Just Published in European Journal of Inorganic Chemistry

Authors: Heidi Schneider, Andreas Hock, Alma D. Jaeger, Dieter Lentz,* Udo Radius*

Abstract: We present herein the utilization of NHC‐stabilized alane adducts of the type (NHC)·AlH₃[NHC = Me₂Im (1), Me₂Im^Me (2), iPr₂Im (3), iPr₂Im^Me (4), Dipp₂Im (5)] and (NHC)·AliBu₂H [NHC = iPr₂Im (6), Dipp₂Im (7)] as novel hydride transfer reagents in the hydrodefluorination (HDF) of different fluoroaromatics and hexafluoropropene. Depending on the alane adduct used, HDF of pentafluoropyridine to 2,3,5,6‐tetrafluoropyridine in yields of 15–99 % was observed. The adducts 1, 2, and 5 achieved a quantitative conversion into 2,3,5,6‐tetrafluoropyridine at room temperature immediately after mixing the reactants. Studies on the HDF of fluorobenzenes with the (NHC)·AlH₃ adducts 1, 3, and 5 and (Dipp₂Im)·AliBu₂H (7) showed the decisive influence of the reaction temperature on the H/F exchange and that 135 °C in xylene afforded the best product distribution. Although the HDF of hexafluorobenzene yielded 1,2,4,5‐tetrafluorobenzene in moderate yields with traces of 1,2,3,4‐tetrafluorobenzene and 1,2,4‐trifluorobenzene, pentafluorobenzene was converted quantitatively into 1,2,4,5‐tetrafluorobenzene, with (Dipp₂Im)·AliBu₂H (7) showing the highest activity and reaching complete conversion after 12 h at 135 °C in xylene. The HDF of hexafluoropropene with (Me₂Im)·AlH₃ (1) occurred even at low temperatures and preferably at the CF₂ group with the formation of 1,2,3,3,3‐pentafluoropropene (with 0.4 equiv. of 1) or 2,3,3,3‐tetra‐fluoropropene (with 0.9 equiv. of 1) as the main product.

Link: https://onlinelibrary.wiley.com/doi/abs/10.1002/ejic.201800589