Search Results (67)

Reactions of anhydrous Zn(II) iodides with redox-active 1,4-diaza-1,3-butadiene (DAD) and its bis(imino)acenaphtene (BIAN) derivatives in absolute acetonitrile yielded a series of new complexes: [(Mes-DAD)ZnI₂] (1), [(dpp-DAD)ZnI₂] (2), and [(dpp-BIAN)ZnI₂] (3). Single crystals of all compounds were obtained, and their molecular structures were unambiguously determined by X-ray diffraction analysis. Purity of bulk samples in solid state was confirmed by PXRD. Stability of the complexes in solution was investigated by means of UV-Vis and NMR spectroscopy. Cyclic voltammetry revealed two or three quasi-reversible reduction waves in the cathodic region for complexes 1–3. The ability of 3 to accept up to three electrons highlights the potential of these compounds as electrocatalysts for reductive transformations. Full article

Manganese complexes of the general formula [Mn(DAB)(CO)₃Br] featuring sterically demanding α-diimine ligands (DAB) were prepared, characterized, and found to be catalytically active in the hydroboration of ketones. The developed eco-friendly approach allowed straightforward formation of boronic esters in quantitative yields in mild and solvent-free conditions. Full article

Understanding electron density migration along excited-state pathways in photochemical systems is critical for optimizing solar energy conversion processes. In this study, we investigate photoinduced electron transfer (PET) in a covalently linked donor–bridge–acceptor (D-B-A) system, where [Cu(I)-bis(1,10-phenanthroline)]⁺ acts as an electron donor, and anthraquinone, tethered to one of the phenanthroline ligands via a vibrationally active ethyne bridge, behaves as an electron acceptor. Visible transient absorption spectroscopy revealed the dynamic processes occurring in the excited state, including PET to the acceptor species. This was indicated by the spectral features of the anthraquinone radical anion that appeared on a timescale of 30 ps in polar solvents. Time-resolved infrared (TRIR) spectroscopy of the alkyne vibration (CC stretch) of the ethyne bridge provided insight into electronic structural changes in the metal-to-ligand charge transfer (MLCT) state and along the PET reaction coordinate. The observed spectral shift and enhanced transition dipole moment of the CC stretch demonstrated that there was already partial delocalization to the anthraquinone acceptor following MLCT excitation, verified by DFT calculations. An additional excited-state TRIR signal unrelated to the vibrational mode highlighted delocalization between the phenanthroline ligands in the MLCT state. This signal decayed and the CC stretch narrowed and shifted towards the ground-state frequency following PET, indicating a degree of localization onto the acceptor species. This study experimentally elucidates charge redistribution during PET in a Cu(I) diimine D-B-A system, yielding important information on the ligand design for optimizing PET reactions. Full article

Developing organic luminescent materials with the advantages of low cost, high thermal stability, and strong emission performance is incredibly desirable. In this work, we synthesized a new neutral heteroleptic Cu(I) complex characterized by single-crystal X-ray diffraction, FT-IR, NMR, and MALDI-TOF-MS. The neutral heteroleptic Cu(I) complex has a typical distorted tetrahedral configuration, and the complex molecules are connected into 1D chains via C-H···π interactions in crystal. Full article

The polymerization mechanism of para-methoxystyrene catalyzed by cationic α-diimine palladium complexes with various ancillary ligands was rigorously examined using density functional theory. In the classical methyl-based α-diimine palladium complex [{(2,6-ⁱPr₂C₆H₃)-N=C(Me)-C(Me)=N-2,6-ⁱPr₂C₆H₃)}PdMe]⁺ (A⁺), the 2,1-insertion of para-methoxystyrene is favored over the 1,2-insertion, both thermodynamically and kinetically, during the chain initiation step. The resulting thermodynamically favored η³-π-benzyl intermediates face a substantial energy barrier, yielding only trace amounts of polymer, as experimentally verified. In contrast, the dibenzobarrelene-based α-diimine palladium complex [{(2,6-ⁱPr₂C₆H₃)-N=C(R)-C(R)=N-2,6-ⁱPr₂C₆H₃)}PdMe]⁺ (R = dibenzobarrelene, B⁺) shows similar energy barriers for both 2,1- and 1,2-insertions. Continuous 2,1/2,1 or 2,1/1,2 insertions are impeded by excessive energy barriers. However, theoretical calculations reveal that the 1,2-insertion product can seamlessly transition into the chain propagation stage, producing a polymer with high 1,2-regioselectivity. The observed activity of complexes A⁺ or B⁺ towards para-methoxystyrene polymerization stems from the energy barrier differences between the 1,2- and 2,1-insertions, influenced by the steric hindrance from the ancillary ligands. Further investigation into the effects of steric hindrance on the chain initiation stage involved computational modeling of analogous complexes with increased steric bulk. These studies established a direct correlation between the energy barrier difference ∆∆G (1,2–2,1) and the van der Waals volume of the ancillary ligand. Larger van der Waals volumes correspond to reduced energy barrier differences, thus enhancing the regioselectivity for para-methoxystyrene polymerization. Moreover, the experimental inertness of complex B⁺ towards styrene polymerization is attributed to the formation of stable kinetic and thermodynamic 2,1-insertion intermediates, which obstruct further styrene monomer insertion due to an extremely high reactive energy barrier. These findings contribute to a deeper understanding of the mechanistic aspects and offer insights for designing new transition metal catalysts for the polymerization of para-alkoxystyrenes. Full article

