Novel Heterocumulenes: Bisiminopropadienes and Linear Ketenimines

Abstract

Flash vacuum thermolysis (FVT) of suitably substituted isoxazol-5(4H)-ones 7-9 leads to three different types of ketenimines, namely, the isoxazolonoketenimines 2, the novel bisiminopropadienes RN=C=C=C=NR (9, and the C-cyanoketenimines 14, all characterized by a combination of FVT/matrix isolation/IR spectroscopy and FVT/MS. An unusual, linear C=C=N-C backbone in ketenimines 2g and 2h is revealed by their exceptional spectroscopic properties as well as an X-ray crystal structure of 2g. and confirmed by density functional calculations (B3LYP/6-31 G*); these compounds are best described as resonance hybrids of ketenimines and isonitrile

Linear Ketenimines. Variable Structures of C,C-Dicyanoketenimines and C,C-Bis-sulfonylketenimines

“…1,2 Compound 2 has unusual properties for a ketenimine: a strong IR band at 2230 cm -1 (most ketenimines absorb at 2000-2090 cm -1 2,3 ) and 13 C resonances at 52 and 119 ppm that look more like those of a nitrile (37-77 and ca. 190 ppm are typical for the and R carbons of ketenimines, respectively 1,2 ). The X-ray structure of 2 revealed a short CdN bond (1.15 Å) and a linear CCNR moiety (∠CNR ) 179.6°).…”

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

“…Scheme 21 Bis(imino)propadienes 157 are reactive intermediates, obtainable by FVT of bis(aminomethylene)isoxazolones of the type 155. [112] Initial elimination of amine affords ketenimines 156, which are sometimes isolable. The compound 159 is particularly interesting because the X-ray structure, as well as the unusual 13 C NMR and IR data, revealed that the Ar group is collinear with the CϭCϭN moiety.…”

“…The compound 159 is particularly interesting because the X-ray structure, as well as the unusual 13 C NMR and IR data, revealed that the Ar group is collinear with the CϭCϭN moiety. [112] Further studies demonstrate that ketenimines with two electron-withdrawing substituents (X) at the carbon atom tend to have such collinear X 2 CϭCϭNϪR frameworks. [113] When either R or RЈ can be eliminated as an alkene in the bis(imines) 157, isomerization to cyanoketenimines 158 takes place.…”

“…[113] When either R or RЈ can be eliminated as an alkene in the bis(imines) 157, isomerization to cyanoketenimines 158 takes place. [112] A similar sequence of eliminations produces aryliminopropadienethiones 161 from isoxazolones 160 (Scheme 22). [114] Compounds 161 are isolable at liquid nitrogen temperatures and undergo nucleophilic addition reactions with amines.…”

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

“…20 These compounds are generally highly unstable and can only be isolated at low temperatures. The diphenyl derivative 9 was obtained by FVT of the isoxazolone precursor 8 (Scheme 4) at 800…”