Search Results (21)

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

A wide range of platinum(0)-η²-(E)-1,2-ditosylethene complexes bearing isocyanide, phosphine and N-heterocyclic carbene ancillary ligands have been prepared with high yields and selectivity. All the novel products underwent thorough characterization using spectroscopic techniques, including NMR and FT-IR analyses. Additionally, for some compounds, the solid-state structures were elucidated through X-ray diffractometry. The synthesized complexes were successively evaluated for their potential as anticancer agents against two ovarian cancer cell lines (A2780 and A2780cis) and one breast cancer cell line (MDA-MB-231). The majority of the compounds displayed promising cytotoxicity within the micromolar range against A2780 and MDA-MB-231 cells, with IC₅₀ values comparable to or even surpassing those of cisplatin. However, only a subset of compounds was cytotoxic against cisplatin-resistant cancer cells (A2780cis). Furthermore, the assessment of antiproliferative activity on MRC-5 normal cells revealed certain compounds to exhibit in vitro selectivity. Notably, complexes 3d, 6a and 6b showed low cytotoxicity towards normal cells (IC₅₀ > 100 µM) while concurrently displaying potent cytotoxicity against cancer cells. Full article

The coordination chemistry of scorpionate ligands based on borates containing the 7-azaindole heterocycle is relatively unexplored. Thus, there is a requirement to further understand their coordination chemistry. This article outlines the synthesis and characterization of a family of complexes containing anionic flexible scorpionate ligands of the type [(R)(bis-7-azaindolyl)borohydride]⁻ ([^RBai]⁻), where R = Me, Ph or naphthyl. The three ligands were coordinated to a series of copper(I) complexes containing a phosphine co-ligand to form the complexes, [Cu(^MeBai)(PPh₃)] (1), [Cu(^PhBai)(PPh₃)] (2), [Cu(^NaphthBai)(PPh₃)] (3), [Cu(^MeBai)(PCy₃)] (4), [Cu(^PhBai)(PCy₃)] (5) and [Cu(^NaphthBai)(PCy₃)] (6). Additional copper(II) complexes, namely, [Cu(^MeBai)₂] (7) and [Cu(^PhBai)₂] (8), were obtained during attempts to obtain single crystals from complexes 4 and 2, respectively. Complexes 7 and 8 were also prepared independently from CuCl₂ and two equivalents of the corresponding Li[^RBai] salt alongside an additional complex, namely, [Cu(^NaphthBai)₂] (9). The copper(I) and copper(II) complexes were characterized using spectroscopic and analytical methods. Furthermore, a crystal structure was obtained for eight of the nine complexes. In all cases, the boron-based ligand was found to bind to the metal centers via a κ³-N,N,H coordination mode. Full article

Heterocycles functionalized with pentavalent phosphorus are of great importance since they include a great variety of biologically active compounds and pharmaceuticals, advanced materials, and valuable reactive intermediates for organic synthesis. Significant progress in synthesis of P(O)R₂-substituted six-membered heterocycles has been made in the past decade. This review covers the synthetic strategies towards aromatic monocyclic six-membered N-heterocycles, such as pyridines, pyridazines, pyrimidines, and pyrazines bearing phosphonates and phosphine oxides, which were reported from 2012 to 2022. Full article

Phosphine-free ruthenium benzylidene complexes containing imidazole ligands are reported. These catalysts are effective for ring-closing metathesis (RCM) and cross-metathesis (CM) reactions at high temperatures, where the more widely used phosphine-containing N-heterocyclic carbene-based ruthenium catalysts show side reactions. This discovery opens up a pathway to develop more selective ruthenium metathesis catalysts for reactions requiring harsh conditions. Full article

Ag(I) coordination compounds have recently attracted much attention as antiproliferative and antibacterial agents against a wide range of cancer cell lines and pathogens. The bioactivity potential of these complexes depends on their structural characteristics and the nature of their ligands. Herein, we present a series of four Ag(I) coordination compounds bearing as ligands the CH₃-substituted thiadiazole-based thioamide 5-methyl-1,3,4-thiadiazole-2-thiol (mtdztH) and phosphines, i.e., [AgCl(mtdztH)(PPh₃)₂] (1), [Ag(mtdzt)(PPh₃)₃] (2), [AgCl(mtdztH)(xantphos)] (3), and [AgmtdztH)(dppe)(NO₃)]_n (4), where xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene and dppe = 1,2-bis(diphenylphosphino)ethane, and the assessment of their in vitro antibacterial and anti-cancer efficiency. Among them, diphosphine-containing compounds 3 and 4 were found to exhibit broad-spectrum antibacterial activity characteristics against both Gram-(+) and Gram-(–) bacterial strains, showing high in vitro bioactivity with IC₅₀ values as low as 4.6 μΜ. In vitro cytotoxicity studies against human ovarian, pancreatic, lung, and prostate cancer cell lines revealed the strong cytotoxic potential of 2 and 4, with IC₅₀ values in the range of 3.1–24.0 μΜ, while 3 and 4 maintained the normal fibroblast cells’ viability at relatively higher levels. Assessment of these results, in combination with those obtained for analogous Ag(I) complexes bearing similar heterocyclic thioamides, suggest the pivotal role of the substituent groups of the thioamide heterocyclic ring in the antibacterial and anti-cancer efficacy of the respective Ag(I) complexes. Compounds 1–4 exhibited moderate in vitro antioxidant capacity for free radicals scavenging, as well as reasonably strong ability to interact with calf-thymus DNA, suggesting the likely implication of these properties in their bioactivity mechanisms. Complementary insights into the possible mechanism of their anti-cancer activity were provided by molecular docking calculations, exploring their ability to bind to the overexpressed fibroblast growth factor receptor 1 (FGFR1), affecting cancer cells’ functionalities. Full article

