Photoinduced radical chain reactions between alkylcobalt(III) complexes and iodine

Abstract

Cobalt–carbon bonds of various alkylcobalt(III) complexes, cis-[CoR₂(bipy)₂]ClO₄(R = Me, Et, or PhCH₂; bipy = 2,2′-bipyridine), trans-[CoMe₂(L)](L = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioximate), and [CoR(Hdmg)₂(py)](R = Me or Et; Hdmg = dimethylglyoximate; py = pyridine), are readily cleaved by iodine in carbon tetrachloride to yield alkyl iodides via photoinduced radical chain reactions with large quantum yields (e.g.Φ= 7.0 × 10³) under low-energy irradiation (λ 517 nm). The rate-determining step in the radical chain reactions is suggested to be electron transfer from alkylcobalt(III) complexes to iodine atoms (I˙) which are produced by the photodissociation of I₂, based on the formation of by-products that could arise only via electron-transfer processes as well as the kinetic comparison between alkylcobalt(III) complexes and tetra-alkyltin compounds.