Palladation of diimidazolium salts at the C4 position: access to remarkably electron-rich palladium(ii) centers
作者:Marion Heckenroth、Evelyne Kluser、Antonia Neels、Martin Albrecht
DOI:10.1039/b812405a
日期:——
Palladation of C2-protected diimidazolium salts with Pd(OAc)2 afforded complexes comprising C4-bound N-heterocyclic dicarbene ligands. The reactivity of these complexes towards Lewis acids (AgBF4, AgOAc) and Brønsted acids (H2SO4, H3PO4, HOAc) revealed that abnormal C4 bonding of the carbenes markedly increases the nucleophilicity of the coordinated palladium center as compared to C2 bonding. Despite its formal +2 charge, the palladium center in these complexes is best described as a Lewis base. The abnormal carbene bonding mode induces new reaction patterns such as the formation of a Pd–Ag adduct. Based on metallation studies including the palladation of a dissymmetric diimidazolium salt, a rationale for the selective activation of the C4–H bond in the diimidazolium precursor salts is proposed.
用 Pd(OAc)2 对受 C2 保护的二咪唑鎓盐进行钯化反应,可得到由 C4 键合的 N-杂环二碳配体组成的络合物。这些配合物对路易斯酸(AgBF4、AgOAc)和布氏酸(H2SO4、H3PO4、HOAc)的反应性表明,与 C2 键相比,碳烯的异常 C4 键明显增加了配位钯中心的亲核性。尽管这些配合物中的钯中心形式上带有 +2 电荷,但最适合描述为路易斯碱。异常的碳烯成键模式诱发了新的反应模式,如形成钯银加合物。根据金属化研究(包括不对称二咪唑鎓盐的钯化),提出了二咪唑鎓前体盐中 C4-H 键选择性活化的原理。