Tungsten alkylidyne complexes with ancillary imidazolin-2-iminato and imidazolidin-2-iminato ligands and their use in catalytic alkyne metathesis

The imines 1,3-di-tert-butylimidazolidin-2-imine (10) and 4,5-dimethyl-1,3-di-tert-butylimidazolin-2-imine (14) were prepared starting from the corresponding N-heterocyclic carbenes 8 and 11 and trimethylsilyl azide or tert-butyl azide, respectively. Deprotonation of the imines 10 and 14 with methyl lithium and reaction with an equimolar amount of the tungsten benzylidyne complex [PhC W {OCMe(CF3)(2)}(3)(DME)] (16) (DME = 1,2-dimethoxyethane) afforded the complexes [PhC W(L) {OCMe(CF3)(2)}(2)] (L = 1,3-di-tert-butylimidazolidin-2-iminato, 6; L = 4,5-dimethyl-1,3-di-tert-butylimidazolin-2-iminato, 7), which were characterized by H-1, C-13{H-1} and F-19{H-1} NMR spectroscopy and by elemental and X-ray diffraction analysis. Complexes 6 and 7 are efficient catalysts for the homocoupling of 3-pentynyl benzyl ether (17) at room temperature in the presence of 5 angstrom molecular sieve and at low catalyst loadings (1 mol%). (C) 2013 Elsevier B.V. All rights reserved.