Reaction of o-carboranes with sterically demanding N-heterocyclic carbene: synthesis and structural characterization of 1 : 1 adducts

Several nido-carborane–carbene 1:1 adducts were prepared in very high yields from the reaction of o-carboranes with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene in dry THF at room temperature. Single-crystal X-ray analyses reveal that they are zwitterionic salts consisting of a nido carborane cage and imidazolium moiety that are linked by a five-coordinate boron atom. They are inert toward carbenes, but sensitive toward moisture and water, leading to the formation of deboration products, nido-C2B9 ions. These results shed light on the deboration reaction mechanism of o-carboranes.