N‑Heterocyclic\nCarbene (NHC) Ligand Exchange\nof Bis(NHC)–Pd(II) Complexes

N-heterocyclic\ncarbene (NHC)–Pd(II) bonds are\nrecognized\nas rather robust bonds to equip palladium(II) centers with decent\nstability and stereoelectronic tunability. In this report, the authentic\ncarbene–Pd(II) bonds in <i>N</i>-ammonium- and sulfonate-functionalized\nNHC complexes were activated, and NHC ligand exchange was triggered\nto afford four well-defined, sulfobetaine-type, zwitterionic heterobiscarbene\ncomplexes. Combined experimental studies and density functional theory\ncalculations indicated that electrostatic interactions play a minimal\nrole in the energy of this reaction; instead, the exchange appears\nto be driven primarily by the precipitation of the resulting zwitterionic\ncomplexes.