REACTIONS OF SINGLET OXYGEN WITH ORGANOMETALLIC COMPLEXES .2. FORMATION OF A METASTABLE RHODIUM-DIOXYGEN COMPLEX

Photooxidation of the rhodium analogue of Vaska's complex (Rh(CO)Cl(PPh3)2, 1) at low temperature leads to the novel peroxo complex Rh(CO)Cl(PPh3)2O2 (2). The rate constant for combined physical and chemical interaction of singlet oxygen with 1 is (3.1 +/- 0.2) x 10(8) M-1 s-1 in CDC]3; that for chemical reaction alone is (1.2 +/- 0.5) x 10(8) M-1 s-1. Complex 2 is unstable at room temperature and rapidly loses dioxygen to re-form the starting material. Activation parameters for the decomposition are DELTAH(double dagger) = 23 +/- 2 kcal and DELTAS(double dagger) = 13 eu at 0-degrees-C.