Biomimetic oxidation of 3,5-di-tert-butylcatechol by dioxygen via Mn-enhanced base catalysis.
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.
Szigyártó
Imola Cs
IC
Chemical Research Center, Institute of Surface Science and Catalysis, Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary. imcsi@chemres.hu
Simandi
László I
LI
Párkányi
László
L
Korecz
László
L
Schlosser
Gitta
G
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*
D016227:Benzoquinones; D002396:Catechols; D008024:Ligands; D009942:Organometallic Compounds; C054068:3,5-di-tert-butylcatechol; D008345:Manganese; D010100:Oxygen; C025225:2-benzoquinone