Four-electron reduction of benzene by a samarium(ii)-alkyl without the addition of external reducing agents

Abstract

Benzene reduction by molecular complexes remains an important synthetic challenge, requiring harsh reaction conditions involving group I metals. Reductions of benzene, to date, typically result in a loss of aromaticity, although the benzene tetra-anion, a 10π-electron system, has been calculated to be stable and aromatic. Due to the lack of sufficiently potent reductants, four-electron reduction of benzene usually requires the use of group I metals. Here we demonstrate the four-electron reduction of benzene and some of its derivatives using a samarium(ii) alkyl reagent, with no requirement for group I metals. Whereas organosamarium(ii) typically reacts through one-electron processes, the compounds reported here feature a rare two-electron process. Combined experimental and computational results implicate a transient samarium(i) intermediate involved in this reduction process, which ultimately provides the benzene tetra-anion. The remarkably strong reducing power of this samarium(ii) alkyl implies a rich reactivity, providing scope for its application as a reducing agent. Benzene reduction by molecular complexes remains a considerable synthetic challenge, and typically requires harsh reaction conditions involving group I metals. Now it has been shown that a highly polar organometallic samarium alkyl complex enables the reduction of benzene to its tetra-anion without the need for a group I metal.