Ring Contraction by NHC-Induced Pnictogen Abstraction.

The reaction of [Cp'''Co(η4 -P4 )] (1) (Cp'''=1,2,4-tBu3 C5 H2 ) with Me NHC (Me NHC=1,3,4,5-tetramethylimidazol-2-ylidene) leads through NHC-induced phosphorus cation abstraction to the ring contraction product [(Me NHC)2 P][Cp'''Co(η3 -P3 )] (2), which represents the first example of an anionic CoP3 complex. Such NHC-induced ring contraction reactions are also applicable for triple-decker sandwich complexes. The complexes [(Cp*Mo)2 (μ,η6:6 -E6 )] (3 a, 3 b) (Cp*=C5 Me5 ; E=P, As) can be transformed to the complexes [(Me NHC)2 E][(Cp*M)2 (μ,η3:3 -E3 )(μ,η2:2 -E2 )] (4 a, 4 b), with 4 b representing the first structurally characterized example of an NHC-substituted AsI cation. Further, the reaction of the vanadium complex [(Cp*V)2 (μ,η6:6 -P6 )] (5) with Me NHC results in the formation of the unprecedented complexes [(Me NHC)2 P][(Cp*V)2 (μ,η6:6 -P6 )] (6), [(Me NHC)2 P][(Cp*V)2 (μ,η5:5 -P5 )] (7) and [(Cp*V)2 (μ,η3:3 -P3 )(μ,η1:1 -P{Me NHC})] (8).