Tw on aphthalene-diimide (NDI) bis-imidazolium salts have been used as N-heterocyclic carbene (NHC) precursors for the preparation of NDI-functionalized complexes of rhodium and iridium of general formula [MCl(NDI-NHC)(COD)] (M = Rh, Ir;N DI-NHC = NDI-functionalized NHC ligand). Comparison of the IR spectra of the complexes [IrCl(NDI-NHC)(CO) 2 ]a nd their related one-and twoelectron reduced forms,reveal that each one-electron reduction produces ad ecrease of the average n(CO) of 9-10 cm À1 , indicating asignificant enhancement of the electron-richness of the metal. The [MCl(NDI-NHC)(COD)] complexes were tested in the catalytic cycloisomerization of alkynoic acids. The one-electron reduced forms showed greatly enhanced activities.F or the cyclization of 5-hexynoic acid, the twoelectron reduction of the ligand produced further enhancement of the catalytic activity,therefore showing that the catalyst can switch between three redoxspecies with three distinct catalytic activities.

The reaction between an angular bis-imidazolidinium salt and [AuCl(SMe) 2 ] allowed the preparation of a discrete digold complex, with a rigid angular bridging bis-imidazolindiylidene ligand. This complex reacts with a diethynylcarbazole to afford a tetragold cyclophane that contains two bis-imidazolindiylidenes and two carbazolyl-diethynyl ligands. Both the dimetallic and the tetrametallic complexes have been characterized by spectroscopic techniques and by singlecrystal X-ray diffraction. Due to the geometric constraints of the ligands, the cyclophane deviates from the expected planarity and shows a twisted structure. The work demonstrates that the rigid angular di-NHC ligand is a suitable scaffold for the reliable construction of organometallic-based metallosupramolecular assemblies.

A pyrene-connected tetra-imidazolium salt has been prepared starting from commercially available 1,3,6,8-tetrabromopyrene, and used as tetra-NHC precursor in the preparation of tetranuclear Rh­(I) and Ir­(I) complexes. The tetra-NHC ligand displays axial chirality upon coordination to the MCl­(cod) (M = Rh and Ir) fragments, giving rise to right- and left-handed helix conformations. The catalytic activity of the resulting complexes was studied in two relevant reactions that lead to the formation of five- and six-membered oxygen-containing heterocycles, namely, the cyclization of acetylenic carboxylic acid and the coupling of diphenyl­cyclo­propenone with substituted phenylacetylenes.

A pyrene tetraalkynyl ligand has been used for the preparation of three different tetraalkynyl Au(I) complexes. Two of these complexes display fluorescent emission in CH 2 Cl 2 solution, with quantum yields exceeding 90%. Although the emission is mainly due to ligand-centered excited states, the presence of the metal center is key to reaching such excellent quantum yield values, providing an extra rigidity to the system and therefore, minimizing the nonradiative deactivation pathways. To the best of our knowledge, these quantum yields lie among the highest reported for metal-based luminophores in solution, a quality that makes them resemble molecular torches. Preliminary studies on healthy cheek cells show that one of the complexes is efficiently and rapidly taken up into the cell.