Thermodynamic and Kinetic Aspects of Two- and Three-Electron Redox Processes Mediated by Nitrogen Atom Transfer Woo, L. Keith Goll, James Woo, L. Czapla, Donald Hays, J. Alan
dc.contributor.department Chemistry 2018-02-17T09:17:07.000 2020-06-30T01:22:27Z 2020-06-30T01:22:27Z Tue Jan 01 00:00:00 UTC 1991 1991-10-01
dc.description.abstract <p>Treatment of (meso-tetra-p-tolylporphyrinato)manganese(V) nitride, (TTP)Mn==N, with (octaethylporphyrinato) manganese(II), Mn(OEP), in toluene leads to the reversible transfer of the nitrido ligand between the two metal complexes to form (OEP)Mn Nand Mn(TTP). The net result is a formal three-electron reduction of (TTP)MnvN to (TTP)Mn11• This occurs with a second-order rate constant of (5.6 ± 1.2) X 103 M-1 s-1 to form an equilibrium mixture with K~ = 1.2 ± 0.5 at 20 °C. The thermodynamic and activation parameters for this process are t:.H0 = 2.0 ± 0.2 kcalfmol, t:.S = 7 .I ± 0.6 calfmol·K, t:.H* = 9.4 ± 0.7 kcal/mol, and t:.S* = -10 ± 2 cal/mol·K. In THF at 20 °C, the equilibrium constant is 1.8 ± 0.2 and the rate constant drops to 2.3 ± 0.3 M-1 s-1• When a manganese(III) porphyrin complex is used as a reductant, reversible nitrogen atom transfer still occurs but mediates a formal two-electron process. At 22 °C, the exchange process between (TTP)MnCI and (OEP)Mn==N produces (TTP)Mn==N and (OEP)MnCI with a second-order rate constant of 0.010 ± 0.007 M-1 s-1 (t:.H* = 19 ± 2 kcal/mol and t:.S* = -3 ± 6 cal/mol·K) and forms an equilibrium mixture with Keq = 24.3 ± 3.3 (t:.H 0 = -7.0 ± 0.6 kcal/mol and t:.S 0 = -17 ± 2 cal/mol·K). Evidence for the formation of a binuclear wnitrido intermediate is presented for both processes. For the two-electron redox reaction, kinetic studies and mechanistic probes support a pathway which involves an initial chloride dissociation from the Mn(III) complex. Nitrogen atom transfer subsequently occurs between the Mn==N complex and the four-coordinate Mn(III) cationic species.</p>
dc.description.comments <p>Reprinted (adapted) with permission from <em>Journal of the American Chemical Society </em>113 (1991): 8478, doi:<a href="" target="_blank">10.1021/ja00022a040</a>. Copyright 1991 American Chemical Society.</p>
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dc.identifier.articleid 1727
dc.identifier.contextkey 7961144
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dc.language.iso en
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dc.source.uri 10.1021/ja00022a040
dc.subject.disciplines Chemistry
dc.title Thermodynamic and Kinetic Aspects of Two- and Three-Electron Redox Processes Mediated by Nitrogen Atom Transfer
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relation.isOrgUnitOfPublication 42864f6e-7a3d-4be3-8b5a-0ae3c3830a11
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