Factors governing the equilibrium between metalalkyl, alkylidene and alkylidyne: MCX2R, XMCXR and X2MCR

The reactions of vinyl ethers, H2CCH(OR), with RuHClL2 (L=PiPr3) furnish the carbene complexes RuHCl[C(CH3)(OR)]L2 by H migration. Os(H)3ClL2 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)L2. DFT calculations furnish insight into the relative thermodynamic stability of the various isomeric species, and are consistent with the major influence of π-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 (D0=π-donor) towards MHClL2 versus Cp2ZrHCl shows the dominant influence of metal π-donor power. Ruthenium and osmium complexes containing an MCF3 subunit show remarkably facile isomerization to FMCF2 carbenes.