This manuscript describes the design, synthesis, characterization, and reactivity studies of organometallic Ni complexes of general structure TpNi(R)(R) (Tp = tris(pyrazolyl)borate). With appropriate selection of the R and R ligands, the complexes are stable at room temperature and can be characterized by cyclic voltammetry, EPR spectroscopy, and X-ray crystallography. Upon heating, many of these Ni compounds undergo C(sp)-C(sp) or C(sp)-C(sp) bond-forming reactions that are challenging at lower oxidation states of nickel.

This Article describes the development of a stable Ni IV complex that mediates C(sp 2 )−H trifluoromethylation reactions. This reactivity is first demonstrated stoichiometrically and then successfully translated to a Ni IV -catalyzed C−H trifluoromethylation of electron-rich arene and heteroarene substrates. Both experimental and computational mechanistic studies support a radical chain pathway involving Ni IV , Ni III , and Ni II intermediates.

The treatment of pyridine-and pyrazole-ligated Ni II σaryl complexes with Selectfluor results in C(sp 2 )−F bond formation under mild conditions. With appropriate design of supporting ligands, diamagnetic Ni IV σ-aryl fluoride intermediates can be detected spectroscopically and/or isolated during these transformations. These studies demonstrate for the first time that Ni IV σ-aryl fluoride complexes participate in challenging C(sp 2 )−F bond-forming reductive elimination to yield aryl fluoride products.

This communication describes the synthesis of an organometallic NiIV complex bearing a labile trifluoroacetate (OTFA) ligand via the oxidation of a NiII precursor with PhI­(OTFA)2. Intramolecular C­(sp2)–O bond-forming reductive elimination from this NiIV complex is relatively slow, requiring 6 h at 70 °C to reach completion. In contrast, transmetalation with TMSCF3 occurs within just 1 h at room temperature to generate a NiIV–CF3 complex. These studies show that intermolecular reactions such as transmetalation can be competitive with intramolecular reductive elimination processes at NiIV centers.

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