Effects of methyl substituents at the cyclopentadienyl ligand on the properties of C5H5TiCl3 and C5H5TiAl2Cl8-x(C2H5)x (x = 0–4) complexes

The methyl substituents in the series of CpTiCl3 compounds (CP = Cp, MeCp, Me3Cp, Me4Cp, Me5 Cp and EtMe4Cp) shift the position of their CT absorption band from λ = 384 nm to max. 438 nm and decrease the rate of reduction of CpTiCl3 by ethylaluminium compounds yielding the trinuclear CpTiAl2Cl8 - xEtx (x = 0–4) complexes. In the CpTiCl3/excess Et2AlCl systems the rate of reduction was controlled by pseudomonomolecular decomposition of the proposed octahedral intermediate CpTiEt(Cl2AlEt2)(Cl3AlEt). The rate constants for reduction decreased in the above series of CpTiCl3 compounds from 1.10 × 10−3 to 6.15 × 10−5 s−1. The methyl substituents in the CpTiAl2Cl8-xEtx 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 Me5Cp the thermal stability of the CpTiAl2Cl8 complexes decreased while the complexes CpTiAl2Cl4Et4 became stable even with the excess of Et3Al. The CpTiAl2Cl8-xEtx complexes were also formed in the redox reaction of non-dimerizing methylcyclopentadienes (Me3CpH/EtMe4CpH) with bis(di-μ-chloroalane)(benzene)titanium(II) complexes C6H6 · TiAl2Cl8-xEtx (x = 0–2). The reaction was found stoichiometric except for the perchloro complexes forming diamagnetic byproducts.