Alkali metal complexes of tridentate amine-bis(phenolate) ligands and their rac-lactide ROP activity

•Amine-bis(phenolate) complexes of alkali metals were synthesized.•A potassium complex exhibiting arene bonding was structurally characterized.•The Li, Na and K complexes are active lactide polymerization catalysts.

Three complexes were prepared using lithium, sodium and potassium reagents and an amine-(bis)phenol proligand. The proligand, benzylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol) (abbreviated H2[L]), was reacted with n-butyllithium to give the lithium complex, Li2[L] (1), and NaH or KH to give the sodium, Na2[L] (2), and potassium, K2[L] (3), complexes, respectively. The compounds were also found to contain varying numbers of coordinated THF molecules. These complexes were characterized using 1H, 13C, and 7Li NMR (for the lithium complex), MALDI-TOF MS, elemental analysis and FT-IR. The potassium complex (3) was characterized in the solid state and exhibits η6 K-arene bonds as well as η1-bonding of the K ion to the ipso-carbons of the phenolate fragments. The reactivity of 1–3 towards the ring-opening polymerization of rac-lactide to form polylactide (PLA) was explored.

Graphical abstractThe synthesis of Li, Na and K complexes of amine-bis(phenolate) ligands, and their application for ring opening polymerization of rac-lactide is described.Figure optionsDownload full-size imageDownload as PowerPoint slide