Preparation of 2- and 4-substituted 3-hydroxy-5-methylfurans and the aluminum and gallium complexes of 3-hydroxy-5-methyl-2-(N-methylformamido)furan

In model studies designed to study the synthesis of potentially hexadentate chelates based on the linkage of three furan rings to a triamine via amide linkages, new 2- and 4-substituted 3-hydroxy-5-methylfurans have been prepared. Particularly, 3-hydroxy-5-methyl-(N-methylformamido)furan (Hahm) and its Al and Ga complexes (M(ahm)3) have been prepared and thoroughly characterized by a variety of techniques, in the solid state and in solution. Solution equilibrium studies (μ = 0.6 M NaCl, 25 °C) uncovered a complicated set of equilibria in the Al3+/Hahm system; the solution potentiometric data were best explained by the presence of mixed ligand (HL = Hahm, L− = ahm−) hydroxo species [Al3(OH)4L3]2+ and [Al(OH)2L2]−, in addition to the expected [AlLn](3−n)+ (n = 1, 2, 3) species. Further solution studies at HL:M ratios of 3:1 (μ = 0.15 M NaCl, 25 °C) showed that Hahm is a relatively weak complexing agent for both Al and Ga, forming tris-ligand species with overall formation constants of 1019.5 and 1020.6, respectively.