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ChemComm
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DOI: 10.1039/C5CC03518J
COMMUNICATION
ChemComm
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Theoretical evidence for a third structural type, the carbenic nitrile
imines, for compounds such as H2N−CNN−NH2 and F−CNN−F has also
been advanced, see Refs. 4j and 6a. For experimental evidence, see:
E. G. Baskir, D. N. Platonov, Y. V. Tomilov and O. M. Nefedov,
Mendeleev Commun., 2014, 24, 197–200.
For the concept of bond-shift isomers, see: (a) R. Herges, Angew.
Chem., Int. Ed. Engl., 1994, 33, 255 (section 4.4.1); (b) A. Maltsev,
T. Bally, M.-L. Tsao, M. S. Platz, A. Kuhn, M. Vosswinkel and
C. Wentrup, J. Am. Chem. Soc., 2004, 126, 237–249.
structural nature of 1,3-dipolar species. Further studies are
underway in order to expand our understanding of the factors that
allow the observation of bond-shift isomers of nitrile imines.
This work was supported by the Portuguese “Fundação para a
Ciência e a Tecnologia
” (FCT), FEDER, via project PTDC/QUI-
QUI/118078/2010, FCOMP-01-0124-FEDER-021082, cofunded by
QREN-COMPETE-UE, the University of Queensland, and the
Mésocentre de Calcul Intensif Aquitain of the Université de
Bordeaux and at the Université de Pau et de Pays de l’Adour.
C. M. N. and I. R. acknowledge FCT for Postdoctoral Grant No.
SFRH/BPD/86021/2012 and Investigador FCT grant, respectively.
The Coimbra Chemistry Centre is also supported by the FCT through
the project Pest-OE/QUI/UI0313/2014.
10 In the absence of intermolecular interactions, the 2H-tautomer is
usually the most stable form in the gas phase. See: (a) Ref. 4i; (b)
Ref. 7a; (c) S. C. S. Bugalho, A. C. Serra, L. Lapinski, M. L. S. Cristiano
and R. Fausto, Phys. Chem. Chem. Phys., 2002,
11 (a) The UV light at 230 nm corresponds to the maximum UV
absorption of 5-phenyltetrazole (UV/vis (EtOH) λmax = 229.4 nm).
4, 1725–1731.
1
See: B. Elpern and F. Nachod, J. Am. Chem. Soc., 1950, 72, 3379–
3382; (b) The irradiations in this work were done with
monochromatic light generated in
parametric oscillator, see ESI for details.
a
laser-pumped optical
12 The progress of the photochemistry of 1’’ (Figure S3) reveals: (i) in
the initial stage of irradiation, from to (total time),
photoproducts 2A and 2P are formed simultaneously and virtually
exclusively (only traces of start to appear); (ii) for more prolonged
irradiations, after 30–40 s (total time), photoproducts 2A and 2P
stop increasing, whereas is continually formed, simultaneously
Notes and references
0
5 s
1
(a) 1,3-Dipolar Cycloaddition Chemistry, ed. A. Padwa, Wiley, New
York, 1984; (b) Synthetic Applications of 1,3-Dipolar Cycloaddition
Chemistry Toward Heterocycles and Natural Produts, eds. A. Padwa
and W. A. Pearson, Wiley, New York, 2002; (c) A. P. Antonchick,
C. Gerding-Reimers, M. Catarinella, M. Schürmann, H. Preut,
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with other photoproducts; (iii) for irradiation times on the order of a
few minutes, the photoproducts 2A and 2P start to decrease and
disappear (not shown in Figure S3). These results support the
S. Ziegler, D. Rauh and H. Waldmann, Nature Chem., 2010, 2, 735–
740; (d) R. K. V. Lim and Q. Lin, Acc. Chem. Res., 2011, 44, 828–839;
(e) Z. Yu, T. Y. Ohulchanskyy, P. An, P. N. Prasad and Q. Lin, J. Am.
Chem. Soc., 2013, 135, 16766–16769; (f) M. A. Tasdelen and Y. Yagci,
Angew. Chem., Int. Ed., 2013, 52, 5930–5938.
assignment of 2A and 2P as primary photoproducts of 1’’
.
13 After the irradiation of 1’’ at 230 nm, subsequent irradiations were
performed at longer wavelengths under conditions where 1’’ is
unreactive. Starting at 440 nm and gradually decreasing the
2
3
(a) R. Huisgen, Angew. Chem., Int. Ed. Engl., 1963,
(b) R. Huisgen, Angew. Chem., Int. Ed. Engl., 1963, , 633–645.
(a) P. C. Hiberty and G. Ohanessian, J. Am. Chem. Soc., 1982, 104
2, 565–632;
2
wavelength of the tunable UV-light revealed that at ∼400 nm the
,
bands of photoproducts of 1’’ start to be affected. In the range from
400–370 nm, 2A and 2P were selectively consumed as discussed.
14 Subsequent irradiation at 337 nm leads to the photoisomerization of
66–70; (b) S. D. Kahn, W. J. Hehre and J. A. Pople, J. Am. Chem. Soc.,
1987, 109, 1871–1873; (c) D. H. Ess and K. N. Houk, J. Am. Chem.
Soc., 2008, 130, 10187–10198; (d) B. Braida, C. Walter, B. Engels,
and P. C. Hiberty, J. Am. Chem. Soc., 2010, 132, 7631–7637.
