Probing the Role of Secondary versus Tertiary Amine Donor Ligands for Indium Catalysts in Lactide Polymerization

摘要

The role of the central amine donor in a previously reported dinuclear indium catalyst, [N_(Me2)N_HO)InCl]_2(μ-Cl)(μ-OEt) (1), for the polymerization of lactide was investigated through experimental methods. The solid state structural data of a series of dimeric complexes related to 1, including the previously reported bromide derivative [(N_(Me2)N_HO)InBr](μ-Br)(μ-OEt) (2) and the newly synthesized methylated derivative [(N_(Me2)N_(Me)O)InCl]_2(μ-Cl)(μ-OEt) (6), showed that weak hydrogen bonding may be present within some of these complexes in the solid state. The polymerization of rac-lactide with 2, 6, and a related achiral complex [(L_H)InCl]_2(μ-Cl)(μ-OEt) (8) synthesized for this study indicates that hydrogen bonding may not influence the reactivity of these compounds. The nature of the central amine donor may play a role in tuning the reactivity of these types of catalysts. Catalysts with central secondary amine donors, such as complexes 1, 2, and 8, are 2 orders of magnitude more reactive than those with central tertiary amine donors, such as complex 6.