Binuclear manganese(III) complexes of potential biological significance

John E. Sheats, Roman S. Czernuszewicz, G Charles Dismukes, Arnold L. Rheingold, Vasili Petrouleas, JoAnne Stubbe, William H. Armstrong, Robert H. Beer, Stephen J. Lippard

Research output: Contribution to journalArticle

286 Citations (Scopus)

Abstract

The synthesis of several binuclear, oxobis(carboxylato)-bridged dimanganese(III) complexes, [Mn2O(O2CR)2(HB(pz)3)2] where R = CH3 (1), C2H5 (2), or H (3), and HB(pz)3 - is the hydrotris(1-pyrazolyl)borate ligand, is described. X-ray structural studies of 1·CH3CN and 1·4CH3CN reveal two six-coordinate manganese atoms bridged by μ-oxo [av Mn-O,1.78 Å; Mn-O-Mn, 125.1°] and two μ-acetato (av Mn-O, 2.07 Å) groups and capped by two tridentate HB(pz)3 - ligands. Each high spin, d4 Mn(III) center has its empty d-orbital directed toward the short Mn-Ooxo bond axis, the consequences of which are a shortening of Mn-N bonds trans to the μ-oxo group and markedly reduced antiferromagnetic coupling of the two Mn(III) centers compared to the two high spin, d5 Fe(III) centers in the [Fe2O(O2CCH3)2(HB(pz) 3)2] analogue. In the latter, the spin exchange coupling constant J = -121 cm-1, whereas χM vs. T measurements over the range 4.2 <T <300 K for 1 reveal a J value of ∼ -0.5 cm-1. The greater paramagnetism and rapid spin relaxation of the manganese complexes leads to large isotropic shifts and narrow lines in their proton NMR spectra. All protons were observed in the 67 to -56 ppm region, and most could be assigned on the basis of deuterium substitution. The methyl resonance of the bridging acetate ligands in 1 occurs at +65.6 ppm, which should be useful for identifying the {Mn2O(O2CCH2R)2}2+ core in biology. These results suggest that substitution of Mn(III) for Fe(III) in metalloproteins such as hemerythrin or ribonucleotide reductase, that are known or believed to contain such cores, would provide a powerful NMR structural probe. The results of UV-vis, Raman, and infrared spectral studies are reported, including work on isotopically substituted 1, from which the symmetric and asymmetric Mn-O-Mn bridge bond stretching frequencies are assigned at 558 and 717 cm-1, respectively. Electrochemical studies of 1 reveal a quasi-reversible one-electron oxidation at 0.51 V vs. the Fc+/Fc couple to form the mixed valence Mn2(III,IV) complex. The ESR spectrum of a species, which was chemically generated from 1, exhibits a 16-line 55Mn hyperfine pattern that is typical of the Mn2(III,IV) trapped valence state. This spectrum closely matches that observed for the 300 K form of the S2 state of the manganese complex involved in photosynthetic water oxidation in green plants. Further oxidation of the mixed valence species reveals a second, quasi-reversible wave at 1.22 V vs. Fc+/Fc, tentatively assigned as the Mn2(IV,IV) complex.

Original languageEnglish
Pages (from-to)1435-1444
Number of pages10
JournalJournal of the American Chemical Society
Volume109
Issue number5
Publication statusPublished - 1987

Fingerprint

Manganese
Ligands
Oxidation
Protons
Hemerythrin
Substitution reactions
Nuclear magnetic resonance
Metalloproteins
Viridiplantae
Paramagnetism
Ribonucleotide Reductases
Exchange coupling
Borates
Deuterium
Stretching
Paramagnetic resonance
Acetates
X-Rays
Electrons
Infrared radiation

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Sheats, J. E., Czernuszewicz, R. S., Dismukes, G. C., Rheingold, A. L., Petrouleas, V., Stubbe, J., ... Lippard, S. J. (1987). Binuclear manganese(III) complexes of potential biological significance. Journal of the American Chemical Society, 109(5), 1435-1444.

Binuclear manganese(III) complexes of potential biological significance. / Sheats, John E.; Czernuszewicz, Roman S.; Dismukes, G Charles; Rheingold, Arnold L.; Petrouleas, Vasili; Stubbe, JoAnne; Armstrong, William H.; Beer, Robert H.; Lippard, Stephen J.

In: Journal of the American Chemical Society, Vol. 109, No. 5, 1987, p. 1435-1444.

