Copper Complexes of Benzoylacetone Bis-Thiosemicarbazones: Metal and Ligand Based Redox Reactivity

Bis-thiosemicarbazones derived from the beta-diketone benzoylacetone (H(3)banR, R = Me, Et, Ph) are potentially tetradentate N2S2 ligands whose coordination chemistry with copper is reported. In the absence of oxygen and in the presence of base they form anionic Cu-II complexes of the fully deprotonated ligands [Cu-II (banR)](-). Upon exposure to atmospheric oxygen they undergo a complex series of reactions leading to two types of products; one a ligand oxidised ketone complex [Cu-II (banRO)] and the other an unprecedented dimeric di-Cu-III complex [(Cu-III (banR))(2)] depending on the R substituent. Time-resolved UV-vis spectroscopy, cyclic voltammetry, spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy have been used to identify intermediates on the way to stable products formed under both anaerobic and aerobic conditions. It is found that both ligand-centred and Cu-centred oxidation reactions are occurring in parallel leading to this unusually complicated mixture of products.

Automated summary

Bis-thiosemicarbazones derived from beta-diketone benzoylacetone act as potential tetradentate N2S2 ligands when coordinating with copper. Under anaerobic conditions, anionic Cu-II complexes are formed, while exposure to oxygen leads to the formation of oxidized ketone complexes and dimeric di-Cu-III complexes. Various analytical techniques were used to identify intermediates and characterize the complex mixture of products resulting from simultaneous ligand-centered and Cu-centered oxidation reactions.