The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines
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A mechanistic study is presented of the oxidative dehydrogenation of the iron(III) complex [FeIIIL3]3+, 1, (L3 = 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanonane) in ethanol in the presence of molecular oxygen. The product of the reaction was identified by NMR spectroscopy and X-ray crystallography as the identical monoimine complex [FeIIL4]2+, 2, (L4 = 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanon-1-ene) also formed under an inert nitrogen atmosphere. Molecular oxygen is an active player in the oxidative dehydrogenation of iron(III) complex 1. Reduced oxygen species, e.g., superoxide, (O2˙−) and peroxide (O22−), are formed and undergo single electron transfer reactions with ligand-based radical intermediates. The experimental rate law can be described by the third order rate equation, −d[(FeIIIL3)3+]/dt = kOD[(FeIIIL3)3+][EtO−][O2], with kOD = 3.80 ± 0.09 × 107 M−2 s−1 (60 °C, μ = 0.01 M). The reduction O2 → O2˙− represents the rate determining step, with superoxide becoming further reduced to peroxide as shown by a coupled heme catalase assay. In an independent study, with H2O2, replacing O2 as the oxidant, the experimental rate law depended on [H2O2]: −d[(FeIIIL3)3+]/dt = kH2O2[(FeIIIL3)3+][H2O2]), with kH2O2 = 6.25 ± 0.02 × 10−3 M−1 s−1. In contrast to the reaction performed under N2, no kinetic isotope effect (KIE) or general base catalysis was found for the reaction of iron(III) complex 1 with O2. Under N2, two consecutive one-electron oxidation steps of the ligand coupled to proton removal produced the iron(II)-monoimine complex [FeIIL4]2+ and the iron(II)-amine complex [FeIIL3]2+ in a 1 : 1 ratio (disproportionation), with the amine deprotonation being the rate determining step. Notably, the reaction is almost one order of magnitude faster in the presence of O2, with kEtO− = 3.02 ± 0.09 × 105 M−1 s−1 (O2) compared to kEtO− = 4.92 ± 0.01 × 104 M−1 s−1 (N2), documenting the role of molecular oxygen in the dehydrogenation reaction.
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SAUCEDO-VÁSQUEZ, Juan Pablo, Peter M. H. KRONECK, Martha Elena SOSA-TORRES, 2015. The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines. In: Dalton Transactions. 2015, 44(12), pp. 5510-5519. ISSN 1477-9226. eISSN 1477-9234. Available under: doi: 10.1039/C4DT03606ABibTex
@article{SaucedoVasquez2015molec-31184, year={2015}, doi={10.1039/C4DT03606A}, title={The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines}, number={12}, volume={44}, issn={1477-9226}, journal={Dalton Transactions}, pages={5510--5519}, author={Saucedo-Vásquez, Juan Pablo and Kroneck, Peter M. H. and Sosa-Torres, Martha Elena} }
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<rdf:RDF xmlns:dcterms="http://purl.org/dc/terms/" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:bibo="http://purl.org/ontology/bibo/" xmlns:dspace="http://digital-repositories.org/ontologies/dspace/0.1.0#" xmlns:foaf="http://xmlns.com/foaf/0.1/" xmlns:void="http://rdfs.org/ns/void#" xmlns:xsd="http://www.w3.org/2001/XMLSchema#" > <rdf:Description rdf:about="https://kops.uni-konstanz.de/server/rdf/resource/123456789/31184"> <void:sparqlEndpoint rdf:resource="http://localhost/fuseki/dspace/sparql"/> <dc:contributor>Sosa-Torres, Martha Elena</dc:contributor> <dcterms:title>The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines</dcterms:title> <dc:date rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2015-06-17T13:41:56Z</dc:date> <bibo:uri rdf:resource="http://kops.uni-konstanz.de/handle/123456789/31184"/> <dcterms:issued>2015</dcterms:issued> <dc:creator>Kroneck, Peter M. H.