A series of alkylammonium-imidazolium chloride salts [RImH(CH 2) n NMe 2 ]Cl•HCl (R = Me, t-Bu, Mes, n = 2, 3) have been prepared by alkylation of 1-substituted imidazole compounds with the corresponding chloro-alkyl-dimethylamine hydrochloride. These salts are precursors for the synthesis of a library of rhodium (I) complexes containing amino-alkyl functionalized N-heterocyclic carbene (NHC) ligands with hemilabile character by varying the substituent on the heterocyclic ring and the length of the linker with the dimethylamino moiety. The monodeprotonation of alkylammoniumimidazolium salts with NaH in the presence of [{Rh(µ-Cl)(cod)} 2 ] gave the amino-imidazolium salts [RImH(CH 2) n NMe 2 ][RhCl 2 (cod)]. Further deprotonation with NaH under non anhydrous conditions gave the neutral complexes [RhCl(cod)(RIm(CH 2) n NMe 2)] in good yields. The abstraction of the chloro ligand by silver salts rendered the cationic complexes [Rh(cod)(κ 2 C,N-RIm(CH 2) 3 NMe 2)][BF 4 ] (R = Me, Mes) by coordination of the NMe 2 fragment of the sidearm of the functionalized NHC ligands. The catalytic activity of the rhodium complexes in the hydrosilylation of terminal alkynes using HSiMe 2 Ph has been investigated with Ph-C≡CH, t-Bu-C≡CH, n-Bu-C≡CH, and Et 3 Si-C≡CH as substrates. Higher activities were achieved using neutral complexes having small substituents at the heterocyclic ring (R = Me). Excellent selectivities in the β-(Z)-vinylsilane isomer were found in the hydrosilylation of 1hexyne and predominantly the β-(E) and α-bis(silyl)alkene isomers were obtained in the hydrosilylation of triethylsilylacetylene.

Synthesis of a planar, π-conjugated pyridazine-based biscarbene is reported. Starting from 3,6-dimethylpyridazine, the bisimidazolium salt 1*2HPF 6 was prepared in a four-step synthesis by chlorination, amination, formylation, and cyclization. The free carbene 1 can be generated in situ by addition of base. Despite the rigid annelated tricycle, the carbene ligand turns out to be highly flexible upon coordination of transition-metal complexes. With silver(I) oxide or copper(I) oxide binuclear carbene complexes with a bridging coordination mode of the ligand are obtained. Transmetalation of both complexes to the respective gold complex is described. The bridging coordination mode of the carbene ligand is similar to that of 2,2′-bipyridine. Reaction of the bisimidazolium salt 1*2HPF 6 with potassium acetate and [RhCl(COD)] 2 leads to a mononuclear rhodium complex with the chelating binding mode of 1, resembling strongly the coordination properties of 1,10-phenanthroline.

Binuclear complexes of copper, silver, and gold bearing a 2,2′-bipyridine analogue, the pyridazine annelated bis(N-heterocyclic carbene) ligand (vegi) 1, were prepared and structurally characterized. They all feature the shortest metal− metal distances that have been measured so far in complexes with this structural motif bearing neutral bidentate ligands, indicative of d 10 −d 10 interactions. While in the silver complex the linear coordination of each silver atom with two carbene ligands results in a planar complex, the ligand planes are twisted by 70°in the Cu complex 4 and by 31°in the gold complex 3. The copper complex shows a solvent-dependent equilibrium between the [Cu 2 L 2 ] 2+ complex and a [Cu 2 L 3 ] 2+ complex along with solvated CuPF 6 .

Synthesis of a new example of the pyridazine annelated bis(N-heterocyclic carbene) ligand 3b (vegi) bearing benzyl substituents is reported, as well as the synthesis of its cationic Rh(cod) complex 5b. The mechanism of formation of the [Rh(cod)(vegi)] + complexes was investigated, showing a stepwise deprotonation of the imidazolium moieties via the mono-carbene imidazolium Rh(cod)Cl species 4. The [Rh-(cod)(vegi)] + complexes 5a,b show catalytic activity in the transfer hydrogenation of even sterically hindered ketones.