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Nickel anions [(MeCN)Ni(CF3)3]− and [Ni(CF3)4]2– were prepared by the formal addition of 3 and 4 equiv, respectively, of AgCF3 to [(dme)NiBr2] in the presence of the [PPh4]+ counterion. Detailed in...

The deprotonation of N-2,6-diisopropylphenyl-substituted benzoxazolium tetrafluoroborate 1 with NaH results in the formation of electron-rich diaminodioxaethylene 2. The radical cation salt 2·+·BF4– is found to be an intermediate product in the redox reaction leading from 1 to 2.

The nickel anions [(MeCN)Ni(CF3)3]1– and [Ni(CF3)4]2– were prepared by formal addition of three and four equivalents of [AgCF3] to [(dme)NiBr2] in the presence of supporting [PPh4] counter-ion. Detailed insights into the electronic properties of these new compounds were obtained through the use of density functional theory (DFT) calculations, spectroscopy-oriented configuration interaction (SORCI) calculations, X-ray absorption spectroscopy, and cyclic voltammetry. The data collectively show that trifluoromethyl complexes of nickel, even in the most common oxidation state of nickel(II), are highly covalent systems whereby a hole is distributed on the trifluoromethyl ligands and surprisingly rendering the metal to a physically more reduced state. In the cases of [(MeCN)Ni(CF3)3]1– and [Ni(CF3)4]2–, these complexes are better described as physically d9 metal complexes. [(MeCN)Ni(CF3)3]1– is electrophilic and reacts with other nucleophiles like phenoxide to yield the unsupported [(PhO)Ni(CF3)3]2– salt, revealing the broader potential of [(MeCN)Ni(CF3)3]1– in the development of ligandless trifluoromethylations at nickel. Proof-in-principle experiments show that reaction of [(MeCN)Ni(CF3)3]1– with an aryl iodonium salt yields trifluoromethylated arene, presumably via a high valent, unsupported, and formally organonickel(IV) intermediate. Evidence for the feasibility of such intermediates is provided with the structurally characterized [Ni(CF3)4(SO4)][PPh4]2, which was derived through the two electron oxidation of [Ni(CF3)4]2–.

This paper elucidates the redox properties and reactivity of a number of cyclometalated nickel(II) complexes in oxidation processes. Original and robust procedures for the synthesis of nickelacycles with two cyclometalated moieties and halogenated nickelacycles were developed. The complexes were studied by means of electrochemical, ESR, DFT, and single-crystal XRD methods. Notable features of the nickelacycles are unusually low oxidation potentials. Upon electrochemical oxidation the complexes produce carbon–carbon and carbon–heteroatom coupled products, the ratio of which can be tuned by the conditions applied.

The electochemical oxidation of palladium acetate or palladium perfluoroacetate in the presence of 2-phenylpyridine promotes catalytic ortho C–H substitution reactions. As possible intermediates, Pd(II) metallacycles with Pd-bound acetate, perfluoroacetate, and perfluoroheptanoate substituents have been isolated and characterized: binuclear [(PhPy)Pd(μ-OAc)]2 and [(PhPy)Pd(μ-TFA)]2 and mononuclear [(PhPy)Pd(TFA)](CH3CN), [(PhPy)Pd(TFA)](PhPy), and [(PhPy)Pd(PFH)](PhPy). The fluorinated derivatives were found to exist in solvent-dependent equilibria between mononuclear and binuclear forms. Cyclic voltammetry was used to elucidate redox properties of the palladacycles and the oxidation route to the final products.