Leveraging Molecular Nanoclusters for Atomistic Insights into Reactive Interfaces

Abstract

Tuning metal/support interactions represents a powerful strategy to modulate catalytic activity, making supported single-site catalysts that harness these effects an active frontier of research. However, probing the complex interactions that occur at a heterogenous interface is a challenge and generally relies on surface imaging techniques which provide limited insight into the dynamic physiochemical processes that govern catalysis. To this end, we developed two classes of atomically precise nanoclusters which feature either three active sites, or one active site, in direct contact with a metal chalcogenide cluster support. In addition to facile synthetic tunability, these clusters are amenable to molecular characterization techniques which facilitate the systematic study of the electronic and structural changes that occur as the number and identity of the edge metal changes. In the first part of this dissertation, the tri-edge cluster construct is probed, ultimately illustrating how judicial choice of edge identity can be used to tune the electronic structure of the nanocluster construct. Subsequent studies with this system elucidate multi-site communication of the edge sites, manifesting as allosteric ligand binding on the cluster surface. Harnessing this allostericity affords the tri-M cluster as a stimuli responsive nanoblock, which enabled the dimensional control of nanomaterial assembly. In the second part of this dissertation, a single-edge cluster is presented, which circumvents the complexity of the multi-active site dynamics and allows for systematic study of the electronic and structural changes that occur as the identity of the edge metal changes and how that affects catalytic nitrene transfer reactivity. This study finds, that as the degree of electronic interaction between the edge and the support increases a cooperative regime is reached wherein the support can deliver electrons to the catalytic site, increasing the reactivity of key metal-nitrenoid intermediates. Subsequently, in depth interrogation of the Fe single-edge cluster illustrates the edge-support cooperativity upon inner- and outer-sphere oxidation reactions showcasing the redox flexibility of system. Ultimately, the catalytic properties of the tri-M and mono-M clusters are compared illustrating how the metal-support interactions in the two platforms regulate substrate binding and catalytic activity. The last chapter of this dissertation steps away from cluster chemistry and explores a simple organometallic construct and the effects of ligand binding and its reactivity with oxygen and oxo-atom donors. In total, this work presents a thorough analysis of how cluster supported active sites can be manipulated to enable atomistic insights into electronic and structural metal-support interactions.