Pressure as mechanistic indicator in organometallic photochemistry

Abstract

We have recently undertaken a systematic study of the effect of pressure on photosubstitution reactions of organometallic, mostly carbonyl, complexes of the type M(CO) 6, M(CO) 5L and M(CO) 4L⌢L, where M = Cr, Mo and W. In some systems it was possible to measure the effect of pressure on both the photosubstitution quantum yield and the lifetime of the lowest excited state, whereas in others it was only possible to measure the former. The results are discussed in reference to data available for thermal substitution and photo-induced substitution reactions of related complexes. The results demonstrate that pressure is a key parameter, and therefore a mechanistic indicator, to distinguish between associative and dissociative photosubstitution processes of carbonyl complexes, and to discriminate between different pathways that originate from different electronic states.