ナノダイナミクス国際シンポジウム 平成22年1月21日(木) 於長崎大学Nagasaki Symposium on Nano-Dynamics 2010 (NSND2010), January 21, 2010, Nagasaki University, Nagasaki, Japan, Invited Lectur

Arikawa Yasuhiro

Asayama Taiki

Matsumoto Naoki

Onishi Masayoshi

Umakoshi Keisuke

Nagasaki University's Academic Output SITE: NAOSITE

 42  NO Reduction Cycle on Dinuclear Ruthenium Complexes having Hydrotris(pyrazolyl)borato  Yasuhiro Arikawa,1* Taiki Asayama,1 Naoki Matsumoto,1 Keisuke Umakoshi,2 and Masayoshi Onishi2*  1Graduate School of Science and Technology, 2Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan *Tel: +81-95-819-2673, Fax: +81-95-819-2684, E-mail: arikawa@nagasaki-u.ac.jp   Abstract Bacterial nitric oxide reductase (NOR), which is a component of denitrification process in the global nitrogen cycle, catalyzes the reduction of NO to nitrous oxide (N2O) (2 NO + 2 e- + 2 H+ -> N2O + H2O).  On our continuing researches of nitrosylruthenium, we found N–N coupling of the two nitrosyl ligands on dinuclear rutheniums.  Moreover, use of 2 achieved stepwise reproduction of the NOR catalytic process.    Introduction Nitric oxide (NO) is vital to biological system as a signaling molecule in physiological properties and a component of denitrification process in the global nitrogen cycle.  In the latter, metalloenzyme, bacterial nitric oxide reductase (NOR) catalyze the reduction of NO to nitrous oxide (N2O) (2 NO + 2 e- + 2 H+ -> N2O + H2O).  Active sites of NOR compose of close-arranged heme/non-heme diiron active center.  On our continuing researches of nitrosylruthenium with hydrotris(pyrazolyl)borate (Tp) ligand, we found N–N coupling of the two nitrosyl ligands on dinuclear rutheniums.  It is proposed that such N–N coupling would be a key step in the NOR catalytic process.    Experimental The N-N coupled complex (TpRu)2(µ-Cl)(µ-pz){µ-N(=O)-N(=O)-2} (2) were prepared from the reaction of TpRuCl2(NO) (1) with pyrazole in the presence of Et3N (Scheme 1).  Complex 2 was NBN NN NH RuNClNBNNNNHRu NNNNBNNNNHRuNClClN1NNOH2       Et3N, CH2Cl2, refluxNNO O Scheme 1. Nagasaki Symposium on Nano-Dynamics 2010 P 16  43  treated with AgBF4 to give [{TpRu(NO)}2(µ-Cl)(µ-pz)](BF4)2 (3) in 56% yield.  Complex 3 was treated with Zn powder afforded complex 2 in 70% yield.   Complex 2 was transformed into oxo-bridged dinuclear complex (TpRu)2(µ-Cl)(µ-pz)(µ-O) (4) (21% yield) besides 3 (43% yield), by treatment with HBF4·OEt2 in CH2Cl2.  Concomitantly, the evolution of N2O was gas-chromatographically detected.  Complex 4 was protonated by HBF4·OEt2 to give hydroxo-bridged dinuclear complex [(TpRu)2(µ-Cl)(µ-pz)(µ-OH)]BF4 (5) in 76%.  Moreover, for 5, additional protonation, followed by exposure to NO gas reproduced the complex 3 in 53%.    Results and Discussions It was revealed that oxidation of the N–N coupled species 2 brought about cleavage of the N–N bond to give cis-dinitrosyl dinuclear form 3, and also that on reduction this cis-dinitrosyl complex 3 cleanly reformed the N–N coupled species 2.  Interestingly, treatment of the N–N coupled complex 2 with the protic acid afforded the oxo-bridged dinuclear complex 4 with the evolution of N2O.  Moreover, double protonation of the oxo-bridged dinuclear complex 4, followed by exposure to NO gas, regenerated the cis-dinitrosyl complex 3, completing the reduction cycle.  This indicates stepwise reproduction of the NOR catalytic process.    Conclusions We achieved stepwise reproduction of the NOR catalytic process on dinuclear ruthenium complexes.    References 1. Y. Arikawa, T. Asayama, Y. Moriguchi, S. Agari, and M. Onishi, J. Am. Chem. Soc., 129, 14160-14161 (2007).   Tp RuNClTpRuNO ONNTp RuNClTpRuNO ONN2+Tp RuOClTpRuNNN2OReduction+ 2 NO+ 2 H+H2O(+ H+)Oxidation234NO Reduction Cycle (2 NO + 2 e- + 2 H+       N2O + H2O)

NO Reduction Cycle on Dinuclear Ruthenium Complexes having Hydrotris(pyrazolyl)borato

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NO Reduction Cycle on Dinuclear Ruthenium Complexes having Hydrotris(pyrazolyl)borato

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