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Abstract:

Proton-coupled electron transfers (PCETs) are unconventional redox processes in which an electron and proton are exchanged together in a concerted elementary step. While PCET is now recognized to play a central a role in biological redox catalysis and inorganic solar energy conversion technologies, its applications in organic chemistry have only recently begun to be explored. This talk will highlight our group鈥檚 efforts to use PCET as a means to address significant and long-standing synthetic challenges in the areas of free radical chemistry and asymmetric catalysis. In particular we are interested in the ability of PCET to enable catalytic and chemoselective generation of synthetically useful radical intermediates via the direct homolytic activation of common organic functional groups that are energetically inaccessible using conventional H-atom transfer catalysts. Our approach makes use of a simple thermodynamic formalism to rationally identify combinations of proton and electron donors that can formally transfer hydrogen to form very weak bonds (BDFEs <25 kcal/mol) and combinations of proton and electron acceptors that are competent to homolyze strong bonds (BDFEs >110 kcal/mol). Moreover, in PCET reactions the radical intermediates are generated as hydrogen-bonded adducts with the conjugate acid or base of the catalytic proton donor/acceptor. We have found that these non-covalent associations can be strongly stabilizing, providing a basis for asymmetric induction in subsequent bond forming events when chiral proton transfer agents are employed. Recent advances and applications of PCET in method development with a particular emphasis on reactions that can be driven out of equilibrium using excited state PCET events.

Bio:

A native of Virginia鈥檚 Shenandoah Valley, Rob received a B.S in chemistry from the College of William and Mary in 2003. He went on to receive his PhD in synthetic organic chemistry from Caltech in 2008 for his work on natural product synthesis in the labs of Dave MacMillan. Following his doctoral work, Rob moved to Eric Jacobsen鈥檚 lab at Harvard University as a NIH postdoctoral fellow, where his work focused on asymmetric catalysis and new reaction development. Rob joined the Department of Chemistry at听Princeton University in the summer of 2011, where his group鈥檚 work has focused primarily on the applications of proton-coupled electron transfer (PCET) in organic synthesis. In 2017 he was promoted to Professor of Chemistry.

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