Carol L. Reichel

Photogeneration of reactive organometallic species

Abstract : A large number of thermally inert organometallic complexes can be photoactivated for stoichiometric and catalytic reactions using visible or ultraviolet light. In favorable cases, low temperature irradiation leads to the generation of spectroscopically detectable intermediates, e.g. (eta 5-C5H5)W(CO)2C2H5 or Fe(CO)eta(alkene)5-eta, that likely participate in catalytic cycles at higher temperatures where the steady state concentration is too low to detect. The dissociative process of CO or H2 loss and metal-metal bond rupture can lead to the coordinatively unsaturated intermediates that pervade homogeneous and heterogeneous catalytic systems. In some cases, the same catalyst as generated thermally at high temperature can be prepared photochemically at low temperature using the same precursor, as in the case of H4Ru4(CO)12 where loss of CO thermally or photochemically produces an active species. In other situations different catalysis results, as reflected in product ratios, when photo-excitation is used compared to thermal activation as in hydrogenation vs. isomerization using H2Os3(CO10. New spectroscopic techniques such as Fourier transform infrared photoacoustic spectroscopy will become important in the in situ analysis of heterogenizea catalyst precursors, where gas/solid interfacial photoreactions can be monitored.

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)

PHOTOACTIVATION OF ORGANOMETALLIC CATALYSTS

Abstract : Photochemistry offers a technique to synthesize unique catalysts, control catalytic reactions, and perturb and better understand conventional catalytic cycles. Recent studies in the authors laboratory concerning photoinduced catalysis using mono-, di-, and trinuclear organometallic catalyst precursors are summarized. Specific systems considered here are (M(CO)nL5-n) (M = Fe, Ru; L = PPh; n = 5,4,3), (M3(CO)12) (M = Fe, Ru, Os), (Ru3(CO)g(PPh3)3), and (Co2(CO)6L2) (L = P(n-Bu)3, P(OPh)3) used to effect catalytic chemistry of 1-pentene including isomerization, hydrogenation, and hydrosilation. (Author)