Stone J.C.S. Chem. Comm. 1975 3 449; M. Green J. A. K. Howard A. Laguna M. Murray J. L. Spencer and F. G. A. Stone J.C.S. Chem. Comm. 1975,451,and references therein.R. M. Atkins R. MacKenzie P. L. Timms and T. W. Turney J.C.S. Chem. Comm. 1975,764. Organometallic Compounds ,CF 0-C.. I 1 'CF, Pt-Pt /CF,CFCF, z Scheme 10 Formation and Cleavage of C-C Bonds at Metal Sites.-Linking reactions of unsaturated substrates at metal centres are of obvious importance in understanding many organometallic processes but established general reaction classes are rela- tively rare. A common approach is to utilize fluorocarbon species since this frequently stabilizes reactive intermediates. During the past several years oxidative linking such as the reaction of tricarbonyl(butadiene)iron with C2F4 to yield (36) has been shown to be a fairly general reaction. A series of papers published this year'09 shows that several other types of product are also obtained.Thus tricarbonyl(cyc1o- octa- 1,3-diene)iron with GF4 gives the ferracyclopentane (37) in addition to the expected product and tricarbonyl(cyc1ohexa- 1,3-diene)iron with CF,CFCF gives (38) in addition to products related to (36) and (37). Compound (37) is regarded as derived from the initial n-allylic insertion product by n +(+ ally1 interchange. Isolation of (38) together with results on the stereochemistry and position of linking in substituted dienes and fluoro-olefins suggests that the mechanism of the reaction is via endo attack by olefin on the diene to give an ionic intermediate such as (39). The alternative reaction path uia initial attack of fluoro-olefin on Fe cannot be excluded in some cases.Reactions essentially similar to the formation of (36) also occur between M(1,3-diene)(CO) (M = Fe or Ru) and hexafluoroacetone and between Ir(q3-RC3H4)(CO)L (L = PPh or AsPhJ and GF or CF,CrCCF,. In the Ir-GF case an initial adduct (40) is isolated and the linking reaction involves a second C,F molecule which forms [CH A CRCH,CF,CF,fr(q'-C,F,)(CO)L] when R = Me. However when R = H the unusual iridocycle (41) results.'o9 lo9 M. Bottrill R. Goddard M. Green R. P. Hughes M. K. Lloyd S. H. Taylor and P. Woodward J.C.S. Dalton 1975 1150; see also preceding papers in this series and references therein. D.J. Cardin and K. R. Dixon co (42) Extension of this work''' to reactions of hexafluorobut-2-yne. (HFB)with tricar- bonyl(butadiene)iron yields an insertion product analogous to (36) and thermolysis of this product under reflux in hexane gives (42).This overall reaction involves stepwise Diels-Alder addition of HFB to co-ordinated buta- 1,3-diene a result which suggests that previously reported examples of concerted 'forbidden' reactions at transition metals may also have stepwise mechanisms. HFB and tricarbonyl- M. Bottrill R. Goddard M. Green R. P. Hughes M. K. Lloyd B. Lewis and P. Woodward J.C.S. Chem. Comm. 1975,253;J. L. Davidson M. Green F. G. A. Stone and A. J. Welch ibid. p. 286; R. Davis M. Green and R. P. Hughes ibid.,p. 405. Organometallic Compounds 217 (cyclohexa- 1,3-diene)iron give the double insertion product (43) but with tricarbonyl(cyc1oheptatriene)iron a remarkable addition of two molecules of CF3CCCF3 occurs on the endo face of the triene to yield the quadricyclic ligand complex (44).Another unusual product is (45) {obtained by reaction of HFB with [Fe(CO),(q '-C5H5)],} a type of intermediate which has been frequently pos- tulated in metal-catalysed formation of cyclopentadienones and quinones.' lo H H (C0)3Fe' dF3 CF3 CF3 (44) (45) Another important class of reaction is transition-metal cleavage of C-C bonds of cyclic ligands. The classic example here is insertion of PtIV into cyclopropane ring systems and X-ray studies have established that a C-C bond is cleaved even though cyclopropane can be displaced by several donor ligands. '11 An interesting addition this year is the cleavage of trans-divinylcyclopropane by bis(ethy1ene)hexa- fluoroacetylacetonatorhodium(1)to give the bis(ally1) complex (46).'12 However examples for ring systems other than cyclopropane are still rare and the following are therefore of interest.In each case products have been characterized by X-ray diffraction. The final product from reaction of norbornadiene (nbd) with Rb(CO)16 is (47),derived from ring-opening of nbd and possibly a stabilized retro-Diels-Alder intermediate.lI3 Low-temperature n.m.r. spectra of {endo-(RO)C,Ar,}Pd(acac) 0 // (47) R = Me or Et Ar =Ph or p-FC6H4 demonstrate that the ring-closing step in the formation of cyclobutenyl derivatives from PhCCPh and PdCl in alcohols is readily reversible. Isomers (48)and (49) are both present in the ~olufion.''~ Reversible opening of a saturated C ring has been demonstrated in the conversion of (50) into (51).Both compounds contain two of the illustrated structural units joined by chloride bridges. The endo-phenyl analogue of (51) is present during the reaction R. D. Gillard M. Keeton R. Mason M. F. Pilbrow and D. R. Russell J. Organometallic Chem. 1971 33 247. *I2 N. W. Atcock J. M. Brown J. A. Conneely and J. J. Stofko jun. J.C.S. Chem. Comm. 1975 234. 113 J. A. J. Jarvis and R. Whyman J.C.S. Chem. Comm. 1975,562. 114 P. T. Cheng T. R. Jack C. J. May S. C. Nyburg and J. Powell J.C.S. Chem. Comm. 1975,369. D.J.Cardin and K. R. Dixon and has been isolated thus demonstrating that the ring-closure is readily rever~ible."~ Finally perhaps the most unusual of all is the insertion of Pto into an arene C-C bond.[Pt,(Bu'NC),] or trans-stilbenebis(trimethy1phosphine)platinum reacts with hexakis(trifluoromethy1)benzene to give (52; L =Bu'NC or PMe,) which represents a new type of possible intermediate in cyclo-oligomerization reactions of a1 kynes. l6 OR OR Ar Ar Ar 23 Catalytic Processes The 'heterogenizing' of homogeneous catalytic systems is an area of developing interest and has been reviewed re~ently."~ The objective of this research is to combine the ease of recovery of a heterogeneous catalytic system with the great activity selectivity and ease of mechanistic study of a homogeneous system. The most usual approach uses polystyrene cross-linked with divinylbenzene as a polymer support and ligating groups are introduced by substitution on the polymer chain.Papers published this year'18 provide a thorough investigation of a number of typical systems and describe the important new possibility of anchoring more than one type of catalyst to the same polymer chain thus enabling catalysis of sequential multistep reactions. Iron-catalysed bromination of polystyrene followed by reaction with LiPPh leads to the pura-PPh substituted derivative (53). Simple phosphine exchange reactions as shown in Scheme 11 yield the appropriate transition-metal substituted polymers (54)-(58). Among the reactions studied are cyclo-oligomerization of butadiene catalysed by (54)to yield (59) (60),and (61); hydrogenation of these products catalysed by (55) to yield the fully saturated analogues of (59)-(61); and hydrofor- mylation of (59) catalysed by (57) to yield (62) and (63).The product distributions 115 D. J. Mabbott P. M. Bailey and P. M. Maitlis J.C.S. Chem. Comm. 1975 521. 116 J. Browning M. Green A. Laguna L. E. Smart J. L. Spencer and F. G. A. Stone J.C.S.Chem. Comm. 1975,723. 117 J. C. Bailar jun. CatulysisReu. 1974,10 17. 118 c.U.Pittman jun. L.R. Smith and R. M. Hanes J. Amer. Chern. Soc. 1975,97,1742; C. U. Pittman jun. and L. R. Smith ibid. p. 1749. Organometallic Compounds Phl 'f"H(C0)(Ph3 P) (57) Ph 3-x Scheme 11 and responses to excess PPh3 temperature changes and changes in H2or CO pressures demonstrate the mechanistic similarity of the polymer-anchored systems to their homogeneous analogues.Rates are generally somewhat lower than those achieved with the homogeneous analogues probably owing to diffusion retardation in the anchored catalysts. D.J. Cardin and K. R. Dixon In addition to the above processes sequential cyclo-oligomerization of butadiene to (59),(60) and (61) followed by hydrogenation to the fully saturated compounds has been achieved using the catalyst (56) thus demonstrating the possibility of constructing a single catalyst to achieve a multistep conversion in a 'one pot' process. Sequential cyclo-oligomerization of butadiene followed by hydroformylation to (62) and (63) is achieved by catalyst (58)."* Table 1 Molecular structures and electronic configurations of some pentacarbonyl species No.of valence Stereo- shell chemistry * electrons S.P. 15 S.P. 16 S.P. 17 S.P. 17 T.B. 18 T.B. 18 (a) S.P.=square-pyramidal,T.P. =trigonal-bipyramidal.

