Search Results (34)

In this study, we synthesized and characterized new imidazole ligands containing pyridone groups, as well as mononuclear and binuclear ruthenium complexes, which are a new class of water-soluble metallacycles. We studied the antiproliferative activity of these compounds in vitro using the MTT assay on a panel of human cancer cell lines and on primary rat fibroblasts, where we observed a complete absence of cytotoxicity up to a concentration of 1000 µM. For the binuclear metallocycle compounds, we investigated their solubility in water, resistance to hydrolysis, and ability to induce apoptosis in tumor cells. Full article

In this study, we report the first example of acyclic (amino)(N-pyridinium)carbenoid gold(III) complexes synthesized via a coupling reaction between 2-pyridylselenyl chloride and Au(I)-bound isonitriles. The reaction involves an initial oxidative addition of the Se–Cl moiety to Au(I), followed by the nucleophilic addition of the pyridine fragment to the isonitrile’s C≡N bond, furnishing a metallacycle. Importantly, this is the first example of the pyridine acting as a nucleophile towards metal-bound isonitriles. Arguably, such an addition is due to the chelate effect. The structures of the gold(III) carbenoid complexes were unambiguously established using X-ray diffraction and NMR spectroscopy. Theoretical calculations, including DFT, Natural Resonance Theory (NRT), and Meyer bond order (MBO) analyses, were used to analyze the different resonance forms. The reaction mechanism was further elucidated using DFT calculations, which identified the oxidative addition as the rate-determining step with a barrier of 29.7 kcal/mol. The nucleophilic addition proceeds with a minimal barrier, making the reaction highly favorable. The antiproliferative activity of new compounds 2a–2e was tested against two human cancer cell lines: A2780 ovarian adenocarcinoma and the A278Cis cisplatin-resistant variant. Full article

The homoleptic cationic complex formed by reacting suitable manganese(II) salts with 2,2′-bipyridine-1,1′-dioxide (bipyO₂) has been subjected to several studies in the past because of its peculiar absorption and electrochemical features. Here, the first single-crystal X-ray structure determination of a [Mn(bipyO₂)₃]²⁺ salt is reported, where the charge of the cation is balanced by perchlorate anions. The hydrated salt [Mn(bipyO₂)₃](ClO₄)₂ crystallizes in the monoclinic system (P2₁/n space group) and the asymmetric unit contains three cationic complexes and six perchlorate anions. The environment of the manganese(II) ions is best described as octahedral, with scarce variations among the three cations in the asymmetric unit. The bipyO₂ ligands exhibit κ² coordination mode, forming seven-membered metallacycles. The X-ray outcomes have been used as the starting point for DFT and TDDFT calculations, aimed to elucidate the charge transfer origin of the noticeable absorption in the visible range. The MLCT nature is confirmed by the hole and electron distributions associated with the spin-allowed transitions. DFT calculations on the related manganese(III) complex indicate that the geometry of [Mn(bipyO₂)₃]²⁺ changes only slightly upon oxidation, in agreement with the reversible electrochemical behaviour experimentally observed. Full article

This work reports on a novel family of silver metallogels based on discrete coordination complexes. Structurally, they consist of dendrimers containing a trinuclear silver metallacycle at the core, with the general formula [M(μ-pz)]₃, and poly(benzyl)ether branched structures with different numbers or terminal alkoxy chains at the periphery. These silver metallodendrimers are able to gel low-polarity solvents such as dodecane or cyclohexane, giving rise to luminescent organogels at room temperature with the property of aggregation-induced emission (AIE). This property means that in solution or the sol state, they are weak emitters, but in the gel state, luminescence is considerably increased. In this particular case, they exhibit blue luminescence. Two different dendritic scaffolds have been studied, finding significant differences in solubility, gel formation and dependence of luminescence on temperature. The results show that properly tailored silver gelators can show luminescence in the gel state. Full article

Trinuclear metallacyclic oxidovanadium(V) complexes, [{VO(L³⁺²R)}₃] (1–3) with asymmetric multidentate linking ligands (H₃L³⁺²R: R = H, Me, Br), were synthesized. The molecular structure of 1 is characterized as a tripod structure, with each V(V) ion coordinated by ONO-atoms from a tridentate Schiff base site and ON-atoms from a bidentate benzoxazole site of two respective H₃L³⁺²H ligands. The intramolecular V⋯V distances range from 8.0683 to 8.1791 Å. Complex 4 is a mononuclear dioxidovanadium(V) complex, (Et₃NH)[VO₂(HL³⁺²H)]. Cyclic voltammograms of 1−3 in DMF revealed redox couples attributed to three single-electron transfer processes. Full article

