New route to access an acyl-functionalized phosphasilene and a four-membered Si-P-C-O heterocycle

An acyl-functionalized phosphasilene, LSi(COtBu)=P(SiMe₃) (L=PhC(NtBu)₂) was synthesized on a new route by the addition of tBuCOCl to the phosphinosilylene LSiP(SiMe₃)₂ and subsequent Me₃SiCl elimination. DFT studies elucidated its molecular structure, the influence of the acyl group on UV/Vis transitions, and revealed the mechanism. The intermediate LSi(COtBu)ClP(SiMe₃)₂, with a five-coordinate silicon center, was characterized by NMR spectroscopy and X-ray analysis. On the other hand, phosphasilene LSi(SiMe₃)= P(SiMe₃) reacted with tBuCOCl by a [2+2] cycloaddition of the silicon-phosphorus double bond and the carbon-oxygen double bond in addition to Me₃SiCl elimination, thereby affording the novel, fully characterized compound LSi(SiMe₃)[P=C(tBu)O] bearing a Si-P-C-O heterocycle with a phosphorus-carbon double bond. DFT studies suggest that two mechanisms occur simultaneously. Si=P meets C=O: An acyl-functionalized phosphasilene was synthesized from a phosphinosilylene and tBuCOCl. The influence of the acyl group and its mechanism was studied by DFT calculations. The intermediate with a five-coordinate silicon center was structurally characterized. The reaction of tBuCOCl with a phosphasilene yielded a novel Si-P-C-O heterocycle with a carbon-phosphorus double bond as a result of a [2+2] cycloaddition and Me ₃SiCl elimination (TMS = trimethylsilyl).