Mechanism of (Salen)manganese(III)‐Catalyzed Oxidation of Aryl Phenyl Sulfides with Sodium Hypochlorite

Abstract

The oxidation of 4-substituted phenyl phenyl sulfides was carried out with several oxo(salen)manganese(V) complexes in MeCN/H 2 O 9 : 1. The kinetic data show that the reaction is first-order each in the oxidant and sulfide. Electron-attracting substituents in the sulfides and electron-releasing substituents in salen of the oxo(salen)manganese(V) complexes reduce the rate of oxidation. A Hammett analysis of the rate constants for the oxidation of 4-substituted phenyl phenyl sulfides gives a negative 1 value (1 ¼ À 2.16) indicating an electron-deficient transition state. The log k 2 values observed in the oxidation of each 4-substituted phenyl phenyl sulfide by substituted oxo(salen)manganese(V) complexes also correlate with Hammett s constants, giving a positive 1 value. The substituent-, acid-, and solvent-effect studies indicate direct O-atom transfer from the oxidant to the substrate in the rate-determining step.Introduction. -To mimic active intermediates in enzyme-catalyzed oxidation reactions, porphyrinato-and (salen)manganese, -chromium, -ruthenium, and -iron complexes (salen ¼ N,N'-bis (salicylidene) [27], and oxo(salen)iron [28] follow an S N 2 mechanism. However, a dual mechanism has been proposed in some oxidation reactions [29].With the aim of establishing the optimum conditions for the synthesis of sulfoxides and sulfones and the mechanism of oxometal ion oxidation of organic sufides, we have studied extensively the kinetics and mechanism of oxo(salen)metal ion oxidation of organic sulfur compounds [20]

Time-resolved XAS studies reveal sequential oxidative–reductive formation of Na-doped iridium oxide films with enhanced bio-stimulating performance

“…In addition, the exact oxidation steps occurring for Ir 3+ to Ir 5+ is likely to be identical to the oxygen-evolving complex mechanism reported in Mn oxidation where the Mn 3+ complex was oxidized by NaClO to form a Mn 5+ complex with an apical Mn V O bond. 30,31 In our case, the presence of an apical Ir V O bond was validated by EXAFS fitting in which the bonding distance for the apical Ir V O bond was slightly shorter than those of Ir IV –O ones. This shorter distance was reasonably anticipated due to the nature of the double bond (Ir V O).…”

Preparation, Characterization and Reactivity of a Bis-hypochlorite Adduct of a Chiral Manganese(IV) Salen Complex

“…Hammett plot analyses show similar ρ values for these two processes (ρ = −0.84 and −0.92), indicating electrophilic character of the manganese­(IV) bound hypochlorite. The estimated ρ values are smaller than those reported for the sulfoxidation reactions of various manganese­(III) salen complexes with sodium hypochlorite (ρ = −1.55 to −2.38), a nonheme oxomanganese­(IV) complex (ρ = −4.4), and oxomanganese­(V) corrolazines (ρ = −1.29 to −2.99) but close to that of oxomanganese­(V) porphyrin (ρ = −0.65) …”

Oxidation and Reduction

“…The substituent-, acid-, and solvent effects indicated direct transfer of the O-atom from the oxidant to the substrate in the rate-determining step. 78 …”