Versatile Access to Very Short PP Double Bonds in Mixed-Valent 1λ5‑Diphosphenes via 1,3-Silyl Migration

The metathesis reaction of LiP­(SiR3)­Ar* (R = iPr and Ph; Ar* = Mes and Tipp) with Ph2POCl yields Ar*­(R3Si)­P–P­(O)­Ph2. These diphosphane monoxides can be observed by NMR spectroscopy. However, they are intrinsically instable, and 1,3-trihydrylsilyl migration leads to the formation of 1λ5-diphosphenes of the type Ar*PP­(OSiR3)­Ph2 with very large characteristic 1J(P,P) coupling constants. A very short PP bond has been observed for the 1λ5-diphosphene TippPP­(OSiPh3)­Ph2. These 1λ5-diphosphenes are only stable in the crystalline state but degrade in solution to Ph2P–O–SiR3 via elimination of the Ar*P: phosphinidenes which form secondary degradation products such as triaryl-cyclotriphosphanes. Formation of the 1λ5-diphosphene TippPP­(OSiPh3)­Ph2 via 1,3-trihydrylsilyl migration from P to O and the fate due to PP bond cleavage has been verified by theoretical studies.