CHARACTERIZATION OF ORGANOMETALLIC PRODUCTS FROM THE PHOTOCHEMICAL-REACTION OF TRANS-RH(PME(3))(2)(CO)CL WITH BENZENE

Irradiation of trans-Rh(PMe(3))(2)(CO)Cl (1) in benzene/THF (1:3 v/v) at 230 K in the absence of CO affords three main products Rh(PMe(3))(2)(CO)(Cl)(Ph)H (two stereoisomers) (2 and 3) and trans-Rh(PMe(3))(2)(CO)Ph (4). Both 2 and 3 have phenyl and hydride groups cis and 2 has phenyl trans to CO. All three products revert to 1 (thermally) if the reaction mixture is allowed to warm to room temperature. The arylrhodium compound 4 is formed by elimination of HCl from one (or both) of the isomeric rhodium(III) compounds 2 and 3. The arylrhodium complexes 4 and 2 were identified conclusively by independent synthesis and all compounds were fully characterized by NMR techniques. trans-Rh(PMe(3))(2)(CO)Ph (4) reacts with HCl to give only 2. trans-Rh(PMe(3))(2)(CO)Ph (4) reacts thermally with CO to generate Rh(PMe(3))(2)(CO)(2)(COPh) (5). Under an atmosphere of CO, trans-Rh(PMe(3))(2)(CO)Ph (4) reacts photochemically with benzene to produce benzaldehyde, biphenyl, and benzophenone. The thermal decomposition of a mixture of 2 and 3 formed at low temperature was followed by P-31{H-1} NMR at several temperatures and kinetic parameters for the process were obtained. Although 2 decomposes directly to 1, the dominant pathway by which 3 decomposes is by initial isomerization to 2. For the isomerization of 3 to 2, Delta H double dagger = 94 +/- 9 kJ mol(-1) and Delta S double dagger = +50 +/- 36 J mol(-1) K-1. For the decomposition of 2 to 1, Delta H double dagger = 65 +/- 9 kJ mol(-1) and Delta S double dagger = -57 +/- 37 J mol(-1) K-1.