ISSN:0308-6003    

DOI:10.1039/PR9757200179

出版商:RSC    

年代:1975

数据来源: RSC

摘要:

Abbar C. 19 Abel E.W.,212 Adams D.M.,92 Adams R.D.,155 Adedigi F.A. 192 Adolphson D. G.,123 Agapiou A. A. 193 Agarwal R. P.,178 Agarwal V.K.,43 Aime S.,203 Akora S.K.,195 Albano V.G.,205 Alben R. 34 Albrand J. P.,129 Alcock N.W.,126,217 Alder B. J. 14 16 Aldrich H.S. 115 Alefeld B. 41 Alimov I. M.,152 Allcock H.R.,132 Allen A. D.,156 Allinger K.,156 Allison S.,37 Alt H.G.,184 Alyen E.C.,173 Amma E.L.,195 Andersen R.,183 208 Andersen R.A.,95 Anderson D.L.,163 Anderson R.L.,197 Anderson S.J. 175 Anderson S.P.,129 130 Andrews L. 143 144 145 180 Angus P.C.,lX Anisimov K.N. 198 Anisimov S.I. 53 Anker W.J. 205 Annarelli D.L.,187 Antaraitis C.,166 Appel R.132 Aranes A. 171 Arjomand M. 177 Armatis F.J. 123 Armitage F.,194 Armor J. N.,166 167 Arnold. D.P.,119 Arnold E.,194 Arnould-Netillard H.,60 Author Index Ashe A. J. tert. 108 Atkins P. W. 67 69 70 72 73 74 77 80 81 Atkins R. M. 214 Atkinson L.,125 Attig T.G.,174 Atwood J. L.,184 Auel T.,195 Ault B. S.,144 Avakian P.,67 80 88 Averill B. A. 164 165 Azizov A. A. 188 Bacri J. C. 56 Baes M.K.,69 Baggett N.,152 Bailar J. C.,jun. 218 Bailey P.M.,218 Bailey R.T.,16 Baker E.C.,183 Baker W.A, 177 Balch A. L.,175 178 206 Balducci, A. 1 16 Baldwin J. E.,163 Ball C.,159 Bard A.J. 83 84 85 86 87 Barefield E.K.,173 174 Barker G.K.,106 115 Barnett B.L.,123 149 Barnik M.I. 60 Barojas J. 14 Bart J. C.J. 123 Bartell L.S.,129 Bartke. T.C.,195 Bartoli. F.J.. 25 Barton A. F.M. 6 Barton J. J. 187 Barton T.J. 188 Baschetto D.J. 185 Basmanova S.N.,67 Basolo. F.,160 162 163 167 Bastide J. 108 Bates R.B. 195 BaturiE-Rubtit J. 63 Baudler M.,130 Baiant V.,197 Beagley B. 110 Beauchamp J. L. 127 Beavers W.A. 195 22 1 Beck J. D. 115 Beck W.,151 Becker H.J. 108 Bedos R.,68 Beg M.A. A. 174 Beier B. F.,96 Bellon P.L.,205 Benfield F.W.J. 179 Berau G.,175 Bergendahl T.J.. 177 Berkowitz J. I15 Berne B. J. 16 34 Bernstein E.R.,150 Bernstein P.K.,178 Berreman D.W.,53 Bertelo C.A. 185 Bezot P.18 Bhatnagar S.S.,67 Bhattacharya S.,56 Bird R.B. 5 Bimbaum G. 25 Bitter W.,112 Bizot K.F.,178 Bjoerseth A. 195 Black D. L.,111 Black J. D.,198 Blackburn J. F.,185 Blake M.R.,172 Bland W.J. 184 Blinc R.,40 41 58 Blinn E.L.,173 Blinov L.M.,60 Bliot F.,19 Blount J. F. 140 Bock C.R.,200 Bock E.,35 Bock M.,130 Bock P.L.,185 Boden N.,37 Bodkin C.L.,135 Bohland H..153 Boehm J. R. 178 Boggess R. K.,178 Boilini E.,33 Bonfoey D.B. 173 Bopp T. T.,29 Borel J. 33 Boschetto D.J. 185 Bosnich B. 173 222 Bossu F. P. 177 Carr D. D. 193 Bottomley F. 167 Carreira L. A. 129 Bottrill M. 215 216 Carrigan C. R. 60 Boucher L. J. 159 160 Carter R.O. 110 Bouligand Y.,53 54 Carty,A. J. 174,175,204,214 Bounthakna T. 191 Casey C. P. 197 Bowen A. R. 154 Casey F. A. 180 Boyd J. R. 49 Cassar L. 174 Bracher G. 210 Cassoux P. 111 Brainina E. M. 198 Cava M. P. 141 Brandl A. 156 157 Cegielsky R. 67 Braterman P. S. 198 211 Cenini S. 176 Brauer D. J. 206 Ceriotti A. 205 Brauman J. I. 162 Cernia E. 116 Breitenbach J. 68 Cesari M. 116 Brintzinger H. H. 184 Cetinkaya B. 180 181 Brochard F. 53,62 Chamberlain J. 21 Brocklehurst. B. 75 77 Chan S.,101 Brondeau J. 21 Chandrasekhar S.,63 Brookes G. 1'18 Chang C. K. 162 164 Brot C. 18 27 Chang J. J. 37 Brown D. L. S. 192 Chang R. 33 Brown J. M. 217 Charrolin J. 37 Brown L. D. 96 168 Chatt J. 156 157 174 Brown M.P. 212 Chellappa K. L. 177 Brown T. L. 200,203 Cheney R. 173 Browning J. 218 Cheng P. T. 217 Brueser W. 197 Cherwinski W. J. 175 Bruice T. C. 165 Cheung P. S. Y.,14 BrSlet C. R. 156 Chieh P. C. 174 214 Brunvon J. 195 Chigrinov V.G. 60 Bryan P. S. 111 Chini P. 203 205 Bryce W. A. 68 Chisholm,M. H. 152,155,210 Brynor J. B. 178 Christe K. O. 127 145 Bryukhova E. V. 152 Christensen J. J. 140 Bucaro J. A. 25,27 Christensen S.,56 Buchachenko A. L. 67,70 Chu K. S. 42 Buchanan D. H. 185 Chung C. 180 Bunder W. 195 Churchill M. R. 176 Burce G. L. 177 Chvalovsky V.,197 Burger M. 40 Ciani G. 205 Burk P. L. 193 Cihonskii J. L. 137 Burlitch J. M. 194 Cinquini M. 138 Burness J. H. 168 Cladis P. E. 55 63 Burnham R. A.192 Clark C. R. 169 Burns R. E. 111 Clark H. C. 174,210 Busch D. H. 173,207 Clark N. A. 34 Bush R. D. 188 Clark R.J. H. 154 Busolin P. 43 Clarke M. J. 166 Butcher R. J. 173 Clarke R. E. 167 Butler S. 77 Clarkson S. C. 167 Butler W. 155 196 Clendening P. J. 177 Byers B. H. 200 Clugston M. J. 70 Coates G. E. 95 Calabrese J. C.. 170 Coe C. G. 160 Calhoun H. P. 132 Cohen M. A. 203 Callahan K. P. 101 105 106 Collier M. R. 180 Cameron T. S. 132 Collins D. M. 155 Candau S. 47 Collins S. 68 Candau S. J. 24 Collman J. P. 162 164 Cardin D. J. 180 193 Colton