The iridium complex [Cp*Ir(biimH₂)(H₂O)][OTf]₂ (Cp* = η⁵-pentamethylcyclopentadienyl, biimH₂ = 2,2′-biimidazole) was synthesized and developed as a new-type of water-soluble metal–ligand bifunctional catalyst for the N-alkylation of poorly nucleophilic sulfonamides with alcohols in water. In the presence of catalyst (1 mol%) and Cs₂CO₃ (0.1 equiv.), a series of desirable products was obtained in 74–91% yields under microwave irradiation. Mechanistic experiments revealed that the presence of NH units in the imidazole ligand is crucially important for the catalytic activity of the iridium complex. Notably, this research would facilitate the process of water-soluble metal–ligand bifunctional catalysis for the hydrogen autotransfer process.