Synthesis of N -Methyl- o -phenylenediamine-Bridged Bis(phenolato) Lanthanide Alkoxides and Their Catalytic Performance for the (Co)Polymerization of rac -Butyrolactone and l-Lactide.

A series of lanthanide alkoxo complexes supported by ONNO salalen ligands were synthesized and characterized. A one-pot reaction of LH 2 (L = (2-O-C 6 H 2 - t Bu 2 -3,5)CH═N-C 6 H 4 -N(CH 3 )CH 2 (2-O-C 6 H 2 - t Bu 2 -3,5)) with LnCp 3 (THF) in a 1:1 molar ratio followed by the addition of 1 equiv of ROH (R = Bn, i Pr, and CF 3 CH 2 ), afforded the dimeric lanthanide alkoxo complexes [LLn(μ-OCH 2 Ph)] 2 [Ln = Lu ( 1 ), Yb ( 2 ), Sm ( 3 ), Nd ( 4 )], [L 2 Yb(μ-O i Pr)] 2 ( 5 ), and [L 2 Yb(μ-OCH 2 CF 3 )] 2 ( 6 ) in good isolated yields. All these lanthanide complexes were characterized by elemental analysis and FT-IR spectroscopy. In addition, complex 1 has been characterized by NMR spectroscopy. Single-crystal X-ray diffraction analysis of complexes 1 , 2 , 5 , and 6 showed that these lanthanide alkoxo complexes are dimeric in the solid state. Complexes 1 - 6 showed good activity toward the homopolymerization of rac -butyrolactone ( rac -BBL) to give atactic PHB, and ionic radii of central metals have profound influence on the polymerization. The polymerization behavior of l-lactide (l-LA) initiated by complex 2 was also explored. The kinetic study revealed that the polymerizations of rac -BBL and l-LA initiated by salalen lanthanide akoxide are first order for both the monomer and the initiator concentrations. Furthermore, it was found that complexes 1 and 2 showed good activity in the copolymerization of l-LA and rac -BBL, affording gradient copolymers.