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The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines

The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines

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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. 44(12), pp. 5510-5519. ISSN 1477-9226. eISSN 1477-9234. Available under: doi: 10.1039/C4DT03606A

@article{SaucedoVasquez2015molec-31184, title={The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines}, year={2015}, doi={10.1039/C4DT03606A}, 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} }

The role of molecular oxygen in the iron(III)-promoted oxidative dehydrogenation of amines Kroneck, Peter M.H. 2015-06-17T13:41:56Z Sosa-Torres, Martha Elena 2015 Kroneck, Peter M.H. eng Sosa-Torres, Martha Elena 2015-06-17T13:41:56Z 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. Saucedo-Vásquez, Juan Pablo Saucedo-Vásquez, Juan Pablo

Dateiabrufe seit 17.06.2015 (Informationen über die Zugriffsstatistik)

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