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Isolated Organometallic Nickel(III) and Nickel(IV) Complexes Relevant to Carbon–Carbon Bond Formation Reactions

Schultz, Jason W., Fuchigami, Kei, Zheng, Bo, Rath, Nigam P., Mirica, Liviu M.
Journal of the American Chemical Society 2016 v.138 no.39 pp. 12928-12934
chemical bonding, ligands, nickel, oxidants, oxidation, palladium, stereochemistry
Nickel-catalyzed cross-coupling reactions are experiencing a dramatic resurgence in recent years given their ability to employ a wider range of electrophiles as well as promote stereospecific or stereoselective transformations. In contrast to the extensively studied Pd catalysts that generally employ diamagnetic intermediates, Ni systems can more easily access various oxidation states including odd-electron configurations. For example, organometallic Niᴵᴵᴵ intermediates with aryl and/or alkyl ligands are commonly proposed as the active intermediates in cross-coupling reactions. Herein, we report the first isolated Niᴵᴵᴵ–dialkyl complex and show that this species is involved in stoichiometric and catalytic C–C bond formation reactions. Interestingly, the rate of C–C bond formation from a Niᴵᴵᴵ center is enhanced in the presence of an oxidant, suggesting the involvement of transient Niᴵⱽ species. Indeed, such a Niᴵⱽ species was observed and characterized spectroscopically for a nickelacycle system. Overall, these studies suggest that both Niᴵᴵᴵ and Niᴵⱽ species could play an important role in a range of Ni-catalyzed cross-coupling reactions, especially those involving alkyl substrates.