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16-Electron Nickel(0)-Olefin Complexes in Low-Temperature C(sp2)–C(sp3) Kumada Cross-Couplings

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journal contribution
posted on 26.03.2021, 19:44 by Sigrid Lutz, Lukas Nattmann, Nils Nöthling, Josep Cornella
Investigations into the mechanism of the low-temperature C­(sp2)–C­(sp3) Kumada cross-coupling catalyzed by highly reduced nickel-olefin-lithium complexes revealed that 16-electron tris­(olefin)­nickel(0) complexes are competent catalysts for this transformation. A survey of various nickel(0)-olefin complexes identified Ni­(nor)3 as an active catalyst, with performance comparable to that of the previously described Ni-olefin-lithium precatalyst. We demonstrate that Ni­(nor)3, however, is unable to undergo oxidative addition to the corresponding C­(sp2)–Br bond at low temperatures (<−40 °C), thus indicating that the canonical cross-coupling cycle is not operative under this condition. Instead, such binary nickel(0)-olefin complexes capitalize on the long-known Lewis acidity of the Ni(0) center when it is coordinated to olefins to accommodate the incoming charge from the Grignard reagent, forming a nickel(0)-alkylmagnesium complex. We demonstrate that this unique heterobimetallic complex is now primed for reactivity, thus cleaving the C­(sp2)–Br bond and ultimately delivering the C­(sp2)–C­(sp3) bond in high yields.

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