Research output: Contribution to journalArticle

Sheats, JE, Czernuszewicz, RS, Dismukes, GC, Rheingold, AL, Petrouleas, V, Stubbe, J, Armstrong, WH, Beer, RH & Lippard, SJ 1987, 'Binuclear manganese(III) complexes of potential biological significance', Journal of the American Chemical Society, vol. 109, no. 5, pp. 1435-1444.
Sheats JE, Czernuszewicz RS, Dismukes GC, Rheingold AL, Petrouleas V, Stubbe J et al. Binuclear manganese(III) complexes of potential biological significance. Journal of the American Chemical Society. 1987;109(5):1435-1444.
Sheats, John E. ; Czernuszewicz, Roman S. ; Dismukes, G Charles ; Rheingold, Arnold L. ; Petrouleas, Vasili ; Stubbe, JoAnne ; Armstrong, William H. ; Beer, Robert H. ; Lippard, Stephen J. / Binuclear manganese(III) complexes of potential biological significance. In: Journal of the American Chemical Society. 1987 ; Vol. 109, No. 5. pp. 1435-1444.
@article{5d7e11b3d28a45cb9b9c1256f575e6f5,
title = "Binuclear manganese(III) complexes of potential biological significance",
abstract = "The synthesis of several binuclear, oxobis(carboxylato)-bridged dimanganese(III) complexes, [Mn2O(O2CR)2(HB(pz)3)2] where R = CH3 (1), C2H5 (2), or H (3), and HB(pz)3 - is the hydrotris(1-pyrazolyl)borate ligand, is described. X-ray structural studies of 1·CH3CN and 1·4CH3CN reveal two six-coordinate manganese atoms bridged by μ-oxo [av Mn-O,1.78 {\AA}; Mn-O-Mn, 125.1°] and two μ-acetato (av Mn-O, 2.07 {\AA}) groups and capped by two tridentate HB(pz)3 - ligands. Each high spin, d4 Mn(III) center has its empty d-orbital directed toward the short Mn-Ooxo bond axis, the consequences of which are a shortening of Mn-N bonds trans to the μ-oxo group and markedly reduced antiferromagnetic coupling of the two Mn(III) centers compared to the two high spin, d5 Fe(III) centers in the [Fe2O(O2CCH3)2(HB(pz) 3)2] analogue. In the latter, the spin exchange coupling constant J = -121 cm-1, whereas χM vs. T measurements over the range 4.2 <T <300 K for 1 reveal a J value of ∼ -0.5 cm-1. The greater paramagnetism and rapid spin relaxation of the manganese complexes leads to large isotropic shifts and narrow lines in their proton NMR spectra. All protons were observed in the 67 to -56 ppm region, and most could be assigned on the basis of deuterium substitution. The methyl resonance of the bridging acetate ligands in 1 occurs at +65.6 ppm, which should be useful for identifying the {Mn2O(O2CCH2R)2}2+ core in biology. These results suggest that substitution of Mn(III) for Fe(III) in metalloproteins such as hemerythrin or ribonucleotide reductase, that are known or believed to contain such cores, would provide a powerful NMR structural probe. The results of UV-vis, Raman, and infrared spectral studies are reported, including work on isotopically substituted 1, from which the symmetric and asymmetric Mn-O-Mn bridge bond stretching frequencies are assigned at 558 and 717 cm-1, respectively. Electrochemical studies of 1 reveal a quasi-reversible one-electron oxidation at 0.51 V vs. the Fc+/Fc couple to form the mixed valence Mn2(III,IV) complex. The ESR spectrum of a species, which was chemically generated from 1, exhibits a 16-line 55Mn hyperfine pattern that is typical of the Mn2(III,IV) trapped valence state. This spectrum closely matches that observed for the 300 K form of the S2 state of the manganese complex involved in photosynthetic water oxidation in green plants. Further oxidation of the mixed valence species reveals a second, quasi-reversible wave at 1.22 V vs. Fc+/Fc, tentatively assigned as the Mn2(IV,IV) complex.",
author = "Sheats, {John E.} and Czernuszewicz, {Roman S.} and Dismukes, {G Charles} and Rheingold, {Arnold L.} and Vasili Petrouleas and JoAnne Stubbe and Armstrong, {William H.} and Beer, {Robert H.} and Lippard, {Stephen J.}",
year = "1987",
language = "English",
volume = "109",
pages = "1435--1444",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "5",

}

TY - JOUR

T1 - Binuclear manganese(III) complexes of potential biological significance

AU - Sheats, John E.

AU - Czernuszewicz, Roman S.

AU - Dismukes, G Charles

AU - Rheingold, Arnold L.

AU - Petrouleas, Vasili

AU - Stubbe, JoAnne

AU - Armstrong, William H.

AU - Beer, Robert H.

AU - Lippard, Stephen J.

