Bis(tri-tert-butylphosphine)palladium(0)-Catalyzed Iodine–Fluorine Exchange at closo-Carboranes

Abstract

The bis(tri-tert-butylphosphine)palladium(0) [Pd(tBu3P)2]-catalyzed synthesis of fluorinated closo-carboranes from 3D aromatic iodo-closo-carboranes by nucleophilic halogen exchange using silver(I) fluoride is described. Fluorination of 2-iodo-closo-p-carborane proceeded more readily than that of 9-iodo-closo-m-carborane. Iodine–fluorine exchange at 9-iodo-closo-o-carborane was not successful yielding instead a charge-compensated dibutylphosphonio nido-o-carborane. The described methodology advances the understanding of nucleophilic fluorination at aromatic systems by Pd0/PdII catalysis. With further optimization, it could find application in the synthesis of 18F-labeled carboranyl diagnostics for biomedical applications.