Room 209 Havemeyer, 3000 Broadway, New York, NY 10027
Multimetallic Catalysis in Biology and Synthesis
Presented by Prof. Neal Mankad, University of Illinois at Chicago
Activation of thermodynamically strong bonds and kinetically inert substrates often occurs in bioinorganic systems through use of multimetallic active sites. The chemical details of these multinuclear clusters are challenging to elucidate compared to those of mononuclear active sites but can guide rational design of synthetic catalysts. In the first part of this presentation, synthetic models for the catalytic active sites of nitrous oxide reductase (N 2 OR) and aerobic carbon monoxide dehydrogenase (CODH) will be discussed. Mapping the reactivity landscapes of these biomimetic complexes and correlating this data with electronic structure parameters derived from physical measurements, including X-ray absorption near edge structure (XANES) and multiwavelength anomalous diffraction (MAD) analysis, has provided useful insights into the operative mechanisms for the native systems. In the second part of the presentation, efforts to implement catalytic concepts from these bioinorganic systems into synthetic catalysts with abiotic function will be discussed. Transition metal Lewis acid/base pairs have been used for heterolytic bond activation reactions in catalytic scenarios such as arene borylation, alkyne semi-hydrogenation, pyridine hydroboration, and alkyne hydrofunctionalization. In some cases, catalytic behavior complements that of classical mononuclear catalysts in homogeneous solution. Included will be the recent discovery of a heterobinuclear Al/Fe system that was found to activate substrates with C–O bonds via a “radical pair” mechanism, a completely new paradigm for activation of CO 2 . Mechanistic elucidation of the latter case by a combined experimental/computational approach will be described.