Reduction-oxidation properties of organotransition-metal complexes. Part 8. Formation and reactivity of the radical cations [Fe(CO)3L2]+, and the mechanism of the oxidative elimination reaction of [Fe(CO)3L2] with halogens

Abstract

Cyclic-voltammetric studies in CH₂Cl₂ show that [Fe(CO)₃L₂][1; L = PPh₃, AsPh₃, PMePh₂, P(NMe₂)₃, or P(OPh)₃; L₂= Ph₂PCH₂CH₂PPh₂(dppe) or Ph₂PCH₂PPh₂(dppm)] undergoes one-electron oxidation to the radical cation [Fe(CO)₃L₂]⁺(2) which may be chemically generated from (1) using silver(I) salts or [N(C₆H₄Br-p)₃][PF₆]. The complex (2; L = PPh₃) reacts with halogens to give diamagnetic [FeX(CO)₃(PPh₃)₂][PF₆](3) which yields [FeX₂(CO)_4-n(PPh₃)_n](4; X = I, n= 1; X = Br, n= 1 and 2; X = Cl, n= 2) with X^–. Halide ions react directly with (2; L = PPh₃) to give mixtures of (1; L = PPh₃) and (4)via the paramagnetic intermediate [FeX(CO)₃(PPh₃)₂](5). A mechanism is proposed for the oxidative elimination reaction of (1) with halogens; the reactions of (2), and i.r. stopped-flow kinetic studies, implicate (2) and (5) as redox-active intermediates.