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

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 epsilon-caprolactone (epsilon-CL) and rac-lactide (rac-LA) were carried out. The ligand precursors [(5- Bu-t-2-C4H2NH)CH=N(CH2)(2)](2)NH (H2LBu, 1) and [(2-C4H3NH)CH=N(CH2)(2)](2)NH (H2LH, 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 (BuMgOBn)-Mg-n in toluene at 70 degrees C produced dinuclear magnesium complex [(mu-OBn)(2)Mg2LBu] (3). Similar treatment of 1 with EtZnOBn generated [(mu-OBn)(2)Zn2LBu] (4). Reaction of 2 with 2 equiv. of Me2AlOBn in toluene at 70 degrees C afforded aluminum complex [Me2Al(mu-OBn)(2)AlLH] (5). Complexes 3-5 were characterized by H-1 and C-13 NMR spectroscopy, elemental analyses, and single crystal X-ray diffraction techniques. Each of complexes 3-5 is active for the ROP of epsilon-CL and rac-LA. Kinetic studies of the polymerization reactions were performed.