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

Abstract

Four bis-benzimidazolium salts, 1,4-bis[1′-(N-R-benzimidazoliumyl)methyl]-2,3,5,6-tetramethylbenzene 2X– (L1H2·(PF6)2: R = ethyl, X = PF6; L2H2·Br2: R = picolyl, X = Br; L3H2·Br2: R = benzyl, X = Br; and L4H2·Br2: R = allyl, X = Br), and their three N-heterocyclic carbene (NHC) Pd(II) and Ag(I) complexes, L1Pd2Cl4 (1), L2Ag2Br2 (2), and L4(AgBr)2 (3), as well as one anionic complex L3H2·(Ag4Br8)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.