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[(MeCN)Ni(CF3)3]1– and [Ni(CF3)4]2– : Foundations Towards the Development of Trifluoromethylations at Unsupported Nickel

preprint
submitted on 02.04.2020 and posted on 06.04.2020 by Scott T. Shreiber, Ida M. DiMucci, Mikhail Khrizanforov, Charles J. Titus, Dennis Nordlund, Yulia B. Dudkina, Roger E. Cramer, Yulia Budnikova, Kyle M. Lancaster, David Vicic
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–.

Funding

Fundamental Studies Focused on the Organometallic Chemistry of Earth Abundant Metals

Basic Energy Sciences

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SusChEM: CAREER: High-Resolution X-ray Spectroscopic Studies of Base Metal Catalysis

Directorate for Mathematical & Physical Sciences

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History

Email Address of Submitting Author

vicic@lehigh.edu

Institution

Lehigh University

Country

USA

ORCID For Submitting Author

0000-0002-4990-0355

Declaration of Conflict of Interest

none

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