Mono-phenoxy oxo complexes of tungsten(VI)

Article abstract of DOI:10.1016/S0277-5387(97)00288-X

The complexes [WOCl₃(OAr)]_X (Ar = 4-tert-butylphenyl 1, 2,6-dimethylphenyl 2, 2,6-di-isopropylphenyl 3) are prepared by reacting HOAr with an excess of [WOCl₄] but are thermodynamically unstable forming bis-phenoxide complexes on standing. Debutylation occurs with 2,6-di-tert-butylphenol but a monophenoxide 4 was prepared with the lithium phenoxide. The complex debutylates and forms bisphenoxides on standing. An X-ray crystal structure of 2 shows a dimeric chloro-bridged structure with terminal oxo and 2,6-dimethylphenoxide ligands. The oxo ligand acts essentially as a 1σ, 2π donor to tungsten [W-O(1) bond length 1.679(4) A] and the phenoxide as a 1σ, 1π donor [W-O(2) bond length 1.820(4) A]. The phenyl ring positions to reduce interactions of the methyl substituents with the oxo and chloro ligands but NMR spectra show rapid phenoxide rotation in solution. Variable temperature NMR spectral studies of 4 show the tert-butyl groups lock the rotation which may be important in the debutylation process. The complexes have limited catalytic potential due to instability.