Ring Contraction by NHC-Induced Pnictogen Abstraction

The reaction of [Cp ''' Co(eta(4)-P-4)] (1) (Cp '''=1,2,4-tBu(3)C(5)H(2)) with (NHC)-N-Me ((NHC)-N-Me=1,3,4,5-tetramethylimidazol-2-ylidene) leads through NHC-induced phosphorus cation abstraction to the ring contraction product [((NHC)-N-Me)(2)P][Cp ''' Co(eta(3)-P-3)] (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)(mu,eta(6:6)-E-6)] (3 a, 3 b) (Cp*=C5Me5; E=P, As) can be transformed to the complexes [((NHC)-N-Me)(2)E][(Cp*M)(2)(mu,eta(3:3)-E-3)(mu,eta(2:2)-E-2)] (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)(mu,eta(6:6)-P-6)] (5) with (NHC)-N-Me results in the formation of the unprecedented complexes [((NHC)-N-Me)(2)P][(Cp*V)(2)(mu,eta(6:6)-P-6)] (6), [((NHC)-N-Me)(2)P][(Cp*V)(2)(mu,eta(5:5)-P-5)] (7) and [(Cp*V)(2)(mu,eta(3:3)-P-3)(mu,eta(1:1)-P{(NHC)-N-Me})] (8).