Effects of substituents in cyclopentadienyltitanium trichlorides on electronic absorption and 47,49Ti NMR spectra and styrene polymerization activated by methylalumoxane
Abstract
Correlation of the HOMO-LUMO separation and NMR shifts in the series (η(5)-C5H5-nMen)TiCl3 (n=0-5). In the series of the methylated compounds (η(5)-C5H(5-n)Me(n))TiCl3 (n=0-5) 1-6, linear correlations of lambda(max) of the absorption band and δ (47,49)Ti 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 (η(5)-C5Me4R)TiCl3 7-14 and (η(5)-C5H(1,2,3-)Me3R)TiCl3 15-20 where R = alkyl, silyl or phenyl no correlation between λ(max) and δ 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.