A novel phenolate "constrained geometry" catalyst system.: Efficient synthesis, structural characterization and α-olefin polymerization catalysis

This paper reports the convenient "one-pot" synthesis of a bifunctional -Me4Cp over arc phenolate(-) ligand and the efficient "one-step" synthesis of the corresponding Ti-IV and Zr-IV complexes. The reaction of 2-bromo-4-methylphenol with 2 equiv of (BuLi)-Bu-n followed by addition of 2,3,4,5-tetramethyl-2-cyclopentenone produces the bifunctional mono-Cp phenol ligand precursor 2-(tetramethylcyclopentadienyl)-4-methylphenol ((TCP)H-2, 1). Reaction of 1 with Ti(CH2Ph)(4) at 60 degrees C in toluene cleanly generates (TCP)Ti(CH2Ph)(2) (2), while the corresponding reaction with Zr(CH2Ph)(4) at higher temperatures affords the chelated C-2-symmetric zirconocene (TCP)(2)Zr (3). In solution at room temperature, the two benzyl groups of 2 are magnetically equivalent, however, in the solid state, X-ray diffraction reveals that one benzyl group is coordinated in a normal eta(1)-fashion and the other in an eta(2)-mode. The small Cp(centroid)-Ti-O angle of 107.7(2)degrees in 2 indicates sterically open features in common with amido-based "constrained geometry" polymerization catalysts. Low-temperature NMR-scale reactions of 2 with B(C6F5)(3) and Ph3C+B(C6F5)(4)(-) indicate the formation of the corresponding cationic complexes (TCP)TiCH2Ph+ PhCH2B(C6F5)(3)(-) (4) and (TCP)TiCH2Ph+B(C6F5)(4)(-) (5). Upon activation with Ph3C+B(C6F5)(4)(-), complex 2 is highly active for ethylene, propylene, and styrene polymerization.