UM Chemistry

Professor Johnson is interested broadly in synthetic and mechanistic organotransition metal and inorganic chemistry. These research interests include discovery of new synthetic methods for both inorganic and organic synthesis. This entails the preparation, isolation, and characterization of transition metal and actinide complexes that exhibit novel reactivity by virtue of their unusual coordination environments. This in turn is facilitated by careful ligand design and construction. This research is directed toward the development of catalysts for the activation and functionalization of small molecules such as dinitrogen and carbon dioxide, as well as new reagents and catalysts for organic synthesis. These compounds are prepared and manipulated using standard inert-atmosphere techniques. A variety of spectroscopic techniques are employed to optimize synthetic conditions, to measure reaction kinetics, and to characterize new compounds. Multinuclear NMR experiments, EPR spectroscopy, and single crystal X-ray diffraction studies are employed routinely for structural elucidation. Two representative projects are briefly outlined below.

Direct nitrogen incorporation into organic molecules.
Transition-metal catalyzed alkyne metathesis is a facile process. The triple bond strengths of alkynes, nitriles, and dinitrogen are such that it is reasonable to propose equilibration of these compounds by a similar process. Synthesis of organonitriles from nitrogen gas and alkynes would constitute a completely new method of nitrogen fixation. Alternatively, the reverse reaction would result in the formation of a carbon-carbon triple bond, starting from nitriles, with nitrogen gas as the only byproduct. Use of dinitrile starting materials would permit the synthesis of poly(aryleneethynylene)s and other polymers with exciting nonlinear optical and other desired properties.

Carbon dioxide as a carbon source in synthesis.
The use of carbon dioxide as a carbon source, with the eventual purpose of recycling some of the carbon lost to the atmosphere through combustion, is one major goal in transition metal catalysis. Isocyanates are important industrial chemicals produced on the megaton scale annually. At present, these compounds are synthesized from amines and toxic phosgene gas. Replacement of phosgene by carbon dioxide would be both safer and less expensive, in addition to being a productive use of a greenhouse gas. Additionally, water is the only byproduct of the new process. This can be achieved via well precedented metal-mediated pairwise oxo-imido exchange reactions.