A Novel Phenolate “Constrained Geometry” Catalyst System. Efficient Synthesis, Structural Characterization, and α-Olefin Polymerization Catalysis
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Abstract
This paper reports the convenient “one-pot” synthesis of a bifunctional -Me4Cp⌒phenolate- ligand and the efficient “one-step” synthesis of the corresponding TiIV and ZrIV complexes. The reaction of 2-bromo-4-methylphenol with 2 equiv of nBuLi followed by addition of 2,3,4,5-tetramethyl-2-cyclopentenone produces the bifunctional mono-Cp phenol ligand precursor 2-(tetramethylcyclopentadienyl)-4-methylphenol ((TCP)H2, 1). Reaction of 1 with Ti(CH2Ph)4 at 60 °C in toluene cleanly generates (TCP)Ti(CH2Ph)2 (2), while the corresponding reaction with Zr(CH2Ph)4 at higher temperatures affords the chelated C2-symmetric zirconocene (TCP)2Zr (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 η1-fashion and the other in an η2-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(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.
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