An ESR study of photochemical reactions of Co 2 (CO) 6 (PBu 3 ) 2 with quinones and phenothiazine

The photochemical reactions of Co 2 (CO) 6 (PBu 3 ) 2 with various quinones and phenothiazine were studied by ESR. The results indicate that the photolysis of Co 2 (CO) 6 (PBu 3 ) 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 Co 2 (CO) 6 (PBu 3 ) 2 was irradiated in the presence of p ‐quinones, only the para‐semiquinone radicals were observed. The photolysis of Co 2 (CO) 6 (PBu 3 ) 2 with phenothiazine in toluene yields phenothiazine radical. The sixteen and eighteen electrons rule have been used to account for these observations.