New Titanium Catalysts Containing Tetrazole for Cycloaddition of CO₂ to Epoxides

A series of new half-sandwich titanocene [(η5-C5H5)­TiLCl2] (1) and nonorganometallic titanium complexes [TiLCl3(THF)] (2) and [TiL2Cl2] (3) containing 5-(2-hydroxyphenyl)­tetrazole (LH) were synthesized in high yield and fully characterized by various spectroscopic methods and X-ray crystallography. In all complexes, the ligand L acted as a monoanionic bidentate ligand and hydrogen bonding between the oxygen of the tetrahydrofuran and hydrogen of the tetrazolyl unit was observed. In the cycloaddition of CO2 to propylene oxide, complex 3 showed the highest activity among the reported Ti complexes.