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

Abstract

The oxidation of [(Cp’’’Co)2(μ,η2 : η2‐E2)2] (E=As (1), P (2); Cp’’’=1,2,4‐tri(tert‐butyl)cyclopentadienyl) with halogens or halogen sources (I2, PBr5, PCl5) was investigated. For the arsenic derivative, the ionic compounds [(Cp’’’Co)2(μ,η4 : η4−As4X)][Y] (X=I, Y=[As6I8]0.5 (3 a), Y=[Co2Cl6‐n I n ]0.5 (n=0, 2, 4; 3 b); X=Br, Y=[Co2Br6]0.5 (4); X=Cl, Y=[Co2Cl6]0.5 (5)) were isolated. The oxidation of the phosphorus analogue 2 with bromine and chlorine sources yielded the ionic complexes [(Cp’’’Co)2(μ‐PBr2)2(μ‐Br)][Co2Br6]0.5 (6 a), [(Cp’’’Co)2(μ‐PCl2)2(μ‐Cl)][Co2Cl6]0.5 (6 b) and the neutral species [(Cp’’’Co)2(μ‐PCl2)(μ‐PCl)(μ,η1 : η1‐P2Cl3] (7), respectively. As an alternative approach, quenching of the dications [(Cp’’’Co)2(μ,η4 : η4‐E4)][TEF]2 (TEF=[Al{OC(CF3)3}4]−, E=As (8), P (9)) with KI yielded [(Cp’’’Co)2(μ,η4 : η4‐As4I)][I] (10), representing the homologue of 3, and the neutral complex [(Cp’’’Co)(Cp’’’CoI2)(μ,η4 : η1‐P4)] (11), respectively. The use of [(CH3)4N]F instead of KI leads to the formation of [(Cp’’’Co)2(μ‐PF2)(μ,η2 : η1 : η1‐P3F2)] (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 XeF2, that are difficult to control.