Abstract
Redox-active azothioformamide (ATF) and azoformamide (AAF) ligands, containing an N=N–C=S and N=N–C=O 1,3-hetero-diene binding moiety, exhibit the unique ability to oxidatively dissolve zerovalent late transition metals, forming coordination complex salts with oxidized metals and reduced ligands. These ligands are synthesized from phenylhydrazine and form either 2:1 or 1:1 (dimerized 2:2) complexes with Cu(I) salts, and while redox-active, remain neutral. In addition to Cu(I) salts these ligands also coordinate with various metal(II) salts such as NiCl2, CuCl2, ZnCl2, and PdCl2. For this project, a library of ATF and AAF ligands was synthesized, modeled for binding association constants, and applied in different sectors such as coordination chemistry, biological studies, and catalysis. Various substitutions on the ATFs were explored, revealing that electron-donating aryl substitutions and locked steric secondary amine groups produced stronger binding with Cu(I) salts. All coordination complexes were characterized using FTIR, UV-Vis, and C, H, N elemental analysis and, when appropriate, NMR (1H, 13C, 19F) and X-ray crystallography. Additionally, ATF ligands were found to form coordinative complexes with Xantphos and [CH3CN)4Cu](BF4), which shows photoluminescent properties in solution. While performing biological testing against microbes and cancer cell lines, most ATF ligands themselves were inactive while many metal-ATF complexes showed high activity, even to sub-micromolar concentrations. Through investigations of ATF and AAF metal complexes we found potential applications in cross-coupling reactions. For example, AAF and ATF ligands formed Pd(II) complexes, yet Pd-AAF complexes excelled in Suzuki, Heck, and Sonogashira reactions, presenting a phosphine-free alternative to traditional palladium catalysts.