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

The synthesis and properties of the molecular reduction device 7b (Co II –V   5 ++ ) consisting of a reduction catalyst (a derivative of vitamin B 12 , Co II ) 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 Co III /Co II 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 Co I –V   5 0 , 7b exhibits multiple reductive elimination of trans ‐1,2‐dibromocyclohexane to cyclohexene under concomitant oxidation to Co II –V   5 ++ . Rate measurements indicate that the reduction occurs via Co I which is regenerated by intramolecular electron transfer from the periphery of the molecule, i.e. by V 0 and V ++ .