6 Organometallic Chemistry Part (i) The Transition Elements By R. PEARCE D. J. THOMPSONf and M. V. TWlGG ICI Corporate Laboratory PO Box 1 I The Heath Runcorn Cheshire WA7 4QE As before we concentrate on applications of organo-transition-metal species in organic synthesis an area for which the recent literature has been reviewed.’ A major section is devoted to olefin metathesis the mechanism of which has been the subject of a remarkable number of publications. This shows strong parallels with the flood of publications in the early 1970’s on metal-catalysed skeletal isomerization which has now subsided and for which we report no major advances in 1976. Reports of reactions involving metal cluster compounds (Section 5) have increased and this appears to be a growth area for the future.1 Metal-catalysed Hydrogenation and Hydrogen-transfer Reactions In metal-catalysed asymmetric synthesis it is now accepted that the matching of ligand to substrate plays a vital part in the optimization of optical yields.’ In this matching additional constraints within the transition state arising from an interac- tion between the ligand and substrate can have a marked and beneficial effect. This is demonstrated in reports on the hydrogenation of ketones and a -acylamido-acrylic acids and the cross-coupling of Grignard reagents with alkenyl halides which involve the ferrocenyl-phosphines (1)and (2) as ligand~.~ Q’”’2 @Z CHMeX R (1) a; X=OH (2) a; R=CHMeNMez b; X = NMe b; R = CH2NMe2 c; X=H c; R=Et Thus in the Rh’-catalysed hydrogenation of pyruvic to lactic acid the hydroxyl- containing compound (la) gave optical yields in the range 59-83% whereas (lc) which contains no polar functional group (other than the tertiary phosphines) that can interact with the carbonyl group in the pyruvic acid gave only 16?40.~* In the A.P. Kozikowski and H. F. Wetter Synthesis 1976,561; ‘Transition Metal Organometallics in Organic Synthesis’ ed. H. Alper Academic Press New York 1976 Vol. 1. * For a review of asymmetric hydrogenation see J. D. Morrison W. F. Masler and M. K. Neuberg Catalysis Rev. 1976 25 81. (a)T. Hayashi T. Mise and M. Kumada TetrahedronLetters 1976,4351; (b)T. Hayashi T. Mise S. Mitachi K. Yamamoto and M. Kumada ibid. p. 1133; (c) T. Hayashi M. Tajika K. Tamao and M.Kumada J. Amer. Chern.Soc. 1976,98,3718. 99 100 R. Pearce D.J. Thompson andM. V.Twigg hydrogenation of a range of ketones optical yields using (la) compare favourably with the alternative procedure of hydr~silylation,~ and are superior to those obtained with DIOP or chiral monophosphines R'R2R3P. In the hydrogenation of the amido-acrylic acids the NMen-substituted (1 b) performed similarly to DIOP.3b In the Nil1-catalysed cross-coupling of a! -phenylethylmagnesium halide with vinyl bromide optical yields in the range 52-63% using the dimethylamino-substituted monophosphines (2a) or (2b) as ligand are markedly better than those with the chelating diphosphine DIOP (7-13%) or with the related (2c) (4%) where interaction with the magnesium of the Grignard reagent is pre~luded.~" The role of the elements of chirality in the ligand in determining asymmetric induction could be examined by comparing (2a) and (2b).The similarities in the optical yields indicated that the planar (ferrocene residue) rather than the central (Rgroup) element was dominant. It may have been expected naively that enantiomerically related ligands would give products differing only in the sign of their optical rotation. Studies on the epimeric neomenthyldiphenylphosphine(NMDPP) and menthyldiphenylphosphine (MDPP) show otherwise. In combination with [Rh(diene)Cl] in the hydrogenation of a-methylcinnamic acid NMDPP gave both a more active catalyst and a higher enantiomeric excess [6O% (R) versus 17% (S)for MDPP].' Conformational factors appear to be responsible.In the search for new chiral ligands reports have included the chelating diamine (3) obtained from a -phenylethylamine," and the sulphoxides R'R2S0.66 Whereas in the Rh'-catalysed hydrogenation of a-acylamido-acrylic acids the ligand (3) behaves similarly to DIOP results with a range of sulphoxides were far from encouraging. PhCHMe PhCHMe (3) The attachment of metal centres to cross-linked resins (heterogenized catalysts) offers many advantages in the ease of catalyst recovery but still poses a number of problems. Conventional resins which swell in non-polar solvents collapse in polar media and are thus unsuitable for use in the hydrogenation of a -acylamido-acrylic acids. To overcome this a new resin has been prepared which is based on a lightly cross-linked hydroxyethyl methacrylate backbone that contains ca.8% of styrene units modified by attachment of a DIOP residue. With Rh'its performance parallels For full details see I. Ojirna,T. Kogure M. Kurnagai S. Horiuchi and T. Sato J. Organometallic Chem. 1976,122,83. 5 A. M. Aguiar C. J. Morrow J. D. Morrison R. E. Burnett W. F. Masler and N. S. Bhacca,J. Org. Chem. 1976,41 1545. (a) M. Fiorini G.M. Giongo F. Marcati and W. Marconi J. Mol. Catalysis 1976,1,45 1; (6) B. R. James R. S. McMillan and K. J. Reimer ibid. p. 439. Organometallic Chemistry -Part (i) The Transition Elements 101 homogeneous DIOP-containing system^.^ Rhodium(1) supported on the novel 2,3- O-bis(diphenylphosphino)-6-O-triphenylmethylcellulose effects stereoselective hydrogenation of 2-phenylbut-1-ene in up to 77% optical yield.This remarkable selectivity with a relatively simple olefin contrasts with the poor optical yield of 17.5% when a!-acetamidocinnamic acid was substrate and emphasizes the need for a careful match of ligand and substrate in the design of asymmetric syntheses.* A surprising improvement in the activity of silica-supported Rh' complexes has been achieved by treatment of silica with a silicone ladder polymer that was subsequently modified via incorporation of organophosphine gro~ps.