from first principles PP-I-1

PP-I-9Quantum Chemical Study of C-H Bond Activation in Methane andMethanol by Au(I) Complexes with Quercetin under Mild ConditionsNikitenko N.G., Shestakov A.F.Institute of Problems of Chemical Physics RAS, Moscow region, Chernogolovka, Russiang_nikitenko@mail.ruSelective catalytic functionalization of methane to form useful organic compounds constitutesan important and challenging problem. Recently it was found that gold containing enzymefrom aurophilic bacteria Micrococcus Luteus can catalyze the oxidation of methane tomethanol by air' oxygen at room temperature and atmospheric pressure and biomimeticmodels based on Au complexes with bioflavonoids (rutin or quercetin) were developed [1].To understand the main features of the mechanism of methane hydroxylation in biomimeticsystems and possible reason for the selectivity of this reaction quantum chemical modelingwas applied. All calculations have been performed by means of PRIRODA program using thenonempirical PBE functional and the extended basis set for SBK pseudopotential. It has beendone using the facilities of Joint Supercomputer Center of the Russian Academy of Sciences.We were found that binuclear Au(I) aqua complex with quercetin [Au 2 Qc 2 (H 2 O) 2 ] is an activecenter in the biomimetic system. Formation of methane complex [Au 2 Qc 2 (H 2 O)(CH 4 )](H 2 O)is favorable for subsequent reaction of heterolytic C-H bond cleavage. It proceeds by meansof proton transfer on the oxygen atom of quercetin ligand via water molecule and require theactivation energy 0.4 kcal/mol. The formation of methane complex is the limiting stage withthe activation energy 16.9 kcal/mol.The interaction of the [Au 2 Qc 2 (H 2 O) 2 ] complex with the product CH 3 OH, gives substitutionH 2 O ligand on CH 3 OH ligand. The isomer structure of complex with activated C-H bond ofCH 3 OH like in methane complex has the energy on 19.3 kcal/mol higher than complex withcoordinated ОН group of CH 3 OH. The energy barrier of the transformation of stable isomerinto reactive isomer is rather high 27.4 kcal/mol. Thus, methanol oxidation rate is muchsmaller than that of methane oxidation, in accordance with experimental data.References:[1] L.A. Levchenko, V.G. Kartsev, A.P. Sadkov, A.F. Shestakov, A.K. Shilova, A.E. Shilov, DokladyChemistry. 412, (2007) 35.125