Trichloro monophenoxide complexes of titanium(IV)

Abstract

Thermalisation of TiCl₄ and phenol (1∶1) in toluene gave [TiCl₃(OC₆H₅)] 1. The more soluble complex [TiCl₃(OC₆H₄CMe₃-4)] 2 is monomeric in benzene and reacts with 4,4′-dimethyl-2,2′-bipyridyl (dmbipy) to give mer-[TiCl₃(OC₆H₄CMe₃-4)(dmbipy)] 3 and the disproportionation product [TiCl₂(OC₆H₄CMe₃-4)₂(dmbipy)]. The complex [TiCl₃(OC₆H₂Me₃-2,4,6)] 4 is monomeric in benzene whereas [TiCl₃(OC₆H₃Prⁱ₂-2,6)] 5 partially disproportionates in solution into [TiCl₂(OC₆H₃Prⁱ₂-2,6)₂] and reacts with dmbipy to give mer-[TiCl₃(OC₆H₃Prⁱ₂-2,6)(dmbipy)] 6 and [TiCl₂(OC₆H₃Prⁱ₂-2,6)₂(dmbipy)]. Thermalisation of 2,6-di-tert-butyl-4-methylphenol and TiCl₄ in toluene caused debutylation but [TiCl₃{OC₆H₂(CMe₃)₂-2,6-Me-4}] 7 forms in light petroleum (bp range 40–60 °C). Complex 7 is monomeric in benzene and does not form adducts with dmbipy or other sigma donors. A crystal structure determination of 7 showed a monomer with distorted tetrahedral co-ordination, a Ti–O bond length of 1.750(2) Å and Ti–Cl bonds longer than in TiCl₄ but shorter than in [TiCl₃(C₅H₅)] or [TiCl₃{C₅H₃(CMe₃)₂-1,3}]. 2,4,6-Tri-tert-butylphenol debutylates when thermalised with TiCl₄ in toluene giving [TiCl₃{OC₆H₄(CMe₃)₂-2,4} ] 8. The complexes [TiCl₃{OC₆H₂(CMe₃)₂-2,6-OMe-4}] 9, [TiCl₃(OC₆H₃CMe₃-2-Me-4)] 10, [TiCl₃(OC₆H₄Ph-2)] 11 and the 1-naphthoxide complex [TiCl₃(OC₁₀H₇)] 12 were also prepared. Density functional calculations performed on the models 4 and [TiCl₃(OMe)] showed both lone pairs on oxygen donate electron density to titanium but O(2p)-to-CC (π*) donation weakens the Ti–O interaction in the phenoxide complex; Cl(2p)-to-Ti(3d) donation is much reduced in the methoxide complex. The system [TiCl₃(OC₆H₄CMe₃-4)]/AlMe₃ is 280 times more active than [TiCl₃Cp] (Cp = cyclopentadienyl)/AlMe₃ for low pressure (6 psi) ethylene polymerisation but  1//₃ less active than TiCl₄/AlMe₃.