An Organocopper(III) Fluoride Triggering C−CF3 Bond Formation

Abstract

Copper(III) fluorides are catalytically competent, yet elusive, intermediates in cross-coupling. The synthesis of [PPh4][CuIII(CF3)3F] (2), the first stable (isolable) CuIII−F, was accomplished via chloride addition to [CuIII(CF3)3(py)] (1) yielding [PPh4][CuIII(CF3)3Cl(py)] (1⋅Cl), followed by treatment with AgF. The CuIII halides 1⋅Cl and 2 were fully characterized using nuclear magnetic resonance (NMR) spectroscopy, single crystal X-ray diffraction (Sc-XRD) and elemental analysis (EA). Complex 2 proved capable of forging C−CF3 bonds from silyl-capped alkynes. In-depth mechanistic studies combining probes, theoretical calculations, trapping of intermediate 4a ([PPh4][CuIII(CF3)3(C≡CPh)]) and radical tests unveil the key role of the CuIII acetylides that undergo facile 2e− reductive elimination furnishing the trifluoromethylated alkynes (RC≡CCF3), which are industrially relevant synthons in drug discovery, pharma and agrochemistry.