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea (1) to cis-[Pt(CNXyl)₂Cl₂] (2) gave a new cyclometallated compound 3. It was characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms (3 and 3·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of 3, two conformers (3A and 3B) were identified, while the structure 3·2MeCN had only one conformer 3A. The conformers differed by orientation of the N,N-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals 3 and 3·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {3A}₂ or {3B}₂, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···d_z²(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [3A]₂ and reveals the d_z²(Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction). Full article

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H₂L¹), nicotinic hydrazide (H₂L²), 2-aminobenzhydrazide (H₂L³), or 4-aminobenzhydrazide (H₂L⁴)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO₂(L^1,2)]_n (1 and 2) and [MoO₂(L^3,4)]₂ (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO₂(L^1-4)(MeOH)] (1a–4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes. Full article

While thiocarbonyl-stabilised phosphonium ylides generally react upon flash vacuum pyrolysis by the extrusion of Ph₃PS to give alkynes in an analogous way to their carbonyl-stabilised analogues, two examples with a hydrogen atom on the ylidic carbon are found to undergo a quite different process. The net transfer of a phenyl group from P to S gives (Z)-configured 1-diphenylphosphino-2-(phenylsulfenyl)alkenes in a novel isomerisation process via intermediate λ⁵-1,2-thiaphosphetes. These prove to be versatile hemilabile ligands with a total of seven complexes prepared involving five different transition metals. Four of these are characterised by X-ray diffraction with two involving the bidentate ligand forming a five-membered ring metallacycle and two with the ligand coordinating to the metal only through phosphorus. Full article

Biaryl monophosphines are important precursors to active catalysts of palladium-mediated cross-coupling reactions. The efficiency of the phosphine-based transition metal complex catalyst has its origin in the electronic structure of the complex used and the sterical hindrance created by the ligand at an active catalyst site. The aim of this paper is to shed some light on the multiverse of coordination modes of biaryl monophosphine ligands. Here, we present the analysis of the X-ray single crystal structures of palladium(II) complexes of a family of biaryl monophosphine ligands and the first crystallographic report on a related phosphine sulfide. Despite the common biaryl monophosphine ligand motif, they show diverse coordination modes (i) starting from the activation of aromatic C atoms and producing a C,P metallacycle, through (ii) the O,P chelation to Pd(II) ions with a simultaneous demethylation reaction of one of the methoxy groups, ending up with (iii) the monodentate coordination to metal cations via P atoms or (iv) via S atoms in the case of phosphine sulfide. We relate our results to the crystal structures found in the Cambridge Structural Database to show the multiverse of coordination modes in the group of biaryl monophosphine ligands. Full article

Due to the different crystallization methods, two Hg(II) complexes of a 19-membered NO₂S₂-macrocycle (L) and its oxidized ligand (HL_ox), exhibiting different stoichiometries, were prepared. First, mercury(II) iodide reacts with L to afford a dinuclear metallacycle complex [Hg₂(L)₂I₄] (1) in which the mercury(II) exists outside the macrocyclic cavity. Meanwhile, the slow diffusion reaction gave an unusual pseudo-square planar-induced mercury(II) complex, which shows three separated parts with the formula [Hg₂(HL_ox)I₅]₂[HgI₂] (2). There are two complex cation units that are exo-coordinated, along with one unit consisting of a metal cluster anion. Surprisingly, L was oxidized in the disulfoxidized form (HL_ox) in this condition. NMR titration was used to monitor both the structural and binding characteristics of the complex formed between L and mercury(II) iodide in a solution. Full article

