Effects of methyl substituents at the cyclopentadienyl ligand on the properties of C 5H 5TiCl 3 and C 5H 5TiAl 2Cl 8- x(C 2H 5) x ( x = 0–4) complexes

Abstract

The methyl substituents in the series of C pTiCl 3 compounds ( C P = Cp, MeCp, Me 3Cp, Me 4Cp, Me 5 Cp and EtMe 4Cp) shift the position of their CT absorption band from λ = 384 nm to max. 438 nm and decrease the rate of reduction of C pTiCl 3 by ethylaluminium compounds yielding the trinuclear C pTiAl 2Cl 8 - x Et x ( x = 0–4) complexes. In the C pTiCl 3/excess Et 2AlCl systems the rate of reduction was controlled by pseudomonomolecular decomposition of the proposed octahedral intermediate C pTiEt(Cl 2AlEt 2)(Cl 3AlEt). The rate constants for reduction decreased in the above series of C pTiCl 3 compounds from 1.10 × 10 −3 to 6.15 × 10 −5 s −1. The methyl substituents in the C pTiAl 2Cl 8- x Et x complexes shifted the charge transfer bands to longer wavelengths, the d-d transition to shorter wavelengths and the ESR g-value away from the free electron value. The opposite shifts were induced by the replacement of the outer chlorine atoms in the chloroaluminate ligands by ethyl groups. On going from Cp to Me 5Cp the thermal stability of the C pTiAl 2Cl 8 complexes decreased while the complexes C pTiAl 2Cl 4Et 4 became stable even with the excess of Et 3Al. The C pTiAl 2Cl 8- x Et x complexes were also formed in the redox reaction of non-dimerizing methylcyclopentadienes (Me 3CpH/EtMe 4CpH) with bis(di-μ-chloroalane)(benzene)titanium(II) complexes C 6H 6 · TiAl 2Cl 8- x Et x ( x = 0–2). The reaction was found stoichiometric except for the perchloro complexes forming diamagnetic byproducts.