
"Accessing High Energy Electrons and New Modes of C-H Activation with Earth-Abundant Metals"
The sustainable delivery of electrons and activation of C-H bonds continue to be critical areas of research in the energy and synthesis sectors. Our research is focused on capturing high energy electrons housed within organometallic redox mediators and leveraging C-H bonds in chelating ligand frameworks to move around protons (H+), hydrides (H-) and hydrogen atoms (H•). We have recently isolated one of the most potent organometallic redox agents in existence and showed that an amine-rich cyclopentadienyl ligand (CpN3) coordinated to iron facilitates electrocatalytic H2 production in the presence of exogenous acid. In the latter case, the mechanism of H2 production involves stereoselective endo-CpN3 protonation to forge a new C-H bond followed by ligand-to-metal proton transfer – a surprising result because Cp ligands are often considered quintessential “spectator” ligands in catalysis. In a separate endeavor, we are interested in understanding the magnitude of C(sp3)-H bond weakening when an alkane moiety interacts with a transition metal (i.e., agostic interactions). To study the C-H bond strength properties, we use diamondoid pincer ligands coordinated to Ni and Pd, which provide unique insights into the thermochemical requirements for C-H activation with unactivated alkanes. By carefully measuring equilibria in nonpolar solvents, we are able to directly compare the differences in agostic C-H bond strengths between Ni and Pd, providing insights as to why Pd is often “better” at C-H activation than Ni.