Intermediates in the time-resolved and matrix photochemistry of (.eta.5-cyclopentadienyl)rhodium complexes. Roles of alkane activation and rhodium-rhodium bond formation

Pulsed laser photolysis studies of solutions of Cp{sub 2}Rh{sub 2}(CO){sub 3}, CpRh(CO){sub 2}, and CpRh(C{sub 2}H{sub 4})CO (Cp = {eta}{sup 5}-C{sub 5}H{sub 5}) are reported using UV/vis and IR detection. Isotopic labeling and polarized photolysis demonstrates that the Rh{sub 2}(CO){sub 2} unit is planar with CO bridges perpendicular to the RhRh axis. Metal-metal bond fission of Cp{sub 2}Rh{sub 2}(CO){sub 3} is observed only in CO-doped matrices. The major photoproduct of Cp{sub 2}Rh{sub 2}(CO){sub 3} in solution is (CpRh({mu}-CO)){sub 2}, which reacts with CO to re-form starting material. The first observable product of photolysis of CpRh(CO){sub 2} in cyclohexane at room temperature is CpRh(CO)(C{sub 6}H{sub 11})H, formed by insertion of CpRhCO into the solvent C-H bonds within 400 ns. The IR experiments show that photolysis of CpRh(C{sub 2}H{sub 4})CO gives a higher yield of CpRh(CO)(C{sub 6}H{sub 11})H than that from CpRh(CO){sub 2}.