Arylazoimidazole compounds of rhenium nitrosyl: Synthesis, spectral characterization and reactivity

Reductive nitrosylation of ReO4- in aqueous alkaline medium by NH2OH · HCl furnishes the Re(NO)3+ moiety which reacts with arylazoimidazoles to give hitherto unknown arylazoimidazole (RaaiR′) complexes of rhenium nitrosyl, [Re(NO)(OH)3(RaaiR′)]. The complexes are non-electrolytes in CH3CN. They exhibit υ(NO) at ca. 1700 cm−1 and are magnetically active. The ESR profiles in the polycrystalline state at 298 K show 〈gav〉 ≈ 2.0. A spin forbidden ESR transition (ΔMs = 2, g ∼ 4) is observed at <1600 Gauss. A well defined sextet due to the metal hyperfine structure is observed. The complexes exhibit a moderately intense visible band at 440–450 nm which may be ascribed to a metal-to-ligand charge transfer transition, along with intraligand charge transfer, π → π∗ and n → π∗, transitions at <400 nm. Cyclic voltammetry exhibits quasireversible to irreversible metal oxidation and ligand reductions. The reaction of [Re(NO)(OH)3(RaaiR′)] with camphor in alkaline medium has assisted C–N bond fusion by synthesizing a camphorquinone monoxime complex.

ReO4- in aqueous alkaline medium has been reduced by NH2OH · HCI and consequently reacted with 1-alkyl-2-(arylazo)imidazoles (RaaiR′) to synthesise [Re(NO)(OH)3(RaaiR′)]. The presence of υ(NO) at ca. 1700 cm−1 confirms the {Re–NO} motif. The complexes are ESR active. The reaction of the product with camphor in alkaline medium results in C–N bond fusion, with the synthesis of the camphorquinone monoxime complex. Cyclic voltammetry shows metal oxidation and reduction of the coordinated NO+ and azoimine ligand.Figure optionsDownload as PowerPoint slide