Halfen Group Research Overview

Research in the Halfen group deals in general with catalysis, as found in biological systems and as applied in industry. Our current primary focus is the development of new transition metal catalysts for the aziridination of olefins. We are also involved in the preparation of synthetic models for metalloenzymes that protect biological systems against the toxic effects of the radical anion superoxide. We use the tools of single crystal X-ray diffraction, FTNMR, FTIR, UV-Visible, EPR (in collaboration with Prof. Lawrence Que at the University of Minnesota) and mass spectroscopies to assist in our research efforts.

Metal-Mediated Olefin Aziridination

Aziridines (at right) are reactive heterocycles that are useful intermediates in multistep organic syntheses, and have also been identified as critical components of several potent antitumor agents. Our research focuses on the use of copper complexes as catalysts for the preparation of aziridines from two organic synthons: olefins (which provide the two carbons found in the three-membered aziridine ring) and a nitrene source (which provides the nitrogen).

 

Our initial efforts resulted in the preparation of a new copper(II) catalyst derived from a hindered triazacyclononane ligand, the X-ray crystal structure of which is shown at right. This complex was shown to effect the aziridination of styrene derivatives in nearly quantitative yields. Most significant was the observation that high yields of aziridines could be obtained at very low catalyst loadings (0.5 mol% catalyst), an order of magnitude less than is required for other copper catalysts.

 

More recently, we have prepared a family of copper(II) catalysts supported by tetradentate, bis(pyridyl)-appended macrocycles. These complexes, such as the example shown at right, also function as catalysts for the aziridination of styrene. However, reactions catalyzed by these complexes proceed at a very slow rate, suggesting that some dynamic process in solution precedes generation of the active catalyst species.

 

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