Influence électronique et stérique du ligand tétraméthylcyclopentadiényle sur les propriétés physiques et sur la réactivité de complexes du titane et du zirconium

Abstract

The complexes (C5Me4H)2MR1R2 (M = Ti, Zr) and (C5Me4H)(C5H5)MR1R2 (M = Ti) have been prepared (R1 = R2 = Cl, CH3, C6H5, p-C6H4CH3, CO; R1 = Cl, R2 = CH3, C6H5, p-C6H4CH3). The NMR and IR spectra of these complexes indicate that C5Me4H exhibits an electron-donor effect more important than C5H5 and a little bit weaker than that of C5Me5. A structural investigation of the complex (C5Me4H)2Zr(C6H5)Cl and the study of the 1H or 13C dynamic NMR properties of the compounds (C5Me4H)2MR1R2 (M = Ti, Zr; R1 = R2 = C6H5, p-C6H4CH3; R1 = Cl, Br, R2 = C6H5, p-C6H4CH3) show clearly that C5Me4H has a steric effect intermediate between C5H5 and C5Me5. The steric or electronic effects of C5Me4H have been used to induce specific isomerization reactions of various alkenes by using (C5Me4H)2Ti(CH3)2 as catalyst. Key words: zirconium, titanium, tetramethylcyclopentadienyl, photo-assisted, isomerization.