PY - 1987

Y1 - 1987

N2 - The synthesis of several binuclear, oxobis(carboxylato)-bridged dimanganese(III) complexes, [Mn2O(O2CR)2(HB(pz)3)2] where R = CH3 (1), C2H5 (2), or H (3), and HB(pz)3 - is the hydrotris(1-pyrazolyl)borate ligand, is described. X-ray structural studies of 1·CH3CN and 1·4CH3CN reveal two six-coordinate manganese atoms bridged by μ-oxo [av Mn-O,1.78 Å; Mn-O-Mn, 125.1°] and two μ-acetato (av Mn-O, 2.07 Å) groups and capped by two tridentate HB(pz)3 - ligands. Each high spin, d4 Mn(III) center has its empty d-orbital directed toward the short Mn-Ooxo bond axis, the consequences of which are a shortening of Mn-N bonds trans to the μ-oxo group and markedly reduced antiferromagnetic coupling of the two Mn(III) centers compared to the two high spin, d5 Fe(III) centers in the [Fe2O(O2CCH3)2(HB(pz) 3)2] analogue. In the latter, the spin exchange coupling constant J = -121 cm-1, whereas χM vs. T measurements over the range 4.2 <T <300 K for 1 reveal a J value of ∼ -0.5 cm-1. The greater paramagnetism and rapid spin relaxation of the manganese complexes leads to large isotropic shifts and narrow lines in their proton NMR spectra. All protons were observed in the 67 to -56 ppm region, and most could be assigned on the basis of deuterium substitution. The methyl resonance of the bridging acetate ligands in 1 occurs at +65.6 ppm, which should be useful for identifying the {Mn2O(O2CCH2R)2}2+ core in biology. These results suggest that substitution of Mn(III) for Fe(III) in metalloproteins such as hemerythrin or ribonucleotide reductase, that are known or believed to contain such cores, would provide a powerful NMR structural probe. The results of UV-vis, Raman, and infrared spectral studies are reported, including work on isotopically substituted 1, from which the symmetric and asymmetric Mn-O-Mn bridge bond stretching frequencies are assigned at 558 and 717 cm-1, respectively. Electrochemical studies of 1 reveal a quasi-reversible one-electron oxidation at 0.51 V vs. the Fc+/Fc couple to form the mixed valence Mn2(III,IV) complex. The ESR spectrum of a species, which was chemically generated from 1, exhibits a 16-line 55Mn hyperfine pattern that is typical of the Mn2(III,IV) trapped valence state. This spectrum closely matches that observed for the 300 K form of the S2 state of the manganese complex involved in photosynthetic water oxidation in green plants. Further oxidation of the mixed valence species reveals a second, quasi-reversible wave at 1.22 V vs. Fc+/Fc, tentatively assigned as the Mn2(IV,IV) complex.

AB - The synthesis of several binuclear, oxobis(carboxylato)-bridged dimanganese(III) complexes, [Mn2O(O2CR)2(HB(pz)3)2] where R = CH3 (1), C2H5 (2), or H (3), and HB(pz)3 - is the hydrotris(1-pyrazolyl)borate ligand, is described. X-ray structural studies of 1·CH3CN and 1·4CH3CN reveal two six-coordinate manganese atoms bridged by μ-oxo [av Mn-O,1.78 Å; Mn-O-Mn, 125.1°] and two μ-acetato (av Mn-O, 2.07 Å) groups and capped by two tridentate HB(pz)3 - ligands. Each high spin, d4 Mn(III) center has its empty d-orbital directed toward the short Mn-Ooxo bond axis, the consequences of which are a shortening of Mn-N bonds trans to the μ-oxo group and markedly reduced antiferromagnetic coupling of the two Mn(III) centers compared to the two high spin, d5 Fe(III) centers in the [Fe2O(O2CCH3)2(HB(pz) 3)2] analogue. In the latter, the spin exchange coupling constant J = -121 cm-1, whereas χM vs. T measurements over the range 4.2 <T <300 K for 1 reveal a J value of ∼ -0.5 cm-1. The greater paramagnetism and rapid spin relaxation of the manganese complexes leads to large isotropic shifts and narrow lines in their proton NMR spectra. All protons were observed in the 67 to -56 ppm region, and most could be assigned on the basis of deuterium substitution. The methyl resonance of the bridging acetate ligands in 1 occurs at +65.6 ppm, which should be useful for identifying the {Mn2O(O2CCH2R)2}2+ core in biology. These results suggest that substitution of Mn(III) for Fe(III) in metalloproteins such as hemerythrin or ribonucleotide reductase, that are known or believed to contain such cores, would provide a powerful NMR structural probe. The results of UV-vis, Raman, and infrared spectral studies are reported, including work on isotopically substituted 1, from which the symmetric and asymmetric Mn-O-Mn bridge bond stretching frequencies are assigned at 558 and 717 cm-1, respectively. Electrochemical studies of 1 reveal a quasi-reversible one-electron oxidation at 0.51 V vs. the Fc+/Fc couple to form the mixed valence Mn2(III,IV) complex. The ESR spectrum of a species, which was chemically generated from 1, exhibits a 16-line 55Mn hyperfine pattern that is typical of the Mn2(III,IV) trapped valence state. This spectrum closely matches that observed for the 300 K form of the S2 state of the manganese complex involved in photosynthetic water oxidation in green plants. Further oxidation of the mixed valence species reveals a second, quasi-reversible wave at 1.22 V vs. Fc+/Fc, tentatively assigned as the Mn2(IV,IV) complex.

UR - http://www.scopus.com/inward/record.url?scp=0000896739&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0000896739&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0000896739

VL - 109

SP - 1435

EP - 1444

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 5

ER -