5942
R. A. Moss et al. / Tetrahedron Letters 51 (2010) 5940–5942
Table 1
Acknowledgments
D
GS-T computed for some arylhalocarbenes
ab
Carbene
D
GS-T
D
GS-T (Ref. 4)b,c
The authors are grateful to the National Science Foundation and
to the Petroleum Research Fund for financial support.
PhCF
PhCCl
PhCBr
p-O2NPhCF
p-O2NPhCCl
p-O2NPhCBr
ꢁ13.71
ꢁ5.18
ꢁ4.29
ꢁ9.22
ꢁ0.89
ꢁ0.011d
0.49e
ꢁ9.56
ꢁ6.69
ꢁ9.56
ꢁ2.10
ꢁ1.29
Supplementary data
Supplementary data associated with this article can be found, in
a
In kcal/mol. Calculated at the R(U)B3LYP/6-311+G(d) level of
theory; see the Supplementary data for details.
b
A negative sign denotes a singlet ground state.
Calculated at the R(U)B3LYP/6-311G(d) level. Converted to kcal/
References and notes
c
mol (ꢂ0.239) from kJ/mol in Ref. 4.
1. For an excellent recent review, see (a) Kable, S. H.; Reid, S. A.; Sears, T. J. Int. Rev.
Phys. Chem. 2009, 28, 435; (b) Wren, S. W.; Vogelhuber, K. M.; Ervin, K. M.;
Lineberger, W. C. Phys. Chem. Chem. Phys. 2009, 11, 4745.
d
All electrons.
e
Effective core potential: R(U)B3LYP/6-311+G(d)/LAN2DZ(pd); cf.,
Supplementary data for details.
2. Jones, M., Jr.; Moss, R. A. In Reactive Intermediate Chemistry; Moss, R. A., Platz, M.
S., , Jones, M., Jr., Eds.; Wiley: Hoboken, N.J., 2004; pp 273–328.
3. Moss, R. A.; Turro, N. J. In Kinetics and Spectroscopy of Carbenes and Biradicals;
Platz, M. S., Ed.; Plenum Press: New York, 1990; pp 213–238.
4. Makihara, T.; Nojima, T.; Ishiguro, K.; Sawaki, Y. Tetrahedron Lett. 2003, 44, 865.
5. Gaspar, P. P.; Hammond, G. S. In Carbene Chemistry; Kirmse, W., Ed.; Academic
Press: New York, 1964; pp 235–274.
6. Carbenes; Jones, M., Jr., Moss, R. A., Eds.; Wiley: New York, 1973; Vol. I.
7. Moss, R. A.; Wang, L.; Weintraub, E.; Krogh-Jespersen, K. J. Phys. Chem. A 2008,
112, 4651.
8. Conditions: 350 nm lamps, Pyrex tubes, nitrogen atmosphere, 25 °C.
9. Terpinski, J.; Denney, D. Z.; Beveridge, R.; Cox, D. P.; Moss, R. A. Magn. Reson.
Chem. 1987, 25, 923. In the present instance, diazirines 2-F and 2-Br were
prepared by nitration of the parent phenylhalodiazirine; see Ref. 7 for the
procedure as developed for diazirine 2-Cl.
0.006
316
100 ns
1600 ns
0.005
0.004
0.003
0.002
0.001
0.000
10. (a) Ruggli, P.; Lang, F. Helv. Chim. Acta 1936, 19, 996; (b) Pfeiffer, P.; Kramer, E.
Chem. Ber. 1914, 46, 3655.
348
324
316
11. (a) Nelsen, S. F.; Bartlett, P. D. J. Am. Chem. Soc. 1966, 88, 137–143; (b) Skinner,
K. J.; Hochster, H. S.; McBride, J. M. J. Am. Chem. Soc. 1974, 96, 4301.
12. Neuman, R. C., Jr.; Alhadeff, E. S. J. Org. Chem. 1970, 35, 3401.
13. For recent reviews of triplet carbenes see: (a) Hirai, K.; Itoh, T.; Tomioka, H.
Chem. Rev. 2009, 109, 3275; (b) Tomioka, H. In Reactive Intermediate Chemistry;
Moss, R. A., Platz, M. S., Jones, M., Jr., Eds.; Wiley: Hoboken, N.J., 2004; pp 375–
461.
