Carbon−Carbon Bonds Functioning as Electron Shuttles: The Generation of Electron-Rich Manganese(II)−Schiff Base Complexes and Their Redox Chemistry

Abstract

The reduction of [Mn(II)-salophen] derivatives [salophen = N,N ‘-ethylenebis(salicylideneaminato) dianion] led to the formation of C−C bridged dimers. Such C−C bonds function as two electron shuttles in electron-transfer reactions. The reduction of [Mn(salophen)(THF)]2 (1) and [Mn(3,5-But4salophen)(THF)]2 (3) with 2 equiv of sodium metal led to the corresponding single C−C bond bridged dimers, [Mn2(salophen2)Na2(DME)4] (5) [salophen2 = C−C bonded salophen dimer] and [Mn2(3,5-But4salophen2)Na2(DME)6] (7), respectively. Complexes 5 and 7 undergo a further two electron reduction to [Mn2(*salophen2*)Na4(DME)6] (6) [*salophen2* = C−C doubly bonded salophen dimer] and [Mn2(*3,5-But4salophen2*)Na4(DME)4] (8), respectively, both containing a double C−C bridge. The obtention of [Mn2{salophen(Me)CH2)}2Na4(DME)4] (9) from [Mn(salophen-Me2)(THF)]2 (2) strongly supports the existence of free radical precursors in the formation of C−C bonds. Complex 6 has been used as a source of four electrons in a number of reactions...