Synthesis, structure, and catalytic activity of titanium complexes with new chiral 11,12-diamino-9,10-dihydro-9,10-ethanoanthracene-based ligands

A new series of organo-titanium complexes have been prepared from the reaction between Ti(NMe2)4 and C2-symmetric ligands, (R,R)-11,12-bis(pyrrol-2-ylmethyleneamino)-9,10-dihydro-9,10-ethanoanthracene (1H2), and (R,R)-bis(diphenylthiophosphoramino)-9,10-dihydro-9,10-ethanoanthracene (2H2), (R,R)-11,12-bis(mesitylenesulphonylamino)-9,10-dihydro-9,10-ethanoanthracene (3H2) and (R,R)-bis(diphenylthiophosphoramino)-1,2-cyclohexane (4H2). Treatment of Ti(NMe2)4 with 1 equiv of 1H2 gives, after recrystallization from a benzene solution, the binuclear double helicate titanium amide (1)2[Ti(NMe2)2]2⋅(5) in 71% yield. While under similar reaction conditions, reaction of Ti(NMe2)4 with 1 equiv of 2H2, 3H2 or 4H2 gives, after recrystallization from a toluene or benzene solution, the mononuclear single helicate titanium amides (2)Ti(NMe2)2 (6), (3)Ti(NMe2)2 (7) and (4)Ti(NMe2)2 (8), respectively, in good yields. All new compounds have been characterized by various spectroscopic techniques, and elemental analyses. The solid-state structures of complexes 5–8 have further been confirmed by X-ray diffraction analyses. The titanium amides are active catalysts for the polymerization of rac-lactide, leading to the isotactic-rich polylactides.