84206-82-6Relevant academic research and scientific papers
Stereoelectronic Aspects of Inter-Metal Nitrogen Atom Transfer Reactions between Nitridomanganese(V) and Chromium(III) Porphyrins
Bottomley, Lawrence A.,Neely, Frank L.
, p. 5435 - 5439 (2008/10/09)
Reactions of nitridomanganese(V) porphyrins with chromium(III) porphyrins resulted in the irreversible formation of nitridochromium(V) porphyrins and manganese(III) porphyrins. The progress of these reactions has been followed spectrophotometrically, electrochemically, and spectroscopically by EPR. Kinetic analysis of the spectrophotometric data obtained during these reactions for a variety of substituted porphyrins showed the reactions to be first order in each of the reactants. Rate constants were dependent upon the electronic and steric effects of the porphyrin substituent, upon the identity of the anion bound to the chromium(III) reactant, and upon the solvent dielectric constant. We propose that the mechanism of these nitrogen atom transfer reactions involves the nucleophilic attack of the nitridomanganese porphyrin donor on the cationic chromium(III) porphyrin acceptor facilitating a net, two-electron redox process mediated by a heterobimetallic μ-nitrido intermediate. This report represents the first systematic study of the stereoelectronic effects involved in the complete, inter-metal nitrogen atom transfer between two metalloporphyrins.
Thermodynamic and kinetic aspects of two- and three-electron redox processes mediated by nitrogen atom transfer
Keith Woo,Goll, James G.,Czapla, Donald J.,Alan Hays
, p. 8478 - 8484 (2007/10/02)
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≡N and Mn(TTP). The net result is a formal three-electron reduction of (TTP)MnvN to (TTP)MnII This occurs with a second-order rate constant of (5.6 ± 1.2) × 103 M-1 s-1 to form an equilibrium mixture with Koq 1.2 ± 0.5 at 20°C. The thermodynamic and activation parameters for this process are ΔH° = 2.0 ± 0.2 kcal/mol, ΔS° = 7.1 ± 0.6 cal/mol·K, ΔH? = 9.4 ± 0.7 kcal/mol, and ΔS? = -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)MnCl and (OEP)Mn≡N produces (TTP)Mn≡N and (OEP)MnCl with a second-order rate constant of 0.010 ± 0.007 M-1 s-1 (ΔH? = 19 ± 2 kcal/mol and ΔS? = -3 ± 6 cal/mol·K) and forms an equilibrium mixture with Keq = 24.3 ± 3.3 (ΔH° = -7.0 ± 0.6 kcal/mol and ΔS° = -17 ± 2 cal/mol-K). Evidence for the formation of a binuclear μ-nitrido 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.
