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Electronic Structure and Multicatalytic Features of Redox-Active Bis(arylimino)acenaphthene (BIAN)-Derived Ruthenium Complexes

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posted on 02.08.2016, 15:22 authored by Arijit Singha Hazari, Ritwika Ray, Md Asmaul Hoque, Goutam Kumar Lahiri
The article examines the newly designed and structurally characterized redox-active BIAN-derived [Ru­(trpy)­(R-BIAN)­Cl]­ClO4 ([1a]­ClO4–[1c]­ClO4), [Ru­(trpy)­(R-BIAN)­(H2O)]­(ClO4)2 ([3a]­(ClO4)2–[3c]­(ClO4)2), and BIAO-derived [Ru­(trpy)­(BIAO)­Cl]­ClO4 ([2a]­ClO4) (trpy = 2,2′:6′,2′′-terpyridine, R-BIAN = bis­(arylimino)­acenaphthene (R = H (1a+, 3a2+), 4-OMe (1b+, 3b2+), 4-NO2 (1c+, 3c2+), BIAO = [N-(phenyl)­imino]­acenapthenone). The experimental (X-ray, 1H NMR, spectroelectrochemistry, EPR) and DFT/TD-DFT calculations of 1an1cn or 2an collectively establish {RuII–BIAN0} or {RuII–BIAO0} configuration in the native state, metal-based oxidation to {RuIII–BIAN0} or {RuIII–BIAO0}, and successive electron uptake processes by the α-diimine fragment, followed by trpy and naphthalene π-system of BIAN or BIAO, respectively. The impact of the electron-withdrawing NO2 function in the BIAN moiety in 1c+ has been reflected in the five nearby reduction steps within the accessible potential limit of −2 V versus SCE, leading to a fully reduced BIAN4– state in [1c]4–. The aqua derivatives ({RuII–OH2}, 3a2+3c2+) undergo simultaneous 2e/2H+ transfer to the corresponding {RuIVO} state and the catalytic current associated with the RuIV/RuV response probably implies its involvement in the electrocatalytic water oxidation. The aqua derivatives (3a2+3c2+) are efficient and selective precatalysts in transforming a wide variety of alkenes to corresponding epoxides in the presence of PhI­(OAc)2 as an oxidant in CH2Cl2 at 298 K as well as oxidation of primary, secondary, and heterocyclic alcohols with a large substrate scope with H2O2 as the stoichiometric oxidant in CH3CN at 343 K. The involvement of the {RuIVO} intermediate as the active catalyst in both the oxidation processes has been ascertained via a sequence of experimental evidence.

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