Journal of the American Chemical Society
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29) Zuev, P.; Sheridan, R. J. Am. Chem. Soc. 2001, 123, 12434.
ACKNOWLEDGMENT
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(30) Platz, M. S.; Senthilnathan, V. P.; Wright, B. B.; McCurdy, C. W.
J. Am. Chem. Soc. 1982, 104, 6494.
(31) Some interesting examples of isomerizations facing high-energy
barriers, and occurring in low-temperature matrices via quantum
This work was supported by the Portuguese “Fundação para
a Ciência e a Tecnologia” (FCT). The Coimbra Chemistry
Centre is supported by the FCT through the project
UID/QUI/0313/2013, co-funded by COMPETE. C. M. N. and
I. R. acknowledge the FCT for Postdoctoral Grant No.
SFRH/BPD/86021/2012 and Investigador FCT Grant, respec-
tively. R.J.M gratefully acknowledges the U.S. National Sci-
ence Foundation for support of this project (CHE-1362264)
and the EPR spectrometer (CHE-0741901).
31a-f
tunneling, are also known in the singlet carbene chemistry. To the
best of our knowledge, no examples of tunneling reactions are
known in the nitrene chemistry. (a) Henkel, S.; Sander, W. Angew.
Chem. Int. Ed. 2015, 54, 4603. (b) Ley, D.; Gerbig, D.; Schreiner, P.
Chem. Sci. 2013, 4, 677. (c) Henkel, S.; Huynh, Y.; Neuhaus, P.; Win-
kler, M.; Sander, W. J. Am. Chem. Soc. 2012, 134, 13204. (d) Schreiner,
P. R.; Reisenauer, H. P.; Ley, D.; Gerbig, D.; Wu, C.-H.; Allen, W. D.
Science 2011, 332, 1300. (e) Schreiner, P. R.; Reisenauer, H. P.; Pick-
ard, F. C.; Simmonett, A. C.; Allen, W. D.; Mátyus, E.; Császár, A. G.
Nature 2008, 453, 906. (f) Zuev, P. S.; Sheridan, R. S.; Albu, T. V;
Truhlar, D. G.; Hrovat, D. A.; Borden, W. T. Science 2003, 299, 867.
(32) Bucher, G. Eur. J. Org. Chem. 2001, 2447–2462.
(33) Tomioka, H.; Matsushita, T.; Murata, S.; Koseki, S. Liebigs Ann.
1996, 1971.
(34) Morawietz, J.; Sander, W. Liebigs Ann. 1996, 2029.
(35) Murata, S.; Sugawara, T.; Iwamura, H. J. Am. Chem. Soc. 1985,
107, 6317.
(36) Other indications of H-abstractions in phenylnitrenes were
obtained by the formation of insertion products in photochemistry
of phenylazide derivatives. However, the mechanism is not com-
pletely clear, especially which is the spin state of the nitrene involved
in the postulated H-abstraction. See: Murata, S.; Tsubone, Y.; Kawai,
R.; Eguchi, D.; Tomioka, H. J. Phys. Org. Chem. 2005, 18, 9.
(37) It is also known that irradiation of the isolated triplet nitrene
may induce H-abstraction reaction.
H-abstraction occurs via excited singlet or hot (triplet) ground-state.
(38) The irradiation wavelength of 308 nm was chosen to match the
first absorption maximum of 5, and also to avoid the absorption of
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REFERENCES
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1) Nitrenes and Nitrenium Ions; Falvey, D. E., Gudmundsdóttir, A.
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5) Platz, M.S. Nitrenes. In Reactive Intermediate Chemistry; Moss, R.
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nitz, C. R.; Platz, M. S. Acc. Chem. Res. 2000, 33, 765.
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This supports the idea that
(
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8) Liu, L.; Yan, M. Acc. Chem. Res. 2010, 43, 1434.
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3
photoproduct 6a with a maximum at 326 nm. The UV-Vis spectrum
A. D. J. Phys. Org. Chem. 2010, 23, 370.
of matrix-isolated 5 is given in Fig. S12. The UV-Vis spectrum of
photoproduct 6a is discussed in the text and given in Fig. 2.
3
(
(
10) Carra, C.; Bally, T.; Albini, A. J. Am. Chem. Soc. 2005, 127, 5552.
11) Tomioka, H. Triplet Carbenes. In Reactive Intermediate Chemis-
(39) The experimental absorptions at 1298 [ν(C–N)] and 747 [γ(CH)]
–
1
3
try; Moss, R. A.; Platz, M. S.; Jones, M. J., Eds.; Jonh Wiley and Sons,
004; pp. 375–462.
cm of the triplet 2-formyl phenylnitrene 6a correlate well with
−
1
2
similar bands observed at 1287 [ν(C–N)] and 746 [γ(CH)] cm for the
simplest triplet phenylnitrene.
