SOLID-STATE PHOTOCHEMICAL DIAG-LAT ISOMERIZATION OF (ETA(5)-C(5)H(4)R)RE(CO)(L)X(2) ON THE SURFACE OF SILICA-GEL

Room-temperature visible illumination (200 W light source) of diag-(et a(5)-C(5)H(4)R)Re(Co,(L)X(2) (R = H, alkyl; L = CO, P(OR)(3); X = Br, I) adsorbed on silica gel results in isomerization of the complexes in to the corresponding lateral isomers in good yield (typically >80%). F or L = CO, the isomerization reactions occurred in the direction rever se to that found in solution in which lat-to-diag isomerization was ob served. It was found that the ratio of diagonal to lateral isomers est ablished on the surface of silica gel was influenced by both X and L, viz. (eta(5)-C(5)H(4)Me>Re(Co)[P(OR)(3)]Br-2 > (eta(5)-C(5)H(4)Me)Re(C O)(2)Br-2 > (eta(5)-C(5)H(4)Me)Re(CO)(2)I-2. Chemical removal of surfa ce hydroxyl soups with Me(2)SiCl(2) revealed that only a monolayer of the rhenium complex chemically adsorbed on the surface of the silica g el underwent isomerization. A mechanism to rationalize the role of the silica surface hydroxyl groups is described.