Mechanistic insight into carbon-fluorine cleavage with a (~iPr_3P)_2Ni source:Characterization of (~iPr_3P)_2NiC_6F_5 as a significant Ni(I) byproduct in the activation of C_6F_6

摘要

The reaction of (~iPr_3P)_2Ni sources such as the anthracene adduct, (~iPr_3P)_2Ni(η~2-C_(14)H_(10)), with hexafluorobenzene provided the C-F activation product trans-(~iPr_3P)_2NiF(C_6F_5) (2) and the unexpected Ni(I) complex (~iPr_3P)_2Ni(C_6F_5) (3). The observation of 3 supports a radical pathway for C-F activation, despite the observation of the mononuclear adduct (~iPr_3P)_2Ni(η~2-C_6F_6) (4) commonly associated with concerted or phosphine-assisted oxidative addition. Carbon-fluorine activation reactions of pentafluorobenzene and all the isomers of tetrafluorobenzene and trifluorobenzene with (~iPr_3P)_2Ni(η~2-C_(14)H_(10)) were also examined. These reacted with varying selectivity and yield. It was found that 1,2,3,4-tetrafluorobenzene reacted selectively at the 2-position to provide a fully characterized C-F activation product, whereas 1,2,4,5-tetrafluorobenzene underwent a hydrodefluorination reaction with none of the expected C-F activation product.