Abstract

The nickel-catalyzed alkyl-alkyl cross-coupling (C-C bond formation) and borylation (C-B bond formation) of unactivated alkyl halides reported in the literature show completely opposite reactivity orders in the reactions of primary, secondary, and tertiary alkyl bromides. The proposed Ni(I) /Ni(III) catalytic cycles for these two types of bond-formation reactions were studied computationally by means of DFT calculations at the B3LYP level. These calculations indicate that the rate-determining step for alkyl-alkyl cross-coupling is the reductive elimination step, whereas for borylation the rate is determined mainly by the atom-transfer step. In borylation reactions, the boryl ligand involved has an empty p orbital, which strongly facilitates the reductive elimination step. The inability of unactivated tertiary alkyl halides to undergo alkyl-alkyl cross-coupling is mainly due to the moderately high reductive elimination barrier.

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