Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene

K. A. Campbell, M. R. Lashley, J. K. Wyatt, M. H. Nantz, R. David Britt

Research output: Contribution to journalArticle

144 Citations (Scopus)

Abstract

Dual-mode electron paramagnetic resonance (EPR), in which an oscillating magnetic field is alternately applied parallel or perpendicular to the static magnetic field, is a valuable technique for studying both half-integer and integer electron spin systems and is particularly useful for studying transition metals involved in redox chemistry. We have applied this technique to the characterization of the Mn(III) salen (salen = N,N′-ethylene bis(salicylideneaminato)) complex [(R,R)-(-)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediaminomanganese(III)], with an S = 2 integer electron spin system. Furthermore, we have used dual-mode EPR to study the Mn salen complex during the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. Our study shows that the additives N-methylmorpholine N-oxide (NMO) and 4-phenylpyridine-N-oxide (4-PPNO), which are used to improve epoxidation yields and enantioselection, bind to the Mn(III) center prior to the epoxidation reaction, as evidenced by the alteration of the Mn(III) parallel mode EPR signal. With these additives as ligands, the axial zero-field splitting values and 55Mn hyperfine splitting of the parallel mode signal are indicative of an axially elongated octahedral geometry about the Mn(III) center. Since the dual-mode EPR technique allows the observation of both integer and half-integer electron spin systems, Mn oxidation states of II, III, IV, and potentially V can be observed in the same sample as well as any radical intermediates or Mn(III,IV) dinuclear clusters formed during the Mn(III) salen-catalyzed epoxidation reaction. Indeed, our study revealed the formation of a Mn(III,IV) dinuclear cluster in direct correlation with expoxide formation. In addition to showing the possible reaction intermediates, dual-mode EPR offers insight into the mechanism of catalyst degradation and formation of unwanted byproducts. The dual-mode technique may therefore prove valuable for elucidating the mechanism of Mn(III) salen catalyzed reactions and ultimately for designing optimum catalytic conditions (solvents, oxidants, and additives such as NMO or 4-PPNO).

Original languageEnglish (US)
Pages (from-to)5710-5719
Number of pages10
JournalJournal of the American Chemical Society
Volume123
Issue number24
DOIs
StatePublished - 2001

Fingerprint

Epoxidation
Electron Spin Resonance Spectroscopy
Paramagnetic resonance
Oxides
Electrons
Magnetic Fields
Magnetic fields
Reaction intermediates
Oxidants
Oxidation-Reduction
Transition metals
Byproducts
Ethylene
Metals
Ligands
Observation
vinyltoluene
disalicylaldehyde ethylenediamine
Mn-salen
Degradation

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. / Campbell, K. A.; Lashley, M. R.; Wyatt, J. K.; Nantz, M. H.; David Britt, R.

In: Journal of the American Chemical Society, Vol. 123, No. 24, 2001, p. 5710-5719.

Research output: Contribution to journalArticle

Campbell, K. A. ; Lashley, M. R. ; Wyatt, J. K. ; Nantz, M. H. ; David Britt, R. / Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. In: Journal of the American Chemical Society. 2001 ; Vol. 123, No. 24. pp. 5710-5719.
@article{a8be155a2b544dd68abab612eef204d0,
title = "Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene",
abstract = "Dual-mode electron paramagnetic resonance (EPR), in which an oscillating magnetic field is alternately applied parallel or perpendicular to the static magnetic field, is a valuable technique for studying both half-integer and integer electron spin systems and is particularly useful for studying transition metals involved in redox chemistry. We have applied this technique to the characterization of the Mn(III) salen (salen = N,N′-ethylene bis(salicylideneaminato)) complex [(R,R)-(-)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediaminomanganese(III)], with an S = 2 integer electron spin system. Furthermore, we have used dual-mode EPR to study the Mn salen complex during the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. Our study shows that the additives N-methylmorpholine N-oxide (NMO) and 4-phenylpyridine-N-oxide (4-PPNO), which are used to improve epoxidation yields and enantioselection, bind to the Mn(III) center prior to the epoxidation reaction, as evidenced by the alteration of the Mn(III) parallel mode EPR signal. With these additives as ligands, the axial zero-field splitting values and 55Mn hyperfine splitting of the parallel mode signal are indicative of an axially elongated octahedral geometry about the Mn(III) center. Since the dual-mode EPR technique allows the observation of both integer and half-integer electron spin systems, Mn oxidation states of II, III, IV, and potentially V can be observed in the same sample as well as any radical intermediates or Mn(III,IV) dinuclear clusters formed during the Mn(III) salen-catalyzed epoxidation reaction. Indeed, our study revealed the formation of a Mn(III,IV) dinuclear cluster in direct correlation with expoxide formation. In addition to showing the possible reaction intermediates, dual-mode EPR offers insight into the mechanism of catalyst degradation and formation of unwanted byproducts. The dual-mode technique may therefore prove valuable for elucidating the mechanism of Mn(III) salen catalyzed reactions and ultimately for designing optimum catalytic conditions (solvents, oxidants, and additives such as NMO or 4-PPNO).",
author = "Campbell, {K. A.} and Lashley, {M. R.} and Wyatt, {J. K.} and Nantz, {M. H.} and {David Britt}, R.",
year = "2001",
doi = "10.1021/ja0027463",
language = "English (US)",
volume = "123",
pages = "5710--5719",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "24",

}

TY - JOUR

T1 - Dual-mode EPR study of Mn(III) salen and the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene

AU - Campbell, K. A.

