The effect of added ligands on the reactions of [Ni(COD)(dppf)] with alkyl halides : halide abstraction may be reversible

Greaves, Megan E. and Ronson, Thomas O. and Maseras, Feliu and Nelson, David J. (2021) The effect of added ligands on the reactions of [Ni(COD)(dppf)] with alkyl halides : halide abstraction may be reversible. Organometallics, 40 (12). pp. 1997-2007. ISSN 0276-7333 (https://doi.org/10.1021/acs.organomet.1c00280)

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Abstract

The reactions of dppf-nickel(0) with alkyl halides proceed via three-coordinate nickel(0) intermediates of the form [Ni(dppf)(L)]. The effects of the identity of the added ligand (L) on catalyst speciation and the rates of reactions of [Ni(COD)(dppf)] with alkyl halides have been investigated using kinetic experiments and density functional theory calculations. A series of monodentate ligands have been investigated in attempts to identify trends in reactivity. Sterically bulky and electron-donating ligands are found to decrease the reaction rate. It was found that (i) the halide abstraction step is not always irreversible and the subsequent recombination of a nickel(I) complex with an alkyl halide can have a significant effect on the overall rate of the reaction and (ii) some ligands lead to very stable [Ni(dppf)(L) 2] species. The yields of prototypical (dppf)nickel-catalyzed Kumada cross-coupling reactions of alkyl halides are significantly improved by the addition of free ligands, which provides another important variable to consider when optimizing nickel-catalyzed reactions of alkyl halides.

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