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 (<b>4</b>) was prepared by sequential metal–halogen exchange reaction of 1-methyl-4,5-diiodoimidazole (<b>1</b>) followed by a quaternization reaction with methyl iodide. The metal–carbene complexes <b>6</b>, <b>8</b>, and <b>10</b> 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 <b>10</b> was found to be catalytically active in Suzuki–Miyaura coupling reactions of aryl bromides