AU - Lashley, M. R.

AU - Wyatt, J. K.

AU - Nantz, M. H.

AU - David Britt, R.

PY - 2001

Y1 - 2001

N2 - Dual-mode electron paramagnetic resonance (EPR), in which an oscillating magnetic field is alternately applied parallel or perpendicular to the static magnetic field, is a valuable technique for studying both half-integer and integer electron spin systems and is particularly useful for studying transition metals involved in redox chemistry. We have applied this technique to the characterization of the Mn(III) salen (salen = N,N′-ethylene bis(salicylideneaminato)) complex [(R,R)-(-)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediaminomanganese(III)], with an S = 2 integer electron spin system. Furthermore, we have used dual-mode EPR to study the Mn salen complex during the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. Our study shows that the additives N-methylmorpholine N-oxide (NMO) and 4-phenylpyridine-N-oxide (4-PPNO), which are used to improve epoxidation yields and enantioselection, bind to the Mn(III) center prior to the epoxidation reaction, as evidenced by the alteration of the Mn(III) parallel mode EPR signal. With these additives as ligands, the axial zero-field splitting values and 55Mn hyperfine splitting of the parallel mode signal are indicative of an axially elongated octahedral geometry about the Mn(III) center. Since the dual-mode EPR technique allows the observation of both integer and half-integer electron spin systems, Mn oxidation states of II, III, IV, and potentially V can be observed in the same sample as well as any radical intermediates or Mn(III,IV) dinuclear clusters formed during the Mn(III) salen-catalyzed epoxidation reaction. Indeed, our study revealed the formation of a Mn(III,IV) dinuclear cluster in direct correlation with expoxide formation. In addition to showing the possible reaction intermediates, dual-mode EPR offers insight into the mechanism of catalyst degradation and formation of unwanted byproducts. The dual-mode technique may therefore prove valuable for elucidating the mechanism of Mn(III) salen catalyzed reactions and ultimately for designing optimum catalytic conditions (solvents, oxidants, and additives such as NMO or 4-PPNO).

AB - Dual-mode electron paramagnetic resonance (EPR), in which an oscillating magnetic field is alternately applied parallel or perpendicular to the static magnetic field, is a valuable technique for studying both half-integer and integer electron spin systems and is particularly useful for studying transition metals involved in redox chemistry. We have applied this technique to the characterization of the Mn(III) salen (salen = N,N′-ethylene bis(salicylideneaminato)) complex [(R,R)-(-)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediaminomanganese(III)], with an S = 2 integer electron spin system. Furthermore, we have used dual-mode EPR to study the Mn salen complex during the Mn(III) salen-catalyzed epoxidation of cis-β-methylstyrene. Our study shows that the additives N-methylmorpholine N-oxide (NMO) and 4-phenylpyridine-N-oxide (4-PPNO), which are used to improve epoxidation yields and enantioselection, bind to the Mn(III) center prior to the epoxidation reaction, as evidenced by the alteration of the Mn(III) parallel mode EPR signal. With these additives as ligands, the axial zero-field splitting values and 55Mn hyperfine splitting of the parallel mode signal are indicative of an axially elongated octahedral geometry about the Mn(III) center. Since the dual-mode EPR technique allows the observation of both integer and half-integer electron spin systems, Mn oxidation states of II, III, IV, and potentially V can be observed in the same sample as well as any radical intermediates or Mn(III,IV) dinuclear clusters formed during the Mn(III) salen-catalyzed epoxidation reaction. Indeed, our study revealed the formation of a Mn(III,IV) dinuclear cluster in direct correlation with expoxide formation. In addition to showing the possible reaction intermediates, dual-mode EPR offers insight into the mechanism of catalyst degradation and formation of unwanted byproducts. The dual-mode technique may therefore prove valuable for elucidating the mechanism of Mn(III) salen catalyzed reactions and ultimately for designing optimum catalytic conditions (solvents, oxidants, and additives such as NMO or 4-PPNO).

UR - http://www.scopus.com/inward/record.url?scp=0034810834&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0034810834&partnerID=8YFLogxK

U2 - 10.1021/ja0027463

DO - 10.1021/ja0027463

M3 - Article

C2 - 11403603

AN - SCOPUS:0034810834

VL - 123

SP - 5710

EP - 5719

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 24

ER -