Ti (IV) Complexes with Bidentate O-Chelating N-Heterocyclic Carbenes for Use in the Homopolymerization of Ethylene and Its Copolymerization with Cyclic Olefins

The synthesis of titanium (IV) complexes bearing bidentate O-chelating N-heterocyclic carbenes (NHCs) is reported. Double deprotonation of the respective NHC precursor ligand and further reaction with one equivalent of TiCl4 center dot THF2 leads to the formation of complexes Ti-1-Ti-3 of the general formula TiCl3(NHC-R-O)(THF), (NHC-R-O=1-(2,6-diisopropylphenyl)-3-(2-O-phenyl)-4,5-dihydroimidazol-2-ylidene, 1-(mesityl)-3-(2-O-phenyl)-4,5-dihydroimidazol-2-ylidene, 1-(2,6-dimethylphenyl)-3-(2-O-phenyl)-4,5-dihydroimidazol-2-ylidene). Furthermore, these Ti-(NHC-R-O) trichloride complexes can be reacted with the bulky aryloxo ligands 2,6-di(t)Bu-4-methylphenolate and 2,2',4,4',6,6'-hexa-Pr-i-terphenoxide, respectively, to form the mixed titanium (aryloxo)(NHC-R-O) dichloride pre-catalysts Ti-4-Ti-6. Single-crystal X-ray structures of complexes Ti-1, Ti-5 and Ti-6 are presented. Depending on the aryloxo ligand used, the complexes possess either a trigonal bipyramidal or square pyramidal ligand sphere. The propensity of Ti-1, Ti-4-Ti-6 to homopolymerize ethylene and to copolymerize ethylene with norborn-2-ene (NBE) and cyclopentene (CPE), respectively, was investigated and access to high-molecular weight (co-)polymers with such complexes is disclosed.