Upon treatment with methyl-lithium followed by HBF,-OEt, a carbon monoxide ligand of the palkylidene complex [Ru,(CO),(p-CO) (p-CMe,) (q-C5H5),] (1) is converted into p-ethylidyne, giving [Ru,(CO),(p-CMe) (p-CMe,) (q-C5H5),] + (2). This is deprotonated readily by water to form the pvinylidene complex [ Ru2( CO),(p-CCH,) (p-CMe,) (q-C5H5),] (3), which quantitatively regenerates (2) with HBF,-OEt,. Addition of NaBH, t o (2) results in hydride attack on p-CMe to yield the di-palkylidene complex [ Ru,(CO),(p-CHMe) (p-CMe,) (q-C5H5),] (4) as cis and trans isomers. The structure of the trans isomer has been established by X-ray diffraction. Crystals are triclinic, space group P i , with Z = 2 in a unit cell for which a = 8.474( 2), b = 7.802(3), c = 12.989(5) A, CI = 99.42(3), p = 96.96(3), and y = 107.73(3)". The structure was solved by heavy-atom methods and refined to R 0.026 (R' 0.031 ) for 4 092 independent intensities. A ruthenium-ruthenium single bond of 2.701 (1) A is symmetrically bridged by ethylidene [mean RU-C 2.079(3)] and isopropylidene [mean RU-C 2.1 07(3) A] ligands to form an approximately planar Ru,C, ring with a non-bonding Me,C CHMe distance of 3.20 A. Upon thermolysis the alkylidenes link to evolve Me,C=CHMe, Me,CHCH=CH,, and Et(Me)C=CH,. The absence of C, and C, hydrocarbons indicates that the alkylidene coupling occurs intramolecularly, and the electronic and stereochemical requirements of this process are discussed. Unlike mono-p-alkylidene complexes, [Flu,( CO),(p-CO) (p-CR,) (q-C5H5),], the cis and trans forms. of (4) d o not interconvert thermally below 145 "C, but U.V. irradiation effects a slow trans to cis isomerisation. U.V. irradiation of (4) in the presence of dimethyl acetylenedicarboxylate promotes ethylidene-alkyne linking to form [ Ru,( CO) (p-CMe,){p-C(CO,Me)C(CO,Me)CHMe}(q-C,H,),],but with ethyne both of the alkylidenes are lost and the ruthenium-ruthenium double-bonded complex [ Ru,(p-CO) (p-C,H,) (q-C5H5),] is produced.The recognition ' that methylene is an important surface species during transition-metal catalysed hydrogenation of carbon monoxide (the Fischer-Tropsch Synthesis) has prompted the synthesis and study of a wide range of p-alkylidene c ~m p l e x e s . ~ However, complexes which contain two p-alkylidene ligands bridging a dinuclear metal centre are and at the time this work was begun their chemistry had been little explored. Yet such species provide an attractive model for alkene generation on a metal surface through alkylidene-alkylidene coupling. In order to investigate this process we have synthesised model di-p-alkylidene diruthenium complexes. We report here on the chemistry of trans-[Ru,(CO),(p-CHMe)(p-CMe2)(q-C5H5)J, which has been outlined in a preliminary form,14 and in the following paper describe that of cis-
[Ru,(CO),(~-CHM~),(~~:~~'-C~H~CH~C~H~)].~~
Results and DiscussionSynthesis of'Di-p-hydrocarbyl Complexes.-In an earlier Part of this Series we described how, employing the technique of Rosenblum and co-workers,'6 a carbonyl ligand could be converted...