Iron(III) [bond] Salen complexes as enzyme models: mechanistic study of oxo(salen)iron complexes oxygenation of organic sulfides.
The oxidation of a series of para-substituted phenyl methyl sulfides was carried out with several oxo(salen)iron (salen = N,N'-bis(salicylidine)ethylenediaminato) complexes in acetonitrile. The oxo complex [O=Fe(IV)(salen)](*+), generated from an iron(III) [bond] salen complex and iodosylbenzene, effectively oxidizes the organic sulfides to the corresponding sulfoxides. The formation of [O [double bond] Fe(IV)(salen)](*+) as the active oxidant is supported by resonance Raman studies. The kinetic data indicate that the reaction is first-order in the oxidant and fractional-order with respect to sulfide. The observed saturation kinetics of the reaction and spectral data indicate that the substrate binds to the oxidant before the rate-controlling step. The rate constant (k) values for the product formation step determined using Michaelis-Menten kinetics correlate well with Hammett sigma constants, giving reaction constant (rho) values in the range of -0.65 to -1.54 for different oxo(salen)iron complexes. The log k values observed in the oxidation of each aryl methyl sulfide by substituted oxo(salen)iron complexes also correlate with Hammett sigma constants, giving positive rho values. The substituent effect, UV-vis absorption, and EPR spectral studies indicate oxygen atom transfer from the oxidant to the substrate in the rate-determining step.
Sivasubramanian
Veluchamy Kamaraj
VK
School of Chemistry, Madurai Kamaraj University, Madurai-625 021, India.
Ganesan
Muniyandi
M
Rajagopal
Seenivasan
S
Ramaraj
Ramasamy
R
D000097:Acetonitriles / Q000737:chemistry; D002384:Catalysis; D002857:Chromium / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004798:Enzymes; D005029:Ethylenediamines / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D008345:Manganese / Q000737:chemistry; D008954:Models, Biological; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman; D013440:Sulfides / Q000737:chemistry; D013454:Sulfoxides / Q000737:chemistry
D000097:Acetonitriles; D004798:Enzymes; D005029:Ethylenediamines; D005290:Ferric Compounds; D009942:Organometallic Compounds; D013440:Sulfides; D013454:Sulfoxides; D002857:Chromium; D008345:Manganese; D012428:Ruthenium; C011452:disalicylaldehyde ethylenediamine