Photochemistry of Surface-Confined Organometallics: Photochemical Release of a Surface-Confined Cobalt Carbonyl Catalyst.

Abstract : Inorganic oxide surfaces, SiO2 and Al2O3, bearing - OH functionality have been functionalized with -Co(CO)4 by first treating the solids with (EtO)3SiH, Me2ClSiH or Cl3SiH to introduce Si(3+)H functionality followed by reaction with Co2(CO)8. Derivatized surfaces have been characterized by infrared spectroscopy and compared to solution analogues to confirm the presence of Si(3+)H and Si(3+)Co(CO)4 groups on the surface. The surface-confined Si(3+)Co(CO)4 undergoes photoreactions that begin with loss of CO subsequent to optical excitation in the near-ultraviolet. The photochemistry closely parallels the behavior of solution R3SiCo(CO)4 analogues; CO can be photosubstituted by P(OPh)3 and the surface confined Si(3+)Co(CO)3(P(OPh)3) species is detectable by infrared spectroscopy. Irradiation of the oxide powders bearing Si(3+)Co(CO)4 suspended in Et3SiH solutions results in the release of the -Co(CO)4 into solution as Et3SiCo(CO)4 concurrent with the regeneration of surface Si(3+)H functionality. Irradiation of the powders (Si(3+)Co(CO)4) in the presence of 1-pentene yields Co4(CO)12 in solution and surface Si(3+)(pentenyl) groups. In the presence of Et3SiH/1-pentene photoactivated catalysis by the derivatized powders (Si(3+)Co(CO)4) occurs to give isomerization of the alkene, hydrosilation to give Et3Si(n-pentyl), and small amounts of n-pentane. Reaction under H2 improves the relative yield of n-pentane, while H2/CO mixtures yield no hydroformylation products and lower the observed rate due to CO competing for the coordinatively unsaturated species.