Cyanoketene and Iminopropadienones

Abstract

Cyanoketene (8) is generated in high yields on flash vacuum thermolysis (FVT) of suitably substituted Meldrum's acid derivatives (5-[(alkylamino)(methylthio or alkylamino)methylene]-2,2-dimethyl-1,3-dioxane-4,6-diones) (3e-j), and also on FVT of cyanoacetic acid derivatives 9e,f,g,j,k,m. The major reaction pathway from 3 proceeds via ketenimines 6 and (alkylimino)propadienones 7, the latter undergoing a retro-ene reaction to 8. A minor pathway is via imidoylketenes 4e,h and oxoketenimines 5e,h, which undergo retro-ene reactions to 9. All intermediates were characterized by Ar matrix FTIR and tandem mass spectrometry (collisional activation MS). Trapping of 4, 5, and 8 with nucleophiles is also reported. The preference of 1,3-X shifts over 1,5-H shifts in imidoylketenes 12 (X = SMe or NMe(2)) is corroborated by the calculated activation barriers. Neat cyanoketene is highly reactive, reacting at or below 80 K, and this is attributed to the availability of a low-lying ketene LUMO. The IR spectrum of cyanoketene (Ar, 14 K) is dominated by two absorptions at 2163 (s; C=C=O) and 2239 (w; CN) cm(-)(1) in excellent agreement with density functional (B3-LYP/6-31G) and ab initio (QCISD/6-31G) calculations.

Iminopropadienones RN=C=C=C=O and bisiminopropadienes RN=C=C=C=NR: Matrix infrared spectra and anharmonic frequency calculations

“…8,13 Route a operates at lower temperatures; hence an appreciable amount of ketenimine I is observed in the matrix IR spectrum resulting from FVT at 600…”

“…6 While the aryliminopropadienones have been the subject of extensive chemical and spectroscopic studies, 6, 7 the alkyliminopropadienones are much less well known. 8 The methyl derivative 1a is a reactive intermediate, which can only a) Authors to whom correspondence should be addressed. Electronic addresses: didier.begue@univ-pau.fr and wentrup@uq.edu.au.…”

Formation of Cumulenes, Triple-Bonded, and Related Compounds by Flash Vacuum Thermolysis of Five-Membered Heterocycles

“…[44,46] This is a useful reaction, which has allowed the preparation of cyanoketenes (for example) by FVT of appropriately substituted acylpyrazoles 63. [47,48] 1-Acyl-1,2,4-triazoles (64) react analogously, to give either ketenes by elimination or oxazoles through sigmatropic shift and N 2 loss. [49] Scheme 7…”

Cyanoketene: the microwave spectrum and structure of an unstable molecule

“…This molecule has found increasing interest during the recent years: a photo electron spectrum, published in 1981 by Bock et al [13], can be considered as the starting point and in 1985 we presented for the first time the microwave spectrum of the parent molecule 14 NB 12 C-( 12 CH)@ 12 C@ 16 O [14]. Extensive theoretical calculations about the structure, reactivity, and energetic quantities have been carried out [15][16][17]. Production of the molecule under high vacuum conditions by flash thermolysis of different precursors allowed the measurement of its heat of formation and an estimate of the ionization energy by mass spectroscopic techniques [18], the determination of the IR-bands in an Ar matrix at 12 K [19], and to find the pathways of its formation also by trapping the different species in an Ar matrix at 14 K [16].…”

“…Extensive theoretical calculations about the structure, reactivity, and energetic quantities have been carried out [15][16][17]. Production of the molecule under high vacuum conditions by flash thermolysis of different precursors allowed the measurement of its heat of formation and an estimate of the ionization energy by mass spectroscopic techniques [18], the determination of the IR-bands in an Ar matrix at 12 K [19], and to find the pathways of its formation also by trapping the different species in an Ar matrix at 14 K [16]. The latter paper contradicts strongly a finding of Efremov et al [20] who claim that cyanoketene can be isolated as a liquid, boiling at )34°C, and who published an NMR spectrum.…”