Element-Element Bond Formation upon Oxidation and Reduction.

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.