Photofragmentation kinetics of some triruthenium carbonyl clusters

Abstract

The photokinetics of fragmentation reactions of [Ru₃(CO)₁₂] with L = PPh₃, P(OPh)₃, AsPh₃, CO, 1-octene, and methyl acrylate in a variety of solvents have been studied. Quantum yields increase to limiting values at high [L] but the limiting values vary significantly with the nature of L. The low efficiency of photochlorination in chlorocarbon solvents, the absence of inhibition by CO of reactions with L = PPh₃, and the absence of appropriate effects of varying incident light intensity all suggest that the first kinetically significant product is a non-radical reactive isomer of [Ru₃(CO)₁₂]. This can revert to [Ru₃(CO)₁₂] or react with L to form [Ru₃(CO)₁₂L] which itself can revert to [Ru₃(CO)₁₂] or undergo fragmentation. The former choice governs the rate of increase with [L] to a limiting quantum yield whereas the latter choice governs the dependence of the values of the limiting quantum yield on the nature of L. This scheme is also applicable to photoreactions of [Os₃(CO)₁₂] and the quantitative behaviour of the two clusters is not significantly different. Only lower limits for quantum yields for formation of the reactive isomers can be deduced from the data and it remains possible that the primary photophysical process is the formation of a very short-lived diradical by homolysis of a metal-metal bond. Photokinetic studies of reactions of [Ru₃(CO)₉L₃] with L (L = PPh₃ or PBuⁿ₃) are also reported.