Stable Osmium Hydrido−Carbene Complexes with CH2 and Secondary Carbenes CHR as Ligands

The five-coordinate compound [OsHCl(CO)(P i Pr 3 ) 2 ] ( 1 ) reacts with diazoalkanes RCHN 2 (R = H, Ph, CO 2 Et, SiMe 3 ) at room temperature to give instead of the expected insertion product [Os(CH 2 R)Cl(CO)(P i Pr 3 ) 2 ] the isomeric osmium(II) hydrido−carbene complexes [OsHCl( CHR)(CO)(P i Pr 3 ) 2 ] ( 2 − 5 ) containing the hydrido and the carbene ligands in trans disposition. Treatment of 3 (R = Ph) with HCl in toluene affords the dichloro complex [OsCl 2 ( CHPh)(CO)(P i Pr 3 ) 2 ] ( 6 ), the molecular structure of which has been determined.