Transition Metal Complexes of a “Half-Parent” Phosphasilene Adduct Representing Silylene→Phosphinidene→Metal Complexes

The first [M­(CO)5] complexes
(M = Cr, Mo, W) bearing
a donor-stabilized “half-parent” phosphasilene, in which
the lone pair of the phosphorus atom coordinates to a metal center,
have been synthesized and fully characterized. The latter complexes 2a (M = Cr), 2b (M = Mo), and 2c (M = W) result from conversion of the “half-parent”
phosphasilene-DMAP adduct 1, LSi­(dmap)PH (DMAP
= 4-N,N-dimethylaminopyridine; L
= CH­[(CCH2)­CMe­(NAr)2]; Ar = 2,6-iPr2C6H3), with [M­(CO)5thf] in 65–72% yields. The somewhat unexpected reactivity
of LSi­(dmap)(H)­P:→W­(CO)5 2c toward the strong Lewis acid tris­(pentafluorophenyl)­borane was investigated.
Strikingly, the borane does not abstract the DMAP donor. Most notable,
the NMR spectroscopic and structural features of 2a–c, in accord with results by density functional theory calculations,
clearly indicate that the already low SiP π-bond character
in 1 is almost quenched through coordination of the [M­(CO)5] group, suggesting that 2a–c rather represent push–pull donor→silylene→phosphinidene→metal
[DMAP→Si­(L):→P­(H):→M­(CO)5] than SiP→M
complexes.