Incremental iodination of the eight-vertex closo monocarborane anion [closo-1-CB7H8](-): Preparation and characterization of [closo-1-CB7H5-6,7,8-I3](-) and [closo-1-CB7H2-2,3,4,6,7,8-I6](-), and the synthesis of the first eight-vertex C-methylated carborane anion [1-CH3-closo-1-CB7H4-6,7,8-I3](-)
Abstract
Iodination of [closo-1-CB7H8](-) (anion 1) with elemental iodine under various controlled conditions yields a continuum from mono-to hexaiodinated derivatives including the previously unknown [closo-1-CB7H5-6,7,8-I3](-) (anion 5) and [closo-1-CB7H2-2,3,4,6,7,8-I6](-) (anion 8). These species, characterized by mass spectrometry and NMR spectroscopy, and, in the case of 8, by single-crystal X-ray diffraction, provide insight into the fluxional molecular behavior of anion 1 in solution.
Investigation of direct electrophilic substitution on the carbon-vertex of anion 1 using standard conditions and reagents (deprotonation by BuLi followed by addition of electrophile) proved futile, but the same conditions when using the new triiodo-deravitive anion 5 resulted in the formation of the first eight-vertex C-methylated carborane anion [1-CH3-closo-1-CB7H4-6,7,8-I3](-) (anion 9), in 60% yield.