The choice of aryl halide or pseudohalide substrate (sp-carbon) is one of the factors that mainly influence the reactivity of the Sonogashira catalytic system. The reactivity of halides is higher towards iodine, and vinyl halides are more reactive than analogous aryl halides. The coupling of aryl iodides proceeds at room temperature, while aryl bromides require heating.
This difference in reactivity can be exploited to selectively couple an aryl iodide but not an aryl bromide, by performing the reaction at room temperature. An example is the symmetrical Sonogashira coupling of two equivalents of 1-bromo-4-iodobenzene with trimethylsilylacetylene (with the trimethylsilyl group removed in-situ) to form bis(4-bromophenyl)acetylene.
Aryl triflates can also be employed instead of aryl halides.