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

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The tetrahydrido complex [WH 4 (κ 4 - P4 )] ( P4 = meso - o -C 6 H 4 (PPhCH 2 CH 2 PPh 2 ) 2 ) reacted with aliphatic nitriles AkCN at 80 °C in toluene to afford a series of the imido complexes, [W(NCH 2 Ak)(κ 4 - P4 )] ( 2 ). Similar reactions with aromatic nitriles ArCN proceeded stepwise, leading to formation of the hydrido–alkylideneamido complexes [WH(N═CHAr)(κ 4 - P4 )] ( 3 ) at the first stage and a subsequent isomerization into the imido complexes [W(NCH 2 Ar)(κ 4 - P4 )] ( 4 ). Conversion of 3 into 4 was accelerated by electron-rich Ar groups such as p -CH 3 OC 6 H 4, while it was completely inhibited when Ar was the considerably electron-deficient p -CF 3 C 6 H 4 . An X-ray crystallographic study on 2 (Ak = p -ClC 6 H 4 CH 2 ) 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 W II –N triple bond. An almost linear W II ═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.