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Kinetic and Thermodynamic Studies of the Disproportionation of Hydrogen Peroxide by Dimanganese( ii,ii ) and ‐( ii,iii ) Complexes of a Bridging Phenolate Ligand
Author(s) -
Dubois Lionel,
Xiang DaoFeng,
Tan XiangShi,
Latour JeanMarc
Publication year - 2005
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200400800
Subject(s) - chemistry , disproportionation , hydrogen peroxide , electron paramagnetic resonance , catalysis , acetonitrile , carboxylate , medicinal chemistry , ligand (biochemistry) , electrospray ionization , reaction mechanism , stereochemistry , photochemistry , mass spectrometry , organic chemistry , biochemistry , physics , receptor , nuclear magnetic resonance , chromatography
The dimanganese( ii,ii ) complexes [Mn 2 (L)(OAc) 2 (CH 3 OH)]‐(ClO 4 ) ( 1a ) and [Mn 2 (L)(OBz) 2 (H 2 O)](ClO 4 ) ( 1b ) as well as the dimanganese( ii,iii ) complex [Mn 2 (L)(OAc) 2 (CH 3 OH)]‐(ClO 4 ) 2 ( 2a ), where HL is the asymmetric phenol ligand2‐[bis(2‐pyridylmethyl)aminomethyl]‐6‐{[(benzyl)(2‐pyridyl‐methyl)amino]methyl}‐4‐methylphenol, react with hydrogen peroxide in acetonitrile solution. The initial reaction rates and their temperature and acid/base dependencies were investigated by monitoring the dioxygen evolution. These studies revealed a first‐order dependence on both the catalyst and H 2 O 2 and a strong influence of the carboxylate. Electrospray ionisation mass spectrometry as well as EPR and UV/Vis spectroscopy were used to monitor the reaction catalysed by 2a . The same bis(μ‐oxo)dimanganese( III,IV ) and (μ‐oxo)dimanganese( ii,iii ) active species as found for 1a were detected in the catalytic medium. The EPR spectra recorded during the catalase‐like reaction revealed the accumulation of the magnetically uncoupled dimanganese( ii,iii ) precursor of the active bis(μ‐oxo)dimanganese( III,IV ) species which dominates the spectra in the case of 1a . This difference can be attributed to the different pH conditions generated by the reaction and reflects differences in the initiation phases for the two catalysts. Overall, the kinetic and thermodynamic studies of H 2 O 2 disproportionation by these dimanganese complexes are fully consistent with the mechanism deduced from our previous extensive spectroscopic studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)