ELECTRONIC AND STERIC INFLUENCE OF THE TETRAMETHYLCYCLOPENTADIENYL LIGAND ON PHYSICAL-PROPERTIES AND REACTIVITY OF TITANIUM AND ZIRCONIUM COMPLEXES

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 H-1 or C-13 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.