The activation of inert C–H bonds remains a challenge in current chemistry. Here, we report the excellent reactivity of the anionic gallylene species [LGa:][Na(THF)₃] (L = [(2,6-iPr₂C₆H₃)NC(CH₃)]₂²⁻, 1) that allows the selective activation one ortho sp² C–H bond of several azobenzene and azide derivatives at ambient temperature, with the transfer of the hydrogen atom to one of the nitrogen atoms. The process leads to the formation of the aryl amido products [LGa-κ²N,C-PhNN(H)(p-R-C₆H₃)][Na(solvent)₃] (2, R = H solvent = DME (1,2-Dimethoxyethane); 3, R = –OMe, solvent = DME; 4, R = –NMe₂ solvent = THF), [LGa-κ²N,C-(m-CH₃-C₆H₄)NN(H)(m-CH₃-C₆H₃)][Na(15-C-5)₂] (5) with new Ga–C and Ga–N bonds. Moreover, 1 is also effective for the C–H activation of two azides RN₃ (R = 2,4,6-Me₃C₆H₂ or 2,6-iPr₂C₆H₃), resulting in the formation of gallium amides [LGa(NH-2-(CH₂)-4,6-Me₂C₆H₂)][Na(15-C-5)₂] (6) and [LGa(NH-2,6-iPr₂C₆H₃)₂][Na(THF)₅] (7) through intra- or intermolecular sp³ C–H amination. Significantly, these reactions occur for the highly challenging activation of inert C(sp²)–H and C(sp³)–H bonds, thus demonstrating the excellent reactivity of the Ga(I) species 1. The products 2–7 were characterized by X-ray crystallography, ¹H and ¹³C NMR, UV–vis spectroscopy, and density functional theory (DFT) calculations. Full article

For square-planar late transition metal pyridine, diimine (Rh, Ir) complexes with hydro-xido, methoxido, and thiolato ligands. We could previously establish sizable metal-O- and S π-bonding interactions. Herein, we report the hydrogenation studies of iridium hydroxido and methoxido complexes, which quantitatively lead to the trihydride compound and water/methanol. The iridium trihydride displays a highly fluctional structure with scrambling hydrogen atoms, which can be described as a dihydrogen hydride system based on NMR and DFT investigations. This contrasts the iridium sulfur compounds, which are not reacting with dihydrogen. According to DFT and LNO-CCSD(T) calculations, hydrogenation of the methoxido complex proceeds by a two-step mechanism, i.e., an oxidative addition step of H₂ to an Ir(III) dihydride intermediate with consecutive reductive O-H elimination of methanol. Based on PNO-CCSD(T) calculations, the reactivity difference between the O- and S-donors can be traced to the stronger H-O bonds in the water/methanol products compared to the S-H bonds in the sulphur congeners, which serves as a driving force for hydrogenation. Full article

This study aims to advance the field of green chemistry and catalysis by exploring alternatives to conventional non-renewable energy sources. Emphasis is placed on hydrogen as a potential fuel, with a focus on the catalytic properties of Ni(II) complexes when coordinated with o-phenylenediamine and diimine ligands. We report the synthesis and comprehensive characterization, with various physical and spectroscopic techniques, of three heteroleptic Ni(II) complexes: [Ni(1,10-phenanthroline)(o-phenylene diamine)] (1), [Ni(2,2-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (2), and [Ni(5,5-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (3). The catalytic activity of these complexes for hydrogen evolution was assessed through photochemical studies utilizing visible light irradiation. Two distinct photosensitizers, fluorescein and quantum dots, were examined under diverse conditions. Additionally, their electrocatalytic behavior was investigated to elucidate the hydrogen evolution reaction (HER) mechanism, revealing a combined proton-coupled electron transfer (PCET)/electron-coupled proton transfer (ECPT) mechanism attributed to the chemical nature of the diamine ligand. The influence of ligand substituent position, ligand chemical nature, and photosensitizer type on catalytic performance was systematically studied. Among the complexes investigated, complex 2 demonstrated superior catalytic performance, achieving a turnover number (TON) of 3357 in photochemical experiments using fluorescein as a photosensitizer. Conversely, complex 1 exhibited the highest TON of 30,066 for HER when quantum dots were employed as the photosensitizer. Full article

