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

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Title Tunable Electrochemical and Catalytic Features of BIAN- and BIAO-Derived Ruthenium Complexes
 
Creator HAZARI, AS
DAS, A
RAY, R
AGARWALA, H
MAJI, S
MOBIN, SM
LAHIRI, GK
 
Subject DENSITY-FUNCTIONAL THEORY
OXYGEN-TRANSFER REACTIONS
WATER OXIDATION
ASYMMETRIC EPOXIDATION
ALKENE EPOXIDATION
HYDROGEN-PEROXIDE
CRYSTAL-STRUCTURE
POLYPYRIDINE COMPLEXES
TERPYRIDINE COMPLEXES
EXCITATION-ENERGIES
 
Description 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(+) approximate to 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.
 
Publisher AMER CHEMICAL SOC
 
Date 2016-01-15T06:05:14Z
2016-01-15T06:05:14Z
2015
 
Type Article
 
Identifier INORGANIC CHEMISTRY, 54(10)4998-5012
0020-1669
1520-510X
http://dx.doi.org/10.1021/acs.inorgchem.5b00615
http://dspace.library.iitb.ac.in/jspui/handle/100/17887
 
Language en