Synthesis, structure, and reactivity of yttrium complexes with chiral biaryldiamine-based N4-ligands

The chiral biaryl-based N4-ligands, (R)-5,5′,6,6′,7,7′,8,8′-octahydro-2,2′-bis(pyrrol-2-ylmethyleneamino)-1,1′-binaphthyl (1H2) and (S)-2,2′-bis(pyrrol-2-ylmethyleneamino)-6,6′-dimethyl-1,1′-biphenyl (2H2), can effectively stabilize the chiral rare earth metal chloride complexes such as 1-YCl(dme) (3) and 2-YCl(dme) (4), which offers important intermediates for the preparation of chiral rare earth catalysts containing the M–C or M–X (X = heteroatom) bonds. For example, treatment of 3 with half equiv of 1Na2 in THF gives the binuclear complex 1-Y(thf)-1-Y(thf)-1 (5) in 70% yield. These complexes have been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analyses. The complex 5 is an active catalyst for the ring-opening polymerization of rac-lactide, affording isotactic-rich polylactides.