65024-11-5Relevant academic research and scientific papers
Inter-Metal Nitrogen Atom Transfer Reactions between Nitridochromium(V) and Chromium (III) Porphyrins
Neely, Frank L.,Bottomley, Lawrence A.
, p. 5432 - 5434 (2008/10/09)
Reactions of nitridochromium(V) porphyrins with chromium(III) porphyrins resulted in reversible, inter-metal nitrogen atom transfer between the two chromium porphyrin complexes. The progress of these reactions was followed spectrophotometrically. Kinetic analysis of the spectral data obtained over time for a variety of substituted porphyrins showed the reactions to be first order in each of the reactants and second order overall. Equilibrium constants were computed from the spectral data and ranged from 0.56 to 2.1 for the reactions between nitridochromium(V) octaethylporphyrin and a series of chlorochromium(III) tetraphenylporphyrins possessing phenyl ring substituents. Forward rate constants were determined for this reaction series and ranged from 6.8 to 1420 M-11 s-1. Electron-withdrawing substituents enhanced the forward rates but diminished the equilibrium constants. It is proposed that the reactions proceed by nucleophilic attack of the nitridochromium porphyrin donor on the cationic chromium(III) porphyrin nitrogen atom acceptor facilitating a net, two-electron redox process mediated by a homobimetallic μ-nitrido intermediate.
Oxygen atom transfer reactions of chromium porphyrins: An electronic rationale for Oxo transfer versus μ-Oxo product formation
Woo, L. Keith,Goll, James G.,Benreau, Lisa M.,Weaving, Rob
, p. 7411 - 7415 (2007/10/02)
Treatment of (meso-tetra-p-tolylporphyrinato)chromium(IV) oxide, (TTP)Cr=O, with (octaethylporphyrinato)- chromium(III) chloride, (OEP)Cr-Cl, in benzene results in the reversible exchange of axial ligands to form (TTP)Cr-Cl and (OEP)Cr=O. The net result is a formal one-electron redox process. This occurs with a second-order rate constant of 0.14 ± 0.01 M-1 s-1 to form an equilibrium mixture with K = 2.7 ± 0.1 at 30°C (ΔH? = 15.4 ± 0.7 kcal/mol, ΔS? = -12 ± 2 cal/(mol·K), ΔH° = -2.0 ± 0.4 kcal/mol, and ΔS° = -4.6 ± 1.2 cal/(mol·K)). Use of pivalate in place of chloride on the Cr(III) complex causes no significant change in the rate of this one-electron redox process. The sterically protected Baldwin's C2-capped (porphyrinato)chromium(III) complex, (CAP)Cr-Cl, also undergoes oxygen atom transfer with (OEP)Cr=O at a similar rate. In addition, excess chloride inhibits the rate of oxygen transfer with chlorochromium(III) complexes. These results support an inner-sphere mechanism involving a μ-oxo intermediate which is formed after an initial ligand (chloride or pivalate) dissociation from the chromium(UI) reductant.
