The catalytic ability of an industrial heterogeneous catalyst is determined by the interactions between the active sites, which are often transition metals, and the support. Insights into the interplay between the active sites and support during catalysis are difficult to gain because of the inherent complexity of heterogeneous surfaces. Alternatively, molecular catalysts are well-defined, and can be studied by a range of spectroscopic characterization techniques. To model multi-active site dynamics on a molecular scale, the Velian group has developed a system involving a cobalt selenide cluster with amido phosphine ligands that are used to tether transition metals that act as catalytically active sites onto the cluster surface. My project is probing the tri-metalated clusters’ (M₃Co₆Se₈L₆; M = Cr, Mn, Fe, Co, Cu, Zn; L = PPh₂N^-Tol, Ph = phenyl, Tol = 4-tolyl) ability to catalyze intramolecular carbon-hydrogen (C-H) amination. Previous work has shown that these clusters are remarkable catalysts for carbodiimide formation, but we have yet to compare reactivity among the tri-metalated clusters. I probed the transformation of aliphatic azides to pyrrolidines, a class of 5-membered-N-heterocycles with. This study seeks to understand how the reactivity of the clusters change as edge metal identity changes, and the role of the three active sites during catalysis. A substrate scope has shown how the steric and electronic profile of the azide affects the capability of the clusters for this reaction. This research provides insights into metal-support interactions that are important for heterogeneous catalysis. Development of next generation catalysts that can perform complex transformations benefits from the information these studies provide.

Black phosphorus (bP), an allotrope of phosphorus, is a 2D Van der Waals material composed of corrugated layers of phosphorus atoms. Few-layer bP is a semiconductor with interesting physical properties, including relatively high carrier mobility and layer-dependent band gap. These properties may be harnessed for applications including nitrogen fixation photocatalysts, thin film transistors, and sensing devices. One limitation that must be overcome before bP can be used in devices is its degradation into phosphoric acid when exposed to oxygen, water, and/or light. Finding passivation methods is crucial for the future use of bP in electronics or photochemistry. As each passivation treatment changes bP’s electronic properties, it is important to find protection methods that are compatible with each use case. To investigate possible methods to reduce surface degradation, we exfoliate bP in solution and treat it with a passivation candidate. We then use ultraviolet-visible light (UV-Vis) spectroscopy to track the amount of unoxidized bP that remains in solution during ambient exposure. Since bP absorbs strongly across the UV-vis region, while the decomposition products, phosphorus oxides, do not, UV-vis is an ideal method for measuring degradation. Possible treatments include attaching alkoxy or thiolate groups via peroxides or disulfides to bP edges to protect the particularly reactive dangling bonds, treatment with radical scavengers such as butylated hydroxytoluene, or noncovalent protection with Tetracyanoquinodimethane (TCNQ).