~ The turnover number with the catalyst was 28 times greater than that obtained with the (Et0)3SiCH2CH2PPh2-modified silica catalyst previously reported by the B.P.Group again highlighting the inadequacy of our knowledge of the role of (modified) inorganic supports in determining catalytic activity. A highly regioselective partial reduction of substituted cyclic anhydrides (e.g. 2,2-dimethylsuccinic anhydride) to y-lactones has been achieved using RuC~~(PP~~)~ as catalyst. lo Hydrogenation occurs at the least hindered carbonyl group contrasting with the reduction with LiA1H4 which affects the more hindered one. Novel catalyst systems have included CoBr(PPh3),/BF3,0Et2,' la which selec- tively hydrogenates conjugated dienes to monoenes via 1,2-hydrogen addition at the more substituted double bond and the Fe(CO)5-photocatalysed system,' lb which complements earlier work on chromium carbonyls.Reactions involving synthesis gas as a chemical feedstock are likely to command increasing attention. In this context it is interesting to report the stoicheiometric production of methoxide ion by bis(pentamethylcyclopentadienyI)zirconium12a(cf. reactions of metal clusters that give methane and ethanediol). Metal formyl inter- mediates are implicated in this reaction (cf. Ref. 126). Transition-metal stearates (Tulupov catalysts) have been the subjects of a number of papers and reviews. In particular homogeneous hydrogenation of aromatics has been claimed. However a recent investigation shows that all is not well they showed neither the reported solubility in ethanol nor were they active in cyclohexene hydr~genation,'~" results confirmed by other workers.13' Monosaccharides are effective donors in Ru"-catalysed [e.g.RuC~~(PP~~)~] trans-fer hydrogenation of a,P -unsaturated ketones. l4 With prochiral substrates asym- metric induction is observed with optical yields up to 34% using 1,2-isopropylidene- a!-D-glucofuranoside as donor. This is the first example of asymmetric transfer hydrogenation. Monosaccharides and related compounds offer a range of readily available optically pure materials that appear to have been largely neglected both as donors and as ligands in asymmetric synthesis (cf.Ref. 8). N. Takaishi H. Imai C. A. Bertelo and J. K. Stille J. Amer. Chem. Soc.,1976 98 5400. Y. Kawabata M. Tanaka and I. Ogata Chem. Letters 1976 1213. J. Conan K. Bartholin and A. Guyot J. Mol.Catalysis 1976 1 375. lo P. Morand and M. Kayser J.C.S. Chem. Comm. 1976 314. l1 (a)K. Kawakami T. Mizoroki and A. Ozaki Chem. Letters 1976,847; (b)M. A. Schroeder and M. S. Wrighton J. Amer. Chem. Soc.,1976,98 551. I* (a)J. M. Manriquez D. R. McAllister R. D. Sanner and J. E. Bercaw J. Amer. Chem. Soc.,1976,98 6733. (b)C. P. Casey and S. M. Neumann ibid. p. 5395. l3 (a)J. W.Larsen and L. W. Chang J. Org. Chem. 1976,41,3332; (b)D. J. Thompson unpublished work. l4 G. Descotes and D. Sinou Tetrahedron Letters 1976 4083. 102 R.Pearce D.J. Thompson,andM. V.Twigg Noble metal salts (e.g.RhCl,) catalyse the homogeneous transfer hydrogenation of aromatic nitro-compounds to aromatic amines. lSQ Indoline was the hydrogen donor. Comparable results have been obtained with the heterogeneous Pd- C/cyclohexene system,lsb which with FeC13 as promoter effects the reduction of aromatic ketones to the corresponding hydrocarbon lbOand gives rapid and selective removal of the benzyloxycarbonyl protecting group from amino-acids.16’ Transition-metal-catalysed activation of saturated hydrocarbons remain as elusive a goal as ever. To this end RuL2H(2-naphthyl) (L =Me2PCH2CH2PMe2)reacts with hydrocarbons RH with loss of CtoHs to give RuL2(H)R.” Hydrocarbons include aromatic compounds activated CH species (e.g. MeCN Me2C0 MeCOzEt or cyclopentadiene) and acetylenes. 2 Dmerization Oligomerization and Polymerization Vollhardt et al. have extended their work which uses benzocyclobutenes as o-xylylene synthons to the generation of naphthalenes and polycyclic systems.*’ The basis of these reactions involves the (q-CsHs)Co(C0)2-catalysed cyclodimerization of Me3SiCrCSiMe3 with 3-substituted hexa- 1,Sdiynes to give benzocyclobutenes (4) as intermediates.With 3-alkoxy-derivatives (R =e.g. OMe or OSiMe,) further reaction with Me3SiCrCSiMe3 yields the naphthalene (5) i.e. the diyne acts as a tetramethynylethylene precursor.18a When R =XCH2YCH,CH=Z (e.g. X =0 Y =CH2 and 2= CH,) intramolecular cycloaddition takes place to give the polycyclic compound (6).186 Me3SimR Me3SicR ~ Me,Si Me,Si \ X-Y Me3Si SiMe Me3Si Me,Si \ / SiMe Me,Si \ Modified organopalladium catalysts (e.g. q 3-allylpalladium acetate in combina- tion with tertiary phosphines) gives good yields (up to 79%) of the head-to-tail dimers of isoprene.’’ These were readily separated from the reaction mixture as 7-chloro-3,7-dimethyloct-1-ene by reaction with HCl.The complex [Pt(MeCN),]- [(BF4)2J catalyses the dimerization of branched olefins. Thus 2-methylbut-2-ene (a)H. Imai T. Nishiguchi and K. Fukuzumi Chem. Letters 1976,655; (b)I. D. Entwhistle R. A. W. Johnstone and T. J. Povall J.C.S. Perkin I 1975 1300. l6 (a)G. Brieger and T.-H. Fu J.C.S. Chem. Comm. 1976,757;(b)A. E. Jackson and R. A. W. Johnstone Synthesis 1976,685. S. D. Ittel C. A. Tolman A. D. English and J. P. Jesson J. Amer. Chem. Soc. 1976,98,6073. (a)R.L. Funk and K. P. C. Vollhardt,J.C.S.Chem.Comm.,1976,833;(b)J.Amer. Chem. Soc. 1976,98 6755. 19 J. P. Neilan R. M. Laine N. Cortese and R.F. Heck J. Org. Chem. 1976,41 3455. Organometallic Chemistry -Part (i) The Transition Elements gave a 3 :1mixture of 2,3,4,4-tetramethylhex- 1-ene and 3,4,4,5-tetramethylhex-2-ene.*O Further insights into the mechanism of diene and acetylene dimerization have come from studies of palladium and platinum complexes.21 Complex (7) has been (7) isolated from the reaction of bis(cyc1o-octa- 1,5-diene)platinum with butadiene and is related to the proposed intermediate in the Nio-catalysed cyclodimerization to 1,2-divinylcycl0butane.~~"The trans-2,5-divinyl structure confirmed by crystal structures of the complexes with L = Bu'NC and L = 1,5-CsHI2 may not be at variance with the cis -2,5-divinyl arrangement in the proposed nickel intermediate but may merely reflect conformational differences imposed by platinum being the larger metal atom.From studies of some hydridoalkynyl-palladiumand -platinum compounds it appears that the pathway for acetylene dimerization involves alkenyl- alkynyl intermediates [M(CH=CHR)CrCR] rather than the alternative hydrido- alkenyl species [M(H)CH=CRCrCR].216 The use of cross-linked resins as carriers in heterogenized catalysts previously largely confined to hydrogenation has been extended to Ziegler-Natta polymeriza- tion catalysts.22 Titanium- or vanadium-based systems have been supported on resins which swell on contact with hydrocarbons e.g. cross-linked ethylene/propylene/diene rubbers grafted with 4-vinylpyridine. In ethylene polymerization polymer was produced in the pores of the resin and was