Zirconocene silanolate complexes and their heterogeneous siliceous analogues as catalysts for phenylsilane dehydropolymerization

Abstract

The efficient catalytic dehydropolymerization of phenylsilane by homogeneous zirconocene bissilanolates ([{(c-C 5H 9) 7Si 8O 12O} 2Zr(η 5-C 5H 5) 2] ( 1a); [{(c-C 5H 9) 7Si 8O 12O} 2Zr(η 5-C 5H 4Bu) 2] ( 1b) [{( c-C 5H 9) 7Si 7O 9(OSiMe 3)O 2}Zr(η 5-C 5H 5) 2] ( 4); [{(Me 3CO) 3SiO} 2Zr(η 5-C 5H 5) 2] ( 5)) and chlorosilanolates ([{(c-C 5H 9) 7Si 8O 12O}ZrCl(η 5-C 5H 4Bu) 2] ( 2); ([{( c-C 5H 9) 7Si 7O 9O 3}Zr 2Cl(η 5-C 5H 5) 4] ( 3a); [{( c-C 5H 9) 7Si 7O 9O 3}Zr 2Cl(η 5-C 5H 4Bu) 4] ( 3b)) has been demonstrated. The presence of at least one silanol ligand in the zirconocene moiety was found essential for high catalytic performance. Solid state structure of complex 1a was determined by single crystal X-ray diffraction analysis. A series of nine zirconocene-siliceous catalysts were prepared by grafting of zirconocene moiety onto silica using three general methods: (a) reaction of [(η 5-C 5H 5) 2ZrCl 2] with silica in the presence of NEt 3; (b) reaction of [(η 5-C 5H 5) 2ZrMe 2] with silica; (c) reaction of solely [(η 5-C 5H 5) 2ZrCl 2] with silica. Supported catalysts were characterized by ICP-MS, FT-IR, TGA and selected examples by XPS analysis. Those catalysts prepared by method (a) and (b) were found efficient in the phenylsilane polymerization although a higher Zr/monomer ratio had to be used in comparison with homogeneous analogues. The low concentration of residual silanol groups in supported catalysts was found essential for their high catalytic performance. Advantageous reusability of supported catalysts was demonstrated using SiO 2(500)/Cp 2ZrCl 2/NEt 3(5.8). The catalytic performance was retained in three consecutive cycles producing polymers with almost identical properties.