title: Biomimetic oxidation of 3,5-di-tert-butylcatechol by dioxygen via Mn-enhanced base catalysis.
abstract: The 6-coordinate dioximatomanganese(II) complex [Mn(HL)(CH3OH)]+ (2, where H2L is [HON=C(CH3)C(CH3)=NCH2CH2]2NH), formed by instant solvolysis of [Mn2(HL)2](BPh4)2 (1) in methanol, accelerates the triethylamine (TEA)-catalyzed oxidation of 3,5-di-tert-butylcatechol (H2dtbc) by O2 to the corresponding o-benzoquinone. Significantly, 2 alone has no catalytic effect. The observed rate increase can be explained by the interaction of 2 with the hydroperoxo intermediate HdtbcO2- formed from Hdtbc- and O2 in the TEA-catalyzed oxidation. The kinetics of the TEA-catalyzed and Mn-enhanced reaction has been studied by gas-volumetric monitoring of the amount of O2 consumed. The initial rate of O2 uptake (V(in)) shows a first-order dependence on the concentration of 2 and O2 and saturation kinetics with respect to both H2dtbc and TEA. The observed kinetic behavior is consistent with parallel TEA-catalyzed and Mn-enhanced oxidation paths. The 3,5-di-tert-butylsemiquinone anion radical is an intermediate detectable by electron spin resonance (ESR) spectroscopy. The dimeric catalyst precursor has been characterized by X-ray diffraction and electrospray ionization mass spectrometry and the monomeric catalyst by ESR spectroscopy.
authors.affiliation: Chemical Research Center, Institute of Surface Science and Catalysis, Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary. imcsi@chemres.hu
authors.forename: Imola Cs
authors.initials: IC
authors.lastname: Szigyártó
authors.forename: László I
authors.initials: LI
authors.lastname: Simandi
authors.forename: László
authors.initials: L
authors.lastname: Párkányi
authors.forename: László
authors.initials: L
authors.lastname: Korecz
authors.forename: Gitta
authors.initials: G
authors.lastname: Schlosser
mesh_terms: D016227:Benzoquinones / Q000138:chemical synthesis / Q000737:chemistry; D032701:Biomimetics; D002384:Catalysis; D002396:Catechols / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007700:Kinetics; D008024:Ligands; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D002396:Catechols; D008024:Ligands; D009942:Organometallic Compounds; C054068:3,5-di-tert-butylcatechol; D008345:Manganese; D010100:Oxygen; C025225:2-benzoquinone