William H. Armstrong
Transition Metal Complexes as Catalysts
Transition metal complexes function as homogeneous catalysts in a wide variety of systems of biological and industrial importance. My group is engaged in working toward the development of catalytically active species with emphasis on those that operate at the oxidizing and reducing extremes of the redox scale. We are particularly interested in multielectron transformations and therefore multinuclear complexes. An example of a process of interest to us that requires a highly oxidizing species is the conversion of water to dioxygen, as carried out in photosynthetic organisms at a tetranuclear manganese center. At the other extreme of the redox scale, we seek highly reducing species capable of fixation of small molecules such as N2, H2, CO, CO2, and CH4. Nitrogenase is an enzyme that employs a metal cluster to catalyze the conversion of atmospheric dinitrogen to ammonia. Our approach to elucidation of the enzyme active site structures involves the synthesis of novel transition metal clusters whose properties may be compared to those of the native system. An ideal biomimetic complex will not only reproduce the structural and spectroscopic properties of the enzyme but will also be able to function as the enzyme does. Once more is understood about the enzyme active site structure and function via the biomimetic approach, we hope to optimize the performance of our artificial catalysts and to extend, or in some cases restrict, their substrate specificities.