REACTION OF 1,3-DIPHOSPHOLYL ANIONS WITH CHLOROTRIMETHYLSILANE - [1,5]-SIGMATROPIC SHIFTS OF THE TRIMETHYLSILYL GROUP AROUND THE 1,3-DIPHOSPHOLYL RING

The protonation of the 4,5-diphenyl-1,3-diphosphoyl anion, [(PhC)2P2CH]-, in the presence of N-phenylmaleimide affords the [4 + 2] cycloadduct of the transient 4,5-diphenyl-2H-1,3-diphosphole, [(PhC)2P2CH2]. The silylation by chlorotrimethylsilane of the [P.W(CO)5]2 complex of this same anion at room temperature affords the corresponding complex of 1-(trimethylsilyl)-4,5-diphenyl-1H-1,3-diphosphole as the sole observable product. However, this 1,3-diphosphole complex is in equilibrium at room temperature 2-(trimethylsilyl)-4,5-diphenyl-2H-1,3-diphosphole via [1,5]-sigmatropic shifts of the silyl group. This 2H-1,3-diphosphole complex can be trapped as a [4 + 2] cycloadduct with dimethyl acetylenedicarboxylate. At -80-degrees-C, these [1,5] shifts are frozen out and the silylation of the same complexed anion takes place exclusively at the carbons of the ring to give the 2-(trimethylsilyl)-4,5-diphenyl-2H-1,3-diphosphole and the 4-(trimethylsilyl)-4,5-diphenyl-4H-1,3-diphosphole complexes whose formation is demonstrated by trapping with dimethyl acetylenedicarboxylate.