Mechanism of Nickel-Catalyzed Dual C–O Bond Activation in the Deoxygenation of Ethers via Reductive Cross-Coupling Reaction: A DFT Study

Nickel-catalyzed C–O bond cleavage provides an important strategy to construct C–C bonds from oxygenated electrophiles. The present study elucidated the mechanisms of ethers (R1OR1) deoxygenation via reductive cross-coupling reaction using density functional theory (DFT) calculations. The results suggest that, in the absence of B2pin2 or at the beginning of the reaction, the most favorable mechanism occurs in six steps: first oxidative addition, reduction, radical production, reduction, radical addition, and reductive elimination. When a significant amount of alkyl radical is formed from the parallel reaction of B2pin2 with the alkoxide anchored in the zinc cluster surface, which contains the waste carbon fragment of ether, the only difference in the reaction mechanism is that the intermediate before de reductive elimination, R1–Ni(II)–R1, is formed directly through a radical addition in the Ni(I)–R1. The presence of B2pin2 is crucial to enable the C–C coupling between two carbon fragments, which may originate from different ether molecules and to ensure that the reaction stoichiometry becomes 1:1. In the presence of B2pin2, the two catalytic cycles are kinetically active and equally competitive (within the DFT error range) with rate determining ΔG‡(THF/Tol.avg.) values of 31.0 and 31.5 kcal/mol, respectively, for the deoxygenation of 2,2’-oxybis(methylene)-dinaphthalene in each cycle.