14. Smith, L. I.; Howard, K. L. Org. Syn. 1944, 24, 53.
15. Li, Y.; Huang, J.-S.; Zhou, Z.-Y.; Che, C.-M.; You, X.-Z. J. Am. Chem. Soc. 2002, 124,
13185.
300
350
400
450
500
λ/nm
16. Savino, T. G.; Soundararajan, N.; Platz, M. S. J. Phys. Chem. 1986, 90, 919.
17. (a) Buckles, R. E.; Hausman, E. A.; Wheeler, N. G. J. Am. Chem. Soc. 1950, 72,
2494; (b) Pestovsky, O.; Shuff, A.; Bakac, A. Organometallics 2006, 25,
2894.
18. A low yield of bibenzyl is formed in the reaction of diphenylcarbene and
toluene. For example, Ph2C reacts at 26 °C with a 1:1 mixture of toluene and
toluene-d8 to give 20% of C–H ‘insertion’, 21% of Ph2CH radical dimer, 8% of
bibenzyl, 11% of benzophenone azine, 7% of carbene dimer, and 5% of
benzophenone.16
Figure 1. LFP of diazirine 2-Cl at 351 nm in 1:1 cumene/pentane solution. UV
transient absorptions are shown at 100 ns (black) and 1600 ns (red) after the laser
flash; see text for discussion.
and for a similar abstraction–recombination mechanism for the
reaction of triplet PNPBC with toluene.
19. Graham, W. H. J. Am. Chem. Soc. 1965, 87, 4396.
Finally, we examined the laser flash photolysis (LFP) of diazirine
2-Cl in a 1:1 cumene/pentane solution; results are illustrated in
Figure 1. At 100 ns after the 351 nm laser flash, the UV spectrum
20. Doyle, R. A.; Taunton, J.; Oon, S.-M.; Liu, M. T. H.; Soundararajan, N.; Platz, M. S.;
Jackson, J. E. Tetrahedron Lett. 1988, 9, 5863.
21. For PhCCl, our value of
D
GS-T (ꢁ5.18 kcal/mol) compares with ꢁ4.59 kcal/mol22
*
(B3LYP/G-31G ). A very high level single point calculation, (QCISD(T)) with
double zeta basis sets, including polarization and diffuse function, gave
ꢁ7.84 kcal/mol.23 We found similar increases in S-T gaps for the nitro analogs,
but cannot be certain of their accuracy due to large spin contamination
(S2 >2.6) in the triplet state calculations.
is dominated by the
p ? p absorbance of singlet PNPCC at
316 nm.7 After 1600 ns, the carbene has substantially decayed,
and other (weak) absorbances can be seen at, for example, 324
and 348 nm. We suggest that the 324 nm absorbance represents
the cumyl radical (12 in Scheme 1), which is reported at 322 nm
in cyclohexane or isooctane.24 The signal at 348 nm is tentatively
assigned to the p-nitrophenylchloromethyl radical (11 in
Scheme 1). This species absorbs at 360 nm in 3 M aqueous isopro-
pyl alcohol,25 but is calculated to absorb at 345 nm in vacuo.26
In conclusion, reaction of PNPCC (1-Cl) with cumene and of
PNPBC (1-Br) with toluene afford C–H abstraction–recombination
products consistent with the incursion of triplet halocarbenes. This
scenario is supported by computational studies and LFP experi-
ments, and dovetails with Sawaki’s findings for the reactions of
PNPCC and PNPBC with oxygen.4
22. Mendez, F.; Garcia-Garibay, M. A. J. Org. Chem. 1999, 65, 7061.
23. Pliego, J. R., Jr.; De Almeida, W. B.; Celebi, S.; Zhu, Z.; Platz, M. S. J. Phys. Chem. A
1999, 103, 7481.
24. (a) Chatgilialoglu, C.; Scaiano, J. C.; Ingold, K. U. Organometallics 1982, 1, 466;
(b) Ikeda, H.; Hoshi, Y.; Namai, H.; Tanaka, F.; Goodman, J. L.; Mizuno, K. Chem.
Eur. J. 2007, 13, 9207.
25. Bays, J. P.; Blumer, S. T.; Baral-Tosh, S.; Behar, D.; Neta, P. J. Am. Chem. Soc. 1983,
105, 320.
26. UB3LYP/6-311+G(d)//UPBEPBE/6-311+G(d). In water (CPCM) the calculated
absorption of 11 is at 363.9 nm, in very good agreement with experiment
(360 nm).