Journal of the American Chemical Society
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role in the rate-limiting step and a deuterium KIE value
consistent with a primary kinetic isotope effect. The
coordination of water to SmBr leads to significant O-H bond-
weakening of over 80 kcal/mol that leads to substrate
reduction through PCET. Interestingly, addition of alcohols
(5)
Szostak, M.; Spain, M.; Parmar, D.; Procter, D. J. Selective
Reductive Transformations Using Samarium Diiodide-Water.
Chem. Commun. 2012, 48, 330–346.
Chciuk, T. V.; Flowers, R. A., II The Role of Solvents and
Additives in Reactions of Samarium Diiodide and Related
Reductants. In Science of Synthesis; Marek, I., Ed.; Georg
Thieme Verlag KG: Stuttgart, 2016; pp 177–261.
Dahlén, A.; Hilmersson, G. Samarium(II) Iodide Mediated
Reductions−Influence of Various Additives. Eur. J. Inorg.
Chem. 2004, 2004, 3393–3403.
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that do not coordinate to SmBr still facilitate the reduction of
(
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anthracene, but reactions are several orders of magnitude
slower than those using water and likely occur through a rate-
limiting ET. Overall, the importance of proton donor
coordination demonstrates that this approach can be used to
create relatively weak C-H bonds and that water can be
employed to generate intermediate radicals through PCET that
(
Duffy, L.; Matsubara, H.; Procter, D. A Ring Size-Selective
Reduction of Lactones Using SmI and H O. J. Am. Chem. Soc.
2
2
2008, 130, 1136–1137.
Guazzelli, G.; Grazia, S. De; Collins, K. D.; Matsubara, H.;
Procter, D. J. Selective Reductions of Cyclic 1, 3-Diesters Using
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are not accessible via sequential ET-PT.
Finally,
2 2
SmI and H O. J. Am. Chem. Soc. 2009, 131, 7214–7215.
proton/reductant compatibility is often times a limiting feature
of this class of reactions. In the examples studied herein,
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Szostak, M.; Spain, M.; Procter, D. J. Selective Synthesis of 3-
Hydroxy Acids from Meldrum’s Acids Using SmI -H O. Nat.
2 2
evolution of H
a significant thermodynamic driving force, yet gas evolution is
relatively slow from SmI -water and increases as iodide
ligands are replaced by bromide and chloride to produce
stronger reductants. Beyond reductant driving force, there is
likely a kinetic barrier to hydrogen evolution of bound water.
We are currently examining the origin of this stability since
this unusual feature may be adapted to other systems and the
results of these studies will be reported in due course.
2
from the Sm(II)-water complexes should have
Protoc. 2012, 7, 970–977.
Shi, S.; Lalancette, R.; Szostak, R.; Szostak, M. Highly
Chemoselective Synthesis of Indolizidine Lactams by SmI
Induced Umpolung of the Amide Bond via Aminoketyl
Radicals: Efficient Entry to Alkaloid Scaffolds. Chem. - A Eur.
J. 2016, 22, 11949–11953.
Huq, S. R.; Shi, S.; Diao, R.; Szostak, M. Mechanistic Study of
2 2 2 2
SmI /H O and SmI /Amine/H O-Promoted Chemoselective
Reduction of Aromatic Amides (Primary, Secondary, Tertiary)
to Alcohols via Aminoketyl Radicals. J. Org. Chem. 2017, 82,
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2
-
2
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6
528–6540.
(13)
Just-Baringo, X.; Procter, D. J. Sm(II)-Mediated Electron
Transfer to Carboxylic Acid Derivatives: Development of
Complexity-Generating Cascades. Acc. Chem. Res. 2015, 48,
ASSOCIATED CONTENT
Supporting Information
1
263–1275.
Chciuk, T. V.; Flowers, R. A., II Proton-Coupled Electron
Transfer in the Reduction of Arenes by SmI –Water Complexes.
J. Am. Chem. Soc. 2015, 137, 11526–11531.
General experimental methods, spectroscopic, rate, and
computational data. This material is available free of charge via
the Internet at http://pubs.acs.org.
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2
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(17)
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Chciuk, T. V.; Anderson, W. R.; Flowers, R. A., II Proton-
Coupled Electron Transfer in the Reduction of Carbonyls by
Samarium Diiodide-Water Complexes. J. Am. Chem. Soc. 2016,
138, 8738–8741.
Chciuk, T. V.; Anderson, W. R.; Flowers, R. A., II High-
Affinity Proton Donors Promote Proton-Coupled Electron
Transfer by Samarium Diiodide. Angew. Chemie - Int. Ed. 2016,
55, 6033–6036.
Chciuk, T. V.; Li, A. M.; Vazquez-Lopez, A.; Anderson, W. R.;
Flowers, R. A., II Secondary Amides as Hydrogen Atom
Transfer Promoters for Reactions of Samarium Diiodide. Org.
Lett. 2017, 19, 290–293.
AUTHOR INFORMATION
Corresponding Authors
*
alex@uaem.mx, *rof2@lehigh.edu
Author Contributions
The manuscript was written through contributions of all authors
who have given approval to the final version of the manuscript.
Chciuk, T. V.; Anderson, W. R.; Flowers, R. A., II Reversibility
of Ketone Reduction by SmI
Organosamarium Intermediates. Organometallics 2017, 36,
579–4583.
2 2 n
Kolmar, S. S.; Mayer, J. M. SmI (H O) Reduction of Electron
2
-Water and Formation of
Notes
4
The authors declare no competing financial interests.
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Rich Enamines by Proton-Coupled Electron Transfer. J. Am.
Chem. Soc. 2017, 139, 10687–10692.
Fuchs, J. R.; Mitchell, M. L.; Shahangi, M.; Flowers, Robert A,
II. The Effect of Lithium Bromide and Lithium Chloride on the
Reactivity of Sml2 in THF. Tetrahedron Lett. 1997, 38, 8157–
ACKNOWLEDGMENTS
RAF is grateful to the National Science Foundation
(20)
(
CHE1565741) for support of this work. ARS thanks support
from CONACYT Basic Science project number 253679. HSM
thanks financial support from DGAPA-UNAM grant No.
IN101599. JHC thanks support from DGAPA-UNAM grant No.
IG100416.
8
158.
Miller, R. S.; Sealy, J. M.; Shabangi, M.; Kuhlman, M. L.;
Fuchs, J. R.; Flowers, R. A., II Reactions of SmI with Alkyl
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(22)
2
Halides and Ketones: Inner-Sphere vs Outer-Sphere Electron
Transfer in Reactions of Sm (II) Reductants. J. Am. Chem. Soc.
2
000, 122, 7718–7722.
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