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

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)9508-9520
Number of pages13
JournalJournal of the American Chemical Society
Volume138
Issue number30
DOIs
Publication statusPublished - Aug 3 2016

Fingerprint

Pterins
Ruthenium
Alkalinity
Electron transitions
Protons
Metals
Ligands
Electrons
Oxidation
Enthalpy
Amines
Hydrogen
Substrates
Rate constants
Polarization
Derivatives
Atoms
Molecules

All Science Journal Classification (ASJC) codes

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

Cite this

@article{ff87a76c017e4643a1b64e436b2685c1,
title = "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",
abstract = "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.",
author = "Hiroumi Mitome and Tomoya Ishizuka and Hiroaki Kotani and Yoshihito Shiota and Kazunari Yoshizawa and Takahiko Kojima",
year = "2016",
month = "8",
day = "3",
doi = "10.1021/jacs.6b03785",
language = "English",
volume = "138",
pages = "9508--9520",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "30",

}

TY - JOUR

T1 - Mechanistic Insights into C-H Oxidations by Ruthenium(III)-Pterin Complexes

T2 - Impact of Basicity of the Pterin Ligand and Electron Acceptability of the Metal Center on the Transition States

AU - Mitome, Hiroumi

AU - Ishizuka, Tomoya

AU - Kotani, Hiroaki

AU - Shiota, Yoshihito

AU - Yoshizawa, Kazunari

AU - Kojima, Takahiko

PY - 2016/8/3

Y1 - 2016/8/3

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=84982686566&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84982686566&partnerID=8YFLogxK

U2 - 10.1021/jacs.6b03785

DO - 10.1021/jacs.6b03785

M3 - Article

VL - 138

SP - 9508

EP - 9520

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 30

ER -