Abstract:
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-nLn (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. Photofragmentation (eg, Ru3(CO)12 + 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. I 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 (eg. Ru3(CO)12 + L Ru3(CO)12L + 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.