Ruthenium complexes of phosphinocarboxamide ligands, and their use to form metallacycles using halide abstraction/deprotonation reactions are reported. Thus, [Ru(p-cym){PPh₂C(=O)NHR}Cl₂; R = ⁱPr (1), Ph (2), p-tol (3)] and [Ru(p-cym){PPh₂C(=O)N(R)C(=O)N(H)R}Cl₂; R = Ph (4), p-tol (5)] were synthesized from [(p-cym)RuCl₂]₂ (p-cym = para-cymene) and phosphinocarboxamides or phosphinodicarboxamides, respectively. Single-crystal X-ray diffraction measurements on 1–5 reveal coordination to ruthenium through the phosphorus donor, with an intramolecular hydrogen bond between the amine-bound proton and a metal-bound chloride. Six-membered metallacycles formed by halide abstraction/deprotonation of complexes 4 and 5 afforded [Ru(p-cym){κ²-P,N-PPh₂C(=O)N(R)C(=O)NR}Cl] [R = Ph (6), p-tol (7)]. These species exist as a mixture of two rotational isomers in solution, as demonstrated by NMR spectroscopy. Full article

Four couples of 5,6-membered bis(metallacyclic) Pt(II) complexes with acetylide and isocyanide auxiliary ligands have been prepared and characterized. The structures of (−)-2 and (−)-3 are confirmed by single-crystal X-ray diffraction, showing a distorted square-planar coordination environment around the Pt(II) nucleus. Both solutions and solid samples of all complexes are emissive at RT. Acetylide-coordinated Pt(II) complexes have a lower energy emission than those isocyanide-coordinated ones. The emission spectra of N^N′*C-coordinated Pt(II) derivatives show a lower energy emission maximum relative to N^C*N′-coordinated complexes with the same auxiliary ligand. Moreover, the difference between cyclometalated N^N′*C and N^C*N′ ligands exerts a more remarkable effect on the emission than the auxiliary ligands acetylide and isocyanide. Cytotoxicity and cell imaging of luminescent 5,6-membered bis(metallacyclic) Pt(II) complexes have been evaluated. Full article

To gain molecular-level insight into the intricate features of the catalytic behavior of chromium–diphosphine complexes regarding ethylene tri- and tetramerizations, we performed density functional theory (DFT) calculations. The selective formation of 1-hexene and 1-octene by the tri- and tetramerizations of ethylene are generally accepted to follow the metallacycle mechanism. To explore the mechanism of ethylene tri- and tetramerizations, we used a real Sasol chromium complex with a nitrogen-bridged diphosphine ligand with ortho- and para-methoxyaryl substituents. We explore the trimerization mechanism for ethylene first and, later on for comparison, we extend the potential energy surfaces (PES) for the tetramerization of ethylene with both catalysts. The calculated results reveal that the formation of 1-hexene and 1-octene with the ortho-methoxyaryl and para-methoxyaryl Cr-PNP catalysts have nearly similar potential energy surfaces (PES). From the calculated results important insights are gained into the tri- and tetramerizations. The tetramerization of ethylene with the para-methoxyaryl Cr-PNP catalyst lowers the barrier height by ~2.6 kcal/mol compared to that of ethylene with the ortho-methoxyaryl Cr-PNP catalyst. The selectivity toward trimerization or tetramerization comes from whether the energy barrier for ethylene insertion to metallacycloheptane is higher than β-hydride transfer to make 1-hexene. The metallacycle mechanism with Cr (I)–Cr (III) intermediates is found to be the most favored, with the oxidative coupling of the two coordinated ethylenes to form chromacyclopentane being the rate-determining step. Full article

Energy-relevant small molecule activations and related processes are often multi-electron in nature. Ferrocene is iconic for its well-behaved one-electron chemistry, and it is often used to impart redox activity to self-assembled architectures. When multiple ferrocenes are present as pendant groups in a single structure, they often behave as isolated sites with no separation of their redox events. Herein, we study a suite of molecules culminating in a self-assembled palladium(II) truncated tetrahedron (TT) with six pendant ferrocene moieties using the iron(III/II) couple to inform about the electronic structure and, in some cases, subsequent reactivity. Notably, although known ferrocene-containing metallacycles and cages show simple reversible redox chemistry, this TT undergoes a complex multi-step electrochemical mechanism upon oxidation. The electrochemical behavior was observed by voltammetric and spectroelectrochemical techniques and suggests that the initial Fc-centered oxidation is coupled to a subsequent change in species solubility and deposition of a film onto the working electrode, which is followed by a second separable electrochemical oxidation event. The complicated electrochemical behavior of this self-assembly reveals emergent properties resulting from organizing multiple ferrocene subunits into a discrete structure. We anticipate that such structures may provide the basis for multiple charge separation events to drive important processes related to energy capture, storage, and use, especially as the electronic communication between sites is further tuned. Full article