1H-diazirine 3 to phenylcarbodiimide 4 (Figure S9 and Table S3). This
constitutes strong proof that the photoisomerization of nitrile
4
(a) P. Caramella and K. N. Houk, J. Am. Chem. Soc., 1976, 98, 6397–
6399; (b) A. S. Shawali, Chem. Rev., 1993, 93, 2731–2777;
imines to carbodiimides occurs via intermediacy of 1H-diazirines. As
proposed previously, the rearrangement of 3 to 4 proceeds by ring
opening (via the NN bond cleavage) followed by a 1,2-phenyl shift.
See refs. 4g and 4i, and also: R. N. Veedu, D. Kvaskoff and
C. Wentrup, Aust. J. Chem., 2014, 67, 457–468.
(c) G. Bertrand and C. Wentrup, Angew. Chem., Int. Ed., 1994, 33
,
527–545; (d) W. Song, Y. Wang, J. Qu and Q. Lin, J. Am. Chem. Soc.,
2008, 130, 9654–9655; (e) S.-L. Zheng, Y. Wang, Z. Yu, Q. Lin and
P. Coppens, J. Am. Chem. Soc., 2009, 131, 18036–18037; (f) Y. Wang,
15 Accounting for the zero-point vibrational energy results in a slight
stabilization (1-2 kJ mol−1) of 2P with respect to 2A, see Table S4.
16 It has been shown previously that for molecules having the same
calculated barrier for the vacuum, and differing only by the size of
substituent, those having a larger substituent, if placed in a
cryogenic matrix, require much higher temperatures of annealing to
overcome the barrier. See: I. D. Reva, S. G. Stepanian, L. Adamowicz
and R. Fausto, Chem. Phys. Lett., 2003, 374, 631–638.
W. Song, W. J. Hu and Q. Lin, Angew. Chem., Int. Ed. Engl., 2009, 48
,
5330–5333; (g) D. Bégué, G. G. Qiao and C. Wentrup, J. Am. Chem.
Soc., 2012, 134, 5339–5350; (h) G. Wang, X. Liu, T. Huang, Y. Kuang,
L. Lin and X. Feng, Org. Lett., 2013, 15, 76–79; (i) C. M. Nunes,
C. Araujo-Andrade, R. Fausto and I. Reva, J. Org. Chem., 2014, 79
3641–3646; (j) D. Bégué and C. Wentrup, J. Org. Chem., 2014, 79
1418–1426.
,
,
5
(a) M. W. Wong and C. Wentrup, J. Am. Chem. Soc., 1993, 115
,
17 DePinto and McMahon needed to anneal to 80-90 K to equilibrate
two conformational isomers of the triplet carbene PhCCCPh,
presumably separated by an extremely small energy barrier.
7743–7746; (b) S. Kawauchi, A. Tachibana, M. Mori, Y. Shibusa and
T. Yamabe, J. Mol. Struct. THEOCHEM, 1994, 310 255–267;
(c) G. Maier, J. Eckwert, A. Bothur, H.-P. Reisenauer and C. Schmidt,
Liebigs Ann. Chem., 1996, 1041–1053; (d) C. Puzzarini and A. Gambi,
Theor. Chem. Acc., 2012, 131, 1135.
,
(J. T. DePinto and R. J. McMahon, J. Am. Chem. Soc., 1993, 115
,
12573–-12574). Similar effects were observed for other carbenes
(K.-i. Yoshida, E. Iiba, Y. Nozaki, K. Hirai, Y. Takahashi, H. Tomioka,
C.-T. Lin and P. Gaspar, Bull. Chem. Soc. Jpn., 2004, 77, 1509–1522).
18 G. Herzberg, Electronic spectra and electronic structure of
polyatomic molecules, Van Nostrand, New York, 1966.
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The subject of the electronic structure of parent nitrile imine is still
controversial: (a) R. C. Mawhinney, H. M. Muchall, G. H. Peslherbe,
Chem. Commun., 2004, 1862–1863; (b) F. Cargnoni, G. Molteni,
D. L. Cooper, M. Raimondi and A. Ponti, Chem. Commun., 2006,
1030–1032.
(a) M. Pagacz-Kostrzewa, M. Mucha, M. Weselski and M.
Wierzejewska, J. Photochem. Photobiol. A, Chem., 2013, 251, 118–
127; (b) M. Pagacz-Kostrzewa, J. Krupa and M. Wierzejewska, J. Phys.
Chem. A, 2014, 118, 2072–2082; (c) D. Bégué, A. Dargelos,
H. Berstermann, K. Netsch, P. Bednarek and C. Wentrup, J. Org.
Chem., 2014, 79, 1247–1253.
19 N. Heineking, J.-U. Grabow and W. Stahl, Mol. Phys., 1994, 81, 1177–
1185.
20 (a) M. P. Bernstein, S. A. Sandford and L. J. Allamandola, Astrophys.
J., 1997, 476, 932–942; (b) C. M. Nunes, I. Reva, T. M. V. D. Pinho e
Melo and R. Fausto, J. Org. Chem., 2012, 77, 8723–8732; (c) C. M.
Nunes, I. Reva, T. M. V. D. Pinho e Melo, R. Fausto, T. Šolomek and
T. Bally, J. Am. Chem. Soc., 2011, 133, 18911–18923.
4 | Chem. Commun., 2015, 00, 1-4
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