General principles driving the chemical reactivity of titanium(IV) alkoxides

The chemical reactivity of titanium(IV) (oxo)alkoxides towards multipodal ligands such as 1,3-propanediol and pentaerythritol is investigated. Two new complexes, [Ti-7(mu(4)-O)(2)(mu(3)-O)(2){O(CH2)(3)O}(mu-OEt)(6)(OEt)(12)] and [Ti-4(mu(2)-OEt)(4)(OEt)(8){mu(4)-(OCH2)(4)C}], have been isolated and characterized using single-crystal X-ray diffraction. The partial charge distribution in these complexes and in previously synthesized ones are described. From these results, it emerges that two general rules govern the chemical reactivity of Ti-IV (oxo) alkoxides. First, bridging OR-groups are systematically more basic than terminal ones and thus should be selectively attacked or substituted by protic XOH reagents. Second, a reduction in coordination is systematically associated with the more electrophilic Ti atoms and thus better solvation of the complexes.