Isolation of a Cyclic Trinuclear Gold(I) Complex with Metalated Phosphorus Ylides: Synthesis and Structural Properties.

The first chiral and luminescent cyclic trinuclear gold(I) complex, [{AuCH(PPh2Me)(Ph2P)}3]3+, has been isolated with metalated phosphorus ylides (PY). This complex was initially obtained through the reaction of either mononuclear [C6F5SAuCH(PPh2Me)(Ph2P)]OTf or dinuclear [C6F5S{AuCH(PPh2Me)(Ph2P)}2](OTf)2 thiolate-gold-phosphane complexes in the presence of NaH, followed by the abstraction of the thiopyridine moiety employing either AgOTf or [Cu(CH3CN)4]PF6. Our quest for a more efficient synthesis route led to the development of a streamlined one-pot synthesis method, employing Ag(acac) as both a halogen abstractor and a base, offering a quicker and more direct path to this intriguing trimer. Comprehensive computational studies have unveiled the luminescent characteristics of this complex, which can be attributed to phosphorescence. These emissions originate from ligand-to-metal (LMCT) and metal-centered (MC) charge transfer excited states. Furthermore, the structural analysis via X-ray crystallography corroborated the formation of a trimeric species, featuring three monomers with the [AuCH(PPh2Me)(Ph2P)] motif. Each monomer exhibits a single chiral center, leading to four possible absolute configurations (RRR, RRS, RSR, and SRR). NMR and X-ray spectroscopy have provided valuable insights, establishing that the former configuration (RRR) is disfavored due to steric hindrance, while the three remaining configurations can interconvert, arising from the structural arrangement of the metallacycle and inherent symmetry operations.

Steric and Electronic Effects in N-Heterocyclic Carbene Gold(III) Complexes: An Experimental and Computational Study.

A series of neutral acridine-based gold(III)-NHC complexes containing the pentafluorophenyl (-C6F5) group were synthesized. All of the complexes were fully characterized by analytical techniques. The square planar geometry around the gold center was confirmed by X-ray diffraction analysis for complexes 1 (Trichloro [1-methyl-3-(9-acridine)imidazol-2-ylidene]gold(III)) and 2 (Chloro-bis(pentafluorophenyl)[1-methyl-3-(9-acridine)imidazol-2-ylidene]gold(III)). In both cases, the acridine rings play a key role in the crystal packing of the solid structures by mean of π-π stacking interactions, with centroid-centroid and interplanar distances being similar to those found in other previously reported acridine-based Au(I)-NHC complexes. A different reactivity when using a bulkier N-heterocyclic carbene ligand such as 1,3-bis-(2,6-diisopropylphenyl)-2-imidazolidinylidene (SIPr) was observed. While the use of the acridine-based NHC ligand led to the expected organometallic gold(III) species, the steric hindrance of the bulky SIPr ligand led to the formation of the corresponding imidazolinium cation stabilized by the tetrakis(pentafluorophenyl)aurate(III) [Au(C6F5)4]- anion. Computational experiments were carried out in order to figure out the ground state electronic structure and the binding formation energy of the complexes and, therefore, to explain the observed reactivity.

Thiolate Bridged Gold(I)-NHC Catalysts: New Approach for Catalyst Design and its Application to Trapping Catalytic Intermediates.

New dinuclear N-heterocyclic gold complexes with bridging thiolate ligands have been designed as catalytic precursors with desired properties such as stability, recyclability and that do not require additives. The dinuclear compound [(AuNHC)2 (µ-SC6 F5 )]OTf could slowly release the active catalytic species [Au(NHC)]+ and the precursor [Au(SC6 F5 )(NHC)] in solution, which means that both species would remain stable throughout the catalytic cycle and the pre-catalyst could easily be recovered. The properties exhibited by the complexes have been taken advantage of to gain new insights on the gold-catalyzed hydroalkoxylation of alkynes, with the aim of clarifying all the steps of the catalytic cycle, together with the characterization of intermediates and final products. Isolation and characterization of the pure final spiroketals and the thermodynamic intermediate have been achieved for the first time. Moreover, the kinetic intermediate has also been detected for the first time.

Recent advances in gold-NHC complexes with biological properties.

This tutorial review covers the recent advances made in the study of gold complexes containing N-heterocyclic carbene ligands with biological properties. The great stability, ease of modulation of the electronic properties and excellent σ-donating capacity displayed by NHCs allow gold-NHC derivatives to reach high stability in biological media and relatively good internalization into cells and for that they have emerged as excellent potential chemotherapeutics. The new gold-NHC derivatives show superior anticancer activity compared to other standards such as Cisplatin or Auranofin. In addition, the application of gold-NHC complexes in the treatment of other human diseases as antibacterial, antioxidant and antiparasitic agents is reviewed for the first time.

Gold Catalyzed Multicomponent Reactions beyond A³ Coupling.

