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Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes.

ABSTRACT: The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr(III)(14-TMC)(O2)(Cl)](+), with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr(IV)(14-TMC)(O)(Cl)](+), via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol nitration chemistry. The Cr(IV)-oxo complex does not react with nitrogen dioxide (NO2), but reacts with NO to afford a Cr(III)-nitrito complex, [Cr(III)(14-TMC)(NO2)(Cl)](+). The Cr(IV)-oxo and Cr(III)-nitrito complexes were also characterized spectroscopically and/or structurally.

SUBMITTER: Yokoyama A

PROVIDER: S-EPMC3864658 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes.

Yokoyama Atsutoshi A Cho Kyung-Bin KB Karlin Kenneth D KD Nam Wonwoo W

Journal of the American Chemical Society 20130930 40

The reaction of an end-on Cr(III)-superoxo complex bearing a 14-membered tetraazamacrocyclic TMC ligand, [Cr(III)(14-TMC)(O2)(Cl)](+), with nitric oxide (NO) resulted in the generation of a stable Cr(IV)-oxo species, [Cr(IV)(14-TMC)(O)(Cl)](+), via the formation of a Cr(III)-peroxynitrite intermediate and homolytic O-O bond cleavage of the peroxynitrite ligand. Evidence for the latter comes from electron paramagnetic resonance spectroscopy, computational chemistry and the observation of phenol n ...[more]

PMID: 24066924

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Project description:The thermodynamic properties of structurally similar Mn(III) and Mn(IV) complexes have been reinvestigated to understand their reactivity with substrates having C-H bonds. The complexes have the general formula [MnH(3)buea(O)](n-), where [H(3)buea](3-) is the tripodal ligand, tris[(N'-tert-butylureaylato)-N-ethylene]aminato. These complexes are unique because of the intramolecular hydrogen-bonding (H-bond) network surrounding the Mn-oxo units. The redox potentials for the Mn(III/IV)(O) couple was incorrectly assigned in earlier reports: the corrected value is -1.0 V vs Cp(2)Fe(+)/Cp(2)Fe in DMSO, while the Mn(IV/V)(O) process is -0.076 under the same conditions. The oxo ligand in the Mn(III)(O) complexes is basic with a pK(a) of 28.3; the basicity of the terminal oxo ligand in the Mn(IV)(O) complex is estimated to be approximately 15. These values were used to re-evalulate the O-H bond dissociation energy (BDE(OH)) of the corresponding Mn(II/III)-OH complexes: BDE(OH) values of 89 and 77 kcal/mol were determined for [Mn(III)H(3)buea(OH)](-) and [Mn(II)H(3)buea(OH)](2-), respectively. Both Mn(O) complexes react with 9,10-dihydroanthracene (DHA) to produce anthracene in nearly quantitative yields. This is surprising based on the low redox potiental of the complexes, suggesting the basicity of the oxo ligand is a major contributor to the observed reactivity. In contrast to the thermodynamic results, a comparative kinetic investigation found that the Mn(III)(O) complex reacts nearly 20 times faster than the Mn(IV)(O) complex. Activation parameters, determined from an Eyring analysis, found that the entropy of activation is significantly different between the two systems (DeltaDeltaS(++) = -35 eu, where DeltaDeltaS(++) = DeltaS(++)(Mn(IV)(O)) - DeltaS(++)(Mn(III)(O)). This unusual kinetic behavior can be explained in the context of the basicity of the oxo ligands that leads to different mechanisms: for [Mn(III)H(3)buea(O)](2-) a proton transfer-electron transfer mechanism is proposed, whereas for [Mn(IV)H(3)buea(O)](-) a hydrogen-atom transfer pathway is likely.

Dataset Information

Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes.

Publications

Reactions of a chromium(III)-superoxo complex and nitric oxide that lead to the formation of chromium(IV)-oxo and chromium(III)-nitrito complexes.

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