Tungsten complexes with strong π-donor and π-acceptor ligands: W(E)Cl 2(L)(PR 3) 2 (E = O, NR, S, and L = CO, CNR, CH 2CHR and OCHMe)

Abstract

The synthesis and characterization of a series of tungsten complexes, W(E)Cl 2(L)(PR 3) 2, containing both a π-donor group (E = oxo, imido, or sulphido) and a π-acceptor ligand (L = CO, CN t Bu, CH 2CHR, OCHMe) is reported (PR 3 = PMe 3, PMePh 2). The compounds are prepared by substitution of a phosphine ligand in W(E)Cl 2(PR 3) 3 by L and by oxidative addition of heterocumulenes EL, epoxides or episulphides to WCl 2(PMePh 2) 4. All of the compounds have an octahedral structure with the π-donor and π-acceptor ligands cis, according to spectroscopic data and X-ray crystal structures of oxo-carbonyl ( 4), oxo-ethylene ( 7) and imido-carbonyl ( 25) complexes. The ethylene ligands are oriented perpendicular to the tungsten-oxygen, -nitrogen, or -sulphur multiple bond, and are non-fluxional by NMR. These geometrical features are a direct result of the electronic structure of the d 2 metal centre. The dihapto coordination of acetaldehyde shows the substantial π-basicity of the tungsten(IV)-oxo centre. The CO stretching frequencies indicate that the donor abilities are in the order: oxo < sulphido < imido (< alkylidene < alkylidyne). Complexes 4, 7 and 25 are significantly distorted from octahedral geometry, also due to the electronic influence of two π-bonding ligands. The structure of WCl 2(PMePh 2) 4 ( 1) shows smaller distortions, a result of the steric bulk of the four phosphine ligands. Crystallographic data for 1: P1̄, a = 11.7401(13), b = 14.2555(12), c = 17.5922(12) Å, α = 76.226(6), β = 70.891(7), γ = 83.476(8)°, Z = 2; for 25: Pbcn, a = 17.764(2), b 15.821(6), c = 23.829(3) Å, Z = 8.