A Reduction Catalyst Powered by Its Own 10‐Electron Battery: Synthesis and properties of a pentaviologen‐linked corrinatocobalt complex

Abstract

AbstractThe synthesis and properties of the molecular reduction device 7b (CoII–V) consisting of a reduction catalyst (a derivative of vitamin B12, CoII) and a covalently linked 10‐electron reservoir (five viologen units, V++) is described. The five viologen subunits were introduced at C(2) and C(3) of the side chains c and g and b, e and f, respectively, of an appropriate derivative of heptamethyl cob(III)yrinate by N‐alkylation of 1‐methyl‐4,4′‐bipyridinium iodide (see Scheme). The pentaviologen‐linked corrinatocobalt(II) complex 7b behaves as a molecular electron trap with respect to the CoIII/CoII redox couple. The phenomenon is related to the structural and thermodynamic relation of the corrin and viologen subunits in 7b, i.e. the relative redoc energies and the spherical inner‐outer arrangement of the types of redox systems. When completely reduced to CoI–V, 7b exhibits multiple reductive elimination of trans‐1,2‐dibromocyclohexane to cyclohexene under concomitant oxidation to CoII–V. Rate measurements indicate that the reduction occurs via CoI which is regenerated by intramolecular electron transfer from the periphery of the molecule, i.e. by V0 and V++.