recovered free from catalyst residues either uia subsequent treatment with hot diluent or by conducting the reaction above the melting point of the polymer.Catalysts could be recycled many times without loss of activity or of metal. With mixed metal systems (e.g.with vanadium and nickel species supported on the same resin) both dimeriza- tion and polymerization occurred to give an ethylene/butene copolymer. A particularly active halogen-free homogeneous polymerization catalyst has been described.23 This is based on cyclopentadienyl-titanium(1v)or -zirconium(Iv) complexes in combination with an aluminoxane (the product of reaction of a trialkylaluminium compound with water). Hitherto no related active zirconium catalyst was known and attempts to prepare halogen-free cyclopentadienyltitanium systems had suffered from problems of lop of activity through reduction to species of lower oxidation state.The R2A10AlR2 unit one of the many 'preferred' activators in the prolific patent literature on heterogeneous TiCL catalysts appears to be the essential ingredient for this stabilization and activation. With ethylene conversions 2o A. de Renzi A. Panunzi A. Vitagliano and G. Paiaro J.C.S. Chem. Comm. 1976,47. 21 (a)G. K. Barker M. Green J. A. K. Howard J. L. Spencer and F. G. A. Stone J. Amer. Chem. Soc. 1976 98 3373; (b) Y. Tohda K. Sonogashira and N. Hagihara J. Organometallic Chem. 1976 110 c53. 22 V. A. Kabanov V. I. Srnetanyuk and V. G. Popov Doklady Akad.Nauk S.S.S.R.,1975,225 1377. 23 A. Andresen H.-G. Cordes J. Herwig W. Kaminsky A. Merck R. Mottweiler J. Pein H. Sinn and H.-J. Vollrner Angew. Chem. Internat. Edn. 1976 15,630. 104 R. Pearce,D.J. Thompson andM. V. Twigg were in the region of 2 x lo4g mmol-' h-' but the catalysts appear to be inactive with propylene. Molecular weights were sensitive to and could be controlled by changes in reaction temperature. Much of the confusion surrounding the mechanism of the transition-metal- catalysed polymerization of 1,3-dienes has been cleared up in a recent paper that includes a summary of much of the literat~re.,~ It has been established that (i) q 3-allylic intermediates are involved; (ii) the anti-isomer is formed initially by kinetic control and subsequently isomerizes to the syn-species; and (iii) the type of polymer produced will depend on the relative stabilities of and on the relative rates of monomer insertion into the syn-and anti-isomers.3 Carbonylation Interest in the carbonylation of the olefins continues and a series of ligand-stabilized Pt" or Pd"-Group 4B halide complexes have been shown to be active catalysts.25 Carbonylation of terminal olefins in the presence of alcohol and catalysts of the type PtCl,(AsPh,),/SnCl or PtC1,[P(OPh),],/SnCI2 gives the linear ester with up to 98% selectivity. The related palladium complexes give lower selectivity (85%) but operate at lower CO pressures. Depending on the conditions employed different products can be obtained in the carbonylationof olefins using palladium catalysts.26 Linear a -olefins in the presence of PdC12/CuC12/MeOH give the p-methoxy-esters RCH(OMe)CH,CO,Me in good yield (>50%) whereas addition of an equimolar amount of sodium acetate gives exclusive formation of the succinic ester RCH(C02Me)CH2C02Me.Cyclic olefins give predominantly the diesters even in the absence of base. An interesting use of phase-transfer catalysis has been described in the carbonyla- tion of aryl benzyl and vinyl halides to the corresponding carboxylic acid.,' The halide in an organic solvent is stirred rapidly with a mixture of aqueous NaOH [PdC12(PPhJ2] and Bu4NI under carbon monoxide. The catalyst stays in the organic phase and can be recycled whilst the product is easily isolated in high yield from the aqueous phase as its sodium salt.Moreover the system can be very selective; for example producing p-bromobenzoic acid from p-dibromobenzene in 90% yield. PdC12/sodium acetate has been used to carboxylate aromatic compounds but the yields are poor. It is now reported that sodium palladium malonate in acetic acid/acetic anhydride however gives good yields of the aromatic acid.28 Benzene for example gives benzoic acid in 72% yield but biphenyl (20%) is produced as a side-product. The yields can be improved by the addition of silver acetate. The first transition-metal-catalysed CO insertion into dienes or enones (8) with CO (40 atm; 20°C) in the presence of [RhCl(CO),] (Scheme 1) gives the corres- ponding aromatic compound (10) in 90% yield.The reaction is thought to go via the intermediate (9).29 24 V. A. Kormer M. I. Lobach V. I. Klepikova and B. D. Babitskii,J. Polymer Sci.,Polymer Letters Edn. 1976,14,317. 25 J. F. Knifton J. Org. Chem. 1976,41 793 2885. 26 D.E. James L. F. Hines and J. K. Stille,J. Amer. Chem. SOC.,1976,98 1810. 27 L.Cassar M. Foi and A. Gardano J. Organometallic Chem. 1976,121,C55. 28 T.Sakakibara and Y. Odaira,J. Org. Chem. 1976,41,2049. 29 R.F. Heldeweg and H. Hogeveen J. Amer. Gem. SOC.,1976,98,6040. Organometallic Chemistry -Part (i) The Transition Elements Reagents i [Rh(C0)2Cl], CO (X=CH2 or 0). Scheme 1 Work on asymmetric hydroformylation is continuing to improve optical yields and to increase our understanding of the reaction mechanism.Using the DIOP- related ligand (11).in the presence of rhodium increased optical yields have been obtained for both styrene (44%) and but-1-ene (~OYO).~' A study of the asymmetric hydroformylation of a-methylstyrene using PdC12/( -)-DIOP in the presence of alcohol has revealed that the optical yield varies with the alcohol CO pressure and metal/ligand ratio.31 The optical yield reaches a maximum with t-butyl alcohol increases with CO pressure (going from 3.5to 50% as the pressure is increased from 50 to 700 atm) and is also favoured by low ligand/metal ratios (59% at 0.4 ligand/metal). At the lower ligand ratios however the reaction rate is slower and by-products are formed. In the asymmetric hydroformylation of straight-chain butenes using PtCI2[( -)-DIOP]/SnCl, the chirality of the product is opposite to that when RhH(C0)- (PPh3)J( -)-DIOP] is used suggesting that the asymmetric induction does not just originate by steric interaction between substrate and ligand.32 Interest in organic reactions of CO involving transition-metal complexes has increased but to date very few synthetic advances have been made in this area.The use of copper cyanoacetate acting as a carrier of activated CO for the conversion of propylene oxide into propylene carbonate in 83% yield however has been described.33 The oligomerization of butadiene in the presence of CO using a palladium phosphine complex gives the lactone (14) in low yield via the acids (12) and (13) together with various butadiene 01igomers.