Electrochemical and spectroelectrochemical studies of C-benzodiazaborolyl-ortho-carboranes

Abstract

Fifteen C-diazaborolyl-ortho-carboranes, 1-R′-2-R′′-1,2-C₂B₁₀H₁₀, where R′ represents the groups 2-(1,3-Et₂-1,3,2-N₂BC₆H₄)-, 2-(1,3-Ph₂-1,3,2-N₂BC₆H₄)-, 2-(1,3-Ph₂-5,6-Me₂-1,3,2-N₂BC₆H₂)-, 2-(1,3-ⁱPr₂-1,3,2-N₂BC₆H₄)-, and 2-(1,3,2-N₂BC₆H₆)- and where R′′ is H, Me, Ph, ^tBu or SiMe₃, were synthesized. Cyclic voltammetry studies of the compounds showed irreversible oxidation waves which are caused by the oxidation of the heterocycle. Those C-diazaborolyl-ortho-carboranes with Ph, tBu and SiMe₃ substituents at the adjacent C-atom of the cage displayed two one-electron reduction waves reflecting the formation of stable radical monoanions with unusual (2n + 3) skeletal electron counts. The geometries of these anions were determined by combinations of infrared, UV-visible spectroelectrochemical and computational studies. Additionally the structures of seven new C-diazaborolyl-ortho-carboranes and one new 2-bromo-1,3,2-benzodiazaborole were determined by X-ray crystallography and compared with previously obtained structures.