One-electron transfer reactions of cyclooctatetraene (cot) complexes: electron spin resonance studies of 60CO γ-irradiated [Fe(CO)2L(η4-cot)][L = CO or P(OPh)3]

Abstract

Exposure of [Fe(CO)₂L(η⁴-cot)][cot = cyclooctatetraene, L = CO or P(OPh)₃] in CFCl₃ at 77 K to ⁶⁰Co γ-rays gave the cation [Fe(CO)₂L(C₈H₈)]⁺ the ESR spectrum of which is consistent with a metal-based radical with considerable spin density on the C₈ ring. In 2-methyltetrahydrofuran or CD₃OD ⁶⁰Co γ-irradiation of [Fe(CO)₃(η⁴-cot)] gave two different radical anions. ESR spectroscopy suggests the primary centre, A, is [Fe(CO)₃(η⁴-cot)]^– in which the unpaired electron is localised largely on the unbound diene fragment of the C₈ ring. On annealing above 77 K, centre A gave a second species, B, the ESR spectrum of which is consistent with migration of the unpaired electron to a d_z²-type metal orbital; one of the alkene-metal bonds of A is cleaved and B is formulated as the 17-electron anion [Fe(CO)₃(η²-cot)]^–. For [Fe(CO)₂{P(OPh)₃}(η⁴-cot)], the primary centre, A′, is very similar to A, the singly occupied molecular orbital being strongly confined to the cot ligand. The second species, B′, is similar to B but gave a large ³¹P hyperfine splitting, suggesting the phosphite ligand lies close to the z axis.