Search Results (5)

Transition metal complexes bearing protic N-heterocyclic carbene (pNHC) ligands are promising precatalysts for organic reactions due to their capacity for unique hydrogen-bonding interactions. Herein, we report the synthesis and structural characterization of the first Pd(II) complex featuring a pNHC derived from 1,2,4-triazole—a heterocyclic system previously unexplored for the preparation of metal/pNHC complexes. The complex was synthesized via oxidative addition of 3-bromo-5-cyclohexyl-1-methyl-1H-1,2,4-triazole to Pd(PPh₃)₄ in the presence of NH₄BF₄. Its molecular structure was characterized by NMR spectroscopy and X-ray diffraction analysis. Full article

Lung cancer is a leading cause of cancer-related death worldwide that needs updated therapies to contrast both the serious side effects and the occurrence of drug resistance. A panel of non-small cell lung cancer (NSCLC) cells were herein employed as cancer models. Eight structurally related gold(I) and gold(III) complexes with NHC and halides or triphenylphosphane ligands were investigated as lung cancer cell growth inhibitors. As expected, gold compounds with PPh₃ were found to be more cytotoxic than homoleptic [(NHC)₂-Au(I)]X or heteroleptic NHC-Au(I)X or NHC-Au(III)X₃ complexes. Mixed ligand gold(I) compounds exhibiting the linear NHC-AuPPh₃ (compound 7) or the trigonal NHC-Au(Cl)PPh₃ (compound 8) arrangements at the central metal were found to be the best lung cancer cytotoxic compounds. Analysis of the TrxR residual activity of the treated cells revealed that these compounds efficiently inhibit the most accredited molecular target for gold compounds, the TrxR, with compound 8 reaching more than 80% activity reduction in lung cells. Some of the current cancer lung therapy protocols consist of specific lung cancer cell cytotoxic agents combined with antifolate drugs; interestingly, the herein gold compounds are both TrxR and antifolate inhibitors. The human DHFR was inhibited with IC₅₀ ranging between 10–21 µM, depending on substrate concentrations, proceeding by a likely allosteric mechanism only for compound 8. Full article

We herein report on the synthesis and structural characterization, as well as on the photophysical properties, of a series of isoleptic Pt(II) and Pd(II) complexes featuring tridentate N^N^N chelators as luminophores while bearing diverse ancillary co-ligands. Six new palladium complexes were synthesized using 2,6-bis(3-(tert-butyl/trifluoromethyl)-1H-1,2,4-triazol-5-yl)pyridine (^tbu or CF₃, respectively) in combination with four distinct ancillary ligands, namely: 4-amylpyridine (AmPy), 2,6-dimethylphenyl isonitrile (CNR), triphenylphosphane (PPh₃), and 1,3,5-triaza-7-phosphaadamantane (PTA). Thus, two novel Pt(II) complexes incorporating the co-ligands CNR and PTA were explored. The remaining platinum-based complexes, namely CF₃-Pt-AmPy, ^tbu-Pt-AmPy, CF₃-Pt-PPh₃, and ^tbu-Pt-PPh₃, were re-synthesized according to our previous work for a systematic comparison with their Pd(II) homologues. Thus, photophysical studies were performed in different solvents and conditions. The Pt(II) complexes demonstrated comparable or superior photophysical characteristics in toluene when compared with their solutions in liquid dichloromethane at room temperature. In contrast, the Pd(II) complexes exhibited no significant photoluminescence in dichloromethane, but a surprisingly clear emission was observed for ^tbu-Pd-AmPy, ^tbu-Pd-CNR, and ^tbu-Pd-PPh₃ in liquid toluene at room temperature. The significant differences regarding excited state lifetimes and photoluminescence quantum yields underscore the impact of solvent selection on photophysical characteristics, emphasizing the need to consider metal-ligand interactions, as well as the surrounding microenvironment, for a comprehensive interpretation of their photophysical properties. In addition, it is clear that AmPy and CNR render better luminescence efficiencies, whereas PTA is only suitable in toluene. Full article

A series of gold(I) complexes of the general composition [Au(naza)(PPh₃)] (1–8) was prepared and thoroughly characterized (e.g., electrospray ionization (ESI) mass spectrometry and multinuclear nuclear magnetic resonance (NMR) spectroscopy). The N1-deprotonated anions of 7-azaindole or its derivatives (naza) are coordinated to the metal centre through the N1 atom of their pyrrole ring, as proved by a single crystal X-ray analysis of the complexes [Au(3I5Braza)(PPh₃)] (7) and [Au(2Me4Claza)(PPh₃)]·½H₂O (8′). The in vitrocytotoxicity of the complexes 1–8 was studied against both the cisplatin-sensitive and -resistant variants of the A2780 human ovarian carcinoma cell line, as well as against the MRC-5 human normal fibroblast cell line. The complexes 4, 5, and 8, containing deprotonated 3-iodo-7-azaindole, 5-bromo-7-azaindole, and 2-methyl-4-chloro-7-azaindole (2Me4Claza), respectively, showed significantly higher potency (IC₅₀ = 2.8–3.5 µM) than cisplatin (IC₅₀ = 20.3 µM) against the A2780 cells and markedly lower effect towards the MRC-5 non-cancerous cells (IC₅₀ = 26.0–29.2 µM), as compared with the mentioned A2780 cancer cells. The results of the flow cytometric studies of the A2780 cell cycle perturbations revealed a G₂-cell cycle phase arrest of the cells treated by the representative complexes 1 and 5, which is indicative of a different mechanism of action from cisplatin (induced S-cell cycle phase arrest). The stability of the representative complex 8 in the water-containing solution as well as its ability to interact with the reduced glutathione, cysteine and bovine serum albumin was also studied using ¹H and ³¹P-NMR spectroscopy (studied in the 50% DMF-d₇/50% D₂O mixture) and ESI+ mass spectrometry (studied in the 50% DMF/50% H₂O mixture); DMF = dimethylformamide. The obtained results are indicative for the release of the N-donor azaindole-based ligand in the presence of the used biomolecules. Full article

5-Azido-4-(dimethylamino)-1-methyl-1,2,4-triazolium hexafluoridophosphate was synthesized from the corresponding 5-bromo compound with NaN₃. Reaction with bicyclo[2.2.1]hept-2-ene yielded a tricyclic aziridine, addition of an N-heterocyclic carbene resulted in a triazatrimethine cyanine, and reduction with triphenylphosphane gave the 5-amino derivative. The crystal structures of three nitrogen-rich salts were determined. Thermoanalysis of the cationic azide and triazene showed exothermal decomposition. The triazene exhibited negative solvatochromism in polar solvents involving the dipolarity π* and hydrogen-bond donor acidity α of the solvent. Full article