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)).