Department of Chemistry Seminar: Ligand Design Towards Metal Dissolution, Catalysis, and Recovery
About the event
Speaker: Dr. Kristopher Waynant, Department of Chemistry, University of Idaho
Host: Dr. Qiang Zhang
Title: Ligand Design towards Metal Dissolution, Catalysis, and Recovery:
Abstract: Redox-active azothioformamide (ATF) ligands, with an N=N–C=S 1,3-heterodiene binding moiety, have the unique ability to oxidatively dissolve zerovalent late transition metals to create coordination complex salts (oxidized metal and reduced ligand). Starting from oxidized salts, specifically CuI salts, the coordination event remains neutral (or non-innocent) and leads to either 2:1 complexes or a variety of 1:1 complexes (found as 2:2 dimers) based on the metal salt source and the substitution patterns on the ligand. UV-Vis titration studies indicate that all complexes fit best with 2:1 binding association models yielding multiple potential complexation binding mechanisms and computational models to support the found X-ray crystal structures. Electron-donating group (EDG) appendages provided the strongest binding associations while both EDG and electron withdrawing group (EWG) appendages were capable of metal dissolution. A small library of ATF ligands were synthesized and tested as both metal dissolution agents and as CuI catalysts and EDG ATFs were found highly effective for the reductive insertion of CO2 into terminal alkynes to create propiolic acids. Mild conditions also promoted decarboxylation of propiolic acids in the absence of CO2 to form Glaser-Hay homodiynes using DMSO as both solvent and oxidant. ATF copper complexes with EDG were equally successful as CuAAC catalysts. Currently, the ATFs are being investigated with mixed heterogenous /homogeneous reactions to employ their lixiviant properties and potentially leading to waste metal recycling or reuse. Lastly, a variation on the ATF, the arylazoformamide (AAF) has been synthesized and shown to catalyze Suzuki cross-coupling reactions. In this seminar, a variety of the merits of ATF ligands, and the variations will be discussed.