Synthesis and Crystal Structure of a “Carbons Apart” Erbacarborane Sandwich: An Example of Novel, One-Pot, Two-Electron Reductive Cage Opening with Concomitant Metalation of the C₂B₄ Carborane Ligand

The reaction between 1,2-(SiMe3)2-closo-1,2-C2B4H4 (1), ErCl3, and K in a 2:1:4 molar ratio, in the absence of an outside electron-transfer agent, produced the erbacarborane sandwich 2,2‘,4,4‘-(SiMe3)4-3,6‘-[(μ-H)2K(THF)2]-1,1‘-commo-Er(η5-2,4-C2B4H4)2 (2) in 82% yield. All experimental observations are consistent with a process in which the erbium metal is acting as both the capping group and an electron-transfer agent.