Reaction of OsHCl( C CHSiMe 3 )(P i Pr 3 ) 2 with HC⋮CSiMe 3 gives OsCl{( E )-CH CHSiMe 3 }(C CHSiMe 3 )(P i Pr 3 ) 2, which reacts with excess CO to give the C−C coupling product OsCl{C(CH CHSiMe 3 ) CHSiMe 3 }(CO) 2 (P i Pr 3 ) 2 . Reaction of [RuH(CO)(P t Bu 2 Me) 2 ] + (as its B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 - salt) with 2 mol of HC⋮CSiMe 3 gives immediately the C−C coupling product [Ru{η 3 -(Me 3 Si)CH C−CH CH(SiMe 3 )}(CO)(P t Bu 2 Me) 2 ] + . The crystal structure of this latter product reveals one agostic t Bu C−H interaction with Ru. Ab initio (DFT B3LYP) calculations show the presence of two isomeric structures as minima on the potential energy surface, one with vinyl and vinylidene ligands, and the other with a butadienyl ligand bonded in an η 3 manner to the metal. The calculations show a strong preference for the butadienyl structure when the metal fragment is Ru(CO)L 2 + and a nearly degenerate situation when the metal fragment is OsClL 2 (L = PH 3 ).
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Huang et al. (1998) studied this question.
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