Tuning of metal-metal interactions in mixed-valence states of cyclometalated dinuclear ruthenium and osmium complexes bearing tetrapyridylpyrazine or-benzene

Takumi Nagashima, Takuya Nakabayashi, Takashi Suzuki, Katsuhiko Kanaizuka, Hiroaki Ozawa, Yu Wu Zhong, Shigeyuki Masaoka, Ken Sakai, Masa Aki Haga

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis-(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)-M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of -1.0 to -1.2 V for the bridging sites and -0.65 to -0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal-C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (δE(1)) and the comproportionation constant (Kcom) of the mixed-valence complexes having the tppz bridging ligand (δE(1) and Kcom values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (δE(1) and Kcom: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π orbitals, which leads to either hole- or electron-transfer exchange mechanisms. (Figure Presented)

Original languageEnglish
Pages (from-to)4893-4904
Number of pages12
JournalOrganometallics
Volume33
Issue number18
DOIs
Publication statusPublished - Sep 22 2014

Fingerprint

Bearings (structural)
Osmium
Ruthenium
osmium
Benzene
ruthenium
Tuning
Metals
tuning
benzene
Ligands
valence
ligands
metals
orbitals
interactions
Electrons
shift
Discrete Fourier transforms
Electron energy levels

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

Cite this

Tuning of metal-metal interactions in mixed-valence states of cyclometalated dinuclear ruthenium and osmium complexes bearing tetrapyridylpyrazine or-benzene. / Nagashima, Takumi; Nakabayashi, Takuya; Suzuki, Takashi; Kanaizuka, Katsuhiko; Ozawa, Hiroaki; Zhong, Yu Wu; Masaoka, Shigeyuki; Sakai, Ken; Haga, Masa Aki.

In: Organometallics, Vol. 33, No. 18, 22.09.2014, p. 4893-4904.

Research output: Contribution to journalArticle

Nagashima, Takumi ; Nakabayashi, Takuya ; Suzuki, Takashi ; Kanaizuka, Katsuhiko ; Ozawa, Hiroaki ; Zhong, Yu Wu ; Masaoka, Shigeyuki ; Sakai, Ken ; Haga, Masa Aki. / Tuning of metal-metal interactions in mixed-valence states of cyclometalated dinuclear ruthenium and osmium complexes bearing tetrapyridylpyrazine or-benzene. In: Organometallics. 2014 ; Vol. 33, No. 18. pp. 4893-4904.
@article{e05dcb4377db412ab005b6ec6a8d975d,
title = "Tuning of metal-metal interactions in mixed-valence states of cyclometalated dinuclear ruthenium and osmium complexes bearing tetrapyridylpyrazine or-benzene",
abstract = "New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis-(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)-M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of -1.0 to -1.2 V for the bridging sites and -0.65 to -0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal-C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (δE(1)) and the comproportionation constant (Kcom) of the mixed-valence complexes having the tppz bridging ligand (δE(1) and Kcom values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (δE(1) and Kcom: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π∗ orbitals, which leads to either hole- or electron-transfer exchange mechanisms. (Figure Presented)",
author = "Takumi Nagashima and Takuya Nakabayashi and Takashi Suzuki and Katsuhiko Kanaizuka and Hiroaki Ozawa and Zhong, {Yu Wu} and Shigeyuki Masaoka and Ken Sakai and Haga, {Masa Aki}",
year = "2014",
month = "9",
day = "22",
doi = "10.1021/om500142t",
language = "English",
volume = "33",
pages = "4893--4904",
journal = "Organometallics",
issn = "0276-7333",
publisher = "American Chemical Society",
number = "18",

}

TY - JOUR

T1 - Tuning of metal-metal interactions in mixed-valence states of cyclometalated dinuclear ruthenium and osmium complexes bearing tetrapyridylpyrazine or-benzene

AU - Nagashima, Takumi

AU - Nakabayashi, Takuya

AU - Suzuki, Takashi

AU - Kanaizuka, Katsuhiko

AU - Ozawa, Hiroaki

AU - Zhong, Yu Wu

AU - Masaoka, Shigeyuki

AU - Sakai, Ken

AU - Haga, Masa Aki

PY - 2014/9/22

Y1 - 2014/9/22

N2 - New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis-(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)-M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of -1.0 to -1.2 V for the bridging sites and -0.65 to -0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal-C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (δE(1)) and the comproportionation constant (Kcom) of the mixed-valence complexes having the tppz bridging ligand (δE(1) and Kcom values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (δE(1) and Kcom: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π∗ orbitals, which leads to either hole- or electron-transfer exchange mechanisms. (Figure Presented)

AB - New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis-(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)-M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of -1.0 to -1.2 V for the bridging sites and -0.65 to -0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal-C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (δE(1)) and the comproportionation constant (Kcom) of the mixed-valence complexes having the tppz bridging ligand (δE(1) and Kcom values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (δE(1) and Kcom: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π∗ orbitals, which leads to either hole- or electron-transfer exchange mechanisms. (Figure Presented)

UR - http://www.scopus.com/inward/record.url?scp=84927595045&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84927595045&partnerID=8YFLogxK

U2 - 10.1021/om500142t

DO - 10.1021/om500142t

M3 - Article

AN - SCOPUS:84927595045

VL - 33

SP - 4893

EP - 4904

JO - Organometallics

JF - Organometallics

SN - 0276-7333

IS - 18

ER -