R. 194 204 Cariati F. 205 Commons C. J. 194 204 Carnowa-Guzman E. 183 Conlin R. T. 120 208 Conneely. J. A. 217 Author Index Connor J. A. 192 Constant E.19 Conti F. 176 Conway A. J. 116 194 Cooper M. J. 96 Cooper N. J. 180 Corben J. L. 159 Corbett J. D. 123 Corbridge D. E. 92 Corey J. Y.,188 Corigliani F. 153 154 Corrigan M. F. 170 Corriu R. J. P. 191 Coskran K.J. 173 Cotter M. A. 33 Cotton F. A. 154 155 161 183,186,194,201,202,204 Cotton S. A. 92 Craddock S. 120 Cragg R. H. 112 Cram D. J. 138 Crane G. R. 153 Creaser C. S. 149 Creaser I. I. 171 Creighton J. A.. 149 Cresswell R. A. 111 Cripps H. N. 88 Crociani B. 152 Cross R. J. 211 Croxton C. A. 6 Cruickshank D. W. J. 132 Crumbliss A. L. 180 Cucinella S. 116 Cummack R. 166 Cummins P. G. 43 Curtis M. D. 155 196 Curtis N. F. 173 Curtis W. D. 137 Curtis C.F. 5 Cusachs L. %. 115 Cutler R. S. 195 Czira G. 192 Dabrowiak J. C. 173 Dahl A. R. 120 Dahl L. F. 205 Dahler J. P. 70 Dahlmann W. 123 Dalley N. K. 140 Daly J. J. 123 Dance. I. G. 170 Daneshrad A. 190 Dang T. P. 171 Daniels W.B. 63 Dapporto P. 172 208 Dardy H. 24 Darmon I. 27 Dasannacharya B. A. 16 Davidson I. M. T. 119 Davidson J. L. 186 216 Davidson P. J. 182 Davies G. J. 21 Davies M. 17 19 21 44 Davis A. R. 150 Author Index Davis R. 216 Davison A.,150 Day P. 125 Day V. W.,150 157,160 DeBoer B.G. 176 de Boer J. L. 184 Debrinner P. G. 163 Degenkolb E. O.,77 de Gennes P. G. 31.65 Dehmer J. L.,115 Delhez R.,67 De Liefde-Meijer H.J.184 Deloche B.,37 Del Piero G. 116 Delpuech J. J. 115 Demers J. P. 185 DeStefano A. 112 Deuling H.J. 53 Deutch J. M. 16 Deutsch E. 170 Devaure J. 25 Dewan J. C.,150 de Zwart M. 60 Diaddario L. L. 178 Diamantis A. A.,157 166 Dianoux A.J. 46 Dickinson R.J. 172 Diehl P.,35 Di Gennaro T.M. 29 Dill J. F. 25 Dillard J. G.,168 Dillon K.B. 174 Dilworth J. R.,156 Di Pasquale S.,153 154 Dixon D. A.,96 Dixon K.R.,175 Dixon R.S.,75 Doane J. W.,41 58 Dobbs A.J. 72,81 Doedens R.J. 177 Dotz K.H.,181 Dolphin D. 164 174 Domiano P.,173 Domka F. 67 Donaldson J. D. 125 Dong R. Y.,35 Doonan D. J. 175,206 Dori Z. 168 Dormond A. 150,191 Dougherty J.P.,118 Doyle M.J. 180 193 Dozzi G. 116 Drake J. E. 120 Dreher R. 53 Drew M. G. B. 149 Druskovich D. M.,154 Dubois J. E. 193 Dubois-Violette E. 60 Ducruix A. 206 Duggan D.M. 177 Dullenkopf W. 123 Dunmur D. A.,43 Dunn J. G. 184 Durand G. 32 60 Dung J. R. 110 111,129 Dustin D. F. 101 Dvolaitzky M. 37 D’yakov V. M.,190 Dyarek D. 63 Dye J. L. 123 Dyson J. 132 Dzyaloshinskii I. E. 53 Eaborn C. 190 Eady C.R.,179 Ebner J. R.,161 Ebsworth E. A. V. 120 Eckberg R. P. 177 Edwards D. 184 Edwards P. A. 123 Efner H.F. 179 Egelstaff P. A.,9 16 Eidenschenk,R.,190 Einstein F. B. 150 Eisch J. J. 108 116 187 Eisenberg R.,175 206 Eley D. D. 69 Elian M.199 Ellis J. E. 196 Ellis P.D. 110 Elmitt K. 184 Elson I. H.,211 Ely N.,183 Elzaro R.A.,11 1 Empsall H.D. 100 171 Emsley J. W.,35 37 Endell R.,156 157 Enemark J. H.,178 Engelhardt G. 190 Engler E. M. 141 Epstein I. R.,96 Erbland M. L. 129 Esparza F. 130 Etemad S.,141 Evans G. J. 19 Evans G. T.,70,80 Evans I. P.,167 Evans J. 201 203 Evans M. 19 21 26 39,44 Evans R.H.,140 Evans W.J. 101,106 Everett G. W.,167 Ewings P. F. R. 124 Extine M. 152,155 Fabelinskii I. L. 21 Faber T.E. 53.58 Fachinetti G. 185 196 Faller J. W.,183 Fallon G. D. 170 Faltynek R. A. 196 Farkas L. 69 Farrar T. C.,29 Farrugia. L. 197 Faulkner L. R.,83,84 85 Fawcett J. P.200 Fay R. C.,150 152 Felkin H.,206 Fellner H. 56 Felter K.,97 Felton R.H.,174 Feltz A.,153 Ferguson G.. 170 173 Fick H.G. 151 Figueras Roca F.,67 Fild M.,129 Finn P. A.,152 Finocchiaro P. 152 Fischer E.O.,181 Fischer R.G. 204 Fisher R. C.,159 Fitzpatrick N.J.; 110 Flanders P. J. 50 Horiani C.,185 196 Foa M. 174 Foley P. 124 Fong C. W.,212 Foord A.,110 Ford P. C.,167 171 Forder R.A.,184 Forster A. 203 Forster D. 16,55 Franczek F. R.,168 Frank A.,130 181 Frank U.,123 Franke R.,190 Frankel R.B. 164 165 Frankevitch E. L. 78 Franklin W. 42,56 Franks M. L. 154 Franulovit K.. 63 Fredrickson A. G. 40 Freed J. H.,45 75 Frenz B.A.,154,155 161 Frlec B.146 Fuller H. J. 190 Fujita I. 174 Fumagelli A.,203 Furman R.,167 Gabay M. 53 Gagne R. R.,162 Gainsford G. J. 194 Galerne Y.,44 60 Galle J. E.,108 Gallici R. R. 187 Galyer L. 209 Garber A. R.,97 Gardy E. M.,75 Gargano M. 207 Garito A. F. 141 142 Garner C.D. 152 155. 