Synthesis of cis-dichloride complexes of Group 6 transition metals bearing alkyne and chalcogen-bridged chelating bis(aryloxo) ligands as catalyst precursors for ring-opening metathesis polymerization

Abstract

Dichlorotungsten complexes, W(η 2-RCCR)(R′ 2tbp)Cl 2 ( 1- C s : R=Ph, R′ 2tbp=2,2′-thiobis(4-methyl-6- tert-butylphenoxo) ( t Bu 2tbp); 2- C s : R=Et, R′ 2tbp=2,2′-thiobis(4,6-dimethylphenoxo) (Me 2tbp); 3- C 1: R=Et, R′ 2tbp= t Bu 2tbp; 4- C 1: R=SiMe 3, R′ 2tbp= t Bu 2tbp), W(η 2-PhCCPh)( t Bu 2Tebp)Cl 2 ( 3- C 1: t Bu 2Tebp=2,2′-tellurobis(4-methyl-6- tert-butylphenoxo) ( 5- C 1) and Mo(η 2-PhCCPh)( t Bu 2tbp)Cl 2 ( 6- C s ) were prepared by the reaction of W(η 2-RCCR)Cl 4 (R=Ph, Et, SiMe 3) with 2,2′-thiobis(4-methyl-6- tert-butylphenol), 2,2′-thiobis(4,6-dimethylphenol) or with 2,2′-tellurobis(4-methyl-6- tert-butylphenol). The C s symmetric complex 1- C s isomerized to the C 1 isomer 1- C 1 in solution at room temperature. The molecular structures of 1- C 1, 3- C 1, 5- C 1 and 6- C s were determined to reveal their six coordinated pseudo-octahedral geometry by X-ray crystallography. The MC(alkyne) bond distances in the C s complexes 2- C s and 6- C s ranging from 2.014(7) to 2.035(6) Å are apparently shorter than those in the corresponding C 1 complexes 1- C 1, 3- C 1 and 5- C 1 ranging from 2.04(1) to 2.09(1) Å. In accordance with the structural data, the resonances of the alkyne carbons of the C s complexes in 13C-NMR spectra appeared at 233.1–244.5 ppm, typical for four electron donating alkynes, and those of the C 1 complexes appeared at 198.6–215.4 ppm, typical for two electron donating alkynes. The substituent effects of the ligands on the catalytic behavior of the complexes for the ring-opening metathesis polymerization of norbornene derivatives were studied in the presence of Mg(CH 2SiMe 3) 2 as a cocatalyst. The catalytic activities of the sulfur-bridged complexes tend to increase with increasing the bulkiness of acetylene ligand. The tellurium-bridged complex 5- C 1 was found to be remarkably more active than the corresponding sulfur-bridged complexes.