Multiredox chemistry with 2,2?-Bipyridine Equipped with a Disulfide/Dithiol Switch. Synthesis, electrochemistry and complexes

SIEWERT, INKE; SCHIEWER, CHRISTINE; MEYER, FRANC; SCHOBER, ANNE; DECHERT, SEBASTIAN; CATTANEO, MAURICIO

New Orleans

Congreso; 255th ACS National Meeting, New Orleans, LA; 2018

American Chemical Society (ACS)

Key steps in redox catalysis, including most of the chemical reactions relevant for energy conversion schemes, often involve the transfer of multiple electrons and protons, which is particularly important for the transformation of small molecule such as the making and breaking of H2. Disulfide/dithiol interconversion is extensively used by nature for mediating 2e−/2H+ processes, and synthetic dithiins appear to be particularly well suited for exploiting this concept in artificial devices, and for achieving multiple charge storage.We report a new new dithiine that amalgamates the disulfide/dithiol switch with the versatile 2,2?-bipyridine metal binding capabilities, and the Ru polipyridine complex with it. Via in-depth electrochemical characterisation of this molecule we show that protonation by a weak acid such as water facilitates the second reduction which then occurs at slightly lower potential than the first one; hence protonation triggers potential inversion. Specifically, using detailed electrochemical studies we demonstrate that an EEC mechanisms, or an ECEC mechanism in the presence of water, are operative, with injection of the second electron providing the driving force for S?S bond rupture. These findingsoffer exciting prospects for metal complexes in which the 2,2?-bipyridine unit serves as a common N,N?-chelate ligand.Such systems may potentially mediate two-electron two-proton conversions via reversible making and breaking of the peripheral S?S bond, electronically coupled to, or triggered by, redox or photochemical processes involving the metal ion. The present rigorous examination of the redox properties and interconversion and its 2e−/H+ reduced dithiol congener provides fundamental insight how S−S bond breakage in disulfides is correlated with electron injection and protonation, and it establishes the basis for applying this new 2,2?-bipyridine derivative towards PCET processes in coordination chemistry. Ru polipridine complex with this ligand enhance its properties for accumulation of redox equivalents.