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.