Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes

Abstract

This article deals with a class of ruthenium-BIAN-derived complexes, [Ru(II)(tpm)(R-BIAN)Cl]ClO4 (tpm = tris(1-pyrazolyl)methane, R-BIAN = bis(arylimino)acenaphthene, R = 4-OMe ([1a]ClO4), 4-F ([1b]ClO4), 4-Cl ([1c]ClO4), 4-NO2 ([1d]ClO4)) and [Ru(II)(tpm)(OMe-BIAN)H2O](2+) ([3a](ClO4)2). The R-BIAN framework with R = H, however, leads to the selective formation of partially hydrolyzed BIAO ([N-(phenyl)imino]acenapthenone)-derived complex [Ru(II)(tpm)(BIAO)Cl]ClO4 ([2]ClO4). The redox-sensitive bond parameters involving -N═C-C═N- or -N═C-C═O of BIAN or BIAO in the crystals of representative [1a]ClO4, [3a](PF6)2, or [2]ClO4 establish its unreduced form. The chloro derivatives 1a(+)-1d(+) and 2(+) exhibit one oxidation and successive reduction processes in CH3CN within the potential limit of ±2.0 V versus SCE, and the redox potentials follow the order 1a(+) < 1b(+) < 1c(+) < 1d(+) ≈ 2(+). The electronic structural aspects of 1a(n)-1d(n) and 2(n) (n = +2, +1, 0, -1, -2, -3) have been assessed by UV-vis and EPR spectroelectrochemistry, DFT-calculated MO compositions, and Mulliken spin density distributions in paramagnetic intermediate states which reveal metal-based (Ru(II) → Ru(III)) oxidation and primarily BIAN- or BIAO-based successive reduction processes. The aqua complex 3a(2+) undergoes two proton-coupled redox processes at 0.56 and 0.85 V versus SCE in phosphate buffer (pH 7) corresponding to {Ru(II)-H2O}/{Ru(III)-OH} and {Ru(III)-OH}/{Ru(IV)═O}, respectively. The chloro (1a(+)-1d(+)) and aqua (3a(2+)) derivatives are found to be equally active in functioning as efficient precatalysts toward the epoxidation of a wide variety of alkenes in the presence of PhI(OAc)2 as oxidant in CH2Cl2 at 298 K, though the analogous 2(+) remains virtually inactive. The detailed experimental analysis with the representative precatalyst 1a(+) suggests the involvement of the active {Ru(IV)═O} species in the catalytic cycle, and the reaction proceeds through the radical mechanism, as also supported by the DFT calculations.

Synthesis, Electronic Structure and Interaction of Rhodium(I) and Iridium(I) Bisimine-Acenaphthalene Complexes with Co2

“…Inspection of the FMO distributions for these complexes indicate that the first and second reduction events in all cases are ligand centred and delocalised across the bisimine N=C-C=N moiety, whereas the first oxidation event in all cases is metal centred, with the second and third oxidations delocalised across one of the arylsubstituents each. These observations are in good correlation to electrochemical, EPR and computational results of previously reported BIAN complexes of various transition metals [22,[68][69][70][71][72][73][74]. The redox behaviour of complexes 1a, 2d, 3a, 4a and 4c are discussed here as representative examples for comparative purposes.…”

Alkene Epoxidation Catalysts [Ru(pdc)(tpy)] and [Ru(pdc)(pybox)] Revisited: Revealing a Unique RuIV═O Structure from a Dimethyl Sulfoxide Coordinating Complex

“…Ruthenium-based epoxidation catalysts have received much attention because of the well-developed Ru chemistry and the easy access of various redox states of Ru complexes. − In particular, Nishiyama et al reported the first use of [Ru­(pdc)­(tpy)] ( 1 ; H 2 pdc = 2,6-pyridyl dicarboxylic acid; tpy = 2,2′:6′,2″-terpyridine; Figure ) as an alkene-epoxidation catalyst in the presence of non-atom-economic oxidants such as PhI­(OAc) 2 , O 2 / t BuCHO, and t BuOOH . Later on, Beller and co-workers developed a series of catalysts of [Ru­(pdc)­(pybox)] (pybox = pyridine-bis­(oxazoline) ligands; complex 2 ; Figure ) that use hydrogen peroxide as the oxidant, with high activity and selectivity toward asymmetric epoxidation of alkenes. − The anionic ligand pdc 2– is essential to suppress the decomposition of hydrogen peroxide and to improve the efficiency of the Ru-pdc/H 2 O 2 system toward alkene epoxidation.…”

Chemical and Electrochemical Reductions of Monoiminoacenaphthenes

“…Correspondingly, the MIANs steric properties and redox activity are intermediate in this series, suggesting the formation of a new type of complexes with unpredictable reactivity [1,2]. MIANs are strong coordinating ligands [3][4][5][6] because each includes carbonyl and imine functional groups conjugated with the naphthalene fragment.…”

“…In turn, the MIAN complexes have been far less studied (Scheme 1). Thus, it was found that zinc(II) complexes with MIANs are precatalysts for the reaction of the formation of guanidine and urea derivatives [6]. Mn I -MIAN complexes exhibited unusually high sensitivity to visible light, even in the solid state, and rapidly release carbon monoxide (CO) upon illumination [20].…”