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) 2 (μ,η 2  : η 2 -E 2 ) 2 ] (E=As (1), P (2); Cp'''=1,2,4-tri(tert-butyl)cyclopentadienyl) with halogens or halogen sources (I 2 , PBr 5 , PCl 5 ) was investigated. For the arsenic derivative, the ionic compounds [(Cp'''Co) 2 (μ,η 4  : η 4 -As 4 X)][Y] (X=I, Y=[As 6 I 8 ] 0.5 (3 a), Y=[Co 2 Cl 6-n I n ] 0.5 (n=0, 2, 4; 3 b); X=Br, Y=[Co 2 Br 6 ] 0.5 (4); X=Cl, Y=[Co 2 Cl 6 ] 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-PBr 2 ) 2 (μ-Br)][Co 2 Br 6 ] 0.5 (6 a), [(Cp'''Co) 2 (μ-PCl 2 ) 2 (μ-Cl)][Co 2 Cl 6 ] 0.5 (6 b) and the neutral species [(Cp'''Co) 2 (μ-PCl 2 )(μ-PCl)(μ,η 1  : η 1 -P 2 Cl 3 ] (7), respectively. As an alternative approach, quenching of the dications [(Cp'''Co) 2 (μ,η 4  : η 4 -E 4 )][TEF] 2 (TEF=[Al{OC(CF 3 ) 3 } 4 ] - , E=As (8), P (9)) with KI yielded [(Cp'''Co) 2 (μ,η 4  : η 4 -As 4 I)][I] (10), representing the homologue of 3, and the neutral complex [(Cp'''Co)(Cp'''CoI 2 )(μ,η 4  : η 1 -P 4 )] (11), respectively. The use of [(CH 3 ) 4 N]F instead of KI leads to the formation of [(Cp'''Co) 2 (μ-PF 2 )(μ,η 2  : η 1  : η 1 -P 3 F 2 )] (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 2 , that are difficult to control.