Factors governing the equilibrium between metal-alkyl, alkylidene and alkylidyne:: MCX2R, X-M=CXR and X2MCR

The reactions of vinyl ethers, H2C=CH(OR), with RuHClL2 (L = (PPr3)-Pr-i) furnish the carbene complexes RuHCl[C(CH3)(OR)]L-2 by H migration. Os(H)(3)ClL2 serves as a surrogate for unknown OsHClL2, to give the analogous carbene, but this transforms further for R=Ph to give the carbyne OsHCl(OPh)(CCH3)L-2. DFT calculations furnish insight into the relative thermodynamic stability of the various isomeric species, and are consistent with the major influence of pi -donation by OR, as well as the preference of Os (versus Ru) for saturation and higher oxidation state. Comparison of the reactivity of H2C=CHD0 (D-0 = pi -donor) towards MHClL2 versus Cp2ZrHCl shows the dominant influence of metal pi -donor power. Ruthenium and osmium complexes containing an MCF3 subunit show remarkably facile isomerization to FM=CF2 carbenes. (C) 2001 Published by Elsevier Science B.V.