2, 3. Advantages of the CGC (constrained geometry catalyst) over the conventional biscyclopentadienyl metallocene catalysts are thermal stability, high comonomer incorporation, and high molecular weight of the obtained polymers in the ethylene/-olefin copolymerizations, which enables its use in a commercial high temperature solution process.1 Various successful modifications over the standard CGC, [Me2Si(5-Me4Cp)(NtBu)]TiCl2 have been achieved by replacement of the Me4Cp unit with other -donor ligands, but modifications on the bridge unit have not been so successful. Erker reported preparation of alkylidene (R1R2C) or vinylidene (H2C=C) bridged Cp/amido complexes but their activity for ethylene polymerization is significantly lower than the standard CGC.2 Ethylene-bridged complex, [(5-Me4Cp)CH2CH2(NtBu)]TiCl2 was reported to show much reduced incorporation of comonomer. Herein, we present a novel preparation method for ortho-phenylene-bridged Cp/sulfonamido and Cp/amido titanium complexes. Conventionally, aryl-substituted cyclopentadienyl ligands have been prepared by nucleophilic attack of aryl lithium to 2-cyclopentenone derivatives and subsequent acid-catalyzed H2O-elimination. Attempts to prepare the targeted ortho-phenylene-bridged Cp/amide ligand system by the same strategy using 2-LiC6H4N(R)Li was unsuccessful.
A new synthetic route was devised by using the Suzuki-coupling. The key starting material in this route, boronic acid 1 can be prepared in 30g-scale. The boronic acid is excellent substrates for the Suzuki-coupling reaction and the cyclopentenone compounds 2 are afforded in excellent yields. The cyclopentenone compounds can be easily transformed to the cyclopentadiene compounds 3 from which various ortho-phenylene-bridged Cp/sulfonamido and Cp/amido titanium complexes are prepared. Several complexes were characterized by X-ray crystallography and some of them show higher activity, higher incorporation of 1-octene, and higher molecular weights than the standard CGC [(5-Me4Cp)CH2CH2(NtBu)]TiCl2.
