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-C5H9)(7)Si8O12O}(2)Zr(eta(5)-C5H5)(2)] (1a); [{(c-C5H9)(7)Si8O12O}(2)Zr(eta(5)-C5H4Bu)(2)] (1b) [{(c-C5H9)(7)Si7O9(OSiMe3)O-2}Zr(eta(5)-C5H5)(2)] (4); [{(Me3CO)(3)SiO}(2)Zr(eta(5)-C5H5)(2)] (5)) and chlorosilanolates ([{(c-C5H9)(7)Si8O12O}ZrCl(eta(5)-C5H4Bu)(2)] (2); ([{(c-C5H9)(7)Si7O9O3}Zr2Cl(eta(5)-C5H5)(4)] (3a); [{(c-C5H9)(7)Si7O9O3}Zr2Cl(eta(5)-C5H4Bu)(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 [(eta(5)-C5H5)(2)ZrCl2] with silica in the presence of NEt3; (b) reaction of [(eta 5-C5H5)(2)ZrMe2] with silica; (c) reaction of solely [(eta(5)-C5H5)(2)ZrCl2] 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 SiO2(500)/Cp2ZrCl2/NEt3(5.8).
The catalytic performance was retained in three consecutive cycles producing polymers with almost identical properties.