Alkylamino Imidazolium salts as NHC carbene precursors and metal nanoparticles stabilizers

The synthesis of the Boc-protected 1-(2-NHBoc-ethyl)-3-R-imidazolin-2-ylidene, NHBociy, (R = Me, (1a), allyl (1b), benzyl, (1c)) and their straightforward transformation into the deprotected NH2iy (2a-c) is reported. The salts [1]X and [2]X (X = I, Br, PF6, BF4, NO3) are all viscous liquids at room temperature and can be considered as ionic liquids (ILs)1 whereas the tetrachloroaurate salts are yellow solids. Imidazolium salts are typical N-Heterocyclic carbene (NHCs) precursor2 and the reaction with Ag2O leads to the formation of silver carbenes Ag(I)-NHCs presenting in the solid state different bonding motifs determined by X-ray diffraction analysis, whereas PGSE NMR experiments were employed to investigate the hydrodynamic dimension of the imidazolium salts and silver complexes and, consequently, to gain information on the level of aggregation in solution. PGSE NMR studies were complemented by NOE NMR investigations in order to obtain information on anion-cation relative orientation within aggregates.3 Rh(I)- and Pd(II)-NHC complexes were obtained either by i) direct deprotonation of the imidazolium salts with suitable metal precursors or ii) by using the silver complexes as transmetallating agents; properties of the resulting complexes were studied with NMR spectroscopy and X-ray crystallography. Alongside with the NHC research line described above we have started to investigate the role of 2 as stabilizers for the synthesis of gold and silver nanoparticles and in the second part of this contribution preliminary results concerning this topic will be presented.4,5 [1] Wasserscheid, P.; Welton, T. (Ed.), Ionic Liquids in Synthesis, Wiley-VCH, Weinheim, Germany, 2002, p. 1. [2] Crabtree, R.H. Coord. Chem. Rev. 2007, 251, 595 ff.: a volume completely dedicated to recent developments in the organometallic chemistry of N-heterocyclic carbenes. [3] Busetto, L.; Cassani, M.C.; Femoni, C.; Macchioni, A.; Mazzoni, R.; Zuccaccia, D. J.Organomet.Chem. 2008 in press. [4] Dahl, J.A.; Maddux, B.L.S.; Hutchinson, J.E. Chem. Rev. 2007, 107, 2228. [5] Ballarin, B.; Cassani, M.C.; Scavetta, E.; Tonelli, D. Electroch. Acta 2008 in press.