158 Garnett J. L. 172 Garnier F. 193 Gartzke W. 156 Gaspar P.P. 120 Gass D. M.,16 Gasser O.,190 Gatehouse B.M. 170 Gaughan A. P. jun. 118 Gay R. S.,150 Gearhart R.C.,jun. 115 224 Gebala A. E. 183 Gebbie H. A. 21 Gebert E. 145 Geiger W. E. 175 Geoffroy G. L. 169 George T. A. 157 Gerritsma C. J. 54 Gerschel A. 27 Getz D. 168 Ghosh S. K. 33 Giannoccaro P.207 Gibbins S. G. 151 Gibson J. F. 209 Gigukre P. A. 127 Gill J. T. 99 Gillard R. D. 217 Ginley D. S. 155 196 199 Gloviozov I. P. 188 Goddard. R. 215 216 Goggin P. L. 175 Gokel. G. W. 138 Goldberg S. Z. 175 206 Goldwhite H. 129 130 Golino C. M. 188 Gong H. 101 Gonzalez B. 159 Good R.,151 Goodall B. L. 168 Goodfellow R. J. 175 Gordon R. G. 19 Goren S. D. 58 Gornall W. S. 25 Goscianski M.,60 Goto M.,153 Goubeau J. 123 Goulon J. 21 Govil S. 153 Gowenlock B. G. 195 Graf E. 139 Graves V. 179 Gray G. W. 31 Gray H. B. 168,169,170,177 178 Grebenkin M. F. 60 Green D. K. 29 Green M. 106 186,214,215 216,218 Green M.L. H. 179,180,184 194 197 Greenwood N.N. 99 Greffe. J.-L. 21 Gregor I. K. 172 Greiss G. 108 Griend L. J. V. 127 Griffith W. P. 149 Grimes R. N. 101 106 Groff R. P. 80,88 Grubbs R.H. 193 Grunthaner F. J. 177 Gsell R.,124 Gubanova L. I. 190 Guengerich G. P. 167 Guerst J. A. 54 Guest M. F. 152 Guggenberger L. J. 180 196 Gunsalus. I. C. 163 Gupta. A. 74 Gusel’nikov L. E. 188 Gust D. 188 Guyon E. 49.53 55,60 Gysling H. 183 Haaland A. 195 Haas C. H. 119 Habeeb J. J. 117 Hackett P. 196 Haddock S. R. 175 Hadjiminolis S. 125 Haffmanns R. 19 Hagen K. 126 Haines R. J. 193 Hakemi H. 40,41 Halbert T. R. 162 Halgren T. A. 96 Hall J. H. jun. 96 Hall L. w. 110 Halperin B. I. 65 Halpern J.168 210 Halstead G. W. 183 Halstenberg M. 132 Hiammond G. S. 74 169 195 Hanes R. M. 218 Hannan W. 172 Harke E. 153 Harp G. D. 16 Harris D. C. 201 Harris D. H. 124 Harris R. K. 129 Harris R. O. 156 Harrison P. G. 124 Harrod J. F. 152 Hart D. W. 185 Hart F. A. 92 Hartman J. S. 111 Hartshorn A. J. 181 Hasegawa M. 88 Hatfield W. E. 177 Hatzenbuhler,D. A. 80 Haupt H. J. 116 Haworth D. T. 112 Hawthorne M. F. 96 99 101 105 106,108 Hayashi H. 88 Hayes C. F. 56 Heath G. A. 157 186 Heaton B. T. 203 Hedberg K. 126 Hedberg L. 126 Heeger A. J. 142 Heger J. P. 34 Heidemann A. 42 Heil C. A. 120 Heil H. F. 108 Heimrod G. W. 67 Helm F. T. 177 Hendrickson A.-R.170 177 Hendrickson D. N. 177 Hennig H. J. 120 Author Index Herberich G. E. 108 Herbstein F. H. 143 Herman Z. S. 142 Hermanek S. 97 Hermann T. 140 Hershaft A. 123 Herskovitz T. 164 165 166 Hervet H. 46 Hetflejs J. 197 Hewitt R. C. 40 50 Hexmeier R. J.. 155 Heyman L. E. 173 Hidai M.,159 Higashimura T. 77 Hildebrandt R. L. 97 Hill J. D. 96 Hill N. E. 17 Hill W. E. 105 Hillier I. H. 152 Hirayama Y.,178 Hirschfelder J. O. 5 Hitchcock P. B. 116 181 194 Ho J. T. 63 Hoa K. 172 Hobdell M. R. 94 Hodges H. L. 129 Hodges K. C. 214 Hodges R. J. 176 Hodges R. V. 127 Hodgson K. O. 183 Hoeg D. F. 180 Hoel E. L. 96 105 Hoffman K. 187 Hoffman M.Z. 167 Hoffmann B. M. 159 160 162 164 167 Hoffmann R. 199 Hohorst F. A. 145 Holloway J. H. 146 147 Holm R. H. 164 165 166 170 174 Holmerda R. A. 178 Holzinger W. 182 Hoof D. L. 151 Hoover W. G. 14 Hoskins A. F. 194 Hoskins B. J. 204 Hosmane N. 120 Hosokawa T. 174 Hota H. K. 108 Howard A. V.,119 Howard J. A.. 214 Howard W. F. 143 144 145 Howard-Lock H. E. 25 Howe R. F. 168 Howells W. S. 42 Hoytink G. J. 84 Hrncir D. C. 184 Hsieh A. T. T. 116 194 198 Huang C. C. 63 Huang J.-T. J. 77 Hubbard P. S. 25 Huber H. 198 199 Hubert-Pfalzgraf L. G. 153 Author Index H udson A. 198 Huff L. 129 H uffmann J. C. 97 H ughes R. E. 194 H ughes R.P. 215 216 Hughey J. L. 200 H,uheey J. E. 92 Hui E. 151 Hull J. R. 179 Hunter D. L. 201 202 Huttner G. 130 181 H[yde,E. M. 171 H[yde,M. R. 158 Iannuzzi M. M. 154 Ibers J. A. 162 163 164 165 167 170 176 Ichikawa M. 158 Iitaka Y. 170 Inglis T. 154,213 Ioganson A. A. 198 Isbe S. D. A. 157 Ishaq M. 180 Ishigino M. 187 Ishii Y. 170 Ishikawa M. 187 Ishizu K. 178 Isred S. S. 166 Ito T. 196 Itoh K. 170 Ittel S. D. 176 Ivanov D. 197 Ivanov L. L. 195 Izatt R. M. 140 Jablonski C. R. 210 Jack T. R. 217 Jackson R. A, 200 Jackson W. G. 173,203 Jacobson S. E. 175 Jaecker J. A. 161 Jahnig F. 62 Jaenicke O. 179 Janik J. A. 47 Janik J. M. 47 Jaouen G.191 Jarkowitz D. 150 Jarvis J. A. J. 217 Jaworiwsky I. S. 98 Jefferson I. 184 Jeffery J. W. 114 Jellinek F. 184 Jen S. 34 Jenks J. M. 142 Jennische P. 118 Jensen F. R. 185 Job R. G. 165 Joblin K. N. 198 Johns W. S. 210 Johnson A. W. 198 Johnson B. F. G. 175 201 Johnson D. L. 39 Johnson F. A. 105 Johnson H. D. jun. 98 Johnson M. H. 75 Johnson R. C. 78 Johnson W. B. 152 Joklik J. 197 Jolly W. L. 151 Jonas K. 194 Jones C. J. 101 Jones G. H. 137 Jones J. 29 Jones J. T. 75 Jones M. 187 Jones T. E. 178 Joy G. 118 Kabre T. S. 118 Kadooka M.M. 178 Kagan H. B. 171 Kalasinsky V. F. 11 1 Kalbfus W. 181 Kamha M. A. 70 Karninsky W. 196 Kaneko S.68 Kapon M. 143 Kapoor P. N. 153 Kaptein R. 70 Kapur R. N. 67 Karakida T. 153 Karsch H. H. 212 Kasai