Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium (bis-phosphine)(bis-semiquinone) complexes

Boris Le Guennic; Tavon Floyd; Brandon R. Galan; Jochen Autschbach; Jerome B. Keister

doi:10.1021/ic802302v

Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium (bis-phosphine)(bis-semiquinone) complexes

Boris Le Guennic
, Tavon Floyd
, Brandon R. Galan
, Jochen Autschbach
, Jerome B. Keister

Chemistry

SUNY Buffalo
École normale supérieure de Lyon

Research output: Contribution to journal › Article › peer-review

27 Scopus citations

Abstract

Ligand substitution on cis-Ru(PPh ₃)2(1,2-O ₂C ₆H ₄) ₂ gives cis-RuL ¹L ²(1,2-O ₂C ₆H ₄)2 (L ¹ = PPh ₃, L ² = P(OPh) ₃, PBu ₃; L ¹ = L ² = PBu ₃, P(OMe) ₃). Syntheses of cis-Ru(PPh ₃) ₂(3,4-O ₂C ₆H ₂(5-OH)CO ₂Me) ₂ and cis-Ru(PPh ₃) ₂(AGSQ) ₂ (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9, 10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of c/s-Ru(PPh ₃) ₂(1,2-O ₂C ₆H ₄) ₂ was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene.

Original language	English
Pages (from-to)	5504-5511
Number of pages	8
Journal	Inorganic Chemistry
Volume	48
Issue number	12
DOIs	https://doi.org/10.1021/ic802302v
State	Published - Jun 15 2009

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@article{c4d8d0a988b043169038257fcaef0290,

title = "Paramagnetic effects on the NMR spectra of {"}diamagnetic{"} ruthenium (bis-phosphine)(bis-semiquinone) complexes",

abstract = "Ligand substitution on cis-Ru(PPh 3)2(1,2-O 2C 6H 4) 2 gives cis-RuL 1L 2(1,2-O 2C 6H 4)2 (L 1 = PPh 3, L 2 = P(OPh) 3, PBu 3; L 1 = L 2 = PBu 3, P(OMe) 3). Syntheses of cis-Ru(PPh 3) 2(3,4-O 2C 6H 2(5-OH)CO 2Me) 2 and cis-Ru(PPh 3) 2(AGSQ) 2 (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9, 10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of c/s-Ru(PPh 3) 2(1,2-O 2C 6H 4) 2 was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene.",

author = "Guennic, \{Boris Le\} and Tavon Floyd and Galan, \{Brandon R.\} and Jochen Autschbach and Keister, \{Jerome B.\}",

year = "2009",

month = jun,

day = "15",

doi = "10.1021/ic802302v",

language = "English",

volume = "48",

pages = "5504--5511",

journal = "Inorganic Chemistry",

issn = "0020-1669",

publisher = "American Chemical Society",

number = "12",

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TY - JOUR

T1 - Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium (bis-phosphine)(bis-semiquinone) complexes

AU - Guennic, Boris Le

AU - Floyd, Tavon

AU - Galan, Brandon R.

AU - Autschbach, Jochen

AU - Keister, Jerome B.

PY - 2009/6/15

Y1 - 2009/6/15

N2 - Ligand substitution on cis-Ru(PPh 3)2(1,2-O 2C 6H 4) 2 gives cis-RuL 1L 2(1,2-O 2C 6H 4)2 (L 1 = PPh 3, L 2 = P(OPh) 3, PBu 3; L 1 = L 2 = PBu 3, P(OMe) 3). Syntheses of cis-Ru(PPh 3) 2(3,4-O 2C 6H 2(5-OH)CO 2Me) 2 and cis-Ru(PPh 3) 2(AGSQ) 2 (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9, 10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of c/s-Ru(PPh 3) 2(1,2-O 2C 6H 4) 2 was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene.

AB - Ligand substitution on cis-Ru(PPh 3)2(1,2-O 2C 6H 4) 2 gives cis-RuL 1L 2(1,2-O 2C 6H 4)2 (L 1 = PPh 3, L 2 = P(OPh) 3, PBu 3; L 1 = L 2 = PBu 3, P(OMe) 3). Syntheses of cis-Ru(PPh 3) 2(3,4-O 2C 6H 2(5-OH)CO 2Me) 2 and cis-Ru(PPh 3) 2(AGSQ) 2 (AGSQ = the semiquinone derived from 1,2,3-trihydroxyanthracene-9, 10-dione) are also reported. The upfield chemical shifts and line broadening of the semiquinone 4,5-proton resonances in the NMR spectra indicate that these complexes, while having no detectable magnetic moments, have a weak, temperature-, ligand- and solvent-variable residual paramagnetism, not previously recognized in this series. Density functional theory (DFT) calculations predict a low-lying triplet state, about 14 kJ/mol (0.15 eV) above the singlet ground state. The paramagnetic effects on the NMR spectra are attributed to singlet-triplet equilibria. Temperature dependence of the proton resonances of the semiquinone rings of c/s-Ru(PPh 3) 2(1,2-O 2C 6H 4) 2 was used to calculate the singlet-triplet free energy difference as 17.5-18.0 kJ/mol in toluene.

UR - https://www.scopus.com/pages/publications/67149083073

U2 - 10.1021/ic802302v

DO - 10.1021/ic802302v

M3 - Article

AN - SCOPUS:67149083073

SN - 0020-1669

VL - 48

SP - 5504

EP - 5511

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 12

ER -

Paramagnetic effects on the NMR spectra of "diamagnetic" ruthenium (bis-phosphine)(bis-semiquinone) complexes

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