~~ 30 M. Tanaka Y.Ikeda and I. Ogata Chem. ktters 1975 11 15. 31 G. Consiglio and P. Pino Chimia (Swirz.) 1976 30 193. 32 G. Consiglio and P. Pino Helv. aim. Acta 1976,59 642. 33 T. Tsuda Y. Chujo and T. Saegusa J.C.S. Gem. Comm. 1976,415. Y. Sasaki Y. Jnoue and H. Hashimoto J.C.S. Gem. Cbmm. 1976,605. R.Pearce D.J. Thompson,andM. V.Twigg 4 Synthesis of N-Heterocyclic Compounds Transition-metal complexes are finding increasing use in the synthesis of organic heterocyclic compounds. They often give better yields and selectivity than the more conventional synthetic methods and it can be anticipated that much progress will be made in this area over the next few years. Alper and Prichett have studied the reaction of 2-aryl-azirines (15)with a variety of transition-metal complexes and have obtained an interesting array of reaction products (see Scheme 2).35 The styrylindoles (16) which could be useful inter- mediates in alkaloid synthesis are obtained in up to 90% yield using either CO~(CO),~~'" or [RhC1(C0)2]2.356 The reaction of (15) with Fe2(CO)9 gives the 2,5-diarylpyrrole (17),35cwhereas reaction with silver perchlorate gives the 2,5- diarylpyrazine (18)in up to 35% yield.35d (15) \ iii Reagents i Fe2(CO),; ii Co2(CO)8 or [Rh(C0)2Cl]2; iii Ag+.Scheme 2 The organocobalt-catalysed synthesis of substituted pyridine from alk- 1-ynes and nitriles has been extended further by the discovery that the reaction is catalysed by the easily obtainable cobaltocene Co(q5-C5H5)2.36 Acetylene reacts with substituted nitriles to give 2-substituted pyridines in up to 60% yield whereas monosubstituted 35 (a)H.Alper and J. E. Prickett Tetrahedron Letters 1976,2589; (b) J.C.S. Chem. Comm. 1976,483; (c) ibid. p. 191; (d)ibid. p. 983. 36 Y. Wakatsuki and H. Yarnazaki Synthesis 1976 26. Organometallic Chemistry -Part (i) The Transition Elements acetylenes react to give mixtures of 2,4,6- and 2,3,6-trisubstituted pyridines [(19) and (20)] in moderate yield. (19) (20) Although $-unsaturated ketoximes (21) are known to cyclize at around 300 "C the reaction can be induced under much milder conditions in the presence of PdC12(PPh3)2/NaOPh.37 The reaction products are substituted pyridines (22) which are obtained in moderate yield. R' R3 Rl,&&,R4 PdC12(PPh3)2-NaOPh ______* :Q:: NOH (21) (22) Substituted indoles (24) can be synthesized by cyclization of compounds of the type (23) in the presence of [Ni(PPh3)4] followed by Cyclization of the related compounds (25) gives the corresponding oxindole (26)in up to 70% yield.386 CH2R oIrR a Ni(PPh3)4 Me Me U (23) ( C R Ni(PPh3)4) (24) CH2Ra* Me Me (25) (26) Another synthesis (Scheme 3) of indoles (29) involves intramolecular cyclization of the o -allylaniline (28) using [PdC12(MeCN)2].39 Yields are good (70-85%) and the starting materials can be readily synthesized by the reaction of ?r-allylnickel bromide with the corresponding o -bromoaniline (27).The reaction of the palladium complex (30) with an isocyanide gives the stable complex (31).40 This complex thermally decomposes at 100"C to give the 3-imino- 2-phenylindazoline (32) whereas the reaction of the complex (31)with COyields the 3-0x0-2-phenylindazoline (33) both reactions proceeding in good yield.37 T. Hosokawa N. Shimo K. Maeda A. Sonoda and S. I. Murahashi Tetruhedron Letters 1976,383. 38 (a)M. Mori and Y. Ban Tetrahedron Letters 1976 1803; (6)ibid. p. 1807. 39 L. S. Hegedus G. F. Allen and E. L. Waterman,J. Amer. Chem. Soc.,1976,98,2674. 40 Y. Yamamoto and H. Yamazaki Synthesis 1976,750. R. Pearce,D.J. Thompson andM. V.Twigg Reagents i (r-allyl)NiBr; ii PdC12(MeCN)2; iii Et,N. Scheme 3 Ph Ph I I N=N C1 AN=N ,Pd C1 L/ \/z u&/ A d ,Pd + 2RNC -+ 100°C X\ NPh \ CNR 0 X X NR x\ NPh e 0 (33) Rearrangement of the aziridine (34) with a catalytic amount of [PdC12(PhCN)2] gives the N-carboxynortropidine (35) in quantitative yield.4' This is a particularly useful reaction since the product (35)is the backbone of the tropane alkaloids.(34) (35) An interesting (4+2) cycloaddition across the diheterodiene system in the copper complex (36) occurs with dimethyl acetylenedicarboxylate to give the substituted 1,4-benzoxazines(37).42 Yields are excellent (ca. 90%) for a variety of substituted complexes and it is noteworthy that no reaction occurs with the uncomplexed nitroso-phenols Ra \; +/ cq + 111 C02Me I I 0-OH (36) (37) 4' G. R. Wiger and M. F. Rettig J. Amer. Chem. Soc. 1976,98 4168. 42 A.McKillop and T. S. B. Sayer J. Org. Chem. 1976,41 1079. Organometallic Chemistry -Part (i) The Transition Elements The reaction of N-sulphinylaniline (38) with diphenylcyclopropenone (39) in the presence of Ni(C0)4 gives the pyrroline-2,5-dione (40) in 78% yield.43 The reaction is thought to go via the complex (41) followed by exchange of the S=O group by CO. In contrast the reaction of N-sulphinylcyclohexylanilinegives the substituted isothiazolone 1-oxide (42) in 36% yield and no product is found in which CO is exchanged for SO. 0 Ni(CO)4 phA,,+ R-N=S=O (R=Ph) 06 0 R (39) (38) (40) Ni(CO)4 (R = cyclohexyl) 1 An extension of the work on co-oligomerization has led to an efficient synthesis of 1,2-diaza- 1,5,9-~yclodecatrienes (43).44 Thus co-oligomerization of butadiene with ketazines or aldazine in the presence of a nickel phosphine or phosphinite catalyst gives the cyclic products (43) in 50-80% yield.R2 R’ R2 I1 I 5 The Use of Metal Cluster Complexes in Catalysis Although a lot of work has been done on the structure and synthesis of metal cluster complexes it is only recently that they have begun to find use as catalysts. A very good review45 was published last year which compared the chemical and catalytic properties of discrete metal clusters with those of metal surfaces. Metal clusters are beginning to emerge which have very interesting catalytic properties. One of the most important industrial applications has been the conver- sion of CO/H mixtures into ethylene glycol.Various rhodium precursors have been employed and appear to work through a common RhI2 intermediate 43 A. Baba Y. Ohshiro and T. Agawa Chem. Letters 1976 11. 