43145-42-2Relevant academic research and scientific papers
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.
