The crystal structure of (η6-C6Me6)Ti2 and the catalytic activity of the (C6Me6)TiAl2Cl8-xEtx (x = 0-4) complexes towards butadiene

Article abstract of DOI:10.1016/0022-328X(92)83267-L

The composition of (C6Me6)TiAl2Cl_8-xEt_x complexes in (C6Me6)TiAl2Cl8 + n Et3Al (n = 0.5-6) systems was studied by UV-Vis spectroscopy and the X-ray crystal structure of one of them, (η⁶-C6Me6)Ti<(μ-Cl)2(AlClEt)>2 (IIa-2), has been determined.The complex crystallizes in the orthorhombic space group Pna2₁ with Z = 4 and lattice parameters a 15.634(3), b 11.355(2), c 14.417(a) Angstroem.The ethyl groups of IIa-2 reside in outer positions of aluminate ligands farther away from the C6Me6 ligand.The other part of the complex does not differ remarkably from structures of other (arene)Ti^II complexes.Negligible activity of (C6Me6)TiAl2Cl8 towards the butadiene cyclotrimerization is considerably increased by addition of 2.5-3.0 equivalents of Et3Al.As follows from UV-Vis spectra, such systems contain mainly the (C6Me6)TiAl2Cl5Et3 complex.It is suggested that the introduction of three Et substituents destabilizes the Ti-(η⁶-C6Me6) bond so that the replacement of hexamethylbenzene by butadiene in the first step of a catalytic cycle becomes more feasible.