Reactivity of Proton at C2 Position in Imidazolium Ion

The strong acidity of the proton at the C2 position of a [AMIM] ion has been well recognized 183). This cation can react with palladium complexes to form inactive l,3-dialkylimidazol-2-ylidene palladium complexes 200), as confirmed in a study of the conventional Pd(OAc)2/PPh3/base catalyst in ionic liquids for the telomerization of butadiene with methanol at 85°C 201). 

The detrimental effect of the reactive proton-donor group in the [AMIM] ion was further confirmed by the use of an ionic liquid with the proton at the C2 position replaced by a methyl group. The palladium catalyst in [BDMIM]PF6 showed high activity and selectivity in a biphasic system that allowed reaction with multiple recycles and little loss of activity. 

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