The preparation of complex architectures has inspired the search for new methods and new processes in organic synthesis. Multicomponent reactions have become an interesting approach to achieve such molecular diversity and complexity. This review intends to illustrate important gold-catalyzed examples for the past ten years leading to interesting skeletons involved in biologically active compounds.

Cytotoxicity and biodistribution studies of luminescent Au(i) and Ag(i) N-heterocyclic carbenes. Searching for new biological targets.

A range of fluorescent and biologically compatible gold(i)-N-heterocyclic carbenes bearing acridine as a wingtip group and either a 2-mercaptopyridine or a tetra-O-acetyl-1-thio-ß-d-glucopyranoside as an ancillary ligand has been synthesised. Their luminescence, cytotoxicity and biodistribution have been investigated together with those of analogous gold(i) and silver(i) chloride- and bis-NHC complexes. All complexes displayed emissions based on IL transitions centred on the acridine moiety. The cytotoxic activity measured in lung, A549, and pancreatic, MiaPaca2, carcinoma cell lines revealed a general cytotoxicity pattern (thiolate > biscarbene > chloride derivatives) and flow cytometry assays pointed towards apoptosis as the cell death mechanism. Moreover, fluorescence cell microscopy disclosed an unusual biodistribution behavior, being mainly localised in lysosomes and to a lesser extent in the nucleus. Preliminary DNA interaction experiments suggested the metal fragment and not the acridine moiety as responsible for such biodistribution, which widen the scope for new biological targets.

Highly Efficient Catalysis of Retro-Claisen Reactions: From a Quinone Derivative to Functionalized Imidazolium Salts.

A new and efficient method for the preparation of several imidazolium salts containing an ester group in the C4 position of the aromatic ring through a retro-Claisen reaction pathway between a quinone derivative and several alcohols is described. This new organic transformation proceeds in the absence of a catalyst, but it is greatly catalyzed by different Lewis acids, especially with AgOAc at a very low catalyst loading and in very short reaction times. The process takes place by the nucleophilic attack of the carbonyl groups by the alcohol functionality, thus promoting a double C-C bond cleavage and C-H and C-O bond formation. This reaction represents the first example of this type between a quinone derivative and alcohols.

N-Heterocyclic carbene metal complexes: photoluminescence and applications.

This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine.

Three-coordinate gold(I) N-heterocyclic carbene complexes: a new class of strongly luminescent derivatives.

A selected group of cationic three-coordinate Au(I)-NHC complexes of the form [Au(NHC)(dppbz)]OTf have been prepared from a commercially available bidentate phosphine. All complexes have been fully characterised by NMR and mass spectroscopy. The [Au(NHC)](+) fragment shows a pronounced tendency to form linear complexes which is confirmed by the molecular structure of [Au(IPr)(dppbz)]OTf in the solid state. The complexes are brightly luminescent and present very high quantum yield values in the solid state. The assignments of the electronic transitions involved in the emissions are of a phosphorescent nature and it is proposed that the origin of the emissions is derived from the ligand (dppbz) to metal-ligand (Au-NHC) charge-transfer (LML'CT) transition.

Simple and efficient synthesis of [MCI(NHC)] (M = Au, Ag) complexes.

A facile and efficient synthetic route leading to catalytically relevant N-heterocyclic carbene (NHC) gold complexes is described. The method consists of one pot synthesis starting from readily available imidazolium salts and [AuCl(tht)], in the presence of K2CO3. Using the same protocol NHC silver complexes have been synthesised starting from AgNO3.

Influence of the group 11 metal on the emissive properties of complexes [M{(PR2)2C2B9H10}L].

The metal atoms in group 11 complexes [M{(PR2)2C2B9H10}L] [R = Ph, (i)Pr; L = tertiary phosphane; M = Au, Ag, Cu] play an important role in the emissive properties of these compounds. The influence of the metal follows the order Au ≫ Ag ≥ Cu. The three-coordinated complexes are obtained from the reaction of [AuClL], [Ag(OTf)L], or [Cu(NO3)(PPh3)2] with the closo carborane diphosphane in refluxing ethanol. For L = PPh2NHPy, cleavage of the P-N bond and the formation of the monophosphane PPh2OEt are observed, depending on the metal and the nido carborane diphosphane substituent ((i)Pr or Ph).

N-Heterocyclic carbene ligands as modulators of luminescence in three-coordinate gold(I) complexes with spectacular quantum yields.

The first three-coordinate gold(I) N-heterocyclic carbene (NHC) complexes have been prepared with the nido-carborane diphosphine. The complexes are brightly luminescent and present very high quantum yield values. The carbene ligand is able to modulate the energy of the emissions and, depending upon the substituent, the luminescence changes from blue to green. Theoretical calculations corroborate that the emissions are phosphorescence and arise from charge transfer (LML'CT) transitions from nido-carborane ligand (L) to metal/ligand group "gold(I)-NHC ligand" (ML').