Tungsten(II) Alkylimido Complexes from Insertion of Nitriles into Tungsten Hydride: Alkylideneamido Intermediate Stage and Nitrene Group Transfer to Isocyanide

The tetrahydrido complex [WH4(κ4-P4)] (P4 = meso-o-C6H4(PPhCH2CH2PPh2)2) reacted with aliphatic nitriles
AkCN at 80 °C in toluene to afford a series of the imido complexes,
[W­(NCH2Ak)­(κ4-P4)] (2). Similar reactions with aromatic nitriles ArCN proceeded
stepwise, leading to formation of the hydrido–alkylideneamido
complexes [WH­(NCHAr)­(κ4-P4)]
(3) at the first stage and a subsequent isomerization
into the imido complexes [W­(NCH2Ar)­(κ4-P4)] (4). Conversion of 3 into 4 was accelerated by electron-rich Ar groups such
as p-CH3OC6H4, while
it was completely inhibited when Ar was the considerably electron-deficient p-CF3C6H4. An X-ray crystallographic
study on 2 (Ak = p-ClC6H4CH2) and 4 (Ar = p-tolyl) has disclosed a distorted-square-pyramidal coordination geometry,
in which the apical position is occupied by the imido ligand with
a WII–N triple bond. An almost linear WIINC linkage of 3 (Ar = p-tolyl) has also been determined. Complex 2 was capable
of nitrene group transfer to isocyanide to produce carbodiimide.