Molecular and crystal structures obtained preparing Cu-bipyridine complexes in presence of chlorinated solvents in oxidizing environment

Copper-bipyridines (Cu-Bpy) are among the most investigated metal–organic complexes thanks to their easy tunability and wide applicability, especially in the opto-electronic and catalysis sectors. In this contribution, the crystallographic structures of two novel Cu-Bpy complexes are solved for the first time by X-ray diffraction, complemented by SEM/EDX, Raman, and mass spectroscopy analyses and first principles calculations. These compounds were serendipitously obtained, in the attempt of crystallizing oxidated Cu-Bpy active form of the catalyst, by the counter-solvent approach after contacting tert-butyl hydroperoxide with two solutions of [(6,6’-dimethyl-2,2’-bipyridine) 2 Cu] + [PF 6 ] − in dichloromethane (DCM) at different concentrations. The higher concentration (5 mM) leads to the formation of the counterparts of the complex bearing an ancillary fifth chloride ligand coming from DCM, which is enough to stabilize the pentacoordinated systems. On the other hand, a lower concentration (1 mM) induces the destruction of the complex which likely reacts with the solvent to obtain a complex in which the double negative charge of a tetrachlorocuprate anion ( ) is counterbalanced by a double positive charge localized onto a bipyridinium cation ( ). This exotic complex is remarkably stabilized by highly directional hydrogen bonds from the moieties of the cation to two of the four chloride atoms of the tetrachlorocuprate anion. The solved structures, and the complementary physical chemical data, demonstrated the active part of DCM, the unique chlorine source during the whole synthetic path, and the possibility of exploring alternative synthetic routes to obtain new molecules and metallic complexes. • Copper-bipyridines are used as catalyst toward the allylic oxidation of cyclohexene. • Cu-(dimethylpyridine) 2 evolves to two different compounds in oxidizing condition. • Dichloromethane had an active role with the addition of Chlorine to Cu atom. • [(6,6’-dimethyl- 2,2’-bipyridine) 2 Cu] was formed at higher catalyst concentration. • A CuCl 4 dianion with a ([BpyH 2 ] dication was observed at lower catalyst concentration.