44 P. Heimbach B. Hugelin H. Peter A. Roloff and E. Troxler Angew. Chem.Internat. Edn. 1976,15,49. 45 E. L. Muetterties,Bull. SOC.chim.belges 1975 84 959. 110 R. Pearce D.J. Thompson and M. V. Twigg [Rh12(C0)30)2-.46 Typical reaction conditions are 2 10-250 "C and 500-2000 atm; the other major reaction products are methanol glycerine and ethanol. In contrast with the rhodium clusters OS~(CO)~~ and Ir4(C0)12 catalyse the specific reduction of CO to methane.47 The reaction proceeds under fairly mild conditions (140 "C 2 atm) but the reaction rate is slow.Addition of Ph3P to the iridium system increases the rate of production of methane but ethane and propane are also produced. Using trimethyl phosphite the rate is three times faster than the Ph,P/Ir4(C0)12 system and moreover the selectivity for methane production is maintained. A large number of mononuclear complexes were examined but none were active for the reduction of carbon monoxide. The complexes [(Co2B)loRhH6] and [(Ni2B)10Rh15] are prepared from Co'' or Ni" chloride and RhCl in the presence of NaBI-L.48 These cluster complexes are active catalysts for the hydrogenation of olefins and by contrast with Raney nickel give no isomerization products. They are also catalysts €or the reduction of carbon monox- ide to methane. [RU~(CO)~~] is an active catalyst for the isomerization of pent-1-ene giving a mixture of pent-1-ene (3%) cis-pent-2-ene (23'/0) and trans-pent-2-ene (74%).49n In the presence of a small amount of acetic acid there is a ten-fold increase in reaction rate but the initial cis/trans ratio is unchanged.Since no scrambling of hydrogen between the acid and the pentenes is observed on using MeC02D a metal hydride addition-elimination mechanism is excluded and a v-ally1 metal hydride inter- mediate is suggested. os3(co)1249b also show catalytic activity and &RU(CO)~~~" for the isomerization of pent- 1-ene to cis- and trans-pent-2-enes. A series of active supported nickel clusters have been prepared by pyrolysis of [Ni(q '-C5HJ2] [Ni(q 5-C5H5)2(C0)2] and [Ni3(q '-C5H5)3(CO)2] dispersed on silica.50 Although acetylene trimerizes readily at room temperature in 75% yield over dispersed nickel from (q'-C,H,),Ni there is no reaction with the other two nickel clusters.All three clusters however are active for H2/D2 exchange and hydrogenation of ethylene and benzene. Pyrolysis of platinum clusters of the type [Pt,(C0)4][NEt4]2 (x = 3,6,9,12 or 15) dispersed on silica or alumina gives highly dispersed platinum crystallites which are active catalysts for the dehydrocyclization of n-he~ane.~~ The smaller platinum aggregates from Ptd and Pt3 on y-alumina gave methylcyclopentane with up to 94% selectivity and negligible skeletal isomerization. 6 Oleh Metathesis The high level of interest in olefin metathesis has continued with some fifty relevant publications appearing in 1976.Most are concerned with elucidating the mechanism of this reaction. A detailed review was also p~blished.~' 46 e.g. U.S.P. 3974259. 47 M. G. Thomas B. F. Beier and E. L. Muetterties J. Amer. Chem. Soc. 1976 98 1296. 48 R. W. Mitchell L. J. Pandolfi and P. C. Maybury J.C.S. Chem. Gbmm. 1976 172. 49 (a)M. Castiglioni L. Milone D. Osella G. A. Vaglio and M. Valle Zmrg. Chem. 1976,15,394; (6)R. P. Ferrari and G. A. Vaglio Znorg. Chim. Acta 1976,20 141; (c)M. Valle D. Osella and G. A. Vaglio ibid. p. 213. M. Ichikawa J.C.S. Chem. Comm. 1976 26. 51 M. Ichikawa,J.C.S. Chem. Comm. 1976 11. 52 N. Calderon E. A. Ofstead and W. A. Judy Angew. Chem. Internat. Edn. 1976,15,401. Organometallic Chemistry -Part (i) The Transition Elements 111 Mechanistic Aspects.-The current consensus is that the mechanism of olefin metathesis involves a metal-carbene chain process.Failure to detect cyclobutane products was an important factor arguing against earlier proposed mechanisms based on ‘quasicyclobutane’ transition states. It is therefore noteworthy that Gassman and Johnson found that the diolefin (44)is smoothly converted into the thermally stable cyclobutane (45)by a catalyst system typically used for metathesis e.g. [W(Ph)(CO),] activated with AlC13. Some related diolefins do not undergo cyclization but the corresponding cyclobutanes are rapidly converted into diolefins on exposure to cata~yst.~~ (44) (45) Support for the feasibility of metallocyclobutane-carbene interconversions comes from a number of studies (i) Reaction of Metallocyclobutanes.It is suggested that the photolysis of some tungsten complexes causes a q5-C5H5to q3-C5Hs shift in (46);rearrangement to co-ordinated carbene and olefin in the 16-electron species then takes place leading to free olefin that contains one less carbon atom than the initial metallocyclob~tane~~ (Scheme 4). (v-C5H5)*W R2 5 (46) Scheme 4 (ii) Initiation by Metal-Carbene Complexes. Further support has been obtained for the metal-carbene chain mechanism. Several isolable metal-carbene complexes initiate metathesis. In the presence of TiCI4 [W(C0)5C(OEt)R] is a very active catalyst for cyclopentene polymerization but thermal or photo-activation is neces- sar~.’~~ More reactive complexes e.g.[W(C0)5CAr2] are active in the absence of 53 P. G. Gassman and T. H. Johnson J. Amer. Gem. Soc. 1976,98,861. 54 M. Ephritikhine and M. L. H. Green J.C.S. Chem. Comm. 1976,926. 55 (a) E. 0. Fischer and W. R. Wagner J. Organometallic Chem. 1976 116 C21; Y. Chau-vin D. Commereuc and D. Cruypelinck Makromol. Chern. 1976. 177 2637; (6)T. J. Katz and N. Acton TetrahedronLetters 1976,4251;T. J. Katz S. J. Lee and N. Acton ibid. p. 4247; (c)J. McGinnis T. J. Katz and S. Hurwitz,J. Amer. Chem. Soc. 1976,98,605; T. J. Katz J. McGinnis and C. Altus ibid. p. 606; C. P. Casey H. E. Tuinstra and M. C. Saeman ibid. p. 608. 112 R.Pearce,D.J. Thompson andM. V.Twigg co~atalyst.