NHC Pd(II) and Ag(I) Complexes: Synthesis, Structure, and Catalytic Activity in Three Types of C–C Coupling Reactions

Four bis-benzimidazolium salts, 1,4-bis[1'-( N -R-benzimidazoliumyl)methyl]-2,3,5,6-tetramethylbenzene 2X - ( L 1 H 2 ·(PF 6 ) 2 : R = ethyl, X = PF 6 ; L 2 H 2 ·Br 2 : R = picolyl, X = Br; L 3 H 2 ·Br 2 : R = benzyl, X = Br; and L 4 H 2 ·Br 2 : R = allyl, X = Br), and their three N -heterocyclic carbene (NHC) Pd(II) and Ag(I) complexes, L 1 Pd 2 Cl 4 ( 1 ), L 2 Ag 2 Br 2 ( 2 ), and L 4 (AgBr) 2 ( 3 ), as well as one anionic complex L 3 H 2 ·(Ag 4 Br 8 ) 0.5 ( 4 ), have been synthesized and characterized. Complex 1 adopts a funnel-like type of structure, complex 2 adopts a cyclic structure, and complex 3 is an open structure. In the crystal packing of 1 - 4 , one-dimensional polymeric chains and two-dimensional supramolecular layers are formed via intermolecular weak interactions, including hydrogen bonds, π-π interactions, and C-H···π contacts. The catalytic activities of NHC Pd(II) complex 1 in three types of C-C coupling reactions (Suzuki-Miyaura, Heck-Mizoroki, and Sonogashira reactions) were studied. The results show that this catalytic system is efficient for these C-C coupling reactions.