Carborane Substituents Promote Direct Electrophilic Insertion over Reduction–Metalation Reactions

Two‐electron reduction of 1,1′‐bis( o ‐carborane) followed by reaction with [Ru(η‐mes)Cl 2 ] 2 affords [8‐(1′‐1′,2′‐closo‐C 2 B 10 H 11 )‐4‐(η‐mes)‐4,1,8‐ closo ‐RuC 2 B 10 H 11 ]. Subsequent two‐electron reduction of this species and treatment with [Ru(η‐arene)Cl 2 ] 2 results in the 14‐vertex/12‐vertex species [1‐(η‐mes)‐9‐(1′‐1′,2′‐ closo ‐C 2 B 10 H 11 )‐13‐(η‐arene)‐1,13,2,9‐ closo ‐Ru 2 C 2 B 10 H 11 ] by direct electrophilic insertion, promoted by the carborane substituent in the 13‐vertex/12‐vertex precursor. When arene=mesitylene (mes), the diruthenium species is fluxional in solution at room temperature in a process that makes the metal–ligand fragments equivalent. A unique mechanism for this fluxionality is proposed and is shown to be fully consistent with the observed fluxionality or nonfluxionality of a series of previously reported 14‐vertex dicobaltacarboranes.