~~~ Results of detailed product analysis of reactions of octa- 1,7-diene and 2,2'-divinylbiphenyl with their specifically deuteriated derivatives are in conflict with mechanistic schemes involving the union of two olefin molecules but in agreement with the carbene (iii) Addition of Carbene Traps.Addition of a typical Michael acceptor (such as ethyl acrylate) to metathesis reactions catalysed by [W(Ph)(C0)5]/AlC13 completely quenched the process and in keeping with the trapping of carbenes low yields of the appropriate cyclopropane derivatives were isolated. These observations suggest that the metal-carbene complex has a nucleophilic carbon. An important feature is that ethyl acrylate does not quench the formation of the cyclobutane (45)from the diolefin (44).56d (iv) In Situ Generationof Curbenes.Solvent dependency in metathesis reactions is well known and it has now been shown that solvent can influence the first formed carbene species. In chlorobenzene propylidene intermediates are initially formed during the metathesis of octa- 1,7-diene catalysed by [Re(CO)5CI]/EtAlCIz but with [Mo(CO)~(~~)]/E~A~C~~/BU~NCI, ethylidene is the initially formed carbene. How- ever propylidene species are involved in the latter system when heptane is the sohen t .56c Although strong evidence is available for the metal-carbene mechanism the mode of carbene generation is not clear. Routes involving alkyl or hydride species have been proposed but in several instances this course is not readily available. In suitable cases 1,2-hydride shift in a co-ordinated olefin via q3-allyl formation could provide a paths7" (Scheme 5).A related co-ordinated olefin-carbene interconver- H 1T Scheme 5 sion takes place in [W(C0)4C(Ph)CHzR] where the co-ordinated carbene rapidly changes to the olefin PhCH=CHR.57b The problem of initiation is particularly pertinent with heterogeneous catalysts. The generation and role of metal hydride 56 (a) R. H. Grubbs D. D. Carr C. Hoppin and P. L. Burk J. Amer. Chem. Soc. 1976,98,3478; (b)R. Rothchild and T. J. Katz ibid. p. 2519; (c) M. F. Farona and V. W. Motz J.C.S. Cltem. Comm. 1976 930; W. S. Greenlee and M. F. Farona Znorg. Gem. 1976 17 2129; (d) P. G. Gassman and T. H. Johnson J. Amer. Chem. SOC.,1976,98,6055. 57 (a)M. Ephritikhine M. L. H. Green and R.E. MacKenzie J.C.S. Chem. Comm. 1976,619; (6) E. 0. Fischer and W. Held J. Orgunometallic Chem. 1976,112 C59; (c) D. T. Laverty J. J. Rooney and A. Stewart J. Cutulysis,1976,45 110;(d)M. T. Mocella R. Rovner and E. L. Muetterties J. Amer. Chem. Soc. 1976,98,4689. Organometallic Chemistry -Part (i) The Transition Elements 113 species has been discussed and carbene formation via a 1,2-hydride shift process is Potential difficulties in obtaining reliable quantitative results (a well- known problem for more conventional radical processes) are emphasized by the fact that traces of oxygen or water are essential for activity of commonly used [WC16]- metal alkyl catalysts. This is not the case for WOCL which can be activated when water and oxygen are rigorously excluded.Similarly new soluble catalysts based on [W(OMe)6] or [WO(Me)J are not impaired by these procedures but for high activity it appears that chlorine must be present in the co~atalyst.~'~ Applications.-'Muscalure' [(Z)-tricos-9-ene] the sex pheromone of the house fly has been obtained from the metathesis of octadec-9-ene and hexadec-2-ene. Typi- cally [WC16]/EtAlC12/EtOH gave the desired cis-product in ca. 10-20% yield. A number of related bioactive compounds were similarly An attempted novel application of olefin metathesis involved the use of 1-methylcyclobutene in the addition of an isoprene equivalent to a terpene but only poor yields were obtained [equation ( 1)].58b Polyisoprene is obtained from the metathesis of 1-methylcyclobutene using a carbene catalyst.It is noteworthy that a consequence of the carbene mechanism is the formation of a (2)('cis ')-polymer.55b e:eAc + dMe + $?"-(1) Me 'Me Me Polymerization double-bond migration alkylation of solvent etc. can be trouble- some. Addition of polar molecules such as esters can suppress these During an investigation of side-reactions it was discovered that WCl6/A1EtCl2 catalyses the conversion of polyalkylbenzenes into monosubstituted species a reaction having possible An unusual use of a metathesis catalyst (WCI6/LiPh) is for the arylation of ethers and aminesSSe [equation (2)] which in some cases gives high yields. Ph / Et2O EtOCH (2) 'Me A major problem associated with olefin metathesis is that with few exceptions functionally substituted olefins normally poison the catalyst.59 The reactivities of a number of substituted acyclic olefins towards metathesis have been reinvestigated.Apart from alkenes with ester groups remote from the double bond only low conversions were observed.60u Other examples of metathesis of unsaturated esters (a)F.-W. Kupper and R. Streck Z. Nuturforsch.,1976,31b 1256; (b)S. R. Wilson and D. E. Schalk,J. Org. Chem. 1976,41,3928; (c)K. Ichikawa and K. Fukuzumi ibid. p. 2633; (d)L. Hocks A. Noels. A. Hubert and P. Teyssie ibid. p. 1631; (e)J. Levisalles H. Rudler and D. Villemin J. Organometuflic Chem. 1976,122 C15. 59 R. Streck Chem. Ztg. 1975,99 397. (a)R. Nakamura S. Matsumoto and E. Echigoya Gem. LRtters 1976,1019; (b)W.Ast G.Rheinwald and R. Kerber Makromol. Chem. 1976,177 1341; (c)ibid. p. 1349. 114 R.Pearce D.J. Thompson andM. V. Twigg include ring opening of lactones with remote double bonds to give unsaturated po1yesters,60bsC and the ring-opening polymerization of (47) to give an unusual polymer (48). p-Alkyl- and p-halogeno-allylbenzenes undergo normal metathesis whereas the presence of a methoxy-group completely inhibits the reaction.61 H C0,Et X CHCO2Et /\ + [=CH( CH2)2 CH-CH(CH& CH=] Alkyl-substituted cyclopropanes are readily fragmented by [W(Ph)CI,]/AICI to give ethylene and substituted olefin. It is thought that the proceeds via metallocyc- lobutanes. In this way bicyclo[2,1,0]pentane is converted into cyclobutene in 70% yield suggesting that this reaction may have use in the preparation of some unusual olefins which reluctantly enter into metathetical reactions.62a The related cross-metathesis of deactivated olefins e.g.(49; R = C02Me) with alkyl-substituted cyclopropanes has some potential but is restricted by low yields [equation (3)].626 H R' H R2 x + x + CH2=CHRZ +CH2=CHR1 (3) (49) 7 Isomerization The smooth isomerization of a variety of cycloalkenones has been shown to be catalysed by rhodium trichloride in ethanol at 100"C. This convenient new enone transposition reaction is also effective when the double bond is not a part of the cyclic [e.g. equation (4)J.Ethylene bis(tri-o-tolyl phosphite)nickel(o) in the 0& -0% presence of HCl is a useful catalyst for the rapid isomerization of alkenes with polar functional groups.For example hex-5-enal is converted into a mixture of cis-and trans-4-isomers and ethyl pent-4-enoate is converted into a mixture of ethyl cis-and trans -pent-3-enoates without the usual formation of crp-unsaturated com- pounds. Alcohols having unsubstituted double bonds are slowly converted into saturated carbonyl compounds in high yield but the catalyst is not long-lived.a 61 P. Chevalier D. Sinou G. Descotes R. Mutin and J. Basset J. Organometalfic Chem. 1976 113 1. 