MONO-PHENOXY OXO COMPLEXES OF TUNGSTEN(VI)

The complexes [WOCl3(OAr)](x) (Ar = 4-tert-butylphenyl 1, 2,6-dimethyl phenyl 2, 2,6-di-iso-propylphenyl 3) are prepared by reacting HOAr wit h 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 phenox ide. The complex debutylates and forms bis-phenoxides 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 ac ts essentially as a 1 sigma, 2 pi donor to tungsten [W-O(1) bond lengt h 1.679(4) Angstrom] and the phenoxide as a 1 sigma, 1 pi donor [W-O(2 ) bond length 1.820(4) Angstrom]. The phenyl ring positions to reduce interactions of the methyl substituents with the oxo and chloro ligand s but NMR spectra show rapid phenoxide rotation in solution. Variable temperature NMR spectral studies of 4 show the re,l-butyl groups lock the rotation which may be important in the debutylation process. The c omplexes have limited catalytic potential due to instability. (C) 1998 Elsevier Science Ltd. All rights reserved.