C₁-Symmetric {cyclopentadienyl/indenyl}-metallocene catalysts: synthesis, structure, isospecific polymerization of propylene and stereocontrol mechanism

A series of new Me2Si-bridged cyclopentadiene/indene proligands {Me2Si(R-2(2 & PRIME;,5 & PRIME;)-R-2(3 & PRIME;,4 & PRIME;)-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, {Me2Si(Me4Cp)(Ind)}ZrCl2 (2a-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph-Ind)}MCl2 (2b-M), {Me2Si(Me4Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2c-Zr), {Me2Si(Me4Cp)(2-Me,4-Ph,5-OMe,6-tBu-Ind)}MCl2 (2d-M), {Me2Si(Me4Cp)(2-R & PRIME;,4-(3 & PRIME;,5 & PRIME;-tBu(2),4 & PRIME;-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2, R & PRIME; = Me (2e-Zr), R & PRIME; = Et (2f-Zr), {Me2Si(2,5-Ph-2-3,4-Me-2-Cp)(2-Me,4-(3 & PRIME;,5 & PRIME;-tBu(2),4 & PRIME;-OMe-C6H2),5-OMe,6-tBu-Ind)}ZrCl2 (2g-Zr), {Me2Si(Me4Cp)(2-Me,4-(3 & PRIME;,6 & PRIME;-tBu(2)-carbazol-4 & PRIME;-yl)-Ind)}ZrCl2 (2h-Zr), {Me2Si(2,5-Me-2,3,4-iPr(2)-Cp)(2-Me,4-Ph-Ind)}ZrCl2 (2i-Zr), {Me2Si(2,5-Me-2,3,4-iPr(2)-Cp)(2-Me,4-Ph,6-tBu-Ind)}ZrCl2 (2j-Zr) and {Me2Si(Me4Cp)(2-Me-4,5-[a]anthracene-Ind)}MCl2 (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 & DEG;C up to 161 000 kg(PP) mol(Zr)(-1) h(-1), affording highly isotactic polypropylenes (iPP) with [m](4) up to 96.5% and T-m up to 157 & DEG;C. Also, metallocene complexes 2b-e-Zr were supported on SiO2-MAO and evaluated in slurry bulk propylene polymerization at 70 & DEG;C, producing iPPs 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.