| Popis: |
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, [(eta(2)-COD)(2)NiSiEt3]K. The internal nucleophilic substitution reaction pathway proceeds through eta(2) complexation of nickel with the C(1)=C(2) bond of 2-methoxynaphthalene. Later, nickel connects to =C(1) through sigma-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 [(eta(2)-COD)(2)NiSiEt3] 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-pi-extended aromatic systems is higher than that of the pi-extended aromatic systems. The overall study manifests that Ni(COD)(2)-catalyzed ipso-silylation of 2-methoxynapthalene operates through an internal nucleophilic substitution pathway. |
