Quinone-functionalized Transition Metal Complexes for Multi-electron Transfer. The Electrochemistry of a Bis -Naphthoquinone-Functionalized Schiff Base Ni(II) complex

Abstract

Ni(II)NQ 2 en, a Ni(II) complex with two naphthoquinone groups incorporated into a Schiff-base ligand, undergoes two reversible reductions in which the naphthoquinone (NQ) groups are each reduced by one electron to naphthsemiquinone radical anions (SQ): $$\\eqalignno{& {\\rm Ni}({\\rm II}){\\rm NQ}_2 {\\rm en} + {\\rm e}^ - \\mathop \ o \\limits^{E_1^{\\,0} }[{\\rm Ni}({\\rm II})({\\rm SQ}, {\\rm NQ}){\\rm en}]^ - \\cr & [{\\rm Ni}({\\rm II})({\\rm SQ}, {\\rm NQ}){\\rm en}]^ - + {\\rm e}^ - \\mathop \ o \\limits^{E_2^{\\,0} } [{\\rm Ni}({\\rm II}){\\rm SQ}_2 {\\rm en}]^{2 - } \\cr}$$ Analysis of the cyclic and differential pulse voltammetry waves shows that $E_2^0 - E_1^0 = - 36\\, {\\rm mV}$ , a j E 0 that corresponds to two noninteracting redox centers.