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

The 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.