The newly prepared carbene precursor 1,3-dimesitylacenaphtho[1,2-d]imidazolinium chloride, (NHC-H)Cl, 3, could be readily converted into the NHC-silver(l) complex, 4, which is an efficient carbene transfer agent and has been used to synthesise thione 5, trans-[PdCl2(NHC)(2)], 6 and [RhCl(NHC)(COD)], 7. All compounds synthesised were characterised by elemental analysis, NMR spectroscopy and the molecular structures of the thione 5 and complex 7 were determined by X-ray crystallography. Complex 7 was converted into cis-[RhCl(NHC)(CO)(2)] and the electron donating properties and trans influence of the NHC ligand were compared with nonamillated counterparts. The catalytic activity in the Heck reaction of 6 and the in situ formed palladium complex was evaluated. The activity of the in situ formed complexes for the Heck coupling of alkenes was high. (c) Wiley-VCH Verlag GmbH & Co.