Protonation of the complexes [M2(CO)(p-CO){p-C(0)C2R2)(q-C5H5)2] [M = Fe or Ru; R2 = H2, Ph, , H (Me), or H (Ph)] with H BF,*OEt, results in rapid carbon-carbon bond cleavage and formation of the p-vinyl cations [M2(CO)2(p-CO){p-C(R)=C(H)R)(q-C5H5)2] +, containing a cis arrangement of R groups. Addition of HBF,*OEt2 to [Ru,(CO) (p-CO){p-C(0)C2Me2}(q-C5H5)2] produces the cation [Ru2(CO) (p-CO)({p-C(H)(O)C,Me,)(q-C,H,),] +, which isomerises slowly to [ R u ~( C O ) ~( ~-C O ) { ~-C ( M ~) = C ( H ) M ~) ( ~-C ~H ~) ~]+. The p-vinyl cations exist in solution as isomers with cis and trans orientations of terminal ligands, shown by variable-temperature n.m.r. to interconvert ; cis isomers additionally display a fluxional oscillation of the p-vinyl ligand. Treatment of the cations with NaBH, yields p-carbene complexes [M2(CO)2(p-CO){p-C(R)CH2R)(q-C5H5)2] in good yield, also as cis and trans isomers which interconvert in solution. These result from hydride addition to the p-carbon of the p-vinyl, but addition to the or-carbon is apparent in the low-yield co-formation of the terminal ethylene complex [Ru2(C0)(p-CO),( C2H,) ( T ~-C ~H ~) ~] from the cation [Ru2(C0),(p-CO) (p-CH=CH2) (q-C5H5)2] +. Addition of sodium tetrahydroborate to [Ru,(CO)(p-CO){p-C( H)(0)C2Me2}(q-C5H5),] + provides the complex [Ru2(CO) (p-CO){p-C(Me)C(Me)CH2)(q-C5H5)2], completing a conversion of metallacyclic CO to CH2. Regeneration of the p-vinyl cation [M2(CO),(p-CO) (p-CH=CH2) ( T ~-C ~H ~) ~] + is achieved by treatment of [M2(C0),(p-CO){p-C( H) Me)(q-C5H5)2] with [CPh,] [BF,]. In Part 1 of this Series we reported the syntheses of di-iron Results and lX~u&On and diruthenium complexes [M2(CO)(p-CO)(p-C(0)C,R,>(rlp-Vinyl Cations.-Synthesis. Addition of HBF,*OEt2 to C5H5)2] (1)--(12) through reactions of alkynes with [M2(CO)4-an acetone or dichloromethane solution of the di-iron and (T)-C~H~)~].* The chemistry of these dimetallacyclopentenone diruthenium complexes [M2(CO)(p-CO){p-C(0)GR2)(q-hydrocarbon~.~*~ Aspects of this work have appeared as preliminary communications.6~' C5H&] (1)-(1 I ) results in immediate cleavage of the alkyne-CO link. The ' alkyne' portion of the dimetallacycle is protonated, generating p-vinyl cations [Mr(C0)2(p-CO)(p-CR'=C(H)R2}(q-C5H5)2][BF4] (1 3)--(23) in which R' and R2are cis to one another, while the metallacyclic ketonic carbonyl is transformed into a terminal ligand. Different behaviour is shown by the diruthenium complex (12), derived from but-2yne, which yields the appropriate p-vinyl cation (24) only very slowly and via a readily isolated intermediate ( 25). This anomaly is discussed in detail below. Infrared spectra indicated that the p-vinyl complexes are formed in clean,

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Rridging methylcarbene complexes [M,(CO),-(p-CO)(p-CHMe)(q-C,H,),] (M = Fe or Ru) react with alkynes RCiR1 (R = R1 = HI Me, C0,Me; R = Me, R1 = H) under U.V. irradiation to produce complexes [M,(CO) (p-CO) (p-q1,q3-CRCR1CHMe) (q-C5H5),], shown through an X-ray diffraction study of [Fe,(CO) (p-C0)-{p-q1,y3-C (C0,Me) C (C0,Me) CHMe 1 (q-C5H5),] to arise from linking of the p-carbene and alkyne. THE chemistry of carbene complexes of transition metals has attracted much investigation, not least because of their implication in the metathesis1p2 of alkenes. Almost all study has been concerned with carbenes co-ordinated a t a mononuclear metal centre and has been associated with mechanistic schemes for metathesis based on monometallocycles. By comparison, the reactivity of carbenes coordinated a t a dinuclear metal centre ( t bridging carbenes') is effectively unexplored. Very recently, however, the possibility of metathesis involving bridging carbenes and ditungsten3 ** metallocycles has been discussed, and it has also been suggested5 that di-iron metallocycles are intermediates in the production of propene from [Fe,(CO),-(p-CH,)] and ethene. In the course of studies*--* on the reactivity of dinuclear metal centres we have developed8 a convenient synthesis of p-carbene di-iron and diruthenium complexes, and now report that these are highly reactive towards ethyne and other alkynes, forming stable dimetallocycles through carbon-carbon bond formation.The p-methylcarbene complexes [M2(C0), (p-CO) (p-CH-Me) (q-C5H5),] (1) exist in solution as cis (predominantly) and trans isomers, the cis iron complex having been found to adopt, in the solid state a t least, the anti methyl group orientation illustrated.8 Each complex (1) reacts with ethyne under U.V. irradiation (toluene solution, silica glass flask, 250 W mercury lamp, 3 and 25 h respectively) to give crystalline olive-green [Fe,(CO) (p-CO) (p-q1,q3-CHCHCH-q3-CHCHCHMe) (q-C5H,),] (2b) (55%) , respectively. No Me) ('q-c5H5)2] (2a) (85%) f or orange [Ru,(CO) (p-co) (p-qlIt (2a): m.p. 178-182 "C(decomp); v(CO)(hexane) 1 961% and 1 793m cm-l; lH n.m.r. (CDCI,) 6 11-86 (d, J 6 Hz, C4H). 4.71 (s,

BS8 I TS Ultraviolet irradiation of the metallacycle [Ru,(CO)(~-CO){~-C(O)C,P~,}(~-C,H~),] (1 ) in tetrahydrofuran (thf) gives the complex [Ru,(p-CO)(p-C,Ph,)(q-C,H,),] (2), shown by X-ray diffraction to have a ruthenium-ruthenium double bond [Ru=Ru 2.505(1) A] bridged transversely by a diphenylacetylene ligand. The loss of two molecules of CO in forming (2) is reversible; under 100 atm of CO at 50 "C complex (2) is converted into (1 ) in 60% yield. Treatment of unsaturated complex (2) with diazoalkanes RCHN, (R = H, Me, or C0,Et) results in the corresponding uptake of two alkylidene units to form [Ru,(CO)(p-CHR){p-C(Ph)C(Ph)CHR}-(q-C5H5),], existing as isomers for R = M e or C0,Et due to differing orientations of the p-CHR substituent. The structure of [Ru,(CO) (p-CH,){p-C( Ph)C( Ph)CH,}(q-C,H,),] Ru( 1)-Ru(2) Ru( 1)-C(3) Ru( 1)-C( 1 1) Ru( 1)-C( 13) Ru( 1)-C( 15)

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