Mechanistic Insights into C-H Oxidations by Ruthenium(III)-Pterin Complexes: Impact of Basicity of the Pterin Ligand and Electron Acceptability of the Metal Center on the Transition States

Hiroumi Mitome, Tomoya Ishizuka, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

研究成果: Contribution to journalArticle

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A ruthenium(II) complex, [Ru(dmdmp)Cl(MeBPA)] (2) (Hdmdmp = N,N-dimethyl-6,7-dimethylpterin, MeBPA = N-methyl-N,N-bis(pyridylmethyl)amine), having a pterin derivative as a proton-accepting ligand, was synthesized and characterized. Complex 2 shows higher basicity than that of a previously reported RuII-pterin complex, [Ru(dmdmp) (TPA)]+ (1) (TPA = tris(2-pyridylmethyl)amine). On the other hand, 1e--oxidized species of 1 (1OX) exhibits higher electron-acceptability than that of 1e--oxidized 2 (2OX). Bond dissociation enthalpies (BDE) of the two RuII complexes having Hdmdmp as a ligand in proton-coupled electron transfer (PCET) to generate 1OX and 2OX were calculated to be 85 kcal mol-1 for 1OX and 78 kcal mol-1 for 2OX. The BDE values are large enough to perform H atom transfer from C-H bonds of organic molecules to the 1e--oxidized complexes through PCET. The second-order rate constants (k) of PCET oxidation reactions were determined for 1OX and 2OX. The logarithms of normalized k values were proportional to the BDE values of C-H bonds of the substrates with slopes of -0.27 for 1OX and -0.44 for 2OX. The difference between 1OX and 2OX in the slopes suggests that the transition states in PCET oxidations of substrates by the two complexes bear different polarization, as reflection of difference in the electron acceptability and basicity of 1OX and 2OX. The more basic 2OX attracts a proton from a C-H bond via a more polarized transition state than that of 1OX; on the contrary, the more electron-deficient 1OX forms less polarized transition states in PCET oxidation reactions of C-H bonds.

元の言語英語
ページ(範囲)9508-9520
ページ数13
ジャーナルJournal of the American Chemical Society
138
発行部数30
DOI
出版物ステータス出版済み - 8 3 2016

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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