Sodium iminoquinolates with cubic and hexagonal prismatic motifs: synthesis, characterization and their catalytic behavior toward the ROP of rac-lactide

Abstract

A series of sodium 2-arylimino-8-quinolates, C1–C8, differing in both the nature of the aryl and quinolate substituents, was prepared and characterized by ¹H/¹³C NMR spectroscopy and elemental analysis. Their X-ray structures reveal multimetallic assemblies adopting a variety of structural cores all based on Na–O repeat units: cubic and tetrametallic for C1, C2 and C4, hexagonal prismatic and hexametallic for C3 and C5, and for tetrametallic C7′ a core resembling a cyclooctatetraene-type tub-shape. In the presence of BnOH, C1–C8 exhibit good activities towards the ring-opening polymerization (ROP) of rac-lactide, affording amorphous polylactides with broad molecular weight distributions. Furthermore, the substituent variation within the ligand frame of C1–C8 affects the catalytic activities of the ROP with the least sterically hindered system, C1, yielding the highest conversion.

The international collaboration between Professor Wen-Hua Sun at the Institute of Chemistry, Chinese Academy of Sciences (CAS) and Dr Gregory A. Solan at the University of Leicester, UK started in 2014 through a combination of shared scientific interests and common research goals. To strengthen this collaboration Dr Solan was awarded a CAS President's International Fellowship for Visiting Scientists in 2015. This scheme supports highly-qualified international scientists to carry out cooperative projects at CAS-affiliated institutions for 1–12 months and covers daily living expenses and international travel costs. The fellowship also aims to strengthen partnerships between CAS host institutions and the recipients’ home institution.

Dr Solan, having first visited the Institute of Chemistry, CAS in Beijing in 2012, has been able to make a more extended 3 month stay during his sabbatical leave in 2016 working in Professor Sun's laboratory for synthesizing a range of important polymeric materials including polyethylenes and polyesters.