P. H. 180 Katoric V. 155 Katz J. J. 193 Keeton M. 217 Keiderling T. A. 150 Kelling H. 190 Kellogg R. E. 80 Kembler M. 176 Kemmitt R. D. W. 184 Kendurkar P. S. 190 Kennelly W. J. 100 Kepert D. L. 150 154 Kesthelyi C. P. 85 Ketterson J. B. 56 Keulen E. 123 Keyes P. H. 63 Keyes T. 25 Khaddar M. R. 115 Khan M. T. 172 Khane G. P. 168 Khotsianova T. L. 152 Kidd D. R. 203 Kiefer G. W. 158 Kielich S. 17 Kiener V. 181 Kiernan P. M. 149 Kiffen A. A. 175 176 Kilgour J. A. 187 188 Kilner M.,154 213 Kilty P. A. 152 Kirnura E. 170 King M.S. 152 King,R. B. 153,214 Kingston B. M. 180 Kirner J. K. 159 Kivelson D. 25 Klabunde K. J. 179 Kleier D. A. 96 Klein H. F. 212 Kleine W. 181 KICman M. 63 64 Klemperer W. 77 Klinger R.J. 155 196 Knobler C. B. 105 Knol J. 184 Knowles W. S. 171 KO D. 130 Kobayashi A. 208 Koch S. 164 Kochi J. K. 211 Kodarna H. 153 Koerner von Gustorf E. A. 179 Kohler F. H. 190 Kolari H. J. 154 Kolb J. R. 100 151 183 196 Kolobova N. E. 198 Kolosov E. E. 68 Korn C. 58 Kouba J. 159 Kovar R. A. 112 Kozima S. 108 Kramer A. V. 211 Kramer P. A. 176 Krause A. 67 Krausz P. 193 Krebs P. 32 39 Kreis G. 181 Kreissl F. R. 181 Kreiter C. G. 181 Krishnamurthy S.S. 132 Krishnamurti D. 33 Krogsrund S. 176 Kroneck P. 178 Kroto H. W. 111 Kruchna O. 197 Krunynski L. 201 Kruger C. 206 Kruger G. J. 41 Kruglaya 0.A. 183 Kubarev S. I. 75 Kubo R. 9 Kubota M. 171 Kuchitsu K. 153 Kuczkowski R. L. 111 Kunynski W. 33 Kundig E. P. 198 199 Kugel R. L. 132 Kuhn N. 132 Kumada M. 187 Kurernire E. M. R. 167 Kuroda R. 118 Kurras E. 190 Kushick J. 34 Kuznesof P. M. 111 Kuznetsov S. L. 152 Kyper J. 178 226 Author Index Labarre J. F. 112 Labert R. L. 187 Labes M. M. 40,41 Labhart H. 86 Labinger J. A. 185 196 Lachowitz A. 196 LaCour T. 186 Lagerwall S. T. 60 Lagow R. J. 180 Lagowski J. J. 179 Laguna A, 214,218 Lahuerta P.201 Laidler D. A. 43 137 Laing M. 169 Lakshmikanthan M. V. 141 Lambert T. P. 77 Lang. G. 162 Langbein H. 153 Lappert M. F. 108 111 115 124 127 151 180 181 182 192,193 Larcher F.,191 Larkin I. 44 Larkin I. W. 19 Larson S. B. 140 Lascombe J. 25 Laskowski E. J. 177 Lathouwers Th. W. 60 Laurie S. H. 178 Lawler R. 70 Leadbetter A. J. 42 Leblanc J. C. 150 191 Le Blanc M. 195 Lechert H. 120 Lechner R. E. 46 Leclerc B. 118 Lednor. P. W. 198 Ledwith D. A. 158 Lkger L. 53 60 Legg J. I. 169 Lehmann T. V. 108 Lehn J. M.,139 Leigh G. J. 157,193 Lemley J. T. 142 Le Moigne F. 150 191 Leshina T. V. 70 Lesin B. I. 78 Letsou A. 130 Leung.M.L. 192 Levason W. 172 Levenson R. A. 137 Levesque D. 14 15 Levine. Y. K. 37 Levy D. H. 77 Lewis B. 216 Lewis D. F. 150 Lewis D. L. 196 Lewis J. 175 201 203 Leyden R. N. 99 108 Liebert L. 37 Lightowlers D. 37 Lin H. S. 168 Lin W. J. 63 Lindmark A. F. 152 Lindon J. C. 35 37 Lindsell W. E. 195 Lindstrom R.H. 132 Lippard S. J. 99 150 196 Lipscomb W. N. 96 Litovitz T. A. 24 25 27 Litster J. D. 32 Little R.G. 163 Litzow M. R. 11 1 Liu C. 140 Lloyd M. K. 215 216 Lo F. Y. 106 Lo S. T. D. 173 Loayza N. 141 Lockhart S.H. 120 Loescher B. R. 156 Lohr L. L. 184 Long M. A. 172 Longini G. 205 Longuet-Higgins H. C. 9 Lopata V.J. 75 Lorenz H. 130 181 Lottes K.151 Lovesey S. W. 9 Lower L. D. 205 Lowie. C. M. 170 Lowry B. A. 49,56 Lubensky T. C. 63 65 Luckhurst G. R. 34 35 37. 39,44 Lukosius E. J. 173 Lund T. 178 Lunsford J. H. 168 171 Lusk D. I. 180 Lusztyk J. 195 Luz Z. 40 Luzar M. 40,41 Mabbott D. J. 218 Mabbs F. E. 158 McCafirey D. J. A. 203 McCarley R. E. 152 155 McCauliffe C. A. 172 McClung R. E. D. 19 McColl J. R. 34 39 MacDiarmid A. G. 142 McDonald J. W. 159 McFarlane H. C. E. 129 McFarlane W. 129 McGee H. A. jun. 112 McGinnis J. 193 McGlinchey M. J. 120 179 Machin D. J. 177 McIntyre D. 13 McKee T. J. 39 MacKenzie R. 214 McLauchlan K. A. 72,81 McLaughlin G. M. 180 McLendon G. 169 McLeod D.180 McLeod T. 175 McLick J. 188 McMillan W. L. 40 62 McNelis E.. 193 McQueen D. H. 56 McQuillin F. J. 92 McTague J. P. 25 McVicker E. M. 129 McVicker G. B. 194 Madan V.,185 Maeda K. 174 Magee J. L. 77 Magelee L. A. 188 Maier M. 111 Maitlis P. M. 208 218 Malet G. 54 Malmberg M. S. 29 Mal’tsev A. 192 Manassero M. 205 Mango F. D. 193 Maniantov G. 145 Mannan K. 132 Manne R. 115 Manning A. R. 196 Manojlovic-Muir Lj. 175 Mantovani A. 210 Maranelli R. S. 160 MarEelja S.,36 March F. C. 157 17 1 Marcieniec B. 67 Marek H. 68 Mares F. 183 Margerum D. W. 177 Marignan J. 54 Markarian Sh. A. 70 Marks S. B. 58 Marks,T. J. 100,151,183,196 Marquardt G.188 Marryot A. A. 29 Marsh R. E. 168 Marshall W. 9 Marsili M. 130 Marstokk K. M. 195 Martell A. E. 169 172 Martin J. L. 149 Martin R. B. 178 Martin R. L. 170 177 Martinengo S. 203,205 Martinoty P.,47 Martire D. E. 33 Maslen H. S. 160 178 Mason R. 157 171 174 186 217 Masood-ul-Hasan 132 Masters C. 175 176 Masuda I.. 160 Matheson K. L. 140 Matheson T. W. 201,203 Mathew M. 175 Mathews N. J. 110 Mathur K. N. 67 Matsuda I. 170 Matsuzaki A. 78 Matteson D. S.,188. 