Synthesis, structure and reactions of 1-(p-chlorophenyl)-3-(2,4,6-tri-t-butylphenyl)-1-aza-3-phospha-allene

A new phosphaazaallene Mes*PCNAr (Mes*=2,4,6-tBu3C6H2, Ar=p-ClC6H4) (1) has been synthesized. Complex 1 reacts with Mes*PHSiMe2tBu to form the phosphaazaallene insertion product Mes*PC(PHMes*)NAr(SiMe2tBu) (2). The treatment of 1 with an excess amount of YCl3 in THF leads to the isolation of the symmetrical dimer Mes*P(μ-CNAr)2PMes* (3), indicating both of the PC and CN bonds of 1 are reactive sites. X-ray structure analysis of 1 indicates that the distance of the PC bond, 1.642(5) Å, is markedly shorter than those of isolated PC bonds (1.66–1.72 Å), and the NCP unit slightly deviates from linearity with the PCN angle of 170.8(4)°. The structure determination of 2 revealed the molecule adopts a planar conformation about PC bond and the mutual orientation of two bulky Mes* moieties is almost orthogonal (92.8°). Complex 3 is a symmetrical four-membered ring structure in which the Mes* rings lie nearly perpendicular to the planes of the Ar ring and the P2C2 ring (84.8 and 75.6°, respectively), while the Ar ring is almost parallel to the plane of the P2C2 ring (25.2°).