Improved Reactivity In The Ring-Opening Polymerization Of Epsilon-Caprolactone With A Trinuclear Titanium(Iv) Oxochloroneopentoxide As Initiator

The complex [Ti-3(O)(Cl)(ONep)(9)] and two iron(II)-containing products, [Fe4Cl8(thf)(6)] and [Fe2Cl3(thf)(6)][FeCl4], were synthesized by a redox reaction involving [Ti-3((OPr)-Pr-i)(11)][FeCl4] and neopentanol; the structures of compounds [Ti-3(O)(Cl)(ONep)(9)] and [Fe2Cl3(thf)(6)][FeCl4] have been confirmed by X-ray diffraction methods. Variable-temperature H-1 NMR analysis of [Ti-3(O)(Cl)(ONep)(9)] revealed signals for three non-equivalent neopentoxides in the 1:1:1 integration ratio, indicating the maintenance of the trinuclear structure in solution. Alkoxide [Ti-3(O)(Cl)(ONep)(9)] was employed as initiator in both bulk and solution polymerization of epsilon-caprolactone (epsilon-CL) at various temperatures, monomer/initiator molar ratios and reaction times. [Ti-3(O)(Cl)(ONep)(9)] produced poly(epsilon-caprolactone) in high yields, with molecular weights ranging from 7100 to 9800 g mol(-1) and PDI (polydispersity index) values between 1.3 to 1.5. The reactivity of [Ti-3(O)(Cl)(ONep)(9)] in the ring-opening polymerization (ROP) of epsilon-CL was compared to those of [Ti-3((OPr)-Pr-i)(11)][FeCl4] and [Ti((OPr)-Pr-i)(4)]. The better polymerization reactivity shown by [Ti-3(O)(Cl)(ONep)(9)] seems to be associated with structural features, as well as with the stronger Lewis basicity of -ONep over-(OPr)-Pr-i ligands and the maintenance of the trimetallic structure in the reaction media.