6z (a) P. G. Gassman and T. H. Johnson J. Amer. Chem. Soc.,1976,98,6057; (6)p. 6058. 63 P. A. Grieco M. Nishizawa N. Marinovic and W. J. Ehmann J. Amer. Chem. Soc. 1976,9% 7102. 64 C. F. Lochow and R. G. Miller J.Org. Chem. 1976,41,3020. Organometallic Chemistry -Part (i) The Transition Elements 8 Reactions of Co-ordinated Ligands and Related Topics Reactions of Co-ordmated Ligands.-Chromium tricarbonyl complexes of indanones and tetralones undergo a highly stereoselective Michael addition reaction with methyl vinyl ketone and an unusual annulation reaction involving activation of a benzylic hydr~gen.~' The isomeric 2-methylindanone complexes (50) give (5 1) as the major product (87%) on treatment with methyl vinyl ketone addition occurring selectively at the exo-face. On treatment with base the normal aldol condensation product (52) was obtained as a minor product (5-lo%) the major product being the unexpected (52) (2 isomers) formed through reaction at the activated benzylic position.This unusual annulation takes place only when the exo-face is unhindered with the isomer of (51) of opposite configuration at C-2 where attack is at the relatively hindered endo -face the normal aldol product [isomer of (52)] predomi- nates. 0 Me + Me 0 0 (53) (52) Scheme 6 Another novel annulation (Scheme 7) occurs in the reaction of tricarbonylmyr- ceneiron (54) with oxalyl chloride to give a mixture of (55) and (56) a cyclization involving the unco-ordinated and unprotected double bond."" Recent reports on cyclopentadienyldicarbonyliron complexes confirm their ver- satility in organic synthe~is.~' The reaction of the tropylium complex (57) with [q'-RCH=CHCH2Fe(C0)2(q '-CsHs)] (58) gives (59) a useful intermediate in the 65 G.Jaouen and A. Meyer TefruhedronL.et&rs 1976,3547. A. J. Birch and A. J. Pearson J.C.S. Chem. Comm. 1976,601. 67 (a)N. Genco D. Marten S. Raghu and M. Rosenblum J. Amer. Chem.Soc. 1976,98,848; (b)A. Rosan and M. Rosenblum J. Org. Chem. 1975,40,3621. R. Pearce,D.J. Thompson andM. V.Twigs Reagents i CIC(O)C(O)CI AICI,; ii Ag+. Scheme 7 HR +Fe(CO) H (57) (59) preparation of substituted hydro-a~ulenes~~" which are not readily available. The ion [C5H5Fe(C0)2]' activates the methyl vinyl ketone towards Michael addition under very mild conditions. Reactions of this type which involve regiospecifically generated silylenolates are particularly useful and provide a route to octalones (Scheme Q6'' Reagents i Fe(CO)2(v -C5H5)(CH2=CHCOMe); ii basic Al2O3.Scheme 8 Three papers deal with new routes to .rr-allylpalladium complexes.68 The first which appears to be the most general involves the reaction between vinylmercuric halides (R'CH=CHHgCl) olefins (R2CH=CH2) and [Li2PdC1,] to give (60).68a Benefits of this route are (i) the mild reaction conditions compared with those used in previous methods; (ii) the fact that a range of functional groups can be tolerated (e.g. R2=H Bu CN or COMe); (iii) the formation of complex carbon skeletons from relatively simple starting materials; and (iv) the capability of preparing isomeric .rr-ally1 species that are not available via the allylic substitution route [e.g. (60; R2= C02Et)]. With products from activated olefins treatment with bases provided a (Q) R.C. Larock and M. A. Mitchell J. Amer. Chem. Soc. 1976,98,6718;(b) S. Staicu I. G. Dinulescu F. Chiraleu and M. Avram J. Organometallic Chem. 1976.113 C69; H. Alper H. des Abbayes and H. des Roches ibid. 1976 121 C3 1. 117 Organometallic Chemistry -Part (i) The Transition Elements route to unsymmetrical 1,3-dienes. The second route involves the reaction of diarylacetylenes (PhCrCAr) and olefins (R'R2C=CH2) with [PdC12(PhCN)2] to give (61).'" As with the first route conditions were mild and the .rr-ally1 complexes were prepared uiu carbon-carbon bond formation from simple starting materials. H R1+ cH R2 ci+ cmlR2 H H Ar H PdCl PdCl (60) (61) Examples were restricted to hydrocarbyl substituents.Finally (q3- allyl)C0(C0)~(PR,) complexes have been obtained under relatively mild conditions from CO~(CO)~ and allylic halides by the use of phase-transfer catalysts. This is one of the first examples of the use of phase-transfer catalysis in organometallic synth- esis.68c (q3-Allyl)palladium complexes have been used in the stereospecific alkylation of the side-chain of Depending on the reaction conditions products of opposite configuration were obtained. Path (a) (Scheme 9) is stoicheiometric in palladium whereas path (b) uses catalytic quantities. This catalytic route is effec- tively a stereospecific SN2displacement with net retention of configuration. H \ Reagents i PdC12 base; ii NaCH(C02R),; iii Me4NOAc heat; iv m-ClC6H4C03H; v LiNEt2 MeCOCI; vi Pd(PPh3)4 NaCH(C02R)2.Scheme 9 Reactions of gem -dihalides with nickel(0) species proyide a route to substituted cycl~alkanes.~~ aro -Dihalides [Br(CH2) Br] and gem -dihalides [R1R2CX2] give the cycloalkanes [R'R2mm] in the presence of stoicheiometric quantities of bis(cyclo-octadiene)nickel.70u Nickelacyclic intermediates [L2Ni(CH2),I3 are 69 B.M. Trost and T. R. Verhoeven J. Amer. Chem. SOC.,1976,98,630. 70 (a)S. Takahashi Y. Suzuki K. Sonogashira and N. Hagihara J.C.S. Chem. Comm. 1976 839; (6)J. Furukawa A. Matsumura Y. Matsuoka and J. Kiji Bull. Chem. Soc. Japan,1976,49,829. 118 R.Pearce,D.J. Thompson,andM. V.Twigg involved (cf. Ref. 71) and good yields are therefore restricted to the cases where n =4 (formation of the most stable ring system).Whereas a mixture of PhCOCHBr and Ni[P(OEt)3]4 gave the expected product PhCOCH=CHCOPh reaction in the presence of bis(cyc1o-0ctadiene)nickel gave 1,2,3-tribenzoylcyclopropane,70bthus providing a rare example of dehalogenative cyclopropanation. Extensions to the field of carbon-carbon bond formation via metal-catalysed cross-coupling reactions have been in asymmetric synthesis (see Section 1 for detail^),^' in the use of alkenylaluminium compounds in stereospecific 01efin7," and 1,3-diene7,' synthesis and in the preparation of a versatile organopalladium catal- y~t.