Homogeneous nickel catalysis is used for the synthesis of pharmaceuticals, natural products, and polymers. These reactions generally proceed via nickel intermediates in the Ni(0), Ni(I), Ni(II), and/or Ni(III) oxidation states. In contrast, Ni(IV) intermediates are rarely accessible. We report herein the design, synthesis, and characterization of a series of organometallic Ni(IV) complexes, accessed by the reaction of Ni(II) precursors with the widely used oxidant S-(trifluoromethyl)dibenzothiophenium triflate. These Ni(IV) complexes undergo highly selective carbon(sp(3))-oxygen, carbon(sp(3))-nitrogen, and carbon(sp(3))-sulfur coupling reactions with exogenous nucleophiles. The observed reactivity has the potential for direct applications in the development of nickel-catalyzed carbon-heteroatom coupling reactions.

Silver carboxylate salts are widely used as additives in palladium-catalyzed C−H functionalization reactions. However, the role of these silver additives is often not fully understood. This paper describes an investigation of the role of AgOPiv in the stoichiometric activation of C 6 F 5 H at a well-defined Pd II complex as well as in the Pd II -catalyzed oxidative dimerization of 2-alkylthiophenes. Both in situ NMR spectroscopy and H/D exchange studies of the reactions of C 6 F 5 H implicate a role for AgOPiv in the C−H cleavage event, generating Ag−C 6 F 5 as an intermediate. The catalytic studies show similar trends despite the different conditions and substrates, suggesting that AgOPiv promotes a similar metalation of the thiophene in the catalytic transformations. This proposal is supported by DFT calculations, which show energetically feasible pathways for concerted metalation−deprotonation of both 2methylthiophene and pentafluorobenzene at [Ag(OPiv)] 2 . These studies suggest that initial metalation of C−H substrates at Ag I carboxylates should be considered as a plausible pathway in C−H functionalization reactions involving mixtures of Ag and Pd salts.

This communication describes the synthesis and reactivity of Ni(IV)(aryl)(CF3)2 complexes supported by trispyrazolylborate and 4,4'-di-tert-butylbipyridine ligands. We demonstrate that isolable Ni(IV) complexes can be accessed under mild conditions via the oxidation of Ni(II) precursors with S-(trifluoromethyl)dibenzothiophenium triflate as well as with diaryliodonium and aryl diazonium reagents. The Ni(IV) intermediates undergo high yielding aryl-CF3 bond-forming reductive elimination. These studies support the potential viability of Ni(IV) intermediates in nickel-catalyzed coupling reactions involving diaryliodonium and aryldiazonium electrophiles.

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.