In this paper, we report the crystal structure of 2-[2-(diphenylphosphoryl)phenyl]-1H-perimidine (L1) obtained from the ring closure reaction of 1,8-diaminonaphthalene and 2-(diphenylphosphino)benzaldehyde, followed by the dehydrogenation reaction with sodium metabisulfite (Na₂S₂O₅). L1 was characterised using ¹H, ¹³C & ³¹P NMR, FT-IR and X-ray single structure analyses. Full article

Deprotonation of a bis(amino)phosphane H₂L = PhP(HNBtd)₂ bearing a heterocyclic Btd = 2,1,3-benzothiadiazol-4-yl substituents at nitrogen atoms by silylamides LiNTms₂ and Y(NTms₂)₃ (Tms = trimethylsilylamide) results in lithium and yttrium complexes with the deprotonated HL^– and L^2– forms as κ²-N and κ⁴-N chelating ligands. A binuclear complex [LiHL]₂ was crystallized from Et₂O, and was shown to reversibly dissociate in thf (tetrahydrofuran) with the NH_(soln)–PH_(crystal) tautomeric shift; the compound [Li₂L] was spectroscopically characterized. Yttrium readily forms stable bis-ligand complexes [YL₂]^– and [YL(HL)]. In the latter, the H atom in HL resides on phosphorus; the coordination sphere remains accessible to another ligands, and it was crystallized as [{YL(HL)}₂(µ-dioxane)] species (YN₈O coordination). In the former complex, the coordination sphere was saturated (YN₈) by closer bound ligands; it was crystallized as a salt with [Li(thf)₄]⁺. The monoligand complex could not be cleanly obtained in a 1:1 reaction of H₂L and Y(NTms₂)₃, and was only crystallographically characterized as a dimer [YL(NTms)₂]₂. Partial oxidation of the central P atom with the formation of phosphine-oxide ligands PhP(O)(NBtd)^2– was observed. They co-crystallize in the same position as non-oxidized ligands in [YL₂]^– and [YL(NTms₂)]₂ species and participate in bonding between two units in the latter. TD-DFT calculations reveal that main transitions in the visible region of electronic spectra correspond to the charge transfer bands mostly associated with the orbitals located on Btd fragments. Full article

The less-expensive and earth-abundant nickel catalyst is highly promising in the copolymerization of ethylene with polar monomers and has thus attracted increasing attention in both industry and academia. Herein, we have summarized the recent advancements made in the state-of-the-art nickel catalysts with different types of ligands for ethylene copolymerization and how these modifications influence the catalyst performance, as well as new polymerization modulation strategies. With regard to α-diimine, salicylaldimine/ketoiminato, phosphino-phenolate, phosphine-sulfonate, bisphospnine monoxide, N-heterocyclic carbene and other unclassified chelates, the properties of each catalyst and fine modulation of key copolymerization parameters (activity, molecular weight, comonomer incorporation rate, etc.) are revealed in detail. Despite significant achievements, many opportunities and possibilities are yet to be fully addressed, and a brief outlook on the future development and long-standing challenges is provided. Full article

The successful use of 1,3,4,2-triazaphospholenes (TAPs) as organo-catalysts stresses the need for efficient synthetic routes to these molecules. In this study, we establish the [1 + 4]-cycloaddition of PBr₃ to azo-pyridines as a new approach to preparing pyrido-annellated TAPs in a single step from easily available precursors. The modular assembly of the azo-component via condensation of primary amines and nitroso compounds along with the feasibility of post-functionalization at the P–Br bond under conservation of the heterocyclic structure allows, in principle, to address a wide range of target molecules, which is illustrated by prototypical examples. The successful synthesis of a transition metal complex confirms for the first time the ability of a TAP to act as a P-donor ligand. Crystallographic studies suggest that hyperconjugation effects and intermolecular interactions induce a qualitatively similar ionic polarization of the P–Br bonds in TAPs as in better known isoelectronic diazaphospholenes. Full article

