Synthesis and structures of adamantyl-substituted constrained geometry cyclopentadienyl–phenoxytitanium complexes and their catalytic properties for olefin polymerization

A number of new constrained geometry titanium complexes, [η5: η1-2-C5Me4-4-R-6-Ad-C6H2O]TiCl2 [Ad = adamantyl, R = Me (8), tBu (9)] and [η5: η1-C5H2Ph2-4-tBu-6-Ad-C6H2O]TiCl2 (10), were synthesized from reactions of TiCl4 either directly with corresponding free ligands, 2-C5Me4H-4-R-6-Ad-C6H2OH [R = Me (5), tBu (6)], or with the dilithium salt of the free ligand 2-C5H3Ph2-4-tBu-6-Ad-C6H2OH (7). These new titanium complexes were fully characterized by 1H and 13C NMR spectroscopy and elemental analyses, and the molecular structures of 8 and 9 were determined by single-crystal X-ray crystallography. Upon activation with AliBu3 and Ph3CB(C6F5)4 (TIBA/B), these complexes exhibit high catalytic activity for 5-ethylidene-2-norbornene (ENB) polymerization as well as ethylene/1-hexene and ethylene/ENB copolymerization with good tacticity-control ability for the ENB polymerization and high comonomer incorporation ability for the copolymerization reactions. It was found that the bulky adamantyl substituent at the ortho position of the phenoxy group in the ligands of these complexes apparently influences the molecular weight and the microstructure of the resultant polymers.