Three reversibly interconvertible redox states of boradigermaallyl: syntheses of radical allyl anion and allyl dianion

Abstract

A methyl derivate of our previously published chloro-boradigermaallyl is synthesized by addition of MeBBr2 to the bis(germylene) A followed by KC8 reduction. Both derivatives, the BCl (1a) and BMe (1b) boradigermaallyls, feature an allyl-type delocalized Ge-B-Ge 2π-electron system. In this work, the reversible two step reduction of both compounds to the persistent radical anions and dianions is presented. EPR data and particularly hyperfine coupling constants to the 11B and 73Ge nuclei confirm allyl-type delocalization of the radicals. Computed spin densities illustrate the structural analogy to the organic allyl radical. Cyclic voltammetry measurements of the boradigermaallyl compounds exhibit one reduction wave within the accessible electrochemical window indicating a reduction potential of the dianionic species beyond -2.2 V [vs. (Ag/Ag⁺)].