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

Dichlorotungsten complexes, W(eta(2)-RCdropCR)(R-2'tbp)Cl-2 (1-C-s: R = Ph, R-2'tbp = 2,2'-thiobis(4-methyl-6-tert-butylphenoxo) ((t)Bu(2)tbp); 2-C-s: R = Et, R-2'tbp = 2 2'-thiobis(4,6-dimethylphenoxo) (Me(2)tbp); 3-C-1: R = Et, R-2'tbp = (t)Bu(2)tbp; 4-C-1: R = SiMe3, R-2'tbp = (t)Bu(2)tbp), W(eta(2)-PhCdropCPh)((t)Bu(2)Tebp)Cl-2 (3-C-1: (t)Bu(2)Tebp = 2,2'-tellurobis(4-methyl-6-tert-butylphenoxo) (5-C-1) and Mo(eta(2)-PhCdropCPh)((t)Bu(2)tbp)Cl-2 (6-C-s) were prepared by the reaction of W(eta(2)-RCdropCR)Cl-4 (R = Ph, Et, SiMe3) 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) Angstrom 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) Angstrom. In accordance with the structural data, the resonances of the alkyne carbons of the C-s complexes in C-13-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(CH2SiMe3)(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. (C) 2002 Elsevier Science B.V. All rights reserved.