Dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands: synthesis, structures, and catalysis toward the ring-opening polymerization of ε-caprolactone and rac-lactide

Abstract

Synthesis and characterization of novel dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands and their catalysis toward the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) were carried out. The ligand precursors [(5-Bu^t-2-C₄H₂NH)CHN(CH₂)₂]₂NH (H₂L^Bu, 1) and [(2-C₄H₃NH)CHN(CH₂)₂]₂NH (H₂L^H, 2) were prepared by condensation of diethylene triamine with 5-tert-butyl-1H-pyrrole-2-carbaldehyde and 1H-pyrrole-2-carbaldehyde, respectively. Treatment of 1 with 2 equiv. of BuⁿMgOBn in toluene at 70 °C produced dinuclear magnesium complex [(μ-OBn)₂Mg₂L^Bu] (3). Similar treatment of 1 with EtZnOBn generated [(μ-OBn)₂Zn₂L^Bu] (4). Reaction of 2 with 2 equiv. of Me₂AlOBn in toluene at 70 °C afforded aluminum complex [Me₂Al(μ-OBn)₂AlL^H] (5). Complexes 3–5 were characterized by ¹H and ¹³C NMR spectroscopy, elemental analyses, and single crystal X-ray diffraction techniques. Each of complexes 3–5 is active for the ROP of ε-CL and rac-LA. Kinetic studies of the polymerization reactions were performed.