Photoactivation of cobalt carbonyl catalysts: generation of reactive mononuclear fragments from dinuclear, metal-metal bonded complexes

Abstract : The metal-metal bonded complexes (CO2(CO)6L2) (l = p(n-Bu)3, P(OPh)3) and Fe(n5-C5H5) (CO)2CO)(CO)3(P(OPh)3)) all undergo efficient (theta greater than 0.1 at 355 nm) photochemical metal-metal bond cleavage to produce reactive 17-valence electron (CO(CO)3L) fragments. In the presence of 1-pentene no alkene isomerization is found for L = P(n-Bu)3; low, but significant, photocatalytic activity is found for L = P(OPh)3 or when the P(n-Bu)3 complex is irradiated in the presence of P(OMe)3. The Co(CO)3L) precursors are strikingly more active when irradiation is carried out in the presence of HSiEt3, a hydride source. Both alkene isomerization and n-pentane formation are observed, along with small quantities of Si-containing products. The Fe(n to the fifth power-C5H5)(CO)2) radical photogenerated independently from (Fe2(n to the fifth power-C5H5)2(CO)4 is not active under any conditons used thus far. The activity of 17-valence electron radicals in this application is Co(CO)3(P(OPh)3)) Co(CO)3(P(n-Bu)3)) Fe(n to the fifth power-C5H5)(CO)2). These species are not themselves effective catalysts but do seem to react with HSiEt3 to form catalytically active, mononuclear Co-hydride complexes. (Author)