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

The reactions of AlMe 3 with the tridentate pyrrole ligand precursor C 4 H 3 NH(2‐CH=NCH 2 Py) 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 AlMe 3 and 1 equiv. of a pyrrole–imine–pyridine ligand in toluene affords [Al{C 4 H 3 N(CHNCH 2 Py)Me 2 }] ( 1 ) in high yield. In addition, the use of 2 equiv. of AlMe 3 with the same tridentate precursor results in the formation of a dialuminum compound [AlMe 3 {C 4 H 3 N(CHNCH 2 ‐Py)AlMe 2 }] ( 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{C 4 H 3 N(CHNCH 2 ‐Py)Me( O ‐2,6‐ i Pr 2 C 6 H 3 )}] ( 3 ) and [Al{C 4 H 3 N(CHNCH 2 ‐Py)}( O ‐2,6‐ i Pr 2 C 6 H 3 ) 2 ] ( 4 ), respectively, as well as an aluminum bis‐diketonate compound, [Al{C 4 H 3 N(CHNCH 2 ‐Py)}(PhCOCHCOPh) 2 ] ( 5 ). All of the aforementioned derivatives were characterized by 1 H and 13 C 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.