Trapping Intermediates in Phosphavinyl Coupling Reactions:  Synthesis and Structural Characterization of a Novel Bis(phosphinoalkylidene)−Tantalum Complex, [{Cp*TaCl₂[C(Bu^t)−P(Cy)−]}₂]

Abstract

The reactions of the stable phosphavinyl Grignard reagent ( Z )-[MgCl(OEt 2 ){C(Bu t ) PCy}] with [Cp*TaCl 4 ] or [Cp*NbCl 4 ] have been investigated. In both cases phosphavinyl coupling reactions are the ultimate outcome to give the known 2,4-diphosphabicyclo[1.1.0]butane, Cy 2 P 2 C 2 Bu t 2, in the former and a mixture of this compound and its 1,2-dihydro-1,2-diphosphete valence isomer in the latter. A novel bis(phosphinoalkylidene)−tantalum complex, [{Cp*TaCl 2 [ C(Bu t )−P(Cy)−]} 2 ], has been isolated and structurally characterized as an intermediate in the tantalum reaction.