Mono-η-cycloheptatrienyltitanium chemistry: synthesis, molecular and electronic structures, and reactivity of the complexes [Ti(η-C7H7)L2X](L = tertiary phosphine, O- or N-donor ligand; X = Cl or alkyl)

Abstract

Bis(η-toluene)titanium reacts with cycloheptatriene in the presence of (AlEtCl₂)₂, at > 60 °C to form [Ti(η-C₇H₇)(η-C₇H₉)] and at room temperature [{Ti(η-C₇H₇)(thf)(µ-Cl)}₂](thf = tetrahydrofuran) is also formed. The crystal structure of the latter has been determined. The dimer reacts with the ligands L₂= R₂PCH₂CH₂PR₂(R = Me or Ph), trans-1,2-bis(dimethylphosphino)cyclopentane, MeOCH₂CH₂OMe, 2PMe₃ or Me₂NCH₂CH₂NMe₂, forming the compounds [Ti(η-C₇H₇)L₂Cl]. Reaction of alkyl Grignard reagents with the appropriate chloroderivatives gives the titanium–alkyls [Ti(η-C₇H₇)L₂R][L₂= Me₂PCH₂CH₂PMe₂, R = Me or Et; L₂=trans-1,2-C₅H₈(PMe₂)₂, R = Me]. The crystal structure of [Ti(η-C₇H₇)(Me₂PCH₂CH₂PMe₂)Et] has been determined: there is no evidence for Ti–H–C interactions between the Ti and the hydrogens of the ethyl group. The photoelectron spectra of several Ti(η-C₇H₇) compounds are discussed in terms of the nature of the Ti(η-C₇H₇) bonding. It is proposed that the chemistry of the Ti(η-C₇H₇) system corresponds most closely to a formal description of the η-C₇H₇ group as having a –3 charge rather than the more conventional description as +1. Homogeneous mixtures of [{Ti(η-C₇H₇)(thf)(µ-Cl)}₂] and aluminium alkyls are shown to catalyse ethylene polymerisation.