Selenium-Containing N-Heterocyclic Carbenes and Their First Palladium(II) Complexes: Synthesis, Structure, and Pendent Alkyl Chain Length Dependent Catalytic Activity for Suzuki–Miyaura Coupling

Abstract

Three new N-alkyl-N′-(2-ethyl-1-selenophenyl)imidazolium salts, L1–L3 (differing in the chain length of alkyl substituent of N), which are precursors to (Se, CNHC) ligands and their N-heterocyclic carbene (NHC) complexes [Pd(L-HX)Cl2] (1–3) [L = L1–L3, X = I/Br], have been synthesized and characterized by multinuclear NMR and HR-MS. For the synthesis of Pd complexes 1–3 from appropriate imidazolium salts (L1–L3), the route of the silver carbene transfer reaction has been adopted. Single-crystal structures of 1 and 2 have been established with X-ray diffraction. Thermally stable, moisture- and air-insensitive complexes 1–3 have been found to be efficient catalysts for Suzuki–Miyaura coupling reactions (yield up to 96% in 2 h at 80 °C). Nanoparticles (NPs) (size of 80–85% particles ∼2–5 nm) formed in the beginning of these reactions (i.e., when the temperature of the reaction mixture reaches 80 °C) appear to be important for catalytic coupling, probably as dispensers of Pd(0), and contain Pd and Se. The Pd:...