Mechanistic insight into carbon-fluorine cleavage with a (iPr3P)2Ni source: Characterization of (iPr3P)2NiC6F5 as a significant Ni(I) byproduct in the activation of C6F6

The reaction of (iPr3P)2Ni sources such as the anthracene adduct, (iPr3P)2Ni(η2-C14H10), with hexafluorobenzene provided the C−F activation product trans-(iPr3P)2NiF(C6F5) (2) and the unexpected Ni(I) complex (iPr3P)2Ni(C6F5) (3). The observation of 3 supports a radical pathway for C−F activation, despite the observation of the mononuclear adduct (iPr3P)2Ni(η2-C6F6) (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 (iPr3P)2Ni(η2-C14H10) 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.40