Acyclic Palladium(II)‐N‐heterocyclic Carbene Metallacrown Ether Complexes: Synthesis, Structure and Catalytic Activity

Abstract

Abstract Novel acyclic Pd(II)‐ N ‐heterocyclic carbene (NHC) metallacrown ethers 5a , 5b have been synthesized. Reaction of the imidazolium salts bearing a long polyether chain with Ag 2 O afforded Ag‐NHC complexes, which then reacted as carbene transfer agent with PdCl 2 (MeCN) 2 to give the desired acyclic Pd(II)‐NHC metallacrown ether complexes 5a and 5b . The 1 H NMR and 13 C NMR spectra show 5a and 5b exist as mixtures of cis and trans isomers in solution. The trans isomer of 5a was characterized by X‐ray diffraction, which clearly demonstrated two pseudo‐crown ether cavities in trans ‐ 5a . Pd(II)‐NHC complexes 5a and 5b have been shown to be highly effective in the Suzuki‐Miyaura reactions of a variety of aryl bromides in neat water without the need of inert gas protection.