1360860-57-6Relevant articles and documents
Mechanistic studies on direct arylation of pyridine N -oxide: Evidence for cooperative catalysis between two distinct palladium centers
Tan, Yichen,Barrios-Landeros, Fabiola,Hartwig, John F.
supporting information; experimental part, p. 3683 - 3686 (2012/04/23)
Direct arylations of pyridine N-oxide (PyO), a convenient method to prepare 2-arylpyridines, catalyzed by Pd(OAc)2 and PtBu3 have been proposed to occur by the generation of a PtBu3-ligated arylpalladium acetate complex, (PtBu3)Pd(Ar)(OAc) (1), and the reaction of this complex with PyO. We provide strong evidence that 1 does not react directly with PyO. Instead, our data imply that the cyclometalated complex [Pd(OAc)(tBu2PCMe2CH2)]2, which is generated from the decomposition of 1, reacts with PyO and serves as a catalyst for the reaction of PyO with 1. The reaction of PyO with 1 occurs with an induction period, and the reaction of 1 with excess PyO in the presence of [Pd(OAc)(tBu2PCMe2CH2)]2 is zeroth-order in 1. Moreover, the rates of reactions of PyO with bromobenzene catalyzed by [Pd(OAc)(tBu2PCMe2CH2)] 2 and [Pd(PtBu3)2] depend on the concentration of [Pd(OAc)(tBu2PCMe2CH2)]2 but not on the concentration of [Pd(PtBu3)2]. Finally, the reaction of 1 with a model heteroarylpalladium complex containing a cyclometalated phosphine, [(PEt3)Pd(2-benzothienyl)(tBu 2PCMe2CH2)], rapidly formed the arylated heterocycle. Together, these data imply that the rate-determining C-H bond cleavage occurs between PyO and the cyclometalated [Pd(OAc)(tBu 2PCMe2CH2)]2 rather than between PyO and 1. In this case, the resulting heteroarylpalladium complex transfers the heteroaryl group to 1, and C-C bond-formation occurs from (PtBu 3)Pd(Ar)(2-pyridyl oxide). This mechanism proposed for the direct arylation of PyO constitutes an example of C-H bond functionalization in which C-H activation occurs at one metal center and the activated moiety undergoes functionalization after transfer to a second metal center.
