The simplest iminophosphane HPNH and its photoisomerization to aminophosphinidene H₂NP

As a heavy analogue of dinitrogen, the diatomic phosphorus mononitride (PN) was the first detected phosphorus-containing compound in the interstellar medium. Hence, small molecules derived from PN including the simplest iminophosphane HPNH and isomeric aminophosphinidene H₂NP with prototype phosphorus-nitrogen multiple bonds were proposed as candidate interstellar species possibly involving in the astrochemical network of PN. However, the existence and reactivity of HPNH and H₂NP remain elusive. Here, we report the synthesis of the cis and trans conformers HPNH through high-vacuum flash pyrolysis of di-tert-butylphosphanamine in the gas phase. In addition to the photo-induced conformational interconversion in HPNH, its photoisomerization to H₂NP in the singlet ground state has also been observed under the matrix-isolation conditions at 10 K. As a singlet phosphinidene, H₂NP is very reactive as demonstrated by its photoreactions with CO and O₂. The synthesis and characterization of the long sought-after [H2, N, P] isomers contribute to the fundamental knowledge about PN in main-group and interstellar chemistry.