Neutral and cationic zirconium benzyl complexes containing bidentate pyridine-alkoxide ligands. Synthesis and olefin polymerization chemistry of (pyCR2O)2Zr(CH2Ph)2 and (pyCR2O)2Zr(CH2Ph)+ complexes

Abstract

The reaction of Zr(CH2Ph)4 with the pyridine alcohols 6-pyCR1R2OH (2a, R1 = R2 = CF3; 2b, R1 = R2 = Me; 2c, R1 = H, R2 = CF3) yields dibenzyl complexes (pyCR1R2O)2Zr(CH2Ph)2 (3a-c). These species adopt distorted octahedral structures with a trans-O, cis-N, cis-C ligand arrangement but undergo rapid inversion of configuration at Zr on the NMR time scale, with racemization barriers in the range from 8.6 (3b) to 10.1 (3c) kcal/mol. 3a and 3b react with B(C6F5)3 to yield [(pyCR1R2O)2Zr(CH2Ph)][PhCH 2B(C6F5)3] (6a,b) and with [HNMe2Ph][B(C6F5)4] to yield [(pyCR1R2O)2Zr(CH2Ph)][B(C 6F5)4] (7a,b). NMR spectra indicate that 6a,b and 7a,b are not strongly ion-paired in CD2Cl2. 6a polymerizes ethylene and 1-hexene to low molecular weight polymers. [{pyCH(CF3)O}2Zr(CH2Ph)][PhCH 2B(C6F5)3] (6c, generated in situ) is much less active for ethylene polymerization than 6a, and 6b is inactive.