 Surprisingly, calculations reveal that the Pd–Ag heterodimeric transition state leads to "meta"-selectivity while the Pd monomeric transition state leads to "ortho"-selectivity.The role of mono-"N"-protected amino acid is proposed as a dianionic ligand which participates in the CMD step assisting the deprotonation of the C–H bond in the rate- and regio-determining step.Originally discovered by Frost and co-workers, the meta selective sulfonation of 2-phenylpyridine using a sulfonyl chloride coupling partner, utilising a ruthenium(II) catalyst.