The Simplest Iminophosphane HPNH and Its Photoisomerization to Aminophosphinidene H2NP

Abstract The simplest iminophosphane HPNH and aminophosphinidene H₂NP are prototype molecules bearing phosphorus-nitrogen multiple bonds; however, both species remain hitherto unobserved. Here, we report the first time synthesis and characterization of HPNH and H₂NP. Specifically, the cis and trans conformers of HPNH have been prepared in the gas phase by high-vacuum flash pyrolysis of di-tert-butylphosphanamine at ca. 950 K and subsequently isolated in solid N₂-matrices at 10 K for the characterization by matrix-isolation IR (with D- and ¹⁵N-isotope labeling) and UV-vis spectroscopy. In addition to the photo-induced conformational interconversion between trans-HPNH and cis-HPNH, their photoisomerization with H₂NP has also been observed in the cryogenic matrices. In accordance with the very recently predicted lower energy of the singlet state than the triplet state by 0.2 kcal mol–¹ for H₂NP, its experimental IR spectrum shows good agreement with the calculations for the singlet state at the CCSD(T)-F12B/VTZ-F12 level using configuration-selective vibrational configuration interaction (VCI) theory. Upon photoexciation at 395 nm, the matrix-isolated H₂NP reacts with CO and O₂ to yield H₂NPCO and H₂NPO₂ as the trapping and oxidation products, respectively.