Element–Element Bond Formation upon Oxidation and Reduction

Abstract

The redox chemistry of [(Cp′′′Co)2(μ,η2:η2-E2)2] (E=P (1), As (2); Cp′′′=1,2,4-tri(tert-butyl)cyclopentadienyl) was investigated. Both compounds can be oxidized and reduced twice. That way, the monocations [(Cp′′′Co)2(μ,η4:η4-E4)][X] (E=P, X=BF4 (3 a), [FAl] (3 b); E=As, X=BF4 (4 a), [FAl] (4 b)), the dications [(Cp′′′Co)2(μ,η4:η4-E4)][TEF]2 (E=P (5), As (6)), and the monoanions [K(18-c-6)(dme)2][(Cp′′′Co)2(μ,η4:η4-E4)] (E=P (7), As (8)) were isolated. Further reduction of 7 leads to the dianionic complex [K(18-c-6)(dme)2][K(18-c-6)][(Cp′′′Co)2(μ,η3:η3-P4)] (9), in which the cyclo-P4 ligand has rearranged to a chain-like P4 ligand. Further reduction of 8 can be achieved with an excess of potassium under the formation of [K(dme)4][(Cp′′′Co)2(μ,η3:η3-As3)] (10) and the elimination of an As1 unit. Compound 10 represents the first example of an allylic As3 ligand incorporated into a triple-decker complex.