Ring Contraction by NHC-Induced Pnictogen Abstraction

Abstract

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,η^6:6 -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,η^3:3 -E₃ )(μ,η^2:2 -E₂ )] (4 a, 4 b), with 4 b representing the first structurally characterized example of an NHC-substituted As^I cation. Further, the reaction of the vanadium complex [(Cp*V)₂ (μ,η^6:6 -P₆ )] (5) with ^Me NHC results in the formation of the unprecedented complexes [(^Me NHC)₂ P][(Cp*V)₂ (μ,η^6:6 -P₆ )] (6), [(^Me NHC)₂ P][(Cp*V)₂ (μ,η^5:5 -P₅ )] (7) and [(Cp*V)₂ (μ,η^3:3 -P₃ )(μ,η^1:1 -P{^Me NHC})] (8).

Keywords: arsenic; carbenes; phosphorus; ring contraction; vanadium.