Reaction of imidazoles with cyanogen bromide: Cyanation at N1 or bromination at C2?

The reaction in acetonitrile solution of a number of imidazoles (1H-, 1-met hyl-, 2-methyl-, 4-methyl-, 1,2-, 1,4- and 1,5-dimethyl-, 1-ethyl-, 1-benzy l- and 1-butyl-imidazole) and imidazole complexes ([Co(NH3)(5)(imH)] (ClO4) (3), [Co(NH3)(5)(im)] (ClO4)(2) and [Co(NH3)(5)(1-Meim)] (ClO4)(3)) with Br CN has been studied. Those imidazoles bearing an N-alkyl substituent and ha ving a hydrogen at C2 react to give the 2-bromo products, while the N-H imi dazoles react to give N-cyano derivatives. The product(s) from the reaction of 1,2-dimethylimidazole with BrCN could not be characterized. Of the comp lexes, only [Co(NH3)(5)(im)] (ClO4)(2) reacts, giving the 2-bromo product. Our observations suggest a lone pair on a ring nitrogen atom is necessary f or an imidazole to react with BrCN, and a possible mechanism is suggested. The X-ray structure of 2-methylimidazole-1-carbonitrile is reported. Crysta l data (-143 degrees C) for C5H5N3: monoclinic, P2(1)/c, a 10.201(5), b 7.1 10(3), c 7.227(3) Angstrom, beta 100.47(2)degrees, V 515.4(4) Angstrom(3), Z 4, d(calcd) 1.380 g cm(-3). Refinement of the structure converged with R- 1 0.0444 for 1183 reflections with F-o > 4F(F-o) and wR(2) 0.1259 for all 1 278 data.