Synthesis and characterization of tri-dentate pyrrole-morpholine ligands and their corresponding aluminum, magnesium, and zinc compounds

Abstract

A series of metal compounds containing tri-dentate monoanionic pyrrole-morpholine ligands was synthesized and characterized. The reaction of O(CH2CH2)2NH·HCl, pyrrole and formaldehyde generated a new type of tri-dentate pyrrole-morpholine ligand, C4H2NH{2,5-[CH2N(CH2CH2)2O]2} (1), in high yield. The reaction of 1 with one equivalent of AlMe3 and ZnMe2 in toluene generated AlMe2{C4H2N{2,5-[CH2N(CH2CH2)2O]2}} (2) and {ZnMe{C4H2N{2,5-[CH2N(CH2CH2)2O]2}}}2 (4), respectively, in moderate yield. The reaction of two equivalents of 1 with MgnBu2 in THF generated a bis-pyrrolyl Mg compound, Mg{C4H2N{2,5-[CH2N(CH2CH2)2O]2}}2(THF) (3), in moderate yield. Compound 4 is sensitive to air and moisture and it decomposed into a hexa-Zn compound, {(ZnMe)2{C4H2N-{2,5-[CH2N(CH2CH2)2O]2}(μ4-O)2(μ2-ZnMe)2} (5), when a small amount of moisture leaked into the flask during the recrystallization process. Compounds 1–4 were characterized by 1H and 13C NMR spectra and the structures of 1, 3, and 5 were also determined by single crystal X-ray diffractometry. Compounds 2 and 3 were tested as initiators for the ring opening polymerization of ε-caprolactone and 3 showed excellent activity.