Ni(COD)2‑Catalyzed ipso-Silylation of 2‑Methoxynaphthalene: A Density Functional Theory Study

Density functional theory has been used for the systematic investigation of the mechanism involved in Ni­(COD)2-catalyzed ipso-silylation of 2-methoxynaphthalene. The two fundamental mechanistic pathways, internal nucleophilic substitution and a nonclassical oxidative addition, have been studied. In both pathways, the first equivalent of KOtBu directly reacts with the silyl boronate (Et3SiBpin) to generate the silyl anion surrogate Et3SiK or silylborate [Et3Si-Bpin­(OtBu)]K (IN3), which further reacts with Ni­(COD)2 to form a substrate–catalyst complex, [(η2-COD)2NiSiEt3]­K. The internal nucleophilic substitution reaction pathway proceeds through η2 complexation of nickel with the C(1)C(2) bond of 2-methoxynaphthalene. Later, nickel connects to C(1) through σ-bond formation and coordinates with oxygen of the −OMe group. Simultaneously, the −SiEt3 group approaches C(2) possessing −OMe followed by rearomatization which is facilitated by coordination of K+ with nickel and methoxy oxygen. In a nonclassical oxidative addition, the chelation of K+ with −OMe as well as −SiEt3 from [(η2-COD)2NiSiEt3] is the key step which promotes the insertion of NiSiEt3 to the C(2) carbon of 2-methoxynaphthalene. We also observed that the activation energy barrier in the non-π-extended aromatic systems is higher than that of the π-extended aromatic systems. The overall study manifests that Ni­(COD)2-catalyzed ipso-silylation of 2-methoxynapthalene operates through an internal nucleophilic substitution pathway.