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me₂Ph Fe1, 2,6-Et₂Ph Fe2, 2,6-i-Pr₂Ph Fe3, 2,4,6-Me₃Ph Fe4, and 2,6-Et₂-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 10⁶ g (PE) mol⁻¹ (Fe) h⁻¹ seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (M_w/M_n = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol⁻¹ and MAO: 4.9 kg mol⁻¹), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol⁻¹ and MAO: 72.4–95.5 kg mol⁻¹). Moreover, analysis of these polyethylenes by ¹H and ¹³C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system. Full article

Palladium(II) complexes of the general formula [Pd(η³-C₃H₅)(L)](PF₆), where L is 4,7-diphenyl-1,10-phenanthroline (1), 2,9-dimethyl-1,10-phenanthroline (2), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (3), 5-methyl-1,10-phenanthroline (4), 3,4,7,8-tetramethyl-1,10-phenanthroline (5), and 2-(2′-pyridyl) quinoxaline (6), were synthesized and characterized using high-resolution ESI-MS, NMR techniques and, in the case of (6), single-crystal X-ray diffraction methods. In addition, their photophysical properties were investigated. Complexes (1)–(6) were emitted in the greenish-blue region, with those containing methyl-substituted phenanthrolines having the higher quantum yield (≈14%) in the solid state. Full article

In this review, we present a timeline that shows the origin of mixed chelate copper (II) complexes, registered as Mark Title Casiopeínas^®, as the first copper (II) compounds proposed as anticancer drugs in 1988 and 1992. In the late twentieth century, the use of essential metals as anticancer agents was not even considered, except for their antifungal or antibacterial effects; also, copper, as gold salts, was used for arthritis problems. The use of essential metals as anticancer drugs to diminish the secondary toxic effects of Cisplatin was our driving force: to find less toxic and even more economical compounds under the rational design of metal chelate complexes. Due to their chemical properties, copper compounds were the choice to continue anticancer drug development. In this order of ideas, the rational designs of mixed chelate–copper (II) complexes (Casiopeínas, (Cas) homoleptic or heteroleptic, depending on the nature of the secondary ligand) were synthesized and fully characterized. In the search for new, more effective, and less toxic drugs, Casiopeína^® (Cas) emerged as a family of approximately 100 compounds synthesized from coordinated Cu(II) complexes with proven antineoplastic potential through cytotoxic action. The Cas have the general formula [Cu(N–N)(N–O)]NO₃ and [Cu(N–N)(O–O)]NO₃, where N–N is an aromatic substituted diimine (1,10-phenanthroline or 2,2′-bipyridine), and the oxygen donor (O–O) is acetylacetonate or salicylaldehyde. Lately, some similar compounds have been developed by other research groups considering a similar hypothesis after Casiopeína’s discoveries had been published, as described herein. As an example of translational medicine criteria, we have covered each step of the established normative process for drug development, and consequently, one of the molecules (Casiopeína III ia (CasIIIia)) has reached the clinical phase I. For these copper compounds, other activities, such as antibacterial, antiparasitic and antiviral, have been discovered. Full article

