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 K+OtBu 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. [ABSTRACT FROM AUTHOR]