Synthesis and characterization of mononuclear Ruthenium(III)Pyridylamine complexes and mechanistic insights into their catalytic alkane functionalization with m-chloroperbenzoic acid
SCIE
SCOPUS
- Title
- Synthesis and characterization of mononuclear Ruthenium(III)Pyridylamine complexes and mechanistic insights into their catalytic alkane functionalization with m-chloroperbenzoic acid
- Authors
- Kojima, T; Hayashi, KI; Iizuka, SY; Tani, F; Naruta, Y; Kawano, M; Yuji Ohashi; Hirai, Y; Ohkubold, K; Matsuda, Y; Fukuzumi, S
- Date Issued
- 2007-01
- Publisher
- WILEY-V C H VERLAG GMBH
- Abstract
- A series of mononuclear Ru-III complexes [RuCl2(L)](+), where L is tris(2-pyridylmethyl)amine (TPA) or one of four TPA derivatives as tetradentate ligand, were prepared and characterized by spectroscopic methods, X-ray crystallography, and electrochemical measurements. The geometry of a Ru-III complex having a non-threefold-symmetric TPA ligand bearing one dimethylnicotinamide moiety was determined to show that the nicotine moiety resides trans to a pyridine group, but not to the chlorido ligand. The substituents of the TPA ligands were shown to regulate the redox potential of the ruthenium center, as indicated by a linear Hammett plot in the range of 200 mV for Ru-III/Ru-IV couples with a relatively large p value (+ 0.150). These complexes act as effective catalysts for alkane functionalization in acetonitrile with m-chloroperbenzoic acid (mCPBA) as terminal oxidant at room temperature. They exhibited fairly good reactivity for oxidation of cyclohexane (C-H bond energy 94 kcalmol(-1)), and the reactivity can be altered significantly by the electronic effects of substituents on TPA ligands in terms of initial rates and turn-over numbers. Catalytic oxygenation of cyclohexane by a Ru-III complex with O-16-mCPBA in the presence of (H2O)-O-18 gave O-18-labeled cyclohexanol with 100% inclusion of the O-18 atom from the water molecule. Resonance Raman spectra under catalytic conditions without the substrate indicate formation of a Ru-IV=O intermediate with lower bonding energy. Kinetic isotope effects (KIEs) in the oxidation of cyclohexane suggest that hydrogen abstraction is the rate-determining step and the KIE values depend on the substituents of the TPA ligands. Thus, the reaction mechanism of catalytic cyclohexane oxygenation depends on the electronic effects of the ligands.
- Keywords
- N ligands; oxygenation reaction; mechanisms; redox chemistry; ruthenium; ISOTOPICALLY LABELED WATER; HINDERED RUTHENIUM COMPLEX; NONHEME IRON CATALYST; RAY CRYSTAL-STRUCTURE; METHANE MONOOXYGENASE; DIOXYGEN ACTIVATION; CIS-DIHYDROXYLATION; MOLECULAR-OXYGEN; HYDROCARBON OXYGENATION; PORPHYRIN COMPLEX
- URI
- https://oasis.postech.ac.kr/handle/2014.oak/26026
- DOI
- 10.1002/CHEM.200700190
- ISSN
- 0947-6539
- Article Type
- Article
- Citation
- CHEMISTRY-A EUROPEAN JOURNAL, vol. 13, no. 29, page. 8212 - 8222, 2007-01
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