Theoretical studies on the role of bridging group of CGC type ligands for the Ziegler–Natta catalysis

The potential energy surfaces of the initial reactions of ethylene polymerization with the Ziegler–Natta catalysis related to the constrained geometric catalysts (CGCs) were studied by the B3LYP density functional method. Three metals (Ti, Zr, and Hf) in the Ziegler–Natta catalysis and eight bridging groups (BH, CH2, NH, O, AlH, SiH2, PH, and S) between cyclopentadienyl (Cp) and NH ligands were treated. The reaction occurs through two steps as that of Kaminsky type: the first step produces the complex without a barrier and the second is the insertion of ethylene into the metal–carbon bond through the transition state. The complex formation energy for each metal system correlates linearly to the electronegativity of the bridging atom for each row atom of the periodic table except for those of the BH-bridging systems. The energies of the reactions for the BH-bridging systems could be explained with the through-bond model as the reactions of ansa-metallocenes and the π back-donation of BN double bond.

Graphical abstractThrough-bond model for electronic effects.Figure optionsDownload full-size imageDownload as PowerPoint slide