Limitations in solubility of bis-urea molecules used to form thermoreversible gels in organic solutions has brought interest in examining mono-urea molecules to form organometallogelators as an alternative. Work by Carr et al found success in gelling THF solutions utilizing a mono-urea ligand with a metal coordinating pyridyl group, and with metal coordinating carboxylate group. However, coordination of first row transition metals with these ligands proved to be weak or slow, thus making them impractical. To improve metal coordination, a complimentary coordinating motif composed of dicarboxylate amine (1/2 EDTA) containing mono-urea ligand was designed, synthesized, and studied (Fig. A). It is believed that the dicarboxylate amine urea ligand when deprotonated in the presence of a +2-metal cation will coordinate to the metal in an octahedral complex (Fig. B), creating a bis-urea organogelator in-situ. Synthesis of mono-urea ligand begins with 3,5-dihydroxybenzaldehyde, which was alkylated under basic conditions in dimethylformamide with 1-bromododecane, yielding the diether in 99% yield. The aldehyde of the diether was then converted to the benzylic amine in one pot by the reduction of the in-situ oxime in 94% yield and stored for later use. The metal-binding region synthesis begins by mono-protection of 1,6-hexanediamine with di-tert-butyl dicarbonate, yielding 90% of primary amine. The carbonate amine was doubly alkylated with methyl bromoacetate yielding 79%. The boc protecting group is removed with an acidic work up. Preliminary testing with the benzylic amine was reacted with dimethyl aminopyridine, di-tert-butyl dicarbonate to form the isocyanate, and the alkylated amine is added to the mixture in a 1:1 ratio, producing the urea. Further purification of the final organic product and gel testing are forthcoming.

Synthesis of polydentate ligand and coordination to first row transition metals for organogelation

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