Variation On An HF Fluorination Theme

Hydrogen fluoride has long been used as a low-cost and efficient fluorinating reagent. And when not used directly, HF is used to prepare nearly all other fluorinating reagents. But HF is a hazardous gas at room temperature and hard to handle. A research team led by Gerald B. Hammond and Bo Xu at the University of Louisville has come up with an easy way to tame HF for fluorinations by creating a hydrogen-bonded complex with DMPU, a cyclic urea with a long-winded name that is often used as a polar aprotic solvent (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja508369z). Chemists have previously controlled HF in hydrogen-bonded complexes with organic molecules such as pyridine and triethylamine. Although these complexes work well, the partner molecules are bases that reduce the acidity of the reaction system and bind strongly with transition-metal catalysts, often reducing their activity. DMPU is nonbasic and weakly coordinating with metals, offering an alternative to overcome those problems, the Louisville researchers say. In initial studies, they have shown that DMPU/HF is an easy-to-handle and selective liquid fluorinating reagent for gold-catalyzed mono- and dihydrofluorinations of alkynes.