Reactivity of Diamines in Acyclic Diamino Carbene Gold Complexes

Acyclic diamino carbenes (ADCs) are interesting alternatives to their more widely studied N-heterocyclic carbene counterparts, particularly dueto their greater synthetic accessibility and properties such as increased sigmadonation and structuralflexibility. ADC gold complexes are typically obtainedthrough the reaction of equimolar amounts of primary/secondary amines ongold-coordinated isocyanide ligands. As such, the reaction of diaminenucleophiles to isocyanide gold complexes was expected to lead to bis-ADCgold compounds with potential applications in catalysis or as novel precursorsfor gold nanomaterials. However, the reaction of primary diamines with twoequivalents of isocyanide gold chlorides resulted in only one of the aminegroups reacting with the isocyanide carbon. The resulting ADC gold complexesbearing free amines dimerized via coordination of the amine to the partner goldatom, resulting in cyclic, dimeric gold complexes. In contrast, when secondarydiamines were used, both amines reacted with an isocyanide carbon, leading to the expected bis-ADC gold complexes. Densityfunctional theory calculations were performed to elucidate the differences in the reactivities between primary and secondarydiamines. It was found that the primary amines were associated with higher reaction barriers than the secondary amines and henceslower reaction rates, with the formation of the second carbenes in the bis-ADC compounds being inhibitingly slow. It was alsofound that diamines have a unique reactivity due to the second amine serving as an internal proton shuttle

Automated summary

Acyclic diamino carbenes (ADCs) are interesting alternatives to N-heterocyclic carbenes, offering greater synthetic accessibility and properties such as increased sigma-donation and structural flexibility. The reaction of primary diamines with isocyanide gold chlorides resulted in dimeric gold complexes, while secondary diamines led to the expected bis-ADC gold complexes. Density functional theory calculations showed that primary diamines have higher reaction barriers and slower reaction rates compared to secondary diamines.