Synthesis of novel oxo complexes of tungsten and molybdenum with various chalcogen-bridged chelating bis(aryloxo) ligands and their catalytic behavior for ring-opening metathesis polymerization

Oxo tungsten complexes coordinated by O-E-O (E = S, Te, CH2) chelating bis(aryloxo) ligands, WO[E(4-Me-6-(BuC6H2O)-Bu-t)(2)]Cl-2, (1: E = S, 2: E = Te, 3: E = CH2) were synthesized by the reaction Of WOCl4 with 2,2'-E(4-Me-6-(BuC6H2OH)-Bu-t)(2) [E = S ((t)Bu(2)tbpH(2)), E = Te (TebpH(2)), E = CH2 (mbpH(2))]. Similarly a molybdenum complex, MoO[S(4-Me-6-(BuC6H2O)-Bu-t)(2)]Cl-2 (4), was also prepared. The structures of the oxodichloro tungsten complexes 1 and 3 were determined by single-crystal X-ray analysis to have pseudo C-s symmetry. A mu-oxo binuclear tungsten complex with two (t)Bu(2)tbp ligands, {WO[S(4-Me-6-(BuC6H2O)-Bu-t)2]Cl}(2)(mu-O) (5), was synthesized by refluxing a mixture of W2O3Cl6 and two equivalents of (t)Bu(2)tbpH(2) in THF, whose structure was determined by single-crystal X-ray analysis. We study here the catalytic behavior of these complexes for the ring-opening metathesis polymerization (ROMP) of norbornene. In the catalytic systems, 1-AlEt3 and 2-AlEt3, cis-trans selectivity varies depending on the catalyst concentration and on the polymerization temperature. The resulting poly(norbornene) tend to have higher cis-content with increasing catalyst concentration and with lowering polymerization temperature. Oppositely, the polymerization under low catalyst concentration and at high polymerization temperature gave the trans-rich poly(norbomene). On the other hand, the complex 3 with the methylene-bridged bis(aryloxo) ligand did not show such a dependence of cis-trans selectivity. We proposed that these observations might come from oxotungsten-aluminum interaction. (C) 2002 Elsevier Science B.V. All rights reserved.