197 Matushita T. 160 Maugh T. H. 162 May C. J. 217 Mayerle J. J. 165 Author Index 227 Mays M.J. 194 Maze C. 39 Mazzei A. 116 Mealli C. 172 Meek D. W. 174 Mehrotra R.C. 153 Mehrotra S. K. 153 Meiboom S.. 40,50 Mein F.. 194 Melamud E. 168 Melson G. A. 173 Meneghelli B. J. 101 Menig H. 186 Mennenger H. 190 Mente D. C. 111 127 Mentzer E. 100 Merbach E. 151 Mercer G. D. 101 Merdak S. J. 176 Merrell P. H. 173 Merrifield R. E. 67 78.80 Merryman D. J. 123 Mertis K. 183 208 209 Meshitsuka S. 158 Meyer A. 191 Meyer R. B. 53 Meyer R. J. 40 Meyer T. J. 200 Michalik M. 190 Michalski J. 135 Middleton R. 179 Midollini S. 172,208 Mikotajaak J. 135 Mikulski C. M. 142 Millar M. 174 Miller E. 67 Miller J. R. 201 Miller J. S. 175 206 Miller V. R. 101 Millington. D. 175 Mills J. L. 111 123 127 198 Milone L. 203 Mircea-Roussel A.43,44 Mishima T. 88 Mishra S. P. 127 Miskowski V. M. 168 Mislow K. 188 Mitsui Y. 170 Miyano K. 56 Mocella M. T. 173 174 Modinos A. 175 206 Mohwald H. 39 Moelendal H. 195 Mohai B. 197 Moise C. 150 191 Mol J. C. 193 Molia Yu. N. 70 Mollere P. D. 187 Mondal P. 114 Moneland J. A. 177 Montanari F. 138 Monteil Y. 123 Moody D. C. 97 Moore G. Y. 132 Moore R. D. 184 Moorehead E. L. 158 Morazzoni F.. 171 Moreau J. J. E. 191 Mori H.,9 Moritani I. 174 Moriyama H. 208 Moroi D. S. 42 Morrell D. G. 211 Morrison J. A. 180 Morse J. G. 174 Morse K. W. 174 Mortensen L. E. 165 166 Moskovits M. 199 MOSS,K. L. 175 MOSS,T. H. 166 Moulijn J. A.193 Moutron R. 39 Muller H.-D. 130 Muller J. 181 182 186 Muller W. 123 Miinster A. 10 Muetterties E. L. 96 Muhr G. 68 Muir K. W. 159 175 Mulay I. L. 68 Mulay L. N. 68 Munroe S. E. 56 Murakashi S. I. 174 Murray K. S. 170 Murray M. 214 Murray S. G. 172 Murrell J. N. 75 Murtha D. P. 161 Murthy A. R. V. 132 Musatti A, 173 Musco A. 183 Muscutariu I. 56 Muttner G. 156 Myers E. 108 Nabi S. N. 132 Nagai S. 47 Nagakura S. 78 88 Naghizadeh J. 15 Naik D. V.,204 Nainan K. C. 153 Nakajima M. 208 Nakayama H. 118 Naldini L.. 205 Nametkin N. S. 188 Napoletano T. 171 Nardelli N. 173 Nardi N. 172 Nefedov 0.M. 192 Nehring J. 65 Neumann F. 116 Newkome G.R. 129 Newton W. E. 159 Nicholson B. K. 198 Nickerson M. A. 58 Nicolini M. 152 Niecke E. 112 Nielsen S. E. 70 Nien T. 174 Nishikida K.,145 Nisselson L. A. 152 Noack F. 58 Nolte M. J. 169 Nordio P. L. 35,43 Norman A. D. 120 Norman J. G. 154 Norman T. R. 166 Norton J. R. 175 Novak R. W. 105 Nyburg S. C. 217 Oakley R. T. 132 Ochs J. 190 Odom J. D. 110 111 129 Oehme G. 190 Ogata I. 171 Ogden J. S. 179 Ohi F. 187 Oliver A. J. 208 Oliver J. P. 194 On P. 188 Onak T. 92 O’Neal H. E.,119 O’Neill P. S. 196 Opitz R. 197 Oppenheim E. 39 Orbell J. D. 169 Orioli P. L. 172 Ornstein L. S. 10 Osborn J. A. 211 Osthurd N. S.,144 Otnes K. 47 Overzet F.184 &in. G. A. 198 199 Paddock N. L. 132 Paik H. N. 214 Palenik G. J. 175 204 Pamphilis B. V. 165 Panaiotiev I. 197 Paningo E. B. 177 Pardoe G. W. F. 21 Parish R. V. 172 Parker C. A. 83 Parker G. 206 Parodi O. 54 Parry G. 93,94,95 Parsons J. D. 56 60 Pascard C. 206 Pasinskii A. A. 198 Pasteur G. A.,153 Patel H. A. 204 Patel V. V.,141 Patil D. S. 192 Pattison P. 96 Paul I. C. 173 Paz-Andrade I. M. 192 Pearce. R. 182 Peannan A. J. 156 Pedersen C. T. 141 Pedersen E. 154 161 228 Author Index Pedersen S. G. 116 Pederson S. W. 194 Pedley J. B. 111 115 127 151,192 Peguy A. A. 115 Pell S. D. 167 Penka V. 69 Penney G. J.123 Penney T. 141 Penz P. A. 60 Perego G. 116 Perisamy N. 83 87 Perrin D. D. 178 Perrot M. 25 Pershan P. S. 34 64 Pessine F. B. T. 111 Pettit L. D. 178 Philips D. A. 171 Phillips W. D. 165 Piciulo P. L. 161 Pierce-Butler M. 126 Piersanski P. 49 53 55,60 Pikin S. A. 60 Pilbrow M. F. 217 Pindak R. S. 63 Pines A. 37 Pink D. A. 36 Pinnavaia T. J. 149 Pinnow D. A. 24 PirS J. 40 4 1 Pittman C. U. jun. 218 Pitzer K. S. 148 Plesek J. 97 Plummer J. F. 152 174 Pluth J. J. 168 Podolsky G. 149 Po&,A. J. 198 200 Poggi Y. 33 Poldy F. 37 Polichnowski S. W. 197 Polnaszek C. F. 45 Pompeiro A. J. L. 159 Pong R. G. S. 115 Poolton. D. S. P. 152 Pople J.A. 96 Popowski E. 190 Porter R. F. 112 Poskozim P. S. 170 Poulin J. C. 171 Poupko R. 34,39 Powell J. 217 Powles J. G. 13 14 28 29 Prabha C. S. 33 Pregosin P. S. 210 Preut H. 116 Price A. G. 17 Price A. H. 39,43 Priestley E. B. 32 34 Pritzkow H. 118 Prost J. 64 Prout C. 194 Prout K. 184 Pshenichnov E. A. 75 Puddephatt R. J. 212 Pulham R. J. 93 94 95 Pusatcioglu S. 112 Pye P. L. 181 Que L. 165 