</dc:creator> <dcterms:isPartOf rdf:resource="https://kops.uni-konstanz.de/server/rdf/resource/123456789/28"/> <dc:creator>Sosa-Torres, Martha Elena</dc:creator> <dc:language>eng</dc:language> <dc:creator>Saucedo-Vásquez, Juan Pablo</dc:creator> <dspace:hasBitstream rdf:resource="https://kops.uni-konstanz.de/bitstream/123456789/31184/1/Saucedo-Vasquez_0-288392.pdf"/> <dspace:isPartOfCollection rdf:resource="https://kops.uni-konstanz.de/server/rdf/resource/123456789/28"/> <foaf:homepage rdf:resource="http://localhost:8080/"/> <dc:contributor>Kroneck, Peter M. H.</dc:contributor> <dcterms:hasPart rdf:resource="https://kops.uni-konstanz.de/bitstream/123456789/31184/1/Saucedo-Vasquez_0-288392.pdf"/> <dcterms:abstract xml:lang="eng">A mechanistic study is presented of the oxidative dehydrogenation of the iron(III) complex [Fe<sup>III</sup>L<sup>3</sup>]<sup>3+, </sup>1, (L<sup>3</sup> = 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanonane) in ethanol in the presence of molecular oxygen. The product of the reaction was identified by NMR spectroscopy and X-ray crystallography as the identical monoimine complex [Fe<sup>II</sup>L<sup>4</sup>]<sup>2+</sup>, 2, (L<sup>4</sup> = 1,9-bis(2′-pyridyl)-5-[(ethoxy-2′′-pyridyl)methyl]-2,5,8-triazanon-1-ene) also formed under an inert nitrogen atmosphere. Molecular oxygen is an active player in the oxidative dehydrogenation of iron(III) complex 1. Reduced oxygen species, e.g., superoxide, (O<sub>2</sub>˙<sup>−</sup>) and peroxide (O<sub>2</sub><sup>2−</sup>), are formed and undergo single electron transfer reactions with ligand-based radical intermediates. The experimental rate law can be described by the third order rate equation, −d[(Fe<sup>III</sup>L<sup>3</sup>)<sup>3+</sup>]/dt = k<sub>OD</sub>[(Fe<sup>III</sup>L<sup>3</sup>)<sup>3+</sup>][EtO<sup>−</sup>][O<sub>2</sub>], with k<sub>OD</sub> = 3.80 ± 0.09 × 107 M<sup>−2</sup> s<sup>−1</sup> (60 °C, μ = 0.01 M). The reduction O<sub>2</sub> → O<sub>2</sub>˙<sup>−</sup> represents the rate determining step, with superoxide becoming further reduced to peroxide as shown by a coupled heme catalase assay. In an independent study, with H<sub>2</sub>O<sub>2</sub>, replacing O<sub>2</sub> as the oxidant, the experimental rate law depended on [H<sub>2</sub>O<sub>2</sub>]: −d[(Fe<sup>III</sup>L<sup>3</sup>)<sup>3+</sup>]/dt = kH<sub>2</sub>O<sub>2</sub>[(Fe<sup>III</sup>L<sup>3</sup>)<sup>3+</sup>][H<sub>2</sub>O<sub>2</sub>]), with kH<sub>2</sub>O<sub>2</sub> = 6.25 ± 0.02 × 10<sup>−3</sup> M<sup>−1</sup> s<sup>−1</sup>. In contrast to the reaction performed under N<sub>2</sub>, no kinetic isotope effect (KIE) or general base catalysis was found for the reaction of iron(III) complex 1 with O<sub>2</sub>. Under N<sub>2</sub>, two consecutive one-electron oxidation steps of the ligand coupled to proton removal produced the iron(II)-monoimine complex [Fe<sup>II</sup>L<sup>4</sup>]<sup>2+</sup> and the iron(II)-amine complex [Fe<sup>II</sup>L<sup>3</sup>]<sup>2+</sup> in a 1 : 1 ratio (disproportionation), with the amine deprotonation being the rate determining step. Notably, the reaction is almost one order of magnitude faster in the presence of O<sub>2</sub>, with k<sub>EtO</sub>− = 3.02 ± 0.09 × 10<sup>5</sup> M<sup>−1</sup> s<sup>−1 </sup>(O<sub>2</sub>) compared to k<sub>EtO</sub>− = 4.92 ± 0.01 × 104 M<sup>−1</sup> s<sup>−1</sup> (N<sub>2</sub>), documenting the role of molecular oxygen in the dehydrogenation reaction.</dcterms:abstract> <dc:contributor>Saucedo-Vásquez, Juan Pablo</dc:contributor> <dc:rights>terms-of-use</dc:rights> <dcterms:available rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">2015-06-17T13:41:56Z</dcterms:available> <dcterms:rights rdf:resource="https://rightsstatements.org/page/InC/1.0/"/> </rdf:Description> </rdf:RDF>