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

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.