Pyrazine bridged benzyl dicobaloximes: Competition between π-interaction and steric crowding in crystal structure

Pyrazine (Pz) bridged benzyl dicobaloximes [ArCH2Co(dioxime)2]2-μ-Pz [dioxime = dmgH, dpgH] have been synthesized and characterized with 1H and 13C NMR. The complexes have been synthesized by a simple procedure in one-pot directly from the corresponding benzyl aqua cobaloxime. In the crystal structure of [PhCH2Co(dpgH)2]2-μ-Pz, two cobaloxime units are in eclipsed form whereas they were completely staggered in the reported [EtCo(dpgH)2]2-μ-Pz. This is due to the π–π interaction between the axial benzyl group and phenyl ring of the equatorial dpgH group. Both cis and trans isomer crystallized together in the crystal structure of [PhCH2Co(dpgH)(dmgH)]2-μ-Pz. The cyclic voltammetry study in [PhCH2Co(dioxime)2]2-μ-Pz [dioxime = dmgH, dpgH] shows two cobalt center mixed together due to electron delocalization through pyrazine and behaves like a monocobaloxime and the reduction potentials are much higher than the monocobaloximes.

Graphical abstractA one-pot synthesis of pyrazine (Pz) bridged benzyl dicobaloximes [ArCH2Co(dioxime)2]2-μ-Pz [dioxime = dmgH, dpgH] has been described. Two cobaloxime units attain the eclipsed conformation in [PhCH2Co(dpgH)2]2-μ-Pz due to the π–π interaction between the axial benzyl group and phenyl ring of the equatorial dpgH group whereas both cis and trans isomers crystallize together in [PhCH2Co(dpgH)(dmgH)]2-μ-Pz. The cyclic voltammetry study in [PhCH2Co(dioxime)2]2-μ-Pz [dioxime = dmgH, dpgH] shows two cobalt center are mixed together due to electron delocalization through pyrazine and behave like a monocobaloxime and the reduction potentials are much higher than the monocobaloximes.Figure optionsDownload full-size imageDownload as PowerPoint slide