Tethered Axial Coordination as a Control Element on Dirhodium Paddlewheel Complexes

Date: 
11/13/2020 - 4:00pm to 5:00pm
Location: 
Zoom
Speaker(s) / Presenter(s): 
Dr. Ampofo Darko

Dr. Ampofo Darko

Assistant Professor

Department of Chemistry

University of Tennessee

 

Abstract: Dirhodium paddlewheel(RhII) complexes can mediate a number of transformations through the catalytic decomposition of diazo compounds. The reactivity and selectivity of these reactions are modulated partly by the modification bridging ligands surrounding the metal center. While general strategies for ligand design have largely involved modification of bridging ligands, additives in these reactions have also been observed to affect the reactivity and selectivity of the catalyst. It is speculated that coordination to the axial sites of the catalyst is responsible for the perturbations in catalyst performance. While there are current research efforts to probe the benefits of axial coordination, there is still need for robust methods to clarify their structural and electronic influence on catalyst reactivity and product selectivity. To adequately use axial coordination as a control element, we have designed paddlewheel complexes with tethered Lewis basic groups onto traditional bridging ligands.  In initial studies, thioether ligands proved to be the most robust Lewis base when tethered to oxazolindinate or carboxylate bridging ligands. The novel complexes were then used in diazo-mediated cyclopropanation reactions, Si-H reactions, and C-H insertion reactions. The results of the experiments, along with spectroscopic and computational analyses, provided insight into the role that tethered axial coordination plays in diazo-mediated reactions. This presentation will also discuss our efforts to develop a chromogenic detector based on RhII paddlewheel complexes. It is well studied that RhII complexes can bind a variety of neutral and anionic ligands at its electrophilic active site, which induces a chromogenic response depending of the identity of the incoming ligand. We aim to exploit this feature to detect organophosphate nerve agents based on the by-products of their degradation to enabling timely, selective, and naked-eye detection of all families of organophosphorus nerve agents.

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