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

摘要

Pyrazine (Pz) bridged benzyl dicobaloximes [ArCH2Co(dioxime)(2)](2)-mu-Pz [dioxime = dmgH, dpgH] have been synthesized and characterized with H-1 and C-13 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)-mu-Pz, two cobaloxime units are in eclipsed form whereas they were completely staggered in the reported [EtCo(dpgH)(2)](2)-mu-Pz. This is due to the pi-pi 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)-mu-Pz. The cyclic voltammetry study in [PhCH2Co(dioxime)(2)](2)-mu-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. (c) 2005 Elsevier B.V.. All rights reserved.