In the series of the methylated compounds (eta(5)-C5H5-nMen)TiCl3 (n=0-5) 1-6, linear correlations of lambda(max) of the absorption band and 3 Ti-49,Ti-47 chemical shift with the number of Me groups were found. It is due to the dependence of both the magnitudes on the HOMO-LUMO energy gap which is influenced by electron donating methyl substituents. The catalysts made by combining 1-6 with MAO (molar ratio Al/Ti 500) showed only a gross dependence of decreasing activity with the number of methyl groups. For compounds (eta(5)-C5Me4R)TiCl3 7-14 and (eta(5)-C5H(1,2,3-)Me3R)TiCl3 15-20 where R = alkyl, silyl or phenyl no correlation between lambda(max) and delta was found. Limited DFT calculations were performed to assign HOMO/LUMO orbitals involved. Crystal structures of 16 and 20 were determined and some other inspected to prove the absence of steric hindrance. The poor correlation of the spectroscopic properties with the catalytic activity is not surprising because steric effects of cyclopentadienyl ligands at cationic polymerization centers are generally anticipated. (c) 2006 Elsevier B.V. All rights reserved.