Functionalization of cyanoimidazoles, synthesis of poly(cyanoimidazolyl)amines and their cyanamide analogues towards carbon nitride synthesis.

Abstract

Ethyl 4(5)-cyano-5(4)-imidazolecarboxylate and ethyl 2-bromo-4(5)-cyano-5(4)-imidazolecarboxylate were prepared by monoethanolysis of 4,5-dicyanoimidazole and 2-bromo-4,5-dicyanoimidazole, respectively. These derivatives were methylated at the 1-position using dimethyl sulfate following deprotonation by sodium hydride or triethylamine. The resulting regioisomers were separated by column chromatography or by fractional crystallization. The regioassignments were made by comparison of the chemical shifts of the 1-methyl groups or by nuclear Overhauser effect studies on monocyano substituted 1-methylimidazoles obtained by the hydrolysis of the esters to the acids, using tetraethylammonium hydroxide, followed by thermal decarboxylation. Nucleophilic aromatic substitution (NAS) reactions were explored on ethyl 2-bromo-4-cyano-1-methyl-5-imidazolecarboxylate and also on 2-bromo-4,5-dicyano-1-methylimidazole using n-butylamine, methylamine hydrochloride and dimethylamine hydrochloride. Moderate to low yields were obtained in these reactions. NAS reactions on ethyl 2-bromo-4-cyano-1-methyl-5-imidazolecarboxylate are generally much slower than that on 2-bromo-4,5-dicyano-1-methylimidazoles. In addition, the ester group is susceptible to hydrolysis and aminolysis. Transhalogenation was performed on 2-bromo-4,5-dicyano-1-methylimidazole using potassium fluoride in diglyme to give 4,5-dicyano-2-fluoro-1-methylimidazole. Attempts to transhalogenate ethyl 2-bromo-4-cyano-1-methyl-5-imidazolecarboxylate gave rise to a mixture of products. Aromatic primary amines undergo NAS reactions with 4,5-dicyano-2-fluoro-1-methylimidazole. Reaction of 2-amino-4,5-dicyano-1-methylimidazole with 4,5-dicyano-2-fluoro-1-methylimidazole gave secondary and tertiary amines with 4,5-dicyano-1-methyl-2-imidazolyl groups as the substituents. The secondary amine, namely bis(4,5-dicyano-1-methyl-2-imidazolyl)amine, has a pK$\sb{\rm a}$ of 4.18. The crystal structure of the tertiary amine, tris(4,5-dicyano-1-methyl-2-imidazolyl)amine, was solved in the P$2\sb1 2\sb1 2\sb1$ (#19) space group of the orthorhombic system (a = 10.070(2) A, b = 13.108(3) A, c = 17.551(3) A, Z = 4). The bond angles between the 2-carbons of the imidazoles and the tertiary amine nitrogen are 116.8(3)$\sp\circ,$ 116.7(3)$\sp\circ$ and 117.2(3)$\sp\circ.$. NAS reactions were also performed on 4,5-dicyano-2-fluoro-1-methylimidazoles using cyanamide as the nucleophile to synthesize mixed amines substituted with cyano and cyanoimidazolyl groups. Attempted syntheses of a compound/material with the composition C$\sb3$N$\sb4$ included decomposition of mercury(II) thiocyanate, cyanation of dicyanamide anion using cyanogen chloride and thermal decomposition of salts of N,N$\sp\prime$-dicyano-1,3-diaza-2-thiomethylpropenide and N,N$\sp\prime$,N$\sp{\prime\prime}$-tricyanoguanidine dianion.