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

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(+), 3a(2+)), 4-OMe (1b(+), 3b(2+)), 4-NO2 (1c(+), 3c(2+)), BIAO = [N-(phenyl)imino]acenapthenone). The experimental (X-ray, (1)H NMR, spectroelectrochemistry, EPR) and DFT/TD-DFT calculations of 1a(n)-1c(n) or 2a(n) collectively establish {Ru(II)-BIAN(0)} or {Ru(II)-BIAO(0)} configuration in the native state, metal-based oxidation to {Ru(III)-BIAN(0)} or {Ru(III)-BIAO(0)}, 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 BIAN(4-) state in [1c](4-). The aqua derivatives ({Ru(II)-OH2}, 3a(2+)-3c(2+)) undergo simultaneous 2e(-)/2H(+) transfer to the corresponding {Ru(IV)═O} state and the catalytic current associated with the Ru(IV)/Ru(V) response probably implies its involvement in the electrocatalytic water oxidation. The aqua derivatives (3a(2+)-3c(2+)) 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 {Ru(IV)═O} intermediate as the active catalyst in both the oxidation processes has been ascertained via a sequence of experimental evidence.