Backbone Thio-Functionalized Imidazol-2-ylidene–Metal Complexes: Synthesis, Structure, Electronic Properties, and Catalytic Activity

Abstract

A new synthetic route to prepare imidazolium salts with heteroatom-containing functional groups at the backbone has been reported. Accordingly, the first example of a backbone bis-thiofunctionalized imidazolium salt (4) was prepared by sequential metal–halogen exchange reaction of 1-methyl-4,5-diiodoimidazole (1) followed by a quaternization reaction with methyl iodide. The metal–carbene complexes 6, 8, and 10 were synthesized conveniently through three different routes, namely, (a) an in situ generated carbene route, (b) a transmetalation method, and (c) direct reaction with a basic metal precursor, and structurally characterized. Subsequently the electronic properties of the newly prepared 1,3-dimethyl-4,5-bis(phenylthio)-imidazol-2-ylidene ((SPh)2IMe) was studied by measuring the carbonyl stretching frequency of the corresponding [Ir{(SPh)2IMe}(CO)2(Cl)] complex. In addition, the air-stable palladium–NHC complex 10 was found to be catalytically active in Suzuki–Miyaura coupling reactions of aryl bromides.