Gas‐Phase Generation and Characterization of Nitrileimine, HCNNH: A new, stable isomer of diazomethane

Abstract

A new isomer of diazomethane 1, the nitrile imine, HCNNH (2) is reported to be a stable molecule in the gas phase. Upon neutralizing the a -distonic HCNNH" cation in a beam experiment, this long-time predicted ylide can be generated. The experiments are supported by theoretical calculations (DFT/HF hybride method) on the neutral and cationic diazomethane 1, nitrile imine 2, and N-isocyano amine 3 as well as the transition states for their interconversion.In a recent study, we have been able to demonstrate that hydrogen cyanide Nmethylide HCNCH,, the isoelectronic analogue of fulmic acid HCNO, is a stable molecule in the gas phase [l]. The characterization of this species by mass-spectrometric experiments succeeded only shortly after Maier et al. [2] had reported its matrix isolation. One member of the intriguing family of HCNR ylides (R = 0, NH, CH,) that still lacks compelling evidence for its existence is the nitrile imine molecule HCNNH 2 (hydrogen cyanide-N -imide). . HCNNH (2) represents the parent species of the nitril imines RCNNR', molecules that, until recently, were believed to be reactive intermediates. In the last decade, however, a large number of substituted nitrile imines have been characterized and shown to be stable species, even at room temperature'). That the unsubstituted molecule 2 should be a stable, accessible species, at least in the gas phase or in matrices, has been proposed in a number of theoretical studies dealing with the stabilities of the various possible [H,,C,N,]

A theoretical study on CH2N2 isomers: structure and energetics

“…These can be considered as conservative estimates, which also account for the approximations made and for neglecting higher-order correlation effects. From Tables 1, 2, 3, 4 and 5, it is evident that all isomers considered have been previously studied at different levels of theory [11,[41][42][43][44][45][46][47][48], but we report the first systematic investigation of their molecular structure. As in most cases the method and/or the basis set used are inferior to ours, a detailed comparison of these results to ours is not too meaningful.…”

“…Isocyanamide is subject to fast rearrangement to cyanamide, but despite its unstable nature, valence ionization spectra [8] and rotationinversion spectra in the millimeter-wave region have been observed [9]. Because of its character as reactive intermediate, there is very little direct experimental evidence on the structure of nitrilimine [10,11], the first matrix-spectroscopic identification of HCNNH being reported only 15 years ago [12].…”

X‐ray Structure of the Isodiazomethane Complex Cr(CO)5C≡N‐NH2and [3+2]‐Cycloadditions to the Metallo‐Nitrile‐Imine [Cr(CO)5C≡N‐NH]–[1]

“…The stereochemical equivalent on the part of the isodiazomethane ligand is a C1–N1 distance of only 1.133(4) Å, a typical CN triple bond length as found, e.g., in Cr(CO) 5 N≡C–NEt 2 [1.139(5) Å] 12. Corresponding C≡N bonds in other N‐isocyanide metal complexes ([RuCl 2 ( η ‐C 6 H 2 Me 4 –1,2,4,5)C≡N–NPr i 2 ] ( 2 ): 1.159(9) Å 13, Cr(CO) 5 C≡N–NPPh 3 ( 3 ): 1.151(4) Å 14) and particularly those more recently calculated for the free isodiazomethane (1.173 15, 1.187 16) tend to be (much) longer. Note that the high CN bond order in 1a is also reflected in the IR spectrum with its exceedingly high lying ν (CN) band (Experimental Section).…”

Product Class 2: Nitrile Imines

“…[33] This indicates that the cycloadducts 36 are produced regioselectively in the reaction mixture, followed by aromatization through elimination of the appropriate benzoic acid. Scheme 11 Regioselective Nitrile Imine Cycloadditions to a Captodative Alkene [33] If the tosylhydrazones 38 are treated with lead(IV) acetate in acetonitrile at -30 8C nitrile imine intermediates are generated; these immediately undergo intramolecular cycloaddition with alkyne units already present in the substrates to afford 2,4-dihydro [1]benzopyrano [4,3-c]pyrazoles 39 albeit in modest yields (Scheme 12). [42] Scheme 12 Intramolecular Cyclizations of Nitrile Imines Generated by Lead(IV) Acetate Oxidation of Tosylhydrazones [42] N NHTs [42] Pb(OAc) 4 (1.5 mol equiv) in dry MeCN (20 mL) was added slowly with stirring to the hydrazone 38 in dry MeCN (70 mL) at -5 8C.…”