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

The reaction of Zr(CH2Ph)(4) with the pyridine alcohols 6-pyCR(1)R(2)OH (2a, R-1 = R-2 = CF3; 2b, R-1 = R-2 = Me; 2c, R-1 = H, R-2 = CF3) yields dibenzyl complexes (pyCR(1)R(2)O)(2)Zr(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 [(pyCR(1)R(2)O)(2)Zr(CH2Ph)][PhCH2B(C6F5)(3)] (6a,b) and with [HNMe2Ph][B(C6F5)(4)] to yield [(pyCR(1)R(2)O)(2)Zr(CH2Ph)][B(C6F5)(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}(2)Zr(CH2Ph)][PhCH2B(C6F5)(3)] (6c, generated in situ) is much less active for ethylene polymerization than 6a, and 6b is inactive.