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 - Me 4 Cp⌒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 n BuLi 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(CH 2 Ph) 4 at 60 °C in toluene cleanly generates (TCP)Ti(CH 2 Ph) 2 ( 2 ), while the corresponding reaction with Zr(CH 2 Ph) 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 η 1 -fashion and the other in an η 2 -mode. The small Cp(centroid)−Ti−O angle of 107.7(2)° in 2 indicates sterically open features in common with amido-based “constrained geometry” polymerization catalysts. Low-temperature NMR-scale reactions of 2 with B(C 6 F 5 ) 3 and Ph 3 C + B(C 6 F 5 ) 4 - indicate the formation of the corresponding cationic complexes (TCP)TiCH 2 Ph + PhCH 2 B(C 6 F 5 ) 3 - ( 4 ) and (TCP)TiCH 2 Ph + B(C 6 F 5 ) 4 - ( 5 ). Upon activation with Ph 3 C + B(C 6 F 5 ) 4 -, complex 2 is highly active for ethylene, propylene, and styrene polymerization.