Redox-active azothioformamide (ATF) ligands, with an N=N–C=S 1,3-heterodiene bindinf moiety, have the unique ability to oxidatively dissolve zerovalent late transition metals forming various coordination complexes. Control of the oxidation state upon metal dissolution can provides unique avenues towards metal sources and desired complexes. Yet, when ATF ligands are mixed with MI species, specifically CuI salts, the coordination event remains neutral and leads to either 2:1 or 1:1 complexes (found as 2:2 dimers) based on the metal salt source. UV-Vis titration studies indicate that both the 2:1 and 2:2 dimer complexes fit best with 2:1 binding associations models yielding a variety of potential complexation mechanisms. X-ray crystal structures and binding mechanisms have been computationally modelled to further explore the binding event. The one-pot ATF synthesis allows for rapid access to many substitutions on the ligands to examine the binding effects and potential redox events upon complexation. Para-substituted electron-donating groups (EDG) appendages provide the strongest binding associations without steric influence and X-ray crystal data on these complexes compliment the multi-mechanism binding theory. Similarly, EDG appended ATF ligands, when complexed to CuI salts, produced excellent catalysts for the reductive insertion of CO2 to terminal alkynes creating propiolic acids. Mild conditions also promote decarboxylation of propiolic acids in the absence of CO2 to form diynes. Further expansion of ATF complexes in a variety of catalytic roles will be discussed.

Redox-active azothioformamide ligands: From metal complexation to catalysis

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