Synthesis and Reactivity of Tungsten(II) Methylene Complexes

Abstract

Treatment of the methyl complex Tp‘(CO)(PhC2Me)W−Me (1) or Tp(CO)(PhC2Ph)W−Me (2) with trityl cation yields the corresponding methylene complex [Tp‘(CO)(PhC2Me)WCH2][PF6] (3) (Tp‘ = hydridotris-(3,5-dimethylpyrazolyl)borate) or [Tp(CO)(PhC2Ph)WCH2][PF6] (4) (Tp = hydridotris(pyrazolyl)borate). The carbene complex (3) is unusually persistent for a methylene complex. Complexes 3 and 4 display electrophilic behavior, as evidenced both by addition of nucleophiles and by methylene transfer to electron rich olefins. When bound to either carbene 3 or 4, arylimines are activated toward nucleophilic attack by ethyl diazoacetate (EDA). The net result of the addition of excess arylimine followed by excess EDA to a solution of either 3 or 4 is catalytic aziridine formation. X-ray diffraction studies have revealed the structures of [Tp‘(CO)(PhC2Me)W−CH2PMe3][PF6] (7) and [Tp‘(CO)(PhC2Me)W−CH2N(Me)C(H)(Ph)][PF6] (15). The relative stabilities of 3 and 4 are discussed as well as the mechanism of aziridine catalysis.