Structure of Donor Molecule 9,9-Bis(Methoxymethyl)-Fluorene in Ziegler-Natta Catalyst by Infrared Spectroscopy and Quantum Chemical Calculation

Infrared vibrational spectroscopy has been used to reveal the conformations of the Ziegler−Natta catalysts internal electron donor 9,9-bis(methoxymethyl)-fluorene and its selectively deuterated derivative (9,9-bis(1,1-dideutero-methoxymethyl)-fluorene), in the solid state, complexed with TiCl4 and MgCl2 and in the catalyst precursor. The experimental spectra have been interpreted by means of spectroscopic correlations and theoretical results from quantum chemical calculations on selected molecular models. From experimental and theoretical data two chelating geometries of the donors with both oxygen directly interacting with Ti or Mg atoms turn out to be favorable. They can be identified by the four dihedral angles along the CH3−(O−CH2−R−CH2−O)−CH3 residue that take on conformations of approximately trans (T), gauche+ (G), or gauche− (G′), namely, TGGT and TGG′T. We propose the TGGT conformations for the crystal phase of the donor, the TGG′T when it is complexed with TiCl4, and both TGGT and TGG′T when complexed with MgCl2 along the [110] lateral cut. In the precatalysts, donors molecules are complexed along the [110] MgCl2 lateral cut and likewise the MgCl2 complex. A model for the catalytic sites consisting of TiCl4 species and donor molecules complexed along the [110] lateral cut is proposed.