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

International audience; 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-tBu-Ind)}ZrCl(2) (2c-Zr), {Me(2)Si(Me(4)Cp)(2-Me,4-Ph,5-OMe,6-tBu-Ind)}MCl(2) (2d-M), {Me(2)Si(Me(4)Cp)(2-R’,4-(3’,5’-tBu(2),4’-OMe-C(6)H(2)),5-OMe,6-tBu-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’-tBu(2),4’-OMe-C(6)H(2)),5-OMe,6-tBu-Ind)}ZrCl(2) (2g-Zr), {Me(2)Si(Me(4)Cp)(2-Me,4-(3’,6’-tBu(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-tBu-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 (iPP) 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 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.