TITANOCENE AND ansa-TITANOCENE COMPLEXES BEARING 2,6-BIS(ISOPROPYL)PHENOXIDE LIGAND(S). SYNTHESES, CHARACTERIZATION AND USE IN CATALYTIC DEHYDROCOUPLING POLYMERIZATION OF PHENYLSILANE

摘要

Aryloxychloro and bis(aryloxy) titanocenes of general formula L^sub 2^TiCl^sub 2-x^(OAr')^sub x^ where L = η^sup 5^-C^sub 5^H^sub 5^ (x = 1 (1) and 2 (2)), L^sub 2^ = SiMe^sub 2^(η^sup 5^-C^sub 5^H^sub 4^)^sub 2^ (x = 1 (3) and 2 (4)), and Ar' = 2,6-(CHMe^sub 2^)^sub 2^C^sub 6^H^sub 3^ were prepared by the reaction of corresponding titanocene dichloride with LiOAr' and characterized by spectroscopic methods and compound 3 by single crystal X-ray diffraction analysis. The bulky aryloxy ligand in 1 and 3 exerts a hindered rotation around the Ti-O bond on the 1H NMR time scale, resulting in its dynamic behavior in CDCl^sub 3^ solution. Variable temperature NMR measurements proved the rotation barrier in 3 (ΔG^sup [double dagger]^^sub 298^ = 13.9 ± 0.3 kcal/mol) to be lower than that in 1 (ΔG^sup [double dagger]^^sub 298^ = 14.7 ± 0.2 kcal/mol) as a consequence of the more open titanocene shell in the ansa-structure of 3. The catalytic behavior of complexes 1-4, [(η^sup 5^-C^sub 5^H^sub 5^)^sub 2^TiCl^sub 2^] and [{SiMe^sub 2^(η^sup 5^-C^sub 5^H^sub 4^)^sub 2^}TiCl^sub 2^], was examined in dehydrocoupling polymerization of phenylsilane under comparable conditions, showing a remarkable higher activity for the titanocene complexes with regards to the ansa-titanocene ones. The order of catalytic activities 2 ~ 1 > [(η^sup 5^-C^sub 5^H^sub 5^)^sub 2^TiCl^sub 2^] [{SiMe^sub 2^(η^sup 5^-C^sub 5^H^sub 4^)^sub 2^}TiCl^sub 2^] ~ 3 ~ 4 reveals the aryloxy ligands to have an enhancing effect on activity in the titanocene series. [PUBLICATION ABSTRACT]