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Abstract
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–.
Supplementary materials
Title
Supporting Information Final
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