Aluminum Compounds Containing Pyrrole–Imine Ligand Systems – Synthesis, Characterization, Structure Elucidation, Ring‐Opening Polymerization, and Catalytic Meerwein–Ponndorf–Verley Reaction

Abstract

AbstractThe reactions of AlMe3 with the tridentate pyrrole ligand precursor C4H3NH(2‐CH=NCH2Py) and subsequent treatment of the derivatives with small organic molecules such as 2,6‐diisopropylphenol or dibenzoylmethane were conveniently performed, and the products were characterized. The reaction between 1 equiv. of AlMe3 and 1 equiv. of a pyrrole–imine–pyridine ligand in toluene affords [Al{C4H3N(CHNCH2Py)Me2}] (1) in high yield. In addition, the use of 2 equiv. of AlMe3 with the same tridentate precursor results in the formation of a dialuminum compound [AlMe3{C4H3N(CHNCH2‐Py)AlMe2}] (2) in moderate yield. Furthermore, the combination of 1 with either 1 or 2 equiv. of 2,6‐diisopropylphenol or 2 equiv. of dibenzoylmethane in toluene yields aluminum monophenoxide or diphenoxide compounds [Al{C4H3N(CHNCH2‐Py)Me(O‐2,6‐iPr2C6H3)}] (3) and [Al{C4H3N(CHNCH2‐Py)}(O‐2,6‐iPr2C6H3)2] (4), respectively, as well as an aluminum bis‐diketonate compound, [Al{C4H3N(CHNCH2‐Py)}(PhCOCHCOPh)2] (5). All of the aforementioned derivatives were characterized by 1H and 13C NMR spectroscopy, and their solid‐state molecular structures were determined by single‐crystal X‐ray diffraction. The geometries of 1–5 show that the pyrrole ligand exists in the pyrrolyl–imine and azafulvene–amido resonance forms. Compounds 1, 3, 4 and 5 were used in the ring‐opening polymerization of ϵ‐caprolactone in the presence of BnOH and in the catalytic Meerwein–Ponndorf–Verley (MPV) reaction of 1‐naphthalenemethanol and 2‐naphthalenecarbaldehyde.