Luminescent diimine-Pt(IV) complexes [Pt(N^N)(Me)₂(PhSe)₂], (N^N = 2,2′-bipyridine (bpy, 1b), 1,10-phenanthroline (phen, 2b), and 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy, 3b), PhSe⁻ = phenyl selenide were prepared and identified using multinuclear (¹H, ¹³C{¹H} and ⁷⁷Se{¹H}) NMR spectroscopy. The PhSe⁻ ligands were introduced through oxidative addition of diphenyl diselenide to the non-luminescent Pt(II) precursors [Pt(N^N)(Me)₂], N^N = (bpy, 1a), (phen, 2a), (Me₂bpy, 3a), to give the luminescent Pt(IV) complexes 1b–3b. The UV-vis absorption spectra of 1b–3b are characterised by intense bands in the range 240–330 nm. We assigned them to transitions of essentially π−π* character with small metal and PhSe⁻ ligand contributions with the help of TD-DFT (time-dependent density functional theory) calculations. The weak long-wavelength bands in the range 350–475 nm are of mixed ligand-to-metal charge transfer (L’MCT) (n_(Se)→d_(Pt)/intra-ligand charge transfer (IL’CT) (n_(Se)→π*_(Ph) or π_(Ph)→π*_(Ph))/ligand-to-ligand’ charge transfer (LL’CT) (L = N^N, L’ = PhSe⁻, M = Pt and n = lone pair) character. The Pt(IV) complexes showed broad emission bands in the solid state at 298 and 77 K, peaking at 560–595 nm with a blue shift upon cooling. Structured emission bands were obtained in the range 450–600 nm, with the maxima depending on the N^N ligands and the solvent polarity (CH₂Cl₂ vs. dimethyl sulfoxide (DMSO) and aqueous tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl) buffer). The emissions originate from essentially ligand-centred triplet states (³LC) with mixed IL’CT/L’MCT contributions as concluded from the DFT calculation. Such dominating PhSe contributions to the emissive states are unprecedented in the world of luminescent diimine-Pt(IV) complexes. Full article

The syntheses of new neutral square-planar pyridine di-imine rhodium and iridium complexes with O- and S-donor (OH, OR, SH, SMe and SPh) ligands along with analogous cationic compounds are reported. Their crystal and electronic structures are investigated in detail with a focus on the non-innocence/innocence of the PDI ligand. The oxidation states of the metal centers were analyzed by a variety of experimental (XPS and XAS) and theoretical (LOBA, EOS and OSLO) methods. The dπ-pπ interaction between the metal centers and the π-donor ligands was investigated by theoretical methods and revealed the partial multiple-bond character of the M-O,S bonds. Experimental support is provided by a sizable barrier for the rotation about the Ir-S bond in the methyl thiolato complex and confirmed by DFT and LNO-CCSD(T) calculations. This was corroborated by the high Ir-O and Ir-S bond dissociation enthalpies calculated at the PNO-CCSD(T) level. Full article

The synthesis of a substituted diimine with a bipydirine-type backbone, (3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine, L) and its coordination towards Cu(I) and Ag(I) is studied in the presence of diphosphine ligand bis(diphenylphosphino)methane, dppm. The metal complexes are characterized by IR, ¹H, and ¹³C NMR and single crystal X ray diffraction studies. They are dinuclear, as they are held by diphosphine bridges between the tetrahedral metal centers, forming eight-membered ring with the participation of the bridging diphosphinomethane ligands. Within each ring, the planar orientations of M₂P₂ and of all four P atoms are realized. Solid state excitation spectra are dominated by metal-to-ligand charge transfer bands (MLCT), while geometry relaxation permits only low-intensity emission for the copper compound. Full article

In this work, we obtained three new phosphorescent iridium complexes (Ir1–Ir3) of general stoichiometry [Ir(N^C)₂(N^N)]Cl decorated with oligo(ethylene glycol) fragments to make them water-soluble and biocompatible, as well as to protect them from aggregation with biomolecules such as albumin. The major photophysical characteristics of these phosphorescent complexes are determined by the nature of two cyclometallating ligands (N^C) based on 2-pyridine-benzothiophene, since quantum chemical calculations revealed that the electronic transitions responsible for the excitation and emission are localized mainly at these fragments. However, the use of various diimine ligands (N^N) proved to affect the quantum yield of phosphorescence and allowed for changing the complexes’ sensitivity to oxygen, due to the variations in the steric accessibility of the chromophore center for O₂ molecules. It was also found that the N^N ligands made it possible to tune the biocompatibility of the resulting compounds. The wavelengths of the Ir1–Ir3 emission maxima fell in the range of 630–650 nm, the quantum yields reached 17% (Ir1) in a deaerated solution, and sensitivity to molecular oxygen, estimated as the ratio of emission lifetime in deaerated and aerated water solutions, displayed the highest value, 8.2, for Ir1. The obtained complexes featured low toxicity, good water solubility and the absence of a significant effect of biological environment components on the parameters of their emission. Of the studied compounds, Ir1 and Ir2 were chosen for in vitro and in vivo biological experiments to estimate oxygen concentration in cell lines and tumors. These sensors have demonstrated their effectiveness for mapping the distribution of oxygen and for monitoring hypoxia in the biological objects studied. Full article