This report describes the synthesis of water-soluble silver(I) and platinum(II) complexes bearing sulfonated mono- or dianionic N-heterocyclic carbene ligands. Thus, treatment of the corresponding zwitterionic imidazolium derivative with silver(I) oxide in water afforded the light-sensitive bis(carbene) complexes Ag[Ag(NHC)2] (2 Ag+ ), which were transformed into the stable salts Na[Ag(NHC)2] (2) by addition of sodium chloride. In contrast, the same reaction in dmso afforded mono(carbenes) of general formula Na[AgCl(NHC)] (3). The solvent-dependence of the reaction product can be rationalized on the basis of the equilibrium [AgCl2]− ↔ AgCl + Cl–. The precipitation of silver chloride is more favored in protic solvents than in aprotic solvents such as dmso, thus explaining the formation of bis(carbenes) in water. The formation of silver chloride may also promote the hydrolysis of silver NHC complexes under some conditions. The water-soluble platinum(II) complexes Na[PtCl2(dmso)(NHC)] were synthesized by using either mono(carbene) silver complexes 3 as carbene-transfer agents or by direct metalation of the imidazolium salt with cis-[PtCl2(dmso)2] in the presence of NaHCO3 as base. The (NHC)Pt(II) complexes were tested as catalysts for the hydration of alkynes in the aqueous phase and found to be active in neat water without the need for acidic cocatalysts.

The synthesis and characterization of new watersoluble platinum(0) complexes bearing sulfonated N-heterocyclic carbene (NHC) and divinyltetramethylsiloxane (dvtms) ligands are described. These complexes, of the general formula (NHC)Pt(dvtms), are active and recyclable catalysts for the hydrosilylation of phenylacetylene and other alkynes at room temperature in water. Our findings indicate that the NHC−Pt(0) bonds are reasonably stable under these catalytic conditions, although hydrolysis is observed at temperatures above 80 °C in pure water.

Arylamines have been converted into aryltrimethylammonium salts, which on reaction with sodium trimethylstannide (1) in liquid ammonia afford aryltrimethylstannanes by the S RN 1 mechanism. With (4-methoxyphenyl)-(2), (1-naphthyl)-(4), phenyl-(6), (4-acetylphenyl)-(8), and (4-cyanophenyl)trimethylammonium salts (10) the substitution products are obtained in good to excellent yields (45-100%). Also, the photostimulated reaction of (2-pyridyl)trimethylammonium iodide (12) with 1 leads to the substitution product 13 (50%). With (4-chlorophenyl)trimethylammonium iodide (14) the disubstitution product 19 is obtained in 76% yield. On the other hand, the results obtained in the reaction of (4-bromophenyl)trimethylammonium iodide (15) with 1 clearly indicate a fast HME reaction in the dark. The ET process (S RN 1) competes, although inefficiently, under irradiation.

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Comparative studies were carried out with the addition of different silver salts. Our results indicate that the bulkier complex is the most effective and that the addition of methanol as co-solvent not only shortens reaction times but also stabilizes the less bulky complexes.