Spectroscopic Evidence for Aminomethylene (H−C̈−NH₂)—The Simplest Amino Carbene

Abstract

Although N-heterocyclic carbenes have been well-studied, the simplest aminocarbene, aminomethylene H-C̈-NH , has not been spectroscopically identified to date. Herein we report the gas-phase preparation of aminomethylene by high-vacuum flash pyrolysis of cyclopropylamine and subsequent trapping of the pyrolysate in an inert argon matrix at 12 K. Aminomethylene was characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster computations. After UV irradiation of the matrix aminomethylene rearranges to its isomer methanimine (formaldimine) H C=NH. Based on our experimental results and computations aminomethylene has a singlet ground state with a reaction barrier of almost 46 kcal mol to methanimine so that H-tunneling is excluded.

Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C̈–OH)

“…[1,2] H -tunnelling is completely suppressed in diheteroatom-substituted hydroxycarbenes dihydroxycarbene36 ( 19 ), methoxyhydroxycarbene36 ( 20 ), and aminohydroxycarbene ( 21 ) 4. Even in the simplest aminocarbene, aminomethylene, [1,2] H -tunnelling was not observed due to the strong π-donation of the nitrogen atom 37…”

Carbenes and Nitrenes: Recent Developments in Fundamental Chemistry

“…[35] Tu nneling is not observed or expected in dihydroxy-and aminocarbenes,b ecause these compounds are more highly stabilized by the neighboring lone pairs of electrons. [33,36] Hence,t he isomerization barriers will be higher and also wider.…”

“…Aminocarbene H−C−NH 2 has been prepared by FVP of aminocyclopropane and characterized by both IR and UV spectroscopy as a ground‐state singlet . It is stabilized by the lone pair of electrons on the nitrogen atom in a manner analogous to that in NHCs and the hydroxycarbenes described above [Eq.…”

Preparation and characterization of the enol of acetamide: 1-aminoethenol, a high-energy prebiotic molecule

“…4 Another example is the hydrogenated form of HCN (a molecule abundant in space), namely methanimine (H 2 C]NH) and its tautomer aminocarbene (H-€ C-NH 2 ), whose structure has only very recently been revealed. 5 That is, the higher-energy tautomers of biologically relevant building blocks are likely to play a key role also for the emergence of the molecules relevant to life, but many of these have not been identied and fully characterized. [6][7][8][9] As complex organic molecules including amino acids, 10 sugars, 11 purine bases, 12,13 short peptides, 14 have been identied in meteorites, prebiotic organic reactions must take place in the interstellar medium through the activation of thermodynamically highly stable small molecules such as CO, CO 2 , H 2 O, CH 4 , HCN but also formaldehyde, simple alcohols, and a variety of carboxylic acids and, particularly relevant to the present study, their amides.…”