39a-b
(
(
(
12) Tomioka, H. Bull. Chem. Soc. Jpn. 1998, 71, 1501.
13) Platz, M. S. Acc. Chem. Res. 1995, 28, 487.
14) Morawietz, J.; Sander, W.; Träubel, M. J. Org. Chem. 1995, 60,
Note that ν(C–N) mode is coupled
with the ν(C–C)ring and δ(CH) modes. (a) Kim, S.-J.; Hamilton, T.
P.; Schaefer III, H. F. J. Am. Chem. Soc. 1992, 114, 5349. (b) Hayes, J.
C.; Sheridan, R. S. J. Am. Chem. Soc. 1990, 112, 5879.
6368.
(15) Biewer, M. C.; Platz, M. S.; Roth, M.; Wirz, J. J. Am. Chem. Soc.
(
40) For the simplest triplet phenylnitrene, the strong band at 308
nm is assigned to the n → n and also to the n → π* + π → n tran-
sitions. A weak band at 370 nm and a weak feature that extends to
00 nm were also observed in the UV-spectrum of simplest triplet
1
(
(
(
991, 113, 8069.
z
y
x
x
16) Leyva, E.; Munoz, D.; Platz, M. S. J. Org. Chem. 1989, 54, 5938.
17) McMahon, R. J.; Chapman, O. L. J. Am. Chem. Soc. 1987, 109, 683.
18) Leyva, E.; Young, M. J. T.; Platz, M. S. J. Am. Chem. Soc. 1986,
40a
5
40b
phenylnitrene. In our experiment, the absorption of imino ketene
a in this region precludes the identification of any absorption due
1
08, 8307.
7
(19) Platz, M. S. J. Am. Chem. Soc. 1980, 102, 1192.
3
to triplet nitrene 6a. (a) Gritsan, N. P.; Zhu, Z.; Hadad, C. M.; Platz,
M. S. J. Am. Chem. Soc. 1999, 121, 1202. (b) Leyva, E.; Platz, M. S.;
Persy, G.; Wirz, J. J. Am. Chem. Soc. 1986, 108, 3783.
(
(
1
(
(
20) Platz, M. S.; Burns, J. J. Am. Chem. Soc. 1979, 101, 4425.
21) Kemnitz, C. R.; Karney, W. L.; Borden, W. T. J. Am. Chem. Soc.
998, 120, 3499.
(
41) Dunkin, I. R.; Lynch, M. A.; Withnall, R.; Boulton, A. J.; Hender-
son, N. J. Chem. Soc. Chem. Comm. 1989, 1777.
42) When imino ketene 7a (this work) is compared with the methyl
22) The hydrogen atom abstraction reaction of parent triplet nitrene
NH) with methane to yield two radicals is endothermic (−5.6 kcal
(
−1
mol ), whereas the corresponding reaction of methylene (CH
2
) is
41
imino ketene analogue (literature) , it should be noted that some
differences in the IR and UV spectra arise because of structural
changes: the intramolecular NH···C interaction is removed upon
methyl substitution at the N atom.
−1
exothermic (+7.7 kcal mol ). See: Lias, S. G.; Bartmess, J. E.; Lieb-
man, J. F.; Holmes, J. L.; Levin, R. D.; Mallard, W. G. J. Phys. Chem.
Ref. Data, 1988, 17, Suppl. 1.
(
(
23) Wentrup, C. Top. Curr. Chem. 1976, 62, 173.
24) Travers, M. J.; Cowles, D. C.; Clifford, E. P.; Ellison, G. B. J. Am.
(
(
(
43) See Supporting Information for the details of this estimation.
44) Fisher, J. J.; Michl, J. J. Am. Chem. Soc. 1987, 109, 583.
45) Ley, D.; Gerbig, D.; Schreiner, P. R. Org. Biomol. Chem. 2012, 10,
Chem. Soc. 1992, 114, 8699.
(25) Admasu, A.; Gudmundsdóttir, A. D.; Platz, M. S. J. Phys. Chem.
A 1997, 101, 3832.
3
781.
3
3
(46) The scan connecting 3 to 4 on the triplet manifold shows a
(
(
26) Baer, T. A.; Gutsche, C. D. J. Am. Chem. Soc. 1971, 93, 5180.
27) Another important point is the difference in the electronic
−1
3
−1
barrier of ~27 kcal mol but 4 is ~8 kcal mol higher in energy than
3
3
, making the tunneling virtually impossible (Fig. S13). This can
3
nature between the lowest singlet state of nitrenes and carbenes.
Usually, singlet nitrenes are open-shell akin to biradicals, but singlet
carbenes are closed-shell displaying much stronger Lewis acidity.
explain why triplet 2-methyl phenylnitrene 3 does not rearrange to
the corresponding imine 4 up to 80 K in Xe matrix (Scheme 1).
(
28) Henkel, S.; Ertelt, M.; Sander, W. Chem. Eur. J. 2014, 20, 7585.
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