Small Molecule Redox Reactivity at MOF Secondary Building Units

This project describes a career plan that integrates fundamental studies of small molecule reactivity at redox-active metal-organic framework materials with the creation of interactive inorganic chemistry course materials to be made available to millions of students worldwide and with efforts to increase college applications from high school students in inner-city Boston schools. The materials and small molecule substrates synthesized and studied in this project are representative of large classes of emerging materials of worldwide interest known as metal-organic frameworks (MOFs) and of small molecules relevant in both biology and the chemical industry.

This research addresses the apparent disconnect between the ways Nature and synthetic chemists approach the utilization of small molecules of relevance to biological and industrial catalysis. While living systems use complex supramolecular architectures where multiple factors - folding, active site environment, secondary sphere interactions - contribute to substrate selectivity and overall reactivity, metal complexes that use small molecules as substrates typically rely on ligand design that focuses almost entirely on the primary coordination sphere, and often fall short of the functionality seen in Nature. The research team has shown that microporous MOFs support highly reduced first row transition metal ions in ligand field environments that mimic those found in natural systems. These ions interact with small molecule oxidants in ways that are also reminiscent of reactive intermediates involved in both biological and industrial catalytic cycles. The team's work highlights the unique role that these materials could play as heterogeneous materials by filling an important missing link between metalloenzymes and porous heterogeneous materials such as zeolites. The project focuses on synthesizing new redox-active porous materials capable of engaging small molecules for further reactivity, pursing three main directions: (1) The synthesis and characterization of MOFs with highly redox-active and reduced metal ions, including many that have not yet been isolated within such materials; (2) Exploration of the redox reactivity of the new frameworks, focusing in particular on small, industrially relevant gaseous oxidants such as dioxygen and the halogens; (3) Developing new and predictable soft synthetic methodologies for producing MOFs with redox-active metal centers and a new synthetic toolbox for small molecule redox chemistry in MOFs.