Regioselective B2–6 penta-iodination of the [CB11H12]− monocarborane cluster by palladium catalysis

Abstract

Penta-iodination of the B2–6 positions of the {CB₁₁} monocarborane cluster is reported. Products of the structure [2,3,4,5,6-I₅-CB₁₁H₆-12-X]⁻ (X = H, Me, Et, Ph, Br, I) were obtained and fully characterized. X-ray crystal structures of three new compounds confirm this particular substitution pattern. The synthetic method relies on palladium catalysis/B–H activation, assisted by the C1-COOH directing group. The one-pot procedure enables penta-iodination and subsequent decarboxylation under convenient conditions. The B2–6 regioselectivity is complementary to the commonly observed reactivity of {CB₁₁} clusters, which follows the trend B12 > B7–11 > B2–6 for electrophilic substitution. Thus, for the first time upper-belt halogenation is achieved without prior modification of the lower-belt positions.