Detection of the elusive cyclo−1,2-dihydrotetrazete (N4H2) in the gas phase

Nitrogen hydrides (NnHm) have attracted significant interest for their potential in developing high-energy-density materials. The synthesis of cyclic nitrogen hydrides is particularly challenging due to their inherently high strain energies. Here we report the preparation of the hitherto elusive trans- and cis-cyclo−1,2-dihydrotetrazete (2a and 2b, cyclo-N4H2) along with its open chain isomer azidamide (5a, N=N=N−NH2) by exposing low temperature (5 K) ice of ammonia (NH3) to high-energy electrons. These compounds were detected and discriminated in the gas phase during the temperature programmed desorption phase exploiting isomer selectivity soft photoionization reflectron time-of-flight mass spectrometry. The cyclo−1,2-dihydrotetrazete signifies a free gas phase species containing a tetranitrogen ring existing without recourse to high-pressure conditions or conjugative stabilization. Our approach may provide feasible strategies for designing higher-order nitrogen ring systems and for elucidating their chemical bonding and stability. The synthesis of cyclic nitrogen hydrides is particularly challenging due to their inherently high strain energies. Here the authors report the preparation of trans- and cis-cyclo 1,2-dihydrotetrazete along with its open chain isomer azidamide by exposing low temperature (5 K) ice of ammonia to high-energy electrons.