Quentrec B. 14 18 Quinn M. J. 75 Rahman A. 14 Rakowski M. C. 207 Ranchfuss B. 174 Randall E. W. 203 Ranganathan J. N. 132 Rao K. R. 16 Rapini A. 56 Rasmussen J. R. 185 Raston C. L. 150 Rathousky J. 197 Rault J. 54 Rausch M. D. 184 Raymond K. N. 168 183 Raymond L.176 Reade W. 110 Reed C. A. 159 162 Reeves W. B. 68 Rega H. U. 39 Reichert W. 155 Reinsch E. A. 70 Remmel R. J. 98 Restivo R. J. 173 Reynolds R. 39 Rhee S. G. 116 Rhine W. E. 194 Rice S. A. 15 Richards R. L. 152 156 159 Richter F. 68 Riddle C. 120 Riedel E. F. 145 Rieger P. H. 154 Riess J. G. 153 195 Rietz R. R. 151 Rigatti G. 43 Rigny P. 28 Riley P. N. K. 111 Ring M.A. 119 Rivail J. L. 21 Robbins J. L. 168 Robert J. 33 Roberts J. D. 201 Roberts P. J. 170 Robinson B. H. 203 Robinson P. R. 158 Robinson S. D. 170 Robinson W. R. 116 161 Robinson W. T. 106 162 Rodesiler P. F. 195 Rondelez F. 40,43,44 60 Root C. A. 170 Rorabacker D.B.,178 RoSciszewski K. 42,46,47 Rosenberg. E. 201,203 Rosenberg R. C. 170 178 Rosenthal I. 67 Rosenthal U. 190 Ross S. D. 125 Rossi M. 207 Rost C. A. 178 Rothgery E. F. 112 Rothschild A. J. 187 Roundhill D. M. 174 Routledge V. I. 158 Rowley R. J. 212 Rowlinson J. S. 6 Royl q.,191 Royston G. M. D. 159 Ruben D. J. 37 Rubini P. R. 115 Rudolph R. W. 101 Rumyantsev B. M. 78 Rupprecht G. 161 Rushbrooke G. S. 6 10 Rusin B. M. 78 Russek A. 197 Russell D. R. 217 Russo. P. J. 142 Rutar V. 58 Sabachy M. J. 171 Sacco A. 207 Sacconi L. 172 173,208 Sachsse H. 69 Sackmann E. 32,39 Sagdeev R. 70 Sahajpal A. 170 St. Pierre A. G. 25 Saito T. 208 Saito Y.118 Sakuragi H. 88 Sakuragi M. 88 Salentine C. G. 96 101 105 Salikhov K. M. 70 Sanders J. R. 176 Sansoni M. 205 Santhanam K.S. V. 83,87 Santini G. 195 Saran M. S. 142 Sargent F. P. 75 Sargeson A. M.,167 171 Sasaki Y.,208 Sato S, 118 Sau A. C. 132 Sauer J. D. 129 Saupe A. 65 Savoie R. 127 Schaaf. T. F. 151 Schack. C. J. 127 Schaefer W. P. 168 Schaeffer R. 97 120 Scheidt W. R. 159 161 Scherr V. M. 112 Scherrer 0.J. 132 Schleyer P. von R.,Y6 Schmalfuss,S. 153 Schmid H-G. 130 Schmidbaur H. 190,212 Schmidpeter K. H. 151 Schmidt. H. 68 Schmiedenknecht K. 194 Author Index Schmutz J. L. 132 Schofield P.,9 Scholer F. R. 101 Schram E. P.,152 174 Ghraml J.197 Schrauzer G. N. 157 158 Schrieke R. R. 194 Schrobilgen G. J. 147 Schrock R. R. 180,182,196 Schroeder S. 196 Schrymowyn L. A. 178 Schubert V. 181 Schug K. 167 Schultz F. A. 158 Schwab G. M. 69 Schwartz J. 185,196 Schwendeman R. H. 111 Scoins H. I. 10 Scott B. A. 141 Searle H. T. 132 Self K. 178 Segre U. 35,43 Seibert W. E. 185 Seider P.G. 141 Sellmann D. 156 157 Selwood P.W. 67 Sengers J. V. 13 Senior R. G. 155 Senoff C. V.. 170 Serafini A. 112 Sernin G. K. 152 Setaka M. 34 Sette D. 14 Seuftleber F. C. 175 Seyer J. V.,130 Seyferth D. 187 Shah S. J. 87 Sharavski P. V. 68 Sharp D. W. A. 175 186 Sharp G. J. 115,151 Sharstad P.M.194 Shashidhar R. 63 Shaw B. L. 100 171 197 Shaw R. A. 132 Shchelokov R.N. 183 Shchembelov G. A. 188 Shchukarev A. N. 68 Sheahan R. M. 170 Shein S. M. 70 Sheldrick G. M. 123 Shen Q. 126 Shenav H. 120 Sheng P.,32 Shepherd R. E. 166 Sherwood R. C. 153 Shih C. S. 34 Shilov A. E. 176 Shimp L. A. 180 Shinra K. 160 Shirk A. E. 115 Shirk J. S. 115 Shive L. 155 Shive L. W. 161 Shomo T. 160 Shooter D. 69 Shore S. G. 98 Shriver D. F.. 111 118 Shteinman A. A. 176 Shu P.,108 Sigurdson E. 183,208 Sillescu H. 29 Silver B. L. 168 Silver J. 125 Silvon M. P.,179 Simonneaux G. 191 Simpson P. 135 Simpson S. K. 179 Singh A. 75 Singh B. 195 Singhal V.K. 56 Singleton E. 169 Sinn E. 173 177 Sinn H. 196 Skell P.S. 179 Skinner H. A. 192 Skowrhska A. 135 Sligar S. G. 163 Slutsky J. 187 Smart L. E. 218 Smith I. W. 60 Smith J. D. 116 194 197 Smith J. S. 140 Smith L. R. 198,218 Smith M. A. R. 175 Smyrst N. 145 Snow M. R. 166 Snowden B. S. 29 Solarz R. 77 Solomon E. I. 177 Sommer L. H. 188 Sorrel] T. N. 164 Spalding T. R. 111 Sparrow G. J. 166 Spencer J. L. 106 214 218 Spiesecke J. 41 Spiro T. G. 150 166 168 Springer T. 41 Spruijt A. M. J. 54 Squires R. T. 37 Stachnik R. A. 115 Stannislowski A. G. 186 Starks D. F. 183 Starowieyski K. B. 195 Stec W. J. 135 Steele W. A. 25 Steer I. A. 110 Stein L.145 Steinfeld J. I. 77 Steinfink H. 142 Stelzer O. 127 Stephen M. J. 32 Stephens F. S. 201 Stevens B. 86 Stevens J. R. 156 Stiffen W. L. 175 Stilbs P. 111 Stillinger F. H. 14 Stobart S. R.. 120,192 Stoddart J. F. 137 Stofko J. J. jun. 217 Stohrer M. 58 Stoicheff S. P.,25 Stone F. G. A. 105 106 186 214,216,218 Stone K. 184 Stonfer R. C. 174 Stoppioni P.,172 Straley J. P.,32 35 Stratton C. 132 Strauss H. L. 13 Streitwieser A. 183 Strekas T. C. 168 Strom E. T. 29 Strouse C. E. 105 106 Strumolo D. 205 Stryta B. 33 Strzelecki L. 37 Stucky G.. 194 Stults B. R. 155 160 Su L. S. 129 Subramhanyan H. S. 33 Sudot T. 135 Sugiura V. 178 Sullivan B.P. 99 Sullivan J. C. 170 Summerford J. W. 49 Suna A. 80.88 Sundberg R. J. 166 Suslick K. S. 162 Susuki H. 158 Symons. M. C. R. 127 Tabashima T. 158 Tachikawa H. 85 86 87 Tachiyashiki S. 118 Takats J. 149 Tamaka H. 178 Tamas J. 192 Tameo K. 187 Tan T.