Mechanism for the homolytic cleavage of alkyl hydroperoxides by the manganese(III) dimer Mn{sup III}{sub 2}(2-OHsalpn){sub 2}

Journal Article · Wed Jun 05 04:00:00 EDT 1996 · Inorganic Chemistry

DOI:https://doi.org/10.1021/ic951462u· OSTI ID:476870

Caudle, M T; Riggs-Gelasco, P; Gelasco, A K ^[1]

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1. Univ. of Michigan, Ann Arbor, MI (United States); and others

The oxidation of Mn{sup III}{sub 2}(2-OHsalpn){sub 2}, 1 (2-OHsalpn = 1,3-bis(salicylideneamino)-2-propanol), with tert-butyl hydroperoxide was studied in organic media. A one-electron reaction occurs resulting in initial formation of the oxidized Mn{sup III}Mn{sup IV} (2-OHsalpn){sub 2}OH species 2 and a tert-butoxy radical. The Mn{sup III}Mn{sup IV}(2-OHsalpn){sub 2}OH complex can be readily protonated to yield Mn{sup III}Mn{sup IV} (2-OHsalpn){sub 2}{sup +}. Upon addition of excess tert-butyl hydroperoxide, singlet dioxygen is evolved in an exothermic reaction indicative of radical-induced disproportionation of the hydroperoxide. In the presence of a radical scavenger, the oxygen evolution is strongly attenuated. This system was observed to oxygenate cyclohexene to yield 2-cyclohexen-1-one, 2-cyclohexen-1-ol, and traces of cyclohexene oxide. Cumene is oxygenated to 2-phenyl-2-propanol and acetophenone, and cyclohexane is oxygenated to cyclohexanone and cyclohexanol. However, {sup 18}O-labeling experiments show that the oxygen in the products results exclusively from reactions with aerobic dioxygen and not from the tert-butyl hydroperoxide oxidant. These results indicate that oxygenation occurs by radical-initiated aerobic autoxidation and not via oxo transfer from a high-valent manganese oxo species. 2 was studied by UV-vis, IR, NMR, EXAFS, XANES, and EPR spectroscopies, which support the assignment of a dinuclear manganese (III/IV) terminal hydroxo structure. 2 was also formed by the direct reaction of Mn{sup III}Mn{sup IV}(2-OHsalpn){sub 2}{sup +} with OH{sup {minus}}, further supporting the description of 2 as having a terminal hydroxide ligand. The kinetics of its formation from 1 and tert-butyl hydroperoxide were examined and found to be first-order in peroxide.

• OSTI ID: 476870
• Journal Information: Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 12 Vol. 35; ISSN 0020-1669; ISSN INOCAJ
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ABSORPTION SPECTROSCOPY
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
ELECTRON SPIN RESONANCE
MANGANESE COMPOUNDS
NUCLEAR MAGNETIC RESONANCE
OXIDATION
PEROXIDES
RADICALS
REDUCTION
X-RAY SPECTROSCOPY