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Nickel catalysts have shown unique ligand control of stereoselectivity in the Suzuki-Miyaura cross-coupling of boronates with benzylic pivalates and derivatives involving C(sp 3 )-O cleavage. The SIMes ligand (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) produces the stereochemically inverted C-C coupling product, while the tricyclohexylphosphine (PCy 3 ) ligand delivers the retained stereochemistry. We have explored the mechanism and origins of the ligand-controlled stereoselectivity with density functional theory (DFT) calculations. The oxidative addition determines the stereoselectivity with two competing transition states, an S N 2 back-side attack type transition state that inverts the benzylic stereogenic center and a concerted oxidative addition through a cyclic transition state, which provides stereoretention. The key difference between the two transition states is the substrate-nickel-ligand angle distortion; the ligand controls the selectivity by differentiating the ease of this angle distortion. For the PCy 3 ligand, the nickel-ligand interaction involves mainly σ-donation, which does not require a significant energy penalty for the angle distortion. The facile angle distortion with PCy 3 ligand allows the favorable cyclic oxidative addition transition state, leading to the stereoretention. For the SIMes ligand, the extra d-p back-donation from nickel to the coordinating carbene increases the rigidity of the nickel-ligand bond, and the corresponding angle distortion is more difficult. This makes the concerted cyclic oxidative addition unfavorable with SIMes ligand, and the back-side S N 2-type oxidative addition delivers the stereoinversion.

Mechanism and Origins of Ligand-Controlled Stereoselectivity of Ni-Catalyzed Suzuki–Miyaura Coupling with Benzylic Esters: A Computational Study