Heterobimetallic propargyl gold complexes with p-bound copper or silver with enhanced anticancer activity

Several propargyl functionalised substrates with different heteroatoms (N, O or S) have been used for the preparation of propargyl gold(i) phosphine complexes. The complexes were prepared in high yields either by reaction of the substrate with [Au(acac)PPh3] or by reaction of [AuCl(PPh3)] with potassium hydroxide and the substrate in methanol. Several of the complexes have been characterised by X-ray diffraction showing the presence of secondary bonds such as p-stacking and aurophilic interactions. The reaction of the propargyl gold(i) phosphine complexes with [Cu(NO3)(PPh3)2] or [Ag(OTf)(PPh3)2] afforded heterobimetallic complexes with p-coordination of {Cu(PPh3)2} or {Ag(PPh3)2} to the alkyne bond. When the substituent of the propargyl unit contained more strongly coordinating pyridine moieties, [(PyCH2)2NCH2CCAuPPh3], coordination of the heterometal to the pyridine units occurred, displacing the phosphine groups and giving rise to a dimeric structure. The antiproliferative activity of the complexes against cisplatin resistant lung cancer cell line A549 was determined by MTT assay. The mononuclear gold complexes showed excellent activities with IC50 values < 14 µM. Coordination of copper of silver to the alkynyl fragment resulted in a significant increase in activity suggesting a synergistic effect between the two metal centres

Catalysis-free synthesis of thiazolidine–thiourea ligands for metal coordination (Au and Ag) and preliminary cytotoxic studies

The reaction of propargylamines with isothiocyanates results in the selective formation of iminothiazolidines, aminothiazolines or mixed thiazolidine–thiourea compounds under mild conditions. It has been observed that secondary propargylamines lead to the selective formation of cyclic 2-amino-2-thiazoline derivatives, while primary propargylamines form iminothiazoline species. In addition, these cyclic thiazoline derivatives can further react with an excess of isothiocyanate to give rise to thiazolidine–thiourea compounds. These species can also be achieved by reaction of propargylamines with isothiocynates in a molar ratio of 1 : 2. Coordination studies of these heterocyclic species towards silver and gold with different stoichiometries have been carried out and complexes of the type [ML(PPh3)]OTf, [ML2]OTf (M = Ag, Au) or [Au(C6F5)L] have been synthesised. Preliminary studies of the cytotoxic activity in lung cancer cells have also been performed in both ligands and complexes, showing that although the ligands do not exhibit anticancer activity, their coordination to metals, especially silver, greatly enhances the cytotoxic activity

Alkylation of amines with allylic alcohols and deep eutectic solvents as metal-free and green promoters

A novel approach for the allylic alkylation of anilines, hydrazides, indole derivatives and additional interesting nucleophiles is described, which involves the direct use of a variety of allylic alcohols under very mild conditions, such as room temperature, and the use of sustainable deep eutectic solvents (DESs). The search for the optimum DES to be used in the reaction revealed that a simple mixture of choline chloride (ChCl) and lactic acid provides excellent results for a wide range of substrates with high isolated yields. This methodology represents a significant improvement compared to other procedures described in the literature, for which high temperatures, stronger reaction conditions or metal catalysts are usually required. In some cases, this protocol provides the first examples of trapping allylic carbocations with indole derivatives. In addition, challenging nucleophiles such as amides, carbamates, azides or sulfonamides, among others, have also been successfully used. All these features render this procedure an appealing and green alternative compared to other examples reported in the literature on the alkylation of amines by allylic alcohols. Preliminary mechanistic studies using unsymmetrically substituted alcohols support that the reaction could proceed via an SN1 pathway

Unravelling the role of triisopropylphosphane telluride in Ag(I) complexes

The coordination chemistry of chalcogenide ligands has always attracted significant interest in the field of inorganic chemistry, especially for soft metals such as those of group 11. Despite the scarcity of research on phosphane tellurides, we report on the synthesis and characterisation of five novel silver complexes containing the phosphane telluride ligand, TeP(iPr)3, along with other ancillary ligands such as mono or diphosphanes. Spectroscopic studies were performed to investigate the behaviour of these complexes, including their redox properties, as demonstrated by the 1,1′-diphenylphosphaneferrocene (dppf) silver derivatives. Additionally, these complexes showcase remarkable rapid interchange equilibrium, revealing silver species with distinctive Ag2Te2 cores and a combination of bridging and terminal TeP(iPr)3 ligands. A promising avenue for further investigation and potential applications emerges

