Bimetallic copper(II) and zinc(II) complexes of acyclic Schiff base ligands derived from amino acids

The acyclic Schiff-base ligands (2-(OH)-5-(R3)C6H2-1,3-(HCNC(R1)(R2)CO2H), derived from the dialdehyde 2-hydroxy-5-R-1,3-benzenedicarboxaldehyde (R = Me or t-Bu) and two equivalents of the amino acids glycine, 2,2-diphenylglycine or phenylalanine, have been reacted with the metal acetates M(OAc)2 (M = Cu, Zn) in the presence of triethylamine, affording the complexes [HNEt3][M2(CH3CO2)2(2-(O)-5-(t-Bu)C6H2-1,3-(HCNC(R1)(R2)CO2)2] (M = Cu, R1 = R2 = C6H5, R3 = Me (1); M = Zn, R1 = R2 = H, R3 = t-Bu (2); M = Zn, R1 = R2 = C6H5, R3 = t-Bu (3); M = Zn, R1 = H, R2 = CH2C6H5, R3 = t-Bu (4)) in good yields. The crystal structures of 1·MeCN, 2·112MeOH, 3·2MeOH, and 4·3MeOH have been determined.

Graphical abstractFour copper and zinc di-nuclear complexes supported by acyclic Schiff base ligands were synthesised and structurally characterised. Surprisingly, these anionic complexes were found to be inactive for the ring opening polymerisation of ε-caprolactone in the presence of benzyl alcohol.Figure optionsDownload full-size imageDownload as PowerPoint slide