Biomimetic catalysis of catechol cleavage by O2 in organic solvents - Role of accessibility of O2 to FeIII in 2,11-diaza[3,3](2,6)pyridinophane-type catalysts

Abstract : Three new complexes, [Fe(LN4H2)Cl2]+, [Fe(LN4H2)(Cat)]+, and [Fe(LN4H2)(DBC)]+, were synthesized by using the tetradentate macrocyclic ligand LN4H2 (where LN4H2, Cat, and DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, and 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN4H2)Cl2]+ was determined by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with a = 9.613(1), b = 11.589(1), c = 14.063(2) Å, ß=110.20(2)°, V = 1541.9(3) Å3 and Z = 4. These complexes were found to catalyze the oxidation of catechol groups using O2. This was performed in various organic solvents at 20 °C. The reaction rates were measured for the stoichiometric complexes [Fe(LN4H2)(Cat)]+ and [Fe(LN4H2)(DBC)]+. It was found that despite the relatively high energy of the ligand-to-metal charge transfer O(DBC or Cat)?FeIII, their activity was comparable to that of the fast TPA systems [TPA indicates tris(2-pyridylmethyl)amine]. The oxidation products of DBCH2 have been studied. It has then been shown that the LN4H2 systems catalyse by means of both intra- and extradiol cleavage of catechol groups. The existence of multiple reactive pathways can account for the fast reactivity observed.
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Submitted on : Monday, December 23, 2013 - 8:01:48 AM
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N. Raffard, R. Carina, A.J. Simaan, J. Sainton, Eric Rivière, et al.. Biomimetic catalysis of catechol cleavage by O2 in organic solvents - Role of accessibility of O2 to FeIII in 2,11-diaza[3,3](2,6)pyridinophane-type catalysts. European Journal of Inorganic Chemistry, Wiley-VCH Verlag, 2001, 2001 (9), pp.2249. ⟨10.1002/1099-0682(200109)2001:9<2249::AID-EJIC2249>3.0.CO;2-3⟩. ⟨hal-00918614⟩

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