Three Elements Walk Into a Glovebox: Promoting Uncommon Redox Chemistry with Heterobimetallic Rhodium, Samarium, and Europium Complexes

Abstract

The oxidation states accessible to a given metal center can significantly impact the reactivity that occurs at that site. Thus, an important goal within the field of inorganic and organometallic chemistry is the promotion of uncommon metal oxidation states; accessing these states could enable new chemistry and make positive impacts on, for example, sustainable energy technology. In this thesis, the theme of accessing uncommon oxidation states is explored with three redox-active systems built around rhodium, samarium, and europium heterobimetallic complexes. Chapter 1 describes the impact of ligand-centered redox activity on a metal hydride capable of hydrogen evolution. With a family of [Rh,Fe] heterobimetallic complexes, the thermochemical parameters that govern hydrogen evolution with this system have been determined. The thermochemical calculations predict that iron-centered oxidation acidifies a nearby rhodium hydride by 23 orders of magnitude; in situ proton NMR confirmed the drastic shift in acidity. Chapter 2 describes the use of heterobimetallic frameworks that place secondary redox-inactive metals in close proximity to redox-active lanthanide elements, with the goal of tuning the redox properties of the lanthanides, an area that has received far less attention than it deserves. Here, synthesis, characterization, and electrochemical studies of samarium and europium heterobimetallic complexes are reported; while we find that mono- and heterobimetallic samarium complexes have no observable redox activity under our conditions, the Eu(III/II) reduction potential was found to shift dramatically upon incorporation of secondary redox-inactive metals (350 mV for monocationic sodium and 620 mV for dicationic calcium). Taken together, these chapters reveal the power of secondary metals, both redox-inactive and redox-active, in facilitating reactivity with heterobimetallic complexes.