Modification of aluminum alkoxides with β-ketoesters: New insights into formation, structure and stability

Abstract

[Al(OiPr)2(β-ketoesterate)]2 and Al(β-ketoesterate)3 (β-ketoesterate = methyl, ethyl, iso -propyl, tert-butyl, allyl and 2-(methacryloyloxy)ethyl acetoacetate) were prepared by reaction of [Al(OiPr)3]4 with the corresponding β-ketoesters. Al(β-ketoesterate)3 derivatives were exclusively formed at room temperature, whereas elevated reaction temperatures, causing thermal de-oligomerization of [Al(OiPr) 3]4, were necessary for the formation of [Al(O iPr)2(β-ketoesterate)]2. All compounds were characterized by NMR spectroscopy, and [Al(OiPr) 2(tert-butyl acetoacetate)]2 by a single crystal structure analysis. The [Al(OiPr)2(β-ketoesterate)] 2 derivatives are asymmetrically substituted dimers with one octahedrally and one tetrahedrally substituted aluminum atom, bridged by two iso -propoxo groups, whereas the Al(β-ketoesterate)3 derivatives are monomers with octahedrally coordinated aluminum. Transesterification as a possible side reaction was only observed at elevated temperatures for Al(tert-butyl acetoacetate)3 in the presence of liberated iso -propanol.