An ESR study of photochemical reactions of Co2(CO)6(PBu3)2 with quinones and phenothiazine

Abstract

The photochemical reactions of Co2(CO)6(PBu3)2 with various quinones and phenothiazine were studied by ESR. The results indicate that the photolysis of Co2(CO)6(PBu3)2 in the presence of o-quinones led to the observation of an ESR spectrum, showing a broad 8 or 12 groups of hyperfine lines due to interaction with cobalt (Co, 1 = 7/2). The results show that with o-quinones the cobalt radical adducts are formed via metal chelation to the carbonyl oxygens. However, when Co2(CO)6(PBu3)2 was irradiated in the presence of p-quinones, only the para-semiquinone radicals were observed. The photolysis of Co2(CO)6(PBu3)2 with phenothiazine in toluene yields phenothiazine radical. The sixteen and eighteen electrons rule have been used to account for these observations.