Self-Assembly of Palladium-Based Macrocycles with N-Heterocyclic Carbene as the “Corner” Ligand

Metallacyclic complexes [(MesC−Cmeth)Pd(L)]2(OTf)4 (MesC−Cmeth = 1,1′-dimesityl-3,3′-methylenediimidazolin-2,2′-diylidene; L = 4,4′-dithiodipyridine (L1) (5), 1,2-bis(4-pyridylthio)ethane (L2) (6), 1,3-bis(4-pyridylthio)propane (L3) (7)) were obtained by the self-assembly of [(MesC−Cmeth)Pd(CH3CN)2](OTf)2 with flexible pyridine-based ligands L1−L3 in high yields. The reaction of [(MesC−Cmeth)Pd(CH3CN)2](OTf)2 with a rigid pyrazine ligand led to the formation of mononuclear [(MesC−Cmeth)Pd(pyrazine)2](OTf)2 (4), which can be ascribed to the effect of the steric bulk of the substituent. Complexes 4−6 have been well characterized by elemental analyses, 1H NMR and IR spectra, and single-crystal molecular structure analysis.