Structural aspects and ring opening polymerization of ε-caprolactone using mono- and di-aluminum compounds incorporating bidentate pyrrole-morpholine ligands

Abstract

A series of Al-compounds incorporating the bidentate pyrrole-morpholine precursor C4H3NH [2-CH2N(CH2CH2)2O] (1) and aluminum-alkyl have been conveniently synthesized and characterized by 1H and 13C NMR spectroscopy. Reacting one or two equivalents of 1 with AlMe3 in toluene afforded AlMe2{C4H3N [2-CH2N(CH2CH2)2O]} (2) and AlMe{C4H3N [2-CH2N(CH2CH2)2O]}2 (3), respectively, in moderate yield. Furthermore, compound (4), AlMe2{C4H3N [2-CH2N(CH2CH2)2O]}·AlMe3, was acquired either by the combination of 2 and one equivalent of AlMe3 or directly from the reaction between 1 and two equivalents of AlMe3. The molecular structures of 1, 2, and 4, were determined by single crystal X-ray diffractometry in solid state, showing a distorted tetrahedral arrangement around the Al atom in 2 and 4. All the aluminum compounds could effectively initiate the ring-opening polymerization (ROP) of ε-caprolactone in a well-controlled manner with molecular weight distributions (PDI = 1.03–1.49).