Design and synthesis of bio-inspired hydrogen bond donating ligands: Toward the development of oxidation catalysts that function in supercritical carbon dioxide

Abstract

Hydrogen bonds (H-bonds) are the primary type of non-covalent interactions found in the active site of a metalloprotein. In addition to the metal-ligand covalent interactions, H-bonds influence reactive intermediates formed during reaction processes, and regulate the secondary coordination spheres around the metal ions.

The synthetic systems developed in the Borovik group utilize intramolecular H-bonds to help regulate chemistry of the metal complexes. New urea-based tripodal ligands with either long hydrocarbon chains or fluorinated phenyl rings have been prepared in order to increase the solubility of metal complexes in carbon dioxide based solvents. Reactions of a new tripodal ligand, tris[(N'-pentafluorophenylureayl)-N-ethyl]amine, (H61PF) with Fe(II) salts was studied and a series of Fe(II) complexes with H61PF was developed by varying the amount of base equivalents used during synthesis.

The structural properties of the metal complexes indicate the presence of intramolecular H-bonds and some unusual molecular structures. The Fe(II) hydroxide complex isolate has an unique hexagonal (Fe-OH)3 core in its crystal structure. Reactivity studies with dioxygen have also been carried out with the Fe(II)-H61PF complexes. Preliminary studies on these Fe(II) complexes indicate that they are capable of undergoing oxidation with dioxygen.