Synthesis and Characterization of Carbon-Bridged Bis(phenolate) Lanthanum Alkoxides and Their Catalytic Behavior for the Polymerization of L -Lactide

Four lanthanum alkoxides stabilized by a carbon-bridged bis(phenolate) ligand were synthesized and their catalytic behavior for the ring-opening polymerization of L -lactide was explored. Reactions of [(MBMP)LaCp(THF) 2 ] (MBMP 2− = 2,2′-methylene-bis(6- tert -butyl-4-methyl phenoxo)) with HOCH 2 Ph, HOCH 2 CF 3 , HOCH(CH 3 ) 2 , and HOCH 2 CH 2 N(CH 3 ) 2 , respectively, in a 1:1 molar ratio in THF gave the dimeric lanthanum alkoxo complexes [(MBMP)Ln(Sm-OR)(THF) 2 ] 2 (OR = OCH 2 Ph ( 1 ), OCH 2 CF 3 ( 2 ), OCH(CH 3 ) 2 ( 3 ), OCH 2 CH 2 N(CH 3 ) 2 ( 4 )]. These complexes were well characterized, and the definitive molecular structure of complex 1 was determined. It was found that complexes 1 to 4 are efficient initiators for the ring-opening polymerization of L -lactide. The structure of the alkoxo groups has a significant effect on the catalytic behavior, and complex 2 can initiate L -lactide polymerization in a controlled manner.