Infrared spectra of CX2=CoX2 and CX3-CoX complexes from reactions of laser-ablated cobalt atoms with halomethanes.

Simple cobalt complexes with substantial carbon-cobalt double bond character are produced in Co atom reactions with tetra-, tri-, and dihalomethanes, whereas insertion complexes are identified only in the dihalomethane matrix infrared spectra. These complexes are identified from matrix infrared spectra and comparison with frequencies computed by density functional theory. Exclusive generation of carbenes in the tetrahalomethane systems is consistent with the computational results that the staggered allene-type conformer is the only meaningful energy minimum in the reaction path. Their short C-Co bondlengths of 1.732-1.764 A and CASSCF computed bond orders near 1.7 are also appropriate for carbon-cobalt double bonds. Hence, reactions of laser-ablated Co atoms are effective means to generate rarely reported high oxidation-state Co complexes with carbon-cobalt double bonds. Unlike the Rh and Ir cases, Co carbynes (with C-Co triple bonds) are not formed. The observation of CH(2)Cl-CoF with photoreversible intensity variation in the spectra provides unique insight on halogen migration from interconversion with CH(2)F-CoCl through the CH(2)=CoFCl carbene.