From Disilene (Si=Si) to Phosphasilene (Si=P) and Phosphacumulene (P=C=N)

The generation of heavier double-bond systems without by- or side-product formation is of considerable importance for their application in synthesis. Peripheral functional groups in such alkene homologues are promising in this regard owing to their inherent mobility. Depending on the steric demand of the N-alkyl substituent R, the reaction of disilenide Ar₂Si double bond Si(Ar)Li (Ar=2,4,6-iPr₃C₆H₂) with ClP(NR₂)₂ either affords the phosphinodisilene Ar₂Si double bond Si(Ar)P(NR₂)₂ (for R=iPr) or P-amino functionalized phosphasilenes Ar₂(R₂N)Si—Si(Ar) double bond P(NR₂) (for R=Et, Me) by 1,3-migration of one of the amino groups. In case of R=Me, upon addition of one equivalent of tert-butylisonitrile a second amino group shift occurs to yield the 1-aza-3-phosphaallene Ar₂(R₂N)Si—Si(NR₂)(Ar)—P double bond CNtBu with pronounced ylidic character. All new compounds were fully characterized by multinuclear NMR spectroscopy as well as single-crystal X-ray diffraction and DFT calculations in selected cases.