Collect. Czech. Chem. Commun.
2011, 76, 75-94
https://doi.org/10.1135/cccc2010133
Published online 2011-01-06 09:12:25
Titanocene and ansa-titanocene complexes bearing 2,6-bis(isopropyl)phenoxide ligand(s). Syntheses, characterization and use in catalytic dehydrocoupling polymerization of phenylsilane
Michal Horáčeka, Jan Mernab, Róbert Gyepesc, Jan Sýkorad, Jiří Kubištaa and Jiří Pinkasa,*
a J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 2155/3, 182 23 Prague 8, Czech Republic
b Institute of Chemical Technology, Prague, Department of Polymers, Technická 5, 166 28 Prague 6, Czech Republic
c Charles University, Department of Inorganic Chemistry, Hlavova 2030, 128 43 Prague 2, Czech Republic
d Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, v.v.i., Rozvojová 135, 165 02 Prague 6, Czech Republic
Abstract
Aryloxychloro and bis(aryloxy) titanocenes of general formula L2TiCl2–x(OAr′)x where L = η5-C5H5 (x = 1 (1) and 2 (2)), L2 = SiMe2(η5-C5H4)2 (x = 1 (3) and 2 (4)), and Ar′ = 2,6-(CHMe2)2C6H3 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 CDCl3 solution. Variable temperature NMR measurements proved the rotation barrier in 3 (ΔG‡298 = 13.9 ± 0.3 kcal/mol) to be lower than that in 1 (ΔG‡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, [(η5-C5H5)2TiCl2] and [{SiMe2(η5-C5H4)2}TiCl2], 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 > [(η5-C5H5)2TiCl2] >> [{SiMe2(η5-C5H4)2}TiCl2] ~ 3 ~ 4 reveals the aryloxy ligands to have an enhancing effect on activity in the titanocene series.
Keywords: Titanium; Metallocenes; Polymerizations; Silicon; Titanocene complexes; Dehydrocoupling; Polysilanes; Dynamic NMR spectroscopy; X-Ray diffraction.
References: 50 live references.