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

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

Multifunctional heterometallic Iriii-Aui probes as promising anticancer and antiangiogenic agents

A new class of emissive cyclometallated IrIII-AuI complexes with a bis(diphenylphosphino) methanide bridging ligand was successfully synthesised from the diphosphino complex [Ir(N^C)2(dppm)]+ (1). The different gold ancillary ligand, a triphenylphosphine (2), a chloride (3) or a thiocytosine (4) did not reveal any significant effect on the photophysical properties, which are mainly due to metal-to-ligand charge-transfer (3MLCT) transitions based on IrIII. However, the AuI fragment, along with the ancillary ligand, seemed crucial for the bioactivity in A549 lung carcinoma cells versus endothelial cells. Both cell types display variable sensitivities to the complexes (IC50=0.6–3.5 µM). The apoptotic pathway is activated in all cases, and paraptotic cell death seems to take place at initial stages in A549 cells. Species 2–4 showed at least dual lysosomal and mitochondrial biodistribution in A549 cells, with an initial lysosomal localisation and a possible trafficking process between both organelles with time. The bimetallic IrIII-AuI complexes disrupted the mitochondrial transmembrane potential in A549 cells and increased reactive oxygen species (ROS) generation and thioredoxin reductase (TrxR) inhibition in comparison with that displayed by the monometallic complex 1. Angiogenic activity assays performed in endothelial cells revealed the promising antimetastatic potential of 1, 2 and 4. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH

1,4-Bis(2′-pyridylethynyl)benzene as a ligand in heteronuclear gold–thallium complexes. Influence of the ancillary ligands on their optical properties

The reaction of 1,4-bis(2′-pyridylethynyl)benzene (L) with [{Au(C6X5)2}Tl]n affords new heterometallic AuI/TlI complexes with different stoichiometries, structural arrangements and optical properties depending on the halogens present in the aryl group. The chlorinated derivative [{Au(C6Cl5)2}Tl(L)]n (1) displays polymeric chains built thanks to unsupported Au⋯Tl interactions and bridging bidentate ligands between adjacent chains, while in the fluorinated species [{Au(C6F5)2}2Tl2(L)2]n (2), also containing N-donor bridging ligands and Au⋯Tl contacts, polymerization occurs via Tl⋯Caryl non-bonding interactions between neighbouring molecules. The optical properties of 1 and 2 have been studied experimentally and theoretically, concluding that the luminescence of 1 in the solid state has its origin in the Au⋯Tl interactions, and that the Tl⋯Caryl interactions in 2 favour a non-radiative deactivation pathway that avoids luminescence. The strength of the non-bonding interactions present in 1 has also been theoretically studied at the HF and MP2 levels, revealing the metallophilic contact as the strongest one.This work was supported by the D.G.I. (MEC)/FEDER (CTQ2013-48635-C2-2-P).Peer reviewe

Ultrasound-assisted multicomponent synthesis of 4H-pyrans in water and DNA binding studies

A simple approach to synthesize new highly substituted 4H-pyran derivatives is described. Efficient Et3N acts as a readily accessible catalyst of this process performed in pure water and with only a 20 mol% of catalyst loading. The extremely simple operational methodology, short reaction times, clean procedure and excellent product yields render this new approach extremely appealing for the synthesis of 4H-pyrans, as potentially biological scaffolds. Additionally, DNA interaction analysis reveals that 4H-pyran derivatives behave preferably as minor groove binders over major groove or intercalators. Therefore, this is one of the scarce examples where pyrans have resulted to be interesting DNA binders with high binding constants (Kb ranges from 1.53 × 104 M-1 to 2.05 × 106 M-1)

Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η1-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η3-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2