Triazole-Functionalized N-Heterocyclic Carbene Complexes of Palladium and Platinum and Efficient Aqueous Suzuki-Miyaura Coupling Reaction

Imidazolium salts bearing triazole groups are synthesized via a copper catalyzed click reaction, and the silver, palladium, and platinum complexes of their N-heterocyclic carbenes are studied. [Ag4(L1)(4)](PF6)(4), [Pd(L1)Cl](PF6), [Pt(L1)Cl](PF6) (L1 = 3-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1-(pyrimidin-2-yl)-1H-imidazolylidene), [Pd-2(L-2)(2)Cl-2](PF6)(2), and [Pd(L-2)(2)](PF6)(2) (L-2 = 1-butyl-3-(1-(pyridin-2-yl)-1H-1,2,3-triazol-4-yl)methyl)imidazolylidene) have been synthesized and fully characterized by NMR, elemental analysis, and X-ray crystallography. The silver complex [Ag-4(L1)(4)](PF6)(4) consists of a Ag-4 zigzag chain. The complexes [Pd(L1)Cl](PF6) and [Pt(L1)Cl](PF6), containing a nonsymmetrical NCN' pincer ligand, are square planar with a chloride trans to the carbene donor. [Pd-2(L-2)(2)Cl-2](PF6)(2) consists of two palladium centers with CN2Cl coordination mode, whereas the palladium in [Pd(L-2)(2)](PF6)(2) is surrounded by two carbene and two triazole groups with two uncoordinated pyridines. The palladium compounds are highly active for Suzuki-Miyaura cross coupling reactions of aryl bromides and 1,1-dibromo-1-alkenes in neat water under an air atmosphere.