Photolysis of M(CO)6, where M = Cr, Mo, and W, in Nujol mulls at 77 K resulted in the formation of "free" CO and C4-upsilon M(CO)5 photoproducts. This reaction was found to be photochemically and thermally reversible. Similarly, the photolysis of the metal "half-sandwich" complexes (eta-6-C6H6)Cr(CO)3, (eta-5-C5H5)Mn(CO)3, (eta-5-CH3C5H4)Mn(CO)3 and (eta-5-C5H5)Re(CO)3 in Nujol at 77 K was found to form the corresponding dicarbonyl photoproducts and "free" CO. These reactions were found to be photochemically reversible. (eta-6-C6H6)Cr(CO)3 and (eta-5-C5H5)Re(CO)3 were also found to produce small amounts of dinuclear products directly upon photolysis, while (eta-5-C5H5)Mn(CO)3 and (eta-5-CH3C5H4) Mn(CO)3 formed similar species upon annealing.