Photochemistry of (η6-arene)Mo(CO)3 and the role of alkane solvents in modifying the reactions of coordinatively unsaturated metal carbonyl fragments

The reactions of (eta(6)-arene)Mo(CO)(2)(Sol) and M(CO)(5)(Sol) with CO have been studied in a range of alkane solvents (Sol), and the kinetic and activation parameters have been determined (M = Cr, Ma, or W). For M = Cr the Delta H double dagger is constant (22 +/- 2 kJ mol(-1)), while the Delta S double dagger term becomes less negative as the alkane chain length increases. For the larger metals the variation in kinetic and activation parameters is less significant. Solvent displacement by CO involves an interchange mechanism for the Cr system, while for Mo or W complexes the mechanism is more associative in character. The photochemistry of (eta(6)-arene)Mo(CO)(3) (arene = benzene, mesitylene, p-xylene, or hexamethylbenzene) compounds was investigated by laser flash photolysis, supported by matrix isolation and time-resolved infrared spectroscopy (TRIR). In contrast to the behavior to the analogous (eta(6)-arene)Cr(CO)(3), it is found that the efficiency for photochemical expulsion of CO from (eta(6)-mesitylene)Mo(CO)(3) is markedly wavelength dependent (Phi(CO) = 0.587, 0.120, and 0.053 at 266, 313, and 334 nm, respectively).