Photoreactions of the Triruthenium Cluster Ru₃(CO)₁₂ and Substituted Analogues

Reported is a comprehensive investigation of the medium, ligand, and wavelength effects on the quantum yields and flash photolysis kinetics for the photofragmentation and photosubstitution reactions of the trinuclear ruthenium cluster Ru₃(CO)₁₂. Also described are some related studies of the substituted clusters Ru₃(CO)_12-nL_n (L = P(OCH₃)₃, PPh₃, P(p-tolyl)₃, or P(O(o-tolyl))₃). These results are interpreted in terms of the following model for Ru₃(CO)₁₂ photochemistry. Photo-fragmentation (e.g., Ru₃(CO)_]2 + 3L → 3Ru(CO)₄L) occurs predominantly from the lowest energy excited state and proceeds via an intermediate (I) isomeric to Ru₃(CO)₁₂ but not a diradical. 1 is proposed to have one coordinatively unsaturated ruthenium center trapable by a two-electron donor, i.e., L, to give a second intermediate Ru₃(CO)₁₂L which is the precursor to the photofragmentation products. Kinetic flash photolysis observations demonstrate that the lifetime of the latter intermediate is markedly dependent on the nature of L. Photosubstitution reactions (e.g. Ru₃(CO)₁₂ + L → Ru₃(CO)_nL + CO) are proposed to occur largely from higher energy excited states via CO dissociation to give the unsaturated intermediate Ru₃(CO)₁₁, and flash photolysis studies establish the reactivity of this species with various L to follow the order CO > P(OCH₃)₃ > PPh₃.