Synthesis of carbonylchromium complexes of benzimidazole and quinoxaline derivatives

Two approaches to the preparation of chromium complexes of condensed heterocyclic compounds bearing two nitrogen atoms are approved. The reactions of benzimidazole (L1) and 2-methylbenzimidazole (L2) with triammine(tricarbonyl)chromium (I) give the corresponding pentacarbonylchromium derivatives [(η1-C7H6N2)]Cr(CO)5 (II) and [2-Me-(η1-C7H5N2)]Cr(CO)5 (III) characterized by the nitrogen–chromium σ-bond, and ammine(pentacarbonyl)chromium (Cr(NH3)(CO)5, IV) is formed as a by-product. Analogous reactions involving 1,2,3,4-tetrahydroquinoxaline (L3) and 3-phenyl-1,2-dihydroquinoxaline (L4) afford tricarbonylchromium π-complexes [(η6-C6H4)C2H6N2)]Cr(CO)3 (V) and [3-Ph-(η6-C6H4)C2H3N2)]Cr(CO)3 (VI), respectively. The condensations of (η6-ortho-phenylenediamine)tricarbonylchromium (VII) with benzaldehyde and of ortho- phenylenediamine with (η6-benzaldehyde)tricarbonylchromium (VIII) afford acyclic compounds (azomethines [PhCH=N(η6-C6H4)NH2]Cr(CO)3 (IX) and [(η6-Ph)CH=NC6H4NH2]Cr(CO)3 (X), respectively), whereas the reaction of acetaldehyde with complex VII gives a mixture of heterocyclic products: exo-[1,3-bis-(C2H4OEt)-2-Me-(η6-C6H4)CHN2]Cr(CO)3 (XI) and endo-[1,3-bis-(C2H4OEt)-2-Me-(η6-C6H4)CHN2]Cr(CO)3 (XII). The spectral characteristics of the synthesized compounds are studied, and their purity and individual character are proved. The molecular structures of complexes III and XI are determined by XRD (CIF files CCDC nos. 2245463 (III) and 2362231 (XI)).