Exploring the redox reactivity of the [B20H18]2− ion with carbon-based nucleophiles and electrophiles

•First alkylated [B20H18]2− derivative prepared by nucleophilic attack by a carbon-nucleophile.•Oxidation of the [B20H17OH]4− in the presence of a electrophile and crystal structure of [B20H17OH]2− reported.•Crystal structure of [B20H17CH3]2− reported.•Crystal structure of [μ-B20H17OCH3]2− reported.

The [B20H18]2− ion is characterized by the presence of electron-deficient, three-center, two-electron bonds which are susceptible to nucleophilic attack. Since the first synthesis of the ion in 1962, products of the nucleophilic attack have been reported for oxygen, nitrogen, and sulfur nucleophiles; however, no ions have been reported which result from nucleophilic attack of the [B20H18]2− ion by carbon nucleophiles. Herein we report the preparation and single crystal X-ray analysis of the [B20H17CH3]2− ion, prepared by the oxidation of the [B20H17CH3]4− ion in situ. Oxidation of the [B20H18]4− ion and its derivatives, [B20H17X]4− where X is the nucleophile, have been reported using both ferric chloride and organic oxidants; however, the oxidations only proceed in acidic solution. The [B20H17OH]4− and [B20H17OH]2−, both reported previously, were prepared in order to investigate the oxidation reaction. Single crystals of the [B20H17OH]2− ion were obtained and characterized by X-ray diffraction. Oxidation of the [B20H17OH]4− was achieved in the absence of acid, but in the presence of iodomethane; however, the anticipated methylation was not observed and instead, the [μ-B20H17OCH3]2− was isolated and characterized by single crystal X-ray diffraction. The role of the acid, or the iodomethane, in the oxidation process appears to be as an electrophile in the initiation of the oxidation process.

Graphical abstractCrystal structure of [B20H17CH3]2−.Figure optionsDownload full-size imageDownload as PowerPoint slide