Halogenation and Nucleophilic Quenching: Two Routes to E-X Bond Formation in Cobalt Triple-Decker Complexes (E=As, P; X=F, Cl, Br, I).

The oxidation of [(Cp'''Co) (μ,η  : η -E ) ] (E=As (1), P (2); Cp'''=1,2,4-tri(tert-butyl)cyclopentadienyl) with halogens or halogen sources (I , PBr , PCl ) was investigated. For the arsenic derivative, the ionic compounds [(Cp'''Co) (μ,η  : η -As X)][Y] (X=I, Y=[As I ] (3 a), Y=[Co Cl I ] (n=0, 2, 4; 3 b); X=Br, Y=[Co Br ] (4); X=Cl, Y=[Co Cl ] (5)) were isolated. The oxidation of the phosphorus analogue 2 with bromine and chlorine sources yielded the ionic complexes [(Cp'''Co) (μ-PBr ) (μ-Br)][Co Br ] (6 a), [(Cp'''Co) (μ-PCl ) (μ-Cl)][Co Cl ] (6 b) and the neutral species [(Cp'''Co) (μ-PCl )(μ-PCl)(μ,η  : η -P Cl ] (7), respectively. As an alternative approach, quenching of the dications [(Cp'''Co) (μ,η  : η -E )][TEF] (TEF=[Al{OC(CF ) } ] , E=As (8), P (9)) with KI yielded [(Cp'''Co) (μ,η  : η -As I)][I] (10), representing the homologue of 3, and the neutral complex [(Cp'''Co)(Cp'''CoI )(μ,η  : η -P )] (11), respectively. The use of [(CH ) N]F instead of KI leads to the formation of [(Cp'''Co) (μ-PF )(μ,η  : η  : η -P F )] (12) and 2, thereby revealing synthetic access to polyphosphorus compounds bearing P-F groups and avoiding the use of very strong fluorinating reagents, such as XeF , that are difficult to control.