Photochemistry of 2-azido-4,6-dichloro-s-triazine: matrix isolation of a strained cyclic carbodiimide containing four nitrogen atoms in a seven-membered ring

Abstract

2-Azido-4,6-dichloro-s-triazine 1, matrix-isolated in Ar at 10 K, yields triplet nitrene 2 and the strained cyclic carbodiimide 3 upon photolysis.

References

1. M. S. Platz, Acc. Chem. Res., 1995, 28, 487.
2. G. B. Schuster and M. S. Platz, Advances in Photochemistry, Wiley, New York, 1992, vol. 17, p. 69.
3. N. P. Gritsan, T. Yuzawa and M. S. Platz, J. Am. Chem. Soc., 1997, 119, 5059.
4. R. Born, C. Burda, P. Senn and J. Wirz, J. Am. Chem. Soc., 1997, 119, 5061.
5. W. L. Karney and W. T. Borden, J. Am. Chem. Soc., 1997, 119, 1378.
6. R. A. Evans, M. W. Wong and C. Wentrup, J. Am. Chem. Soc., 1996, 118, 4009.
7. C. Wentrup, C. Thétaz, E. Tagliaferri, H. J. Lindner, B. Klitschke, H.-W. Winter and H. P. Reisenauer, Angew. Chem., Int. Ed. Engl., 1980, 19, 566.
8. M. Kuzaj, H. Lüerssen and C. Wentrup, Angew. Chem., Int. Ed. Engl., 1986, 25, 480.
9. R. Kayama, S. Hasunuma, S. Sekiguchi and K. Matsui, Bull. Chem. Soc. Jpn., 1974, 47, 2825.
10. R. Kayama, H. Shizuka, S. Sekiguchi and K. Matsui, Bull. Chem. Soc. Jpn., 1975, 48, 3309.
11. W. Sander, J. Org. Chem., 1989, 54, 333.
12. Synthesis of 1: The preparation given before (C. V. Hart, J. Am. Chem. Soc., 1928, 50, 1928) gave only mixtures of products that could not be separated by crystallization, and the melting point stated to be 85 °C is most likely incorrect. The following method was successful: To a solution of cyanuric chloride (3.000 g, 16.27 mmol) in acetone (20 ml) in a small separation funnel, a solution of NaN₃(1.000 g, 15.38 mmol) in water (10 ml) was added and the mixture shaken for 5 min. The organic phase was then separated and allowed to evaporate at room temperature. The crystals were chromatographed (silica gel, CH₂Cl₂–light petroleum = 1∶1) to give pure 1(1.13 g, 5.92 mmol, 36%) as a colorless powder, mp 59.5–61 °C; δ_H(300 MHz, CDCl₃) no signal; δ_C(75.5 MHz, CDCl₃) 171.39, 172.60; m/z(FAB) 190.99 (100, M + H⁺)ṽ_nmax/cm^–1(Ar, 10 K) 2168.9 (s), 1531.0 (vs), 1512.0 (vs), 1396.8 (s), 1295.8 (s), 1268.0 (s), 1187.6 (m), 1159.9 (m), 947.9 (w), 857.2 (m), 803.8 (w), 730.5 (vw).
13. The characterization of these final products is in progress; results will be published at a later time.
14. GAUSSIAN 98 software was used in the calculations.
15. Selected data for 2: ṽ_nmax/cm^–1(Ar, 10 K) 1467.6 (s), 1446.4 (vs), 1254.5 (s), 1246.8 (m), 852.9 (w), 848.7 (w), 787.9 (m), 580.0 (w). For 3: ṽ_nmax/cm^–1(Ar, 10 K) 1957.0 (vs), 1951.2 (vs), 1550.0 (m), 1546.2 (m), 1110.2 (m), 1050.0 (vs), 814.4. An N = C = N stretching band at ṽ= 1957.0 cm^–1 for 3 is in the range expected for such a compound. For comparison, simple open-chain N-dialkylamino substituted carbodiimides absorb at v= 2090 cm^–1(ref. 18). The decrease in frequency in 3 reflects the decrease in bond energy induced by strain. A similar trend has been observed in the case of other cyclic carbodiimides (ref. 6).
16. H. Yamada, H. Shizuka and K. Matsui, J. Org. Chem., 1975, 40, 1351.
17. There is a complete lack of absorption beyond λ= 420 nm in the spectra given by Yamada et al. However, a broad band would be expected for a triplet nitrene. In an EPA matrix, trapping of the didehydrotetrazepine by EtOH has to be considered.
18. W. S. Wadsworth, Jr. and W. D. Emmons, J. Org. Chem., 1964, 29, 2816.