Aryloxide ligand modification:: new classical catalytic systems for olefin metathesis

The AM1-calculated partial oxygen charge of several phenoxide anions, potential ligands for tungsten-based classical catalytic systems for olefin metathesis, has been used as an indication of their electronwithdrawing ability. Based on the modeled set, a number of bis(aryloxide) derivatives of tungsten (VI) oxychloride have been synthesized by refluxing the parent phenol and WOCl4 in toluene, and we have explored their ability to catalyze various metathesis applications. The studied complexes are precursors to active metathesis catalysts when heated in the presence of Bu4Sn, and experimental conditions for the catalysis of ring opening metathesis polymerization (ROMP), acyclic diene metathesis (ADMET) polymerization, and ring closing metathesis (RCM) are reported. The catalytic ability of the studied complexes cannot be predicted based on a single structural or electronic parameter since ligand substitution also seems to affect other features such as solubility and chemical stability of the complex. Crystal data for bis(2,4,6-tribromophenoxy)tungsten (VI) oxychloride (7): Space group: P-1, triclinic. a=7.8459(5) Angstrom, alpha=94.100(1)degrees, b= 8.8504(5) Angstrom, beta=42.687(1)degrees, c= 14.2994(9) Angstrom, gamma = 95.359(1)degrees V= 984.64(10) Angstrom(3), R-1 = 0.0258 and wR(2), = 0.0628. (C) 2000 Elsevier Science B.V. All rights reserved.