Synthesis and characterization of aluminum and zinc complexes supported by pyrrole-based ligands and catalysis of the aluminum complexes toward the ring-opening polymerization of ɛ-caprolactone

Abstract

Reaction of quinolin-8-amine with 1 H-pyrrole-2-carbaldehyde or 5- tert-butyl-1 H-pyrrole-2-carbaldehyde catalyzed by HCO 2H forms N-((1 H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL, 3a) or N-((5- tert-butyl-1 H-pyrrol-2-yl)methylene)quinolin-8-amine (≡ HL′, 3b). Treatment of 3a and 3b respectively with AlMe 3 or AlEt 3 in toluene affords corresponding aluminum complexes LAlMe 2 ( 4a), L′AlMe 2 ( 4b) and LAlEt 2 ( 4c). Reaction of 3a and 3b with an equivalent of ZnEt 2 in toluene generates L 2Zn and L′ 2Zn, respectively. A related compound N-((1 H-pyrrol-2-yl)methylene)-2-(3,5-dimethyl-1 H-pyrazol-1-yl)benzenamine (≡ HL″, 7) was prepared by reaction of 2-(3,5-dimethyl-1 H-pyrazol-1-yl)benzenamine with 1 H-pyrrole-2-carbaldehyde in the presence of HCO 2H. Reaction of 7 with AlMe 3 gives L″ 2AlMe ( 8), and with ZnEt 2 yields L″ 2Zn ( 9). All new compounds were characterized by NMR spectroscopy and elemental analysis. The structures of complexes 4b, 5b and 8 were additionally characterized by single crystal X-ray diffraction analyses. Complexes 4a– 4c, and 8 were proved to be active catalysts for the ring-opening polymerization (ROP) of ɛ-caprolactone (ɛ-CL) in the presence of BnOH. The kinetic study of the polymerization reactions catalyzed by 4a and 8 was performed.