C 1 -Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism.

A series of new Me 2 Si-bridged cyclopentadiene/indene proligands {Me 2 Si(R 2',5' 2 -R 3',4' 2 -Cp)(R 2 ,R 4 ,R 5 ,R 6 -Ind)H 2 } (1a-j) with various substitutions both on the indene and cyclopentadiene moieties was prepared. The corresponding C 1 -symmetric group 4 ansa -metallocene complexes (M = Zr, Hf), namely, {Me 2 Si(Me 4 Cp)(Ind)}ZrCl 2 (2a-Zr), {Me 2 Si(Me 4 Cp)(2-Me,4-Ph-Ind)}MCl 2 (2b-M), {Me 2 Si(Me 4 Cp)(2-Me,4-Ph,6- t Bu-Ind)}ZrCl 2 (2c-Zr), {Me 2 Si(Me 4 Cp)(2-Me,4-Ph,5-OMe,6- t Bu-Ind)}MCl 2 (2d-M), {Me 2 Si(Me 4 Cp)(2-R',4-(3',5'- t Bu 2 ,4'-OMe-C 6 H 2 ),5-OMe,6- t Bu-Ind)}ZrCl 2 , R' = Me (2e-Zr), R' = Et (2f-Zr), {Me 2 Si(2,5-Ph 2 -3,4-Me 2 -Cp)(2-Me,4-(3',5'- t Bu 2 ,4'-OMe-C 6 H 2 ),5-OMe,6- t Bu-Ind)}ZrCl 2 (2g-Zr), {Me 2 Si(Me 4 Cp)(2-Me,4-(3',6'- t Bu 2 -carbazol-4'-yl)-Ind)}ZrCl 2 (2h-Zr), {Me 2 Si(2,5-Me 2 ,3,4-iPr 2 -Cp)(2-Me,4-Ph-Ind)}ZrCl 2 (2i-Zr), {Me 2 Si(2,5-Me 2 ,3,4-iPr 2 -Cp)(2-Me,4-Ph,6- t Bu-Ind)}ZrCl 2 (2j-Zr) and {Me 2 Si(Me 4 Cp)(2-Me-4,5-[ a ]anthracene-Ind)}MCl 2 (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) -1 h -1 , affording highly isotactic polypropylenes ( i PP) with [ m ] 4 up to 96.5% and T m up to 157 °C. Also, metallocene complexes 2b-e-Zr were supported on SiO 2 -MAO and evaluated in slurry bulk propylene polymerization at 70 °C, producing i PPs with [ m ] 4 = 91.7-96.6 mol% and low regiodefects (0.2-0.3 mol%) content, with productivities up to 636 000 kg(PP) mol(Zr) -1 h -1 . DFT calculations allowed rationalizing a polymerization reaction mechanism occurring through "chain-stationary" enchainment with preference for 1,2-insertions.