Coupling and cyanating agent. Prepn: H. Giesemann, J. Prakt. Chem. 4(1), 345 (1955); by thermolysis of tetrazolopyrazine: C. Wentrup, Helv. Chim. Acta 55, 565 (1972); P. B. W. McCallum et al., Aust. J. Chem. 52, 159 (1999). Use as a condensing agent: J. P. Ferris et al., Nucleosides Nucleotides 8, 407 (1989); K. J. Luebke, P. B. Dervan, J. Am. Chem. Soc. 113, 7447 (1991); as a cyanating agent: Y. Wu et al., Org. Lett. 2, 795 (2000).