The nine new heteroaryl-substituted imidazolidinium (1a-c), pyrimidinium (2a-c) and diazepinium (3a-c) salts as N-heterocyclic carbene (NHC) precursors were synthesized in good yields and entirely characterized using elemental analyses and conventional spectroscopic methods. In situ formed complexes from heterocyclic salts (1-3), Pd(OAc)(2) and in the presence of KOBu (t) as a base were tested as catalysts for the Mizoroki-Heck coupling reaction in an aqueous media and very high yields were achieved. 1,3-Di(5-methylthiophen-2-ylmethyl)pyrimidinium hexafluorophosphate salt (2b) was structurally characterized by single-crystal X-ray diffraction. In the 2b compound (C16H21N2S2)(+)[PF6](-), the terminal thiophene rings are twisted with a dihedral angle of 72.8(3)A degrees. In the pyrimidine ring, the three successive C atoms between the N atoms are disordered over two positions [occupancy ratio 0.753(12):0.247(12)]. In the crystal, neighboring molecules are linked by C-HaEuro broken vertical bar F hydrogen bonds, running along the b axis.