Element–Element Bond Formation upon Oxidation and Reduction

The redox chemistry of [(Cp′′′Co)(2)(μ,η(2):η(2)‐E(2))(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,η(4):η(4)‐E(4))][X] (E=P, X=BF(4) (3 a), [FAl] (3 b); E=As, X=BF(4) (4 a), [FAl] (4 b)), the dications [(Cp′′′Co)(2)(μ,η(4):η(4)‐E(4))][TEF](2) (E=P (5), As (6)), and the monoanions [K(18‐c‐6)(dme)(2)][(Cp′′′Co)(2)(μ,η(4):η(4)‐E(4))] (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,η(3):η(3)‐P(4))] (9), in which the cyclo‐P(4) ligand has rearranged to a chain‐like P(4) ligand. Further reduction of 8 can be achieved with an excess of potassium under the formation of [K(dme)(4)][(Cp′′′Co)(2)(μ,η(3):η(3)‐As(3))] (10) and the elimination of an As(1) unit. Compound 10 represents the first example of an allylic As(3) ligand incorporated into a triple‐decker complex.