Conformationally dynamic titanium and zirconium cationic complexes of bis(naphthoxy)pyridine ligands: structure, “oscillation” and olefin polymerization catalysis

Discrete ionic complexes {ONO(SiMe2tBu)}M(CH2Ph)((η(6)-Ph)CH2B(C6F5)3) (M = Ti, 2-Ti; Zr, 2-Zr) have been prepared from the parent neutral dibenzyl precursors and B(C6F5)3. Also, a neutral dichloro complex _ONO(SiMe2tBu)_ZrCl2(Me2NH) (3) was synthesized by the reaction of a proligand {ONO(SiMe2tBu)}H2(1-H2) with (Me2N)2ZrCl2(DME). The compounds were characterized by NMR spectroscopy and X-ray crystallography (for 2-Zr and 3). In the solid state, both 2-Zr and 3 feature meso-like binding of the ligand. VT NMR studies of 2-Ti and 2-Zr revealed that the former species dissociates in solution to form an outer-sphere ion pair (OSIP) that features a complicated dynamic behavior, while the latter compound retains an inner-sphere ion pair (ISIP) structure that interconverts between Cs-symmetric (meso-like) and C1-symmetric (rac-like) conformations. The mechanism of this interconversion was assessed by DFT calculations and the corresponding barrier for the straightforward interconversion was calculated.