Carborane Substituents Promote Direct Electrophilic Insertion over Reduction-Metalation Reactions

摘要

Two-electron reduction of 1,1-bis(o-carborane) followed by reaction with [Ru(-mes)Cl-2](2) affords [8-(1-1,2-closo-C2B10H11)-4-(-mes)-4,1,8-closo-RuC2B10H11]. Subsequent two-electron reduction of this species and treatment with [Ru(-arene)Cl-2](2) results in the 14-vertex/12-vertex species [1-(-mes)-9-(1-1,2-closo-C2B10H11)-13-(-arene)-1,13,2,9-closo-Ru2C2B10H11] 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.