-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new MeSi-bridged cyclopentadiene/indene proligands {MeSi(R-R-Cp)(R,R,R,R-Ind)H} (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding -symmetric group 4 -metallocene complexes (M = Zr, Hf), namely, {MeSi(MeCp)(Ind)}ZrCl (2a-Zr), {MeSi(MeCp)(2-Me,4-Ph-Ind)}MCl (2b-M), {MeSi(MeCp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2c-Zr), {MeSi(MeCp)(2-Me,4-Ph,5-OMe,6-Bu-Ind)}MCl (2d-M), {MeSi(MeCp)(2-R',4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl, R' = Me (2e-Zr), R' = Et (2f-Zr), {MeSi(2,5-Ph-3,4-Me-Cp)(2-Me,4-(3',5'-Bu,4'-OMe-CH),5-OMe,6-Bu-Ind)}ZrCl (2g-Zr), {MeSi(MeCp)(2-Me,4-(3',6'-Bu-carbazol-4'-yl)-Ind)}ZrCl (2h-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph-Ind)}ZrCl (2i-Zr), {MeSi(2,5-Me,3,4-iPr-Cp)(2-Me,4-Ph,6-Bu-Ind)}ZrCl (2j-Zr) and {MeSi(MeCp)(2-Me-4,5-[]anthracene-Ind)}MCl (2k-Zr) were synthesized and characterized by NMR spectroscopy and mass spectrometry. The solid-state molecular structures of 2b-Zr, 2d-Zr, 2e-Zr, 2f-Zr, 2j-Zr and 2k-Zr were determined by X-ray crystallography. The zirconocene complexes, once activated with MAO in toluene solution, exhibited propylene polymerization activities at 60 °C up to 161 000 kg(PP) mol(Zr) h, affording highly isotactic polypropylenes (PP) with [] up to 96.5% and up to 157 °C. Also, metallocene complexes 2b-e-Zr were supported on SiO-MAO and evaluated in slurry bulk propylene polymerization at 70 °C, producing PPs with [] = 91.7-96.6 mol% and low regiodefects (0.2-0.3 mol%) content, with productivities up to 636 000 kg(PP) mol(Zr) h. DFT calculations allowed rationalizing a polymerization reaction mechanism occurring through "chain-stationary" enchainment with preference for 1,2-insertions.