Heckenroth Marion, Kluser Evelyne, Neels Antonia, Albrecht Martin
Department of Chemistry, University of Fribourg, Chemin du Musee 9, CH-1700, Fribourg, Switzerland.
Dalton Trans. 2008 Nov 28(44):6242-9. doi: 10.1039/b812405a. Epub 2008 Oct 1.
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C2保护的二咪唑鎓盐进行钯化反应，得到了包含C4键合的N-杂环卡宾配体的配合物。这些配合物对路易斯酸（AgBF₄、AgOAc）和布朗斯特酸（H₂SO₄、H₃PO₄、HOAc）的反应活性表明，与C2键合相比，卡宾的异常C4键合显著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电荷为+2，但最好将其描述为路易斯碱。异常的卡宾键合模式引发了新的反应模式，如形成Pd-Ag加合物。基于包括不对称二咪唑鎓盐钯化反应在内的金属化研究，提出了二咪唑鎓前体盐中C4-H键选择性活化的原理。