-S. 120 Tanaka J. 75 Tanaka M. 171 Tang S. C. 164. 170 174 Tang S.-P. W. 166 Tag Wong K. L. 184 Tanimoto Y.,88 Tano K. 158 Tarr C. E. 58 Tasset E. L. 160 Tatsumi T. 159 Taube H. 154,166 Taupin C. 37 Taylor B. F. 106 Taylor D. 170 177 Taylor K.R. 152 Taylor L. T. 168 Taylor M. J. 92 Taylor N. J. 174 Taylor P.,147 Taylor R. C. 111 Taylor S. H. 215 Tehan F. J. 123 230 Author Index Temme F.P. 42 Temperley H.N.V. 6 Templeton J. L. 155 Terinissi P. A. 178 Tewari R. S. 190 Thiele K. H.,196 197 Thirase G. 120 Thomas J. L. 184 Thomas K. M.,157 171 186 Tietz M. 153 Timko J. M.,138 Timms. P. L. 105 120 179 Tirouflet J. 150 191 Todd L. J. 97 Todd S.M.,132 Topler J. 41 Tofield B.C. 153 Tokel-Takvoryan N. E. 85 Tokumaru K. 88 Tomchuk E.,35 Tomlinson C. H. 179 Torza S.,55 63 Tossell J. A. 114 Towl A. D. C.,203 Tracey A. S.,35 Traylor T. G. 162 Treitel 1. M.,168 Tretyakova K. V. 152 Tribo. M. 101 TrigweIL K.R. 150 Trofter,J 132 Troup J. M.,155 204 Tsutsui M. 183 Tuck D. G. 117 Tucker N. L. 197 Tulinsky A. 149 Tundo P.138 Tune D. 206 Turner C. K. 206 Turner K. 180 181 Turner L. A. 77 Turner R. 53 Turney T. W. 214 "weedale A. 111 Tyabin M. B. 176 Tyler J. K. 130 Uchida Y. 159 Ueda F. 170 Ugo R. 176 Ulmer S. W. 194 Unger E. 127 Upton C. E. E. 212 Ustynyuk Yu. A. 188 Uznhki B.,135 Vaira M. D. 173 Van Dam E. M.,179 Van der Wal H. R. 184 Vanderwielen A. J. 119 van Hove L. 12 Van Konynenburg P. 25 Van Oven H. O. 184 Van Tamelen E. E. 156 Van Vliet P. I. 178 Van Willigen H. 75 Vaughn W. E. 17 Vasapollo G. 207 Vasilev G. 197 Vdovin V. M. 188 Venanzi L. M. 210 Verkade J. G. 127 Verlet L. 15 Vickney T. M. 158 Vidal M. 11 1 Vieillard-Baron J. 33 Vilfan M. 58 Vincent H.123 Vineyard B. D. 171 Virlet J. 28 Visintainer J. J. 35 Visser J. P.,175 Vitagliano A. 178 Voitlander J. 69 Volino F. 46 Vollmer H. J. 196 Volterra V. 24 von Schnering H. G. 123 Voronkov M. G. 190 Vos A. 123 Voss J. 39 Vrieze K.,178 Vyazankin N. S. 183 Waddington T. C. 174 Wade K.,99 126 Wagner B. O. 195 Wagner F. 173 Wagner R. I. 127 Wainwright T. E. 14 16 Waldvogle G. G. 112 Walker F. A. 151 Walker J. M. 151 Walker M. L. 123 Walker R. 175 183 Wallbridge M.G. H. 96 Walser R. 159 Walton D. R. M. 190 197 Walton R. A. 151 161 Ward I. M.,99 Warner L. G. 178 Wasserman E. 77 Watanabe J. 170 Watanabe S. 88 Waters J. H. 177 Waters T.N. 160 178 Watkiss P. J. 125 Webb T. R. 154 Webster D. E. 176 Wegner P. P. 106 Weiker J. F. 165 Weil T. A. 210 Weinkauf J. 171 Weir J. R. 150 Weiser J. D. 97 Weiss E.,1'20 195 Weiss K.,142 181 Weiss R. 41 Weisshaar E. 68 Welch A. J. 106 186. 216 Welker H. 68 Weller A. 86 Wells P. B. 176 Wells P. R. 119 Werner H. 206 Weschler C. J. 160 163 West B. O. 170 Westerhof. A. 184 Westland A. D. 152 Westley J. W. 140 Weston A. F. 112 Weston H. T. 63 Westwood N. P. C. 115 Wetsel G. C. 56 Wharf I. 118 Wherland S. 178 White A. H. 150 White A. J. 201 White C. 208 White W. I. 169 Whiteley R. N. 156 180 Whitesides G. M. 185 Whittingham. A. C. 94 Whyman R.217 Wiersma R. J. 101 Wigner E. P. 69 Wilcsek R. J. 187 Wilkins B. T. 127 Wilkins G. J. 126 Wilkins J. D. 149 152 Wilkinson G. 183 208 209 212 Willet R. D. 145 Willey G. R. 126 Williams C. 53 Williams C. E. 63 Williams F. 145 Williamson D. H. 209 Williams-Smith D. L. 179 Wilmarth W. K. 69 Wilson R. D. 127 145 Windhorst K.A. 171 Winkler E. 181 Wittel K. 115 Wolfel W. 58 Woessner D. E. 29 Wojtowicz P. J. 32 Wolf A. D. 187 Wolf L. K.,179 Wolfbeis 0.. 179 Wolfgang R. 190 Wong C. S. 210 Wong C. w. 2f0 Wong Y. S. 214 Wood R. H. 115 Wood W. W. 14 Woods M. 170 Woods M. 132 Woodward M.R. 56 Author Index Woodward P. 175 206 215 Yamaoka S.142 Zana R. 47 Wozniak W. T. 150 Wreford S. S. 150 Wrighton M. S. 155 196.199 Wulf A. 40 Wurrey C. J. 129 Wyllie G. 18 Wyrsch D. 86 216 Yarno T. 160 Yee S. 159 Yo F. Y. 105 Young D. 179 Young G. B. 211 Younger D. 174 Yun C. K. 40 Zanella A. W. 171 Zannoni C. 34,35,44 Zarella A. W. 167 Zavizion Y. S. 195 Zav’yalov V-I. 188 Zeldin M. 124 190 Zernike F. 10 Zimmer L. C. 178 Yakel H. L. 113 Zachariasse K. 86 Zack N. R. 174 Gintl E. 123 Zumur S. 40 Yamamoto A. 196 Yamamoto Y. 190 Zakharkin L. I. 195 Zakharov P. I. 188 ZupantiE I. 40 41 Zwanzig R. 9 16 23 1

ISSN:0308-6003    

DOI:10.1039/PR9757200221

出版商:RSC    

年代:1975

数据来源: RSC