Synthesis and Structure of Diphosphene-Bridged Dicarborane Dianions with [2n+3] Skeletal Electrons

In contrast to the extensively studied carboranes with even skeletal electron counts ([2n+2], [2n+4]), systems with odd electron counts ([2n+3]) are rare (n = number of skeletal atoms). With the assistance of a diphosphene-bridge, dicarborane dianions {[(Ar)NC(^tBu)C₂B₁₀H₁₀]P}₂^2- [Ar = Dipp (2) or Dmp (4); Dipp = 2,6-ⁱPr₂C₆H₃, Dmp = 2,6-Me₂C₆H₃] with formal [2n+3] skeletal electrons in each carborane cage were obtained via single electron reduction of imine-stabilized carboranyl-phosphinidene or -diphosphene with potassium graphite (KC₈) or cobaltocene (CoCp₂), respectively. The delocalization of the two unpaired electrons across the carborane cages and diphosphene-bridge was evidenced by experimental and theoretical results.