ChemInform Abstract: Synthesis and Coordination Chemistry of 4-Azabenzimidazole Derivatives

A facile method for the preparation of N1- (1a–6a) and N3-alkylated (1b–6b) 4-azabenzimidazole derivatives is presented. Both isomers were obtained by alkylation of 4-azabenzimidazole. The isomers were separated, and the preferred formation of the N1-alkylated derivatives (1a–6a) was observed. The C2-proton in the alkylated benzimidazoles can be exchanged for an iodine atom by treatment with methyl lithium and iodine, leading to N-alkylated 2-iodo-4-azabenzimidazoles 7a,b and 8a. 2,2′-Bis(4-azabenzimidazole) derivatives 9a,b and 10a were isolated as by-products of the proton–halogen exchange. Treatment of the N1- or N3-methyl-4-azabenzimidazoles 1a,b with methyl lithium and N-chlorosuccinimide as a chlorine source proceeded to give 2-chloro-4-azabenzimidazoles 11a,b without formation of the coupling products, but the yield of 2-chloro-1-methyl-4-azabenzimidazole 11a is low (9%) whereas 2-chloro-3-methyl-4-azabenzimidazole 11b has been obtained in reasonable yield (49%). The reaction of 3-butyl-2-iodo-4-azabenzimidazole 7b with [IrCl2Cp*]2 gave the iridium complex 12, where 3-butyl-2-iodo-4-azabenzimidazole is coordinating to the metal center via the N1 atom. The reaction of the N1-alkylated 4-azabenzimidazole with chloroacetone gave the corresponding 1-alkyl-3-(2-oxopropyl)-4-azabenzimidazolium chlorides 13–17 in good yields. The chloride counterion was exchanged for a tetrafluoroborate anion for two derivatives leading to compounds 18 and 19. Carbene complexes were obtained by treatment of 1-butyl-3-(2-oxopropyl)-4-azabenzimidazolium chloride 15 with silver oxide, followed by transmetalation with [AuCl(tht)] or [IrCl2Cp*]2 leading to the gold(I) (20) and iridium(III) complexes (21) with 1-butyl-3-(2-oxopropyl)-4-azabenzimidazolin-2-ylidene ligand. Removal of the 2-oxopropyl protecting group by treatment with silica gel proceeded in the case of the iridium complex to give complex 22, possessing an NH,NR-stabilized carbene ligand, while it failed for the gold(I) complex. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:476–490, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20711