Four‐ and Five‐Coordinate Titanium(IV) Complexes Supported by the dpp‐bian Ligand in ROP of L‐Lactide.

A titanium(IV) alkoxido complex, (dpp‐bian)Ti(OBn)2 (2), as well as alkoxido chlorido complexes (dpp‐bian)TiCl(OCH2CH2OMe) (3) and (dpp‐bian)TiCl2OBn (4), were synthesized from the titanium(IV) dichloride precursor [(dpp‐bian)TiCl2]2 (1) by exchange with corresponding sodium salts (comps. 2 and 3) or by the alcoholysis with BnOH (comp. 4). The compounds 2–4 were fully characterized by elemental analysis, NMR or EPR, and IR spectroscopy. Molecular structures of the metal complexes in the solid state have been determined by single‐crystal XRD analysis. Compounds 2–4 were tested as catalysts in the ROP of L‐lactide in a toluene medium. Whereas complexes 2 and 3 produce cyclic PLAs with broad dispersities and unpredictable molecular weights, complex 4 acts as an efficient ROP catalyst which polymerizes the monomer in a highly controllable manner. It produces BnO‐capped PLAs with narrow molecular weight distributions as well as linear dependence of Mns on monomer conversion. [ABSTRACT FROM AUTHOR]