Catalytic reduction of 1,8-diiodooctane by electrogenerated cobalt(I) salen and formation of μ-(1,8-n-octyl)-bis[(salen)cobalt(III)]

Cyclic voltammetry, controlled-potential electrolysis, ultraviolet-visible spectrophotometry (UV-vis), elemental analysis, and mass spectrometry have been employed to investigate and characterize the catalytic reduction of 1,8-diiodooctane by electrogenerated cobalt(I) salen. A cyclic voltammogram for reduction of cobalt(II) salen in the presence of excess 1,8-diiodooctane exhibits two waves. We attribute the first wave to the formation of cobalt(I) salen and its fast follow-up reaction with 1,8-diiodooctane; the latter reaction gives both 8-iodooctylcobalt(III) salen and mu-(1,8-n-octyl)-bis[(salen)cobalt(III)], the relative amounts of these two species depending on the substrate-to-catalyst ratio. One-electron reduction of 8-iodooctylcobalt(III) salen and two-electron reduction of mu-(1,8-n-octyl)-bis[(salen)cobalt(III)] are responsible for the second voltammetric wave. Controlled-potential electrolyses of the cobalt(II) salen-1,8-diiodooctane system at potentials corresponding to the second wave produce little (if any) current after the first few seconds of the electrolysis. However, when 1,1,1,3,3,3-hexafluoro-2-propanol (a proton donor) is added to the system, the catalytic reduction proceeds normally to afford mainly n-octane and some n-hexadecane. As a part of this investigation, we have prepared and characterized mu-(1,8-n-octyl)-bis[(salen)cobalt(III)]. (C) 1999 Elsevier Science S.A. All rights reserved.