Dianions as Formal Oxidants:Synthesis and Characterization of Aromatic Dilithionickeloles from 1,4-Dilithio-1,3-butadienes and [Ni(cod)2].

Organolithium compounds can behave as reductants but never as oxidants in redox reactions. Reported herein is that 1,4-dilithio-1,3-butadienes reacted with [Ni(cod)2] (cod=1,5-cyclooctadiene) to deliver dilithionickeloles. Single-crystal Xray structural analysis revealed a coplanar structure of dilithionickeloles with an averaging of bond lengths. XPS data confirmed the oxidation state of Ni in dilithionickeloles was Ni2+. 7Li NMR spectra of dilithionickeloles and theoretical calculations revealed a considerable aromatic character. In this redox reaction, the dilithio dianionic compounds behaved as formal oxidants, thus oxidizing Ni0 into Ni2+. These results demonstrated that organolithium compounds with π-conjugation could be used as oxidants and could continue to accept extra electrons. [ABSTRACT FROM AUTHOR]