Unsaturated copolyesters are of great interest in polymer science due to their broad potential applications and sustainability. Copolyesters were synthesized from the ring-opening metathesis copolymerization of ω-6-hexadecenlactone (HDL) and norbornene (NB) using ruthenium-alkylidene [Ru(Cl₂)(=CHPh)(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(PCy₃)] (Ru1), [Ru(Cl)₂(=CHPh)(PCy₃)₂] (Ru2), and ruthenium-vinylidene [RuCl₂(=C=CH(p-C₆H₄CF₃))(PCy₃)₂] (Ru3) catalysts, respectively, yielding HDL-NB copolymers with different ratios of the monomer HDL in the feed. The activity of N-heterocyclic-carbene (NHC) (Ru1) and phosphine (Ru2 and Ru3) ligands containing ruthenium-carbene catalysts were evaluated in the synthesis of copolymer HDL-NB. The catalysts Ru1 with an NHC ligand showed superior activity and stability over catalysts Ru2 and Ru3 bearing PCy₃ ligands. The incorporation of the monomers in the copolymers determined by ¹H-NMR spectroscopy was similar to that of the HDL-NB values in the feed. Experiments, at distinct monomer molar ratios, were carried out using the catalysts Ru1–Ru3 to determine the copolymerization reactivity constants by applying the Mayo–Lewis and Fineman–Ross methods. The copolymer distribution under equilibrium conditions was studied by the ¹³C NMR spectra, indicating that the copolymer HDL-NB is a gradient copolymer. The main factor determining the decrease in melting temperature is the inclusion of norbornene units, indicating that the PNB units permeate trough the HDL chains. The copolymers with different molar ratios [HDL]/[NB] have good thermal stability up to 411 °C in comparison with the homopolymer PHDL (384 °C). Further, the stress–strain measurements in tension for these copolymers depicted the appreciable increment in stress values as the NB content increases. Full article

Rhodium is one of the most used metals in catalysis both in laboratory reactions and industrial processes. Despite the extensive exploration on “classical” ligands carried out during the past decades in the field of rhodium-catalyzed reactions, such as phosphines, and other common types of ligands including N-heterocyclic carbenes, ferrocenes, cyclopentadienyl anion and pentamethylcyclopentadienyl derivatives, etc., there is still lively research activity on this topic, with considerable efforts being made toward the synthesis of new preformed rhodium catalysts that can be both efficient and selective. Although the “golden age” of homogeneous catalysis might seem over, there is still plenty of room for improvement, especially from the point of view of a more sustainable chemistry. In this review, temporally restricted to the analysis of literature during the past five years (2015–2020), the latest findings and trends in the synthesis and applications of Rh(I) complexes to catalysis will be presented. From the analysis of the most recent literature, it seems clear that rhodium-catalyzed processes still represent a stimulating challenge for the metalloorganic chemist that is far from being over. Full article

New water-soluble, N-heterocyclic carbene (NHC) or mixed NHC/tertiary phosphine complexes [RhCl(cod)(sSIMes)], Na₂[Rh(bmim)(cod)(mtppts)], and [Rh(bmim)(cod)(pta)]BF₄ were synthetized and applied for the first time as catalysts in redox isomerization of allylic alcohols in aqueous media. [RhCl(cod)(sSIMes)] (with added sulfonated triphenylphosphine) and [Rh(bmim)(cod)(pta)]BF₄ catalyzed selectively the transformation of allylic alcohols to the corresponding ketones. The highest catalytic activity, TOF = 152 h⁻¹ (TOF = (mol reacted substrate) × (mol catalyst × time)⁻¹) was observed in redox isomerization of hept-1-en-3-ol ([S]/[cat] = 100). The catalysts were reused in the aqueous phase at least three times, with only modest loss of the catalytic activity and selectivity. Full article

N-Heterocyclic carbene gold(I) complexes derived from 1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene (NHC*) represent a promising class of anticancer drugs. Complexes of the type NHC*-Au-L (L = Br⁻, I⁻, C≡C-R) and [NHC*-Au-L]⁺ (L = NHC*, PPh₃) have been synthesised. The X-ray crystal structures of all gold(I) complexes are presented; aurophilic interactions were observed in five of the complexes. The anticancer activity was assessed via MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based proliferation assays against the human colon carcinoma cell line HCT-116^wt and the multidrug-resistant human breast carcinoma cell line MCF-7^topo. Most complexes showed good cytotoxicity with IC₅₀ values in the low micromolar range, while excellent sub-micromolar activity was observed for 2c, 3a and 3b. Generally, the activity of the ligands studied was as follows: carbene > phosphine > alkyne > halide, with an exception for the highly active iodido derivative 2c. Full article

Acyl Suzuki cross-coupling involves the coupling of an organoboron reagent with an acyl electrophile (acyl halide, anhydride, ester, amide). This review provides a timely overview of the very important advances that have recently taken place in the acylative Suzuki cross-coupling. Particular emphasis is directed toward the type of acyl electrophiles, catalyst systems and new cross-coupling partners. This review will be of value to synthetic chemists involved in this rapidly developing field of Suzuki cross-coupling as well as those interested in using acylative Suzuki cross-coupling for the synthesis of ketones as a catalytic alternative to stoichiometric nucleophilic additions or Friedel-Crafts reactions. Full article