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)

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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.

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