Preparation, structure and redox properties of novel ruthenium(II) hexachloromacrobicyclic complexes and the first polyaromatic-terminated diaminoclathrochelate derivative, its physisorption on carbon materials and electrocatalytic activity in the hydrogen evolution reaction 2H+/H2

Abstract

Series of the novel diboron-capped ruthenium(II) hexachloroclathrochelates was prepared using the template condensation of three molecules of dichloroglyoxime, as a chelating ligand synthon, with various aromatic boronic acids, as the Lewis-acidic capping agents, on the ruthenium(II) ion as a matrix. That with two equivalents of para-tolylboronic acid in the presence of the cyclooctadiene–acetonitrile ruthenium(II) complex with tetrafluoroborate counter ion unexpectedly afforded the unique macrobicyclic product with two non-equivalent boron-based apical fragments. The reactive diarylboron-capped ruthenium(II) cage complexes with equivalent cross-linking groups were prepared in the moderate yields starting from the acetonitrile ruthenium(II) complex with iodine counter anions. The same initial compound was used for preparation of the chemically robust tert-butylphenylboron-capped ruthenium(II) hexachloroclathrochelate. Its postsynthetic ribbed functionalization with a phenantrenyl-containing primary amine, as a functionalizing N-nucleophilic agent, afforded the target diphenanthtrenyl-terminated ruthenium(II) diaminoclathrochelate. Thus obtained novel cage 4d-metallocomplexes were characterized using elemental analysis, HR MALDI-TOF mass, ¹H and ¹³C{¹H} NMR, and UV-vis spectra, and by the single-crystal X-ray diffraction experiments. Their 3D-shaped ruthenium(II)-centered molecules possess an intermediate trigonal prismatic – trigonal antiprismatic geometries; the Ru–N distances in them are relatively short (approximately 2.0Å). High physisorption of the designed diphenantrenyl-terminated ruthenium(II) clathrochelate on the surfaces of activated carbon, reduced graphene oxide and carbon paper was found using the UV-vis spectrophotometry method. Redox characteristics of the prepared complexes and their electrocatalytic activity in the hydrogen evolution reaction (HER) 2H⁺/H₂ were studied in homogeneous dichloromethane solutions using the CV and DPV techniques. Electrochemically generated ruthenium(I)-centered cage complexes are the most probable catalytically active intermediates of this clathrochelate - electrocatalyzed redox reaction. The testings of their HER electrocatalytic activity in homogeneous solutions after an addition of H⁺ ions allowed one to observe the corresponding catalytic waves. In the case of a given immobilized ruthenium-based clathrochelate electrocatalysts of HER, consumption of this platinum group metal is very low due to a formation of their monolayers on a surface of cathode materials.