- Structural and spectroscopic characterization of iron(II), cobalt(II), and nickel(II) ortho-dihalophenolate complexes: Insights into metal-halogen secondary bonding
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Metal complexes incorporating the tris(3,5-diphenylpyrazolyl)borate ligand (TpPh2) and ortho-dihalophenolates were synthesized and characterized in order to explore metal-halogen secondary bonding in biorelevant model complexes. The complexes TpPh2ML were synthesized and structurally characterized, where M was Fe(II), Co(II), or Ni(II) and L was either 2,6-dichloro- or 2,6-dibromophenolate. All six complexes exhibited metal-halogen secondary bonds in the solid state, with distances ranging from 2.56 ? for the TpPh2Ni(2,6- dichlorophenolate) complex to 2.88 ? for the TpPh2Fe(2,6-dibromophenolate) complex. Variable temperature NMR spectra of the TpPh2Co(2,6-dichlorophenolate) and TpPh2Ni(2,6-dichlorophenolate) complexes showed that rotation of the phenolate, which requires loss of the secondary bond, has an activation barrier of ~30 and ~37 kJ/mol, respectively. Density functional theory calculations support the presence of a barrier for disruption of the metal- halogen interaction during rotation of the phenolate. On the other hand, calculations using the spectroscopically calibrated angular overlap method suggest essentially no contribution of the halogen to the ligand-field splitting. Overall, these results provide the first quantitative measure of the strength of a metal-halogen secondary bond and demonstrate that it is a weak noncovalent interaction comparable in strength to a hydrogen bond. These results provide insight into the origin of the specificity of the enzyme 2,6-dichlorohydroquinone 1,2-dioxygenase (PcpA), which is specific for ortho-dihalohydroquinone substrates and phenol inhibitors.
- Machonkin, Timothy E.,Boshart, Monica D.,Schofield, Jeremy A.,Rodriguez, Meghan M.,Grubel, Katarzyna,Rokhsana, Dalia,Brennesse, William W.,Holland, Patrick L.
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- Selective ortho-hydroxylation-defluorination of 2-fluorophenolates with a Bis(μ-oxo)dicopper(III) species
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The bis(μ-oxo)dicopper(III) species [CuIII 2(μ-O)2(m-XYLMeAN)]2+ (1) promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols, a reaction that is not accomplishable with a (η2:η2-O2) dicopper(II) complex. Isotopic labeling studies show that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine. O in, F out: [CuIII2(μ-O) 2(m-XYLMeAN)]2+ is a bis(μ-oxo)dicopper(III) species and promotes the electrophilic ortho-hydroxylation-defluorination of 2-fluorophenolates to give the corresponding catechols. Isotopic labeling shows that the incoming oxygen atom originates from the bis(μ-oxo) unit. Ortho-hydroxylation-defluorination occurs selectively in intramolecular competition with other ortho-substituents such as chlorine or bromine.
- Serrano-Plana, Joan,Garcia-Bosch, Isaac,Miyake, Ryosuke,Costas, Miquel,Company, Anna
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supporting information
p. 9608 - 9612
(2014/10/15)
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- A NOVEL, SIMPLE METHOD FOR THE PREPARATION OF HINDERED DIPHENYL ETHERS
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The displacement of the nitro group from substituted nitrobenzenes is used for the synthesis of diphenyl ethers. 1,4-Dinitrobenzene has been converted into a variety of hindered diphenyl ethers using 2,6-disubstituted phenoxides and studies show that the mechanism of formation of the ether (5a) is radical in nature.
- Sammes, Peter G.,Thetford, Dean,Voyle, Martyn
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p. 3229 - 3232
(2007/10/02)
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