Metalloenzymes have an ability to modify substrates in a site-selective manner in aqueous environments. Efforts have been made to mimic this enzymatic activity using transition metal catalysts, such as dirhodium tetraacetate (Rh2(OAc)4), which is both active and stable in water. Rapid, catalytic ligand exchange occurs at the two axial positions on the dirhodium catalyst. Steric hindrance of the axial positions could in fact decrease the catalytic activity of the catalyst. This study proposes: to determine how UV absorbance is affected by catalyst ligation by titrating N-methlyimidazole into a solution of dirhodium catalyst Rh2(OAc)4; to determine the dissociation constant for axial position ligand binding to rhodium catalyst; and to determine how bulky substituents on the rhodium catalyst affect the binding constants. A solution of dirhodium tetraacetate (catalyst) was titrated using a solution of N-methylimidazole (ligand) using UV-vis spectroscopy. As the ligand concentration increased the solution turned from a pale blue to pink. Our results in molecular recognition by the dirhodium catalyst for finding the constant for the N- methylimidazole was not as expected using borate buffer. As the ligand is titrated into the rhodium catalyst, the maximum of the UV spectrum is shifting to a higher energy wavelength.

Analysis of axial ligation of N-methylimidazole to dirhodium tetraacetate catalyst

251st National Meeting (2016)

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