79919-63-4Relevant academic research and scientific papers
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.
