Photogeneration of Reactive Organometallic Species

摘要

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.