~~ trans-Alkenylaluminium complexes (e.g.trans-PhCH=CHAlBui2) are read- ily generated by the stereospecific cis-addition of aluminium hydrides (e.g.HAIBui2) to alkynes which obviates the need for separate preparation of isomerically pure alkenyl halides as is required for the preparation of organo-magnesium and -lithium reagents.Whilst the aluminium complexes are normally unreactive to aryl and alkenyl halides addition of Nio and Pdo triphenylphosphine complexes facilitates coupling between the aluminium compounds and the halides under mild conditions. Yields are high reactions are highly stereospecific (90-99%) and the method appears to be superior to those previously reported for the preparation of (E)-alkenes and (E,E)-and (E,Z)-1,3-diene~.~*"'~ [PdPh(I)(PPh,),] is a convenient and general catalyst for the cross-coupling of Grignard reagents with aryl and alkyl halides and it offers advantages over the existing nickel catalysts.These include (i) an increase in selectivity (e.g.PhMgCl and p-C6&CIBr give PhC6&C1-p); (ii) good yields with ethynyl Grignard reagents (e.g.PhC=CMgBr and PhI give PhCrCPh); and (iii) good yields with hindered arylmagnesium halides (e.g.mesitylmagnesium A newly reported aldehyde-alkene addition reaction appears to share a common hydridoacyl-rhodium(Ir1) intermediate with the well-known Rh'-catalysed decar- bonylation of aldehydes.73 In the presence of chloro- or acetylacetonato-rhodium@) complexes pent-4-enal undergoes cyclization to cyclopentanone while addition of ethylene gives inter alia hex- 1-en-5-one. The reaction sequence presumably involves oxidative addition of the aldehydic C-H insertion into the Rh-H bond (either with ethylene to give an ethylacyl complex or via intramolecular cyclization to give a rhodacyclohexane intermediate) followed by reductive elimination to regenerate the Rh' catalyst.Synthetic Applications.-Rhodium(r1) carboxylates (e.g. the soluble pivalate) are effective catalysts for the cyclopropanation of alkenes by alkyl diaz~acetates.~~ Using this catalyst markedly better yields are obtained from substituted olefins than with the alternative palladium acetate or copper(I1) triflate. A range of di- and tri-oxabicyc10[x72,1]-systemshave been prepared by a novel Pd"/CuC1,-catalysed oxidative intramolecular cyclization reaction.75 Thus the alkenediol (62) obtained via a butadiene telomerization gave the beetle pheromone endo -brevicomin (63).71 M. J. Doyle J. McMeeking and P. Binger J.C.S. Chem. Comm. 1976 376. 72 (a)S. Baba and E.-I. Negishi J.C.S. Chem. Comm. 1976,596; (b)J. Amer. Chem. Soc.,1976,98,6729; (c)A. Sekiya and N. Ishikawa J. OrganometallicChem. 1976 118 349. 73 C. F. Lochow and R. G. Miller J. Amer. Chem. Soc. 1976,98 1281. 74 A. J. Hubert A. F. Noels A. J. Anciaux and P. Teyssit Synthesis 1976,600. 75 N. T. Byrorn R. Grigg and B. Kongkathip J.C.S. Chem. Comm. 1976,216. Organometallic Chemistry -Part (i) The Transition Elements The reaction of acyltetracarbonylferrates [R'COFe(C0)4]- with nitro-compounds (R2N02) provides a new route to amides (R'CONHR2) the ferrate acting as a very mild reducing and acylating agent.76 The hydrido-chromates [K(or Na)HCr2(CO)lo] prepared from potassium/graphite and chromium hexacarbonyl effect the selective reduction of a/3-unsaturated carbonyl compounds and offer an alternative to the well-known hydrido-ferrates [e.g.NaHFe(C0)4].77 A recent patent discloses an unusual homologation reaction of an allylic alcohol. Reactions of allylic alcohols with ketones and carbon monoxide in the presence of K2MCI4/SnCl2(M = Pd or Pt) give the butenols (64).78 R'R2C=CR3CH20H+R4R5C0 3 R'K2C=CR3CH2CR4R50H (64) Secondary kinetic isotope effects in the formation of metal olefin complexes have been used to good effect in the chromatographic separation of the deuteriated ethylenes C2HnD4-n.79 The Rh' complex (65) was used as the stationary phase and was superior to the existing silver nitrate system in this separation.Insertion.-Alkynols in the form of easily prepared titanium complexes [TiC1(OCH2(CH2) C=CH)L2] (L =/3 -diketonate) react regiospecifically under mild conditions with Et2AlCI to give the corresponding trans-ethyl olefins via intramolecular cis-addition to Ti-Et to the triple bond in the ethylated (66) [equation (5) The application of stoicheiometric hydrozirconation reactions to organic synth- esis reported last year has been reviewed and factors such as functional group compatibility have been considered." During 1976 this work was extended to reactions involving 1,3-dienes and halogeno-olefins. The addition of 1,3-dienes to [Zr(q -C5H5)2HC1] in contrast with addition to boron aluminium and many 76 M.Yarnashita Y. Watanabe T. Mitsudo and Y. Takegarni Tetrahedron Letters 1976 1585. 77 G. P. Boldrini A. Umani-Ronchi and M. Panunzio Synthesis 1976 596. 78 U.S.P. 3 9564O8. 79 V. Schurig Angew. Chem. Intemat. Edn. 1976,15 304. R. A. Coleman C. M. O'Doherty H. E. Tweedy T. V. Harris and D. W. Thompson J. Organometallic Chem. 1976,107 C15. J. Schwartz and J. A. Labinger Angew. Chem. Internat. Edn. 1976,15 333. R.Pearce D.J. Thompson andM. V.Twigg Et\ C ,H II H / o'- 0-cH2 / \ Et (66) transition-metal hydrides gives uia simple 1,2-addition the sterically less hindered yS -unsaturated complex (67). Subsequent ready insertion of CO followed by hydrolysis cleanly affords the corresponding yS-unsaturated aldehyde with no products resulting from dimetallation or migration of the double bond.The reaction of (67) with N-bromosuccinimide produces the corresponding unsaturated bromide but with appropriately alkyl-substituted compounds cyclopropane derivatives are also formeds2= (Scheme 10). Cyclopropanes are also obtained in moderate yield uia RR RR P RR Reagents i [Zr(q-C5H5)2HC1]; ii CO H2O;iii NBS. Scheme 10 y-Zr halogen elimination from intermediates obtained from reaction between [Zr(q -CsHs)2HC1] and suitable alicyclic or cyclic halogeno-olefins. Yields are lowered either by p -Zr-halogen elimination or by direct reduction with [Zr(q- CsH5)2HC1](Ref. 826). ZrCL can be used in procedures reminiscent of hydrozirconation. Reaction with LiAlH presumably produces Zr-H species which on addition to an alkene give (after hydrolysis) an alkane or by reaction with bromine an alkyl bromide.82C Mechanistic information is lacking but it will be of interest to see if the more subtle hydrozirconation syntheses can be achieved without employing preformed com- plexes.** (a)C. A. Bertelo and J. Schwartz J. Amer. Chem. Soc. 1976,98,262;(b)W.Tam and M. F. Rettig J. Organometallic Chem. 1976 108 C1;(c) F.Sato S. Sato and M. Sato ibid. 1976,122,C25.