Facile synthesis of a dimeric titanium(IV) complex with terminal Ti=O moieties and its application as a catalyst for the cycloaddition reaction of CO2 to epoxides

In this report, facile and exclusive synthesis of dimeric titanium(IV) complex with a terminal Ti=O moiety from the reaction between novel pyridine-based tridentate ligand (LH2) and Ti(O-i-Pr)(4) under the bubbling of wet air is presented. Alternatively, the same dimeric Ti complex was obtained via wet air bubbling of monomeric LTi(O-i-Pr)(2) or addition of the same equiv. of H2O into LTi(O-i-Pr)(2). All compounds including LH2 and two titanium complexes were characterized by single crystal X-ray analyses. Newly synthesized terminal oxo-titanium compound is the first example of structurally characterized dimeric terminal oxo-titanium compound having no Ti=O -> Ti bonds. Two titanium complexes were used as effective catalysts for the cycloaddition of CO2 to propylene oxide in the presence of various kinds of cocatalysts such as n-Bu4PBr, n-Bu4NI, n-Bu4NBr, n-Bu4NCl, PPNCl, and DMAP.