Organo-bridged dicobaloximes: Synthesis, structure and nuclear magnetic resonance study

This short review describes the synthesis and structural characteristics of methylene, xylylene and biphenyl-bridged dicobaloximes. The bridged dicobaloximes are easily synthesized by oxidative alkylation method and the yield of dicobaloxime depends on many factors like reaction time, solvent, dihalide:Co(I) ratio and also on the nature of dihalide used. The NMR and structural studies have been described. The cobalt-bound CH2 and dioxime protons in xylylene-bridged dicobaloximes become nonequivalent at sub-zero temperature and this is caused by the restricted rotation of the Co–C bond. However, the nonequivalence in biphenyl-bridged dicobaloximes is caused by atropisomerism and/or restricted rotation of C–Ph/Co–C bond. Two cobaloxime units of biphenyl-bridged dicobaloximes are symmetrical, and can be looked at as two independent benzyl cobaloximes and there is no direct or indirect interaction between them. In the xylylene-bridged dicobaloxime, one cobaloxime unit affects the structural parameters of the other unit through axially bridged benzyl group, which is sandwiched between two dioxime wings.

This short review describes the synthesis and structural characteristics of methylene, xylylene and biphenyl-bridged dicobaloximes. The Co–CH2 and dioxime protons in xylylene-bridged dicobaloximes become nonequivalent at sub-zero temperature and this is caused by the restricted rotation of the Co–C bond. However, the nonequivalence in biphenyl-bridged dicobaloximes is caused by atropisomerism and/or restricted rotation of C–Ph/Co–C bond.Figure optionsDownload as PowerPoint slideResearch highlights
► Synthesis and structural characteristics of organo-bridged dicobaloximes
► The nonequivalence of Co–CH2 and dioxime protons in xylylene-bridged and in biphenyl-dicobaloximes.
► Effect of one cobaloxime unit on the structural parameters of the other unit in organo-bridged dicobaloximes.