NOVEL LIQUID-CRYSTALLINE TITANOCENE COMPLEXES WITH CATALYTIC ACTIVITYFOR POLYMERIZATIONS OF ACETYLENE AND PHENYLACETYLENE

We have synthesized a series of novel titanocene complexes with liquid -crystalline (LC) groups as coordination ligands, with the ultimate ai m of developing LC catalytic species available for anisotropic polymer izations of acetylenes. The titanocene complexes were prepared by intr oducing LC groups into cyclopentadienyl ligands as substituents, (PCH5 06Cp)(2)TiCl2 (1), or coordinating them to a titanium atom as symmetri c and asymmetric ligands, Cp2Ti(PCH5060)(2) (2) and Cp2Ti(PCH5060)Cl ( 3) [where Cp = cyclopentadienyl, PCH506 = p-(trans-4-n-pentylcyclohexy l)phenoxyhexyl and 60=p-(trans-4-n-pentylcyclohexyl)phenoxyhexyloxy]. Polarizing optical microscope observations and differential scanning c alorimetry measurements indicated that the titanocene complexes 2 and 3 are the first titanium complexes exhibiting LC behaviour. It is foun d that the titanocene complexes 1 and 2 can polymerize phenylacetylene s to give poly(phenylacetylene)s with the aid of triethylaluminium (Et 3Al) as cocatalyst. The molecular weights and degrees of polymerizatio n of the poly(phenylacetylene)s prepared were comparable or superior t o those prepared with titanocene dichloride and tetra-n-butoxytitanium [Ti(O-n-Bu)(4)] catalysts. The LC titanocene complexes 2 and 3 were a lso confirmed to have catalytic activities for the polymerization of a cetylene. Electron spin resonance spectra of the catalyst systems gave signals of trivalent titanium (Ti (3+)) with no hyperfine structure, suggesting that the catalytically active species is a mononuclear comp lex consisting of Ti3+ rather than a binuclear or trinuclear one. (C) 1998 Elsevier Science Ltd. All rights reserved.