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

Abstract

Oxo tungsten complexes coordinated by OEO (E=S, Te, CH 2) chelating bis(aryloxo) ligands, WO[E(4-Me-6- t BuC 6H 2O) 2]Cl 2, ( 1: E=S, 2: E=Te, 3: E=CH 2), were synthesized by the reaction of WOCl 4 with 2,2′-E(4-Me-6- t BuC 6H 2OH) 2 [E=S ( t Bu 2tbpH 2), E=Te (TebpH 2), E=CH 2 (mbpH 2)]. Similarly a molybdenum complex, MoO[S(4-Me-6- t BuC 6H 2O) 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 μ-oxo binuclear tungsten complex with two t Bu 2tbp ligands, {WO[S(4-Me-6- t BuC 6H 2O) 2]Cl} 2(μ-O) ( 5), was synthesized by refluxing a mixture of W 2O 3Cl 6 and two equivalents of t Bu 2tbpH 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–AlEt 3 and 2–AlEt 3, 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(norbornene). 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.