Photochemistry of Osmium-Carbyne Complexes

Upon charge transfer (Os to carbyne) excitation the carbyne complexes Os(CPh)(CO)(PPh3)2Cl and [Os(CPh)(CO)2(PPh3)2]+ with Ph = C6H5 are converted to the carbene complex Os(CHPh)(CO)(PPh3)2Cl2 in solutions containing HCl. It is suggested that the relaxed CT state can be described as square-pyramidal Os(II) complex containing a bent carbyne ligand which carries a lone pair at the coordinating carbon atom. Product formation occurs by the addition of a proton to the carbyne ligand and by attaching a chloride to the osmium completing an octahedral coordination. The cationic carbene complex thus formed is apparently not stable but undergoes a substitut ion of a CO ligand by chloride.