Syntheses of Sterically Shielded Stable Carbenes of the 1,2,4-Triazole Series and their Corresponding Palladium Complexes: Efficient Catalysts for Chloroarene Hydrodechlorination

The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes 8b-d were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes 9a-d and 10a-d (including the sterically shielded derivatives 9c,d and 10a-d) were carried out via the reactions of the stable carbenes 8a-d with palladium halogenide salts in THF or toluene solution. Complexes 9c,d and 10a-d were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of 8c, 9a,b, and 10a were determined by single-crystal X-ray diffraction.Ukrainian Academy of Sciences 118Robert A. Welch Foundation F-0003Chemistr

A Base Induced Transformation Of A 1,3-Dimethyl-1,3-Di-(1-Adamantyl)Formamidinium Salt Into Beta- Methyl-(1-Adamantyl)Amino Acrylonitriles In Aliphatic Nitriles

A novel 1,3-dimethyl-1,3-di-(1-adamantyl)formamidinium perchlorate has been prepared via the Vilsmeier-Haack reaction of N-methyl-N-(1-adamantyl)formamide and N-methyl-N-(1-adamantyl) amine in a mixture of phosphorus oxychloride and benzene. The new formamidinium salt was found to undergo addition-elimination reactions when treated with sodium hydride in acetonitrile or propionitrile solution, thereby forming the corresponding beta-[methyl(1-adamantyl)amino]acrylonitriles and N-methyl-N-(1-adamantyl) amine. The H-1 and C-13 NMR spectra and the single-crystal X-ray structure of the new formamidinium salt have been determined along with those of the related compound 1,3-di-(1-adamantyl)-1-cyanoamidine and the corresponding beta-(dialkylamino)acrylonitriles.Biochemistr

Tandem Transformations Of 1,2,4-Triazol-5-Ylidenes Into 5-Amidino-1,2,4-Triazoles

The first tandem autotransformations of heteroaromatic carbenes have been found. These reactions involve cleavage of the 1-tert-butyl-3,4-diaryl-1,2,4-triazol-5-ylidenes 1a-d to form benzonitriles and the respective carbodiimides, followed by further reactions of the latter with carbenes 1a-d to afford the 3,4-diaryl-5-(1-tert-butyl-3-arylamidin- 2- yl)-1,2,4- triazoles 5a-d. The X-ray structures of the carbene 1-tert-butyl-3-phenyl-4-n-bromophenyl-1,2,4-triazol-5-ylidene (1a) and the amidinotriazole 3-phenyl-4-p-bromophenyl-5-(1-tert-butyl-3-p-bromophenylamidin-2-yl)- 1,2,4- triazole (5a) were determined. The reactions of 1a with the electrophiles diphenylcarbodiimide, acetonitrile, and diphenyldiazomethane are also described.Biochemistr

Exceptionally Efficient Catalytic Hydrodechlorination of Persistent Organic Pollutants: Application of New Sterically Shielded Palladium Carbene Complexes

A new sterically shielded carbene with branched aromatic substituents (9a) and two palladium halogenide complexes have been prepared. The single crystal X-ray structures of free carbene 9a and palladium carbene complexes 10b and 11a were determined. Very high catalytic efficiencies were evident for the sterically shielded palladium carbene complexes 10b and 11a,b when the latter complexes were employed as catalysts for hydrodechlorination of the chloroarenes p-dichlorobenzene and hexachlorobenzene. When optimized, the foregoing approach is significantly more effective than those of currently known transition metal carbene complexes. The most active catalysts were found to be the monocarbene complexes of palladium chloride and iodide, both of which feature highly branched aromatic substituents (11a,b).Ukrainian Academy of Sciences 140Robert A. Welch Foundation F-0003Chemistr

Synthesis Of Heteroaromatic 3,3 '-Bridged Biscarbenes Of The 1,2,4-Triazole Series And Their Properties

The stable 3,3'-bridged biscarbenes, 1,4- and 1,3-bis[1-alkyl-4-phenyl-1,2,4-triazol-5-yliden-3yl] benzenes (5a,b,d) and 1,3-bis[1-(1-adamantyl)-4-phenyl-1,2,4-triazol-5-yliden-3-yl] butane (5c) have been prepared. Treatment of 5b with copper (I) chloride in tetrahydrofuran/acetonitrile solution and cobalt (II) chloride in acetonitrile or acetonitrile/toluene solution afforded the biscarbene copper (I) complex 8. The reactions of 5d with diphenyldiazomethane and sulfur resulted in the novel bisthione 6 and bisazine (7) derivatives, respectively. The X-ray crystal structures of 5d, 8 were determined.Ukrainian State Fund F25.3/049Robert A. Welch Foundation F0003Biochemistr

Review: Stable Heteroaromatic Carbenes Of The Benzimidazole And 1,2,4-Triazole Series

The review is focused on new data concerning the syntheses and selected properties of stable heteroaromatic monocarbenes of the benzimidazole and 1,2,4-triazole series, biscarbenes, anionocarbenes of the 1,2,4-triazole series, and cryptocarbenes. The syntheses of the precursors to these compounds are also described. Special attention is paid to C-H insertion reactions, X-ray structural data and spectral characteristics of the carbenes and their analogues.Biochemistr