Crystal structure of the pentamethyldiethylenetriamine adduct of 1-lithio-2-methyl-1,2-dicarba-closo-dodecaborane,Li[C2B10H10Me][MeN(CH2CH2NMe2)2], a compound containing a lithium atom terminally bonded to a six-coordinate carbon atom

Li[C₂B₁₀H₁₀Me][MeN(CH₂CH₂NMe₂)₂], prepared by successive reaction of equimolar amounts of n-butyl-lithium and pentamethyldiethylenetriamine with 1-methyl-1,2-dicarba-closo-dodecarborane, C₂B₁₀H₁₁Me, crystallises in the monoclinic space group P2₁/m, with a = 8.242(1), b = 13.522(1), c = 10.799(1) Å, β = 108.75(1)°, Z = 2. The crystal structure has been refined to R = 0.088 from 1128 unique diffractometer data with F > 6σ(F). The compound is unusual in that it contains a lithium atom terminally attached by a formally single LiC bond to the six-coordinate carbon atom of a carborane. Features of the structure are compared with related features of other organolithium compounds, and used to calculate the cone angles and steric requirements of icosahedral carboranyl and methylcarboranyl ligands attached to metal atoms of various sizes.