Ligands For Transition Metals Research Articles

Design of dinuclear osmium complex doped antifouling cellulose nanoparticles for targeting and dual photodynamic/photothermal therapy under near infrared irradiation

Transition metal-ligand has been explored in the treatment of tumors in photodynamic theray (PDT) or photothermal therapy (PTT) and Osmium complex attracts attentration due to its lower toxicity and longer absorption wavelength. However, there was no report about binuclear Os complex for combined therapy of PDT and PTT which could have a synergistic effect and improve the effectiveness. Herein, we synthesis of mono/dinuclear Os complexes (OsY1, OsY2) with dual PDT/PTT capabilities under a single near-infrared (NIR) excitation wavelength. These features arise from the large π-conjugated structure of our dinuclear Os complex coupled with efficient metal-to-ligand charge transfer, which bring in ultralow energy gaps of 0.733 eV and 0.308 eV for OsY1 and OsY2, respectively. Furthermore, we prepared the Osmium complex-doped, aptamer-conjugated cellulose NPs via the emulsion polymerization method. These NPs exhibit a notable ability to target mitochondria and posse a “protein corona-free” status, showing much higher efficiency in tumor ablation (76 %) than the commercialized indocyanine green (ICG) doped cellulose NPs (24 %) under 808 nm irradiation. Consequently, our designed mono/dinuclear Os complex, featuring a single-molecule dual PDT/PTT effect within doped antifouling NPs, holds promise for potential applications in cancer therapy.

Binuclear complexes of all first row 3d metals (Sc to Zn) with a cyclic N4-Tetradentate Ligand: Metal-Metal bond Strengths and bond orders

Metal-metal (MM) bonds in binuclear complexes M2L2 (L = tetradentate ligand) for the first row transition metals are studied using DFT to design novel complexes which mimic lantern complexes having four bidentate ligands. Two orientations for the ligand array are applied − orthogonal (orth) and lateral (lat). Ground states for all complexes are identified from several low-lying spin states, where each orth isomer is generally lower in energy than the corresponding lat isomer. All the MM bonds are assigned formal bond order (fBO) values through MO analysis and/or electron counting. The M2L2orth complexes in many ways mimic the geometrical and electronic structure of known tetragonal lantern complexes. The formal shortness ratio (FSR) and the Wiberg index WMM for the MM bond correlate well with the fBO values, validating their use as measures of intrinsic MM bond strength.

Heteroleptic Triazole-Bisoxazoline Iron Complexes Reveal Lability of the Iron-Carbene Bond Even Within a Chelating Scaffold.

N-Heterocyclic carbenes have proven to be excellent ligands for transition metals, with numerous applications in catalysis and beyond. However, they have also displayed lability with first row transition metals, largely due to the hard-soft mismatch of the metal-carbon bond. Chelation is often considered a suitable methodology for supporting the labile M-C bond through the introduction of a strongly coordinating donor site such as hard phenolates. Herein, we demonstrate that chelating phenolate-carbene ligands are kinetically labile in iron(II) complexes. Specifically, heteroleptic iron complexes [Fe(C^O)(N^N)] were synthesized composed of a phenolate-functionalized triazolylidene (CO) ligand and N,N-bidentate coordinating bisoxazoline ligand (N^N). Stability studies by 1H NMR spectroscopy showed that the heteroleptic complexes preferentially convert to their corresponding homoleptic complexes [Fe(C^O)2] and [Fe(N^N)2], indicating reversible decoordination of the carbene phenolate chelate from the iron center. The rate of this rearrangement is dependent on the substituents on the ligands and increases for triazolylidene wingtip groups mesityl (Mes) < di(isopropyl)aryl (DIPP) < adamantyl (Ad), with significant ligand redistribution for DIPP and Ad systems observed even at room temperature. The most stable heteroleptic complex featured mesityl wingtips on the triazole and phenyl groups as oxazoline substituents and displayed signs of ligand exchange only after 16 h at room temperature. This substitutional lability of carbene ligands even when supported by a phenolate chelating group has direct consequences when designing iron complexes for catalytic applications.

The Role of Carrier Ion‐Ligand Interaction on Intercalation Potentials and Phase Evolution of Berlin Green Cathodes in Rechargeable Batteries

AbstractIntercalation and deintercalation are fundamental processes in battery electrodes that involve the reversible addition and extraction of carrier ions such as lithium (Li) and sodium (Na) into a host framework made of transition metal (TM) ions and ligands. Although TM–ligand interactions are known to primarily determine intercalation potentials, a comprehensive understanding of their interactions involving the carrier ions still remains elusive. This study investigates the complex interactions between carrier ions (Li and Na) and the ligand in Berlin green (BG, Fe3+[Fe3+(CN)6]) cathodes to elucidate their effects on intercalation potentials and phase evolution. Comprehensive X‐ray characterizations and electrochemical analyses reveal that the strong carrier ion–ligand interaction, influenced by the type and concentration of carrier ions, can modify the electronic structure of Fe ions and affect the intercalated structure of BG cathodes, thereby tuning the intercalation potentials. Specifically, the enhanced covalent interaction of the Na–CN units compared with that of the Li–CN units induces rhombohedral distortion in the fully sodiated state and increases the working potential of high‐spin Fe ions. The findings highlight the critical role of carrier ion–ligand interactions in tuning the electrochemical properties of battery electrodes for the design of advanced battery systems.

Mechanochemical Synthesis of Corannulene Flanked N-heterocyclic Carbene (NHC) Precursors and Preparation of Their Metal Complexes.

The synthesis of new compounds is an important pillar for the advancement of the field of chemistry and adjacent fields. In this regard, over the last decades huge efforts have been made to not only develop new molecular entities but also more efficient sustainable synthetic methodologies due to the increasing concerns over environmental sustainability. In this context, we have developed synthetic routes to novel corannulene flanked imidazolium bromide NHC precursors both in the solid-state and solution phases. Our work presents a comprehensive comparative study of mechanochemical routes and conventional solution-based methods. Green metrics and energy consumption comparison were performed for both routes revealing ball-milling generation of these compounds to be an environmentally greener technique to produce such precursors compared to conventional solvent-based methods. In addition, we have demonstrated proof-of-concept of the herein reported corannulene flanked NHCs to be robust ligands for transition metals and their ligand substitution reactions.

Non-rigid metal–oxygen bonding empowered nitrate reduction on ruthenium catalysts

Electrocatalytic nitrate reduction (NitRR) offers exciting potential for mass production of ammonia (NH3) from renewables. However, the rigidity of metal−ligand bonds in most electrocatalysts renders them unable to survive the structural transformations required for NitRR. Herein, we establish a type of non-rigid metal−oxygen bonds by employing graphene oxide (GO) sheets as a 'micron-scale' ligand for transition metals (TM). Because of being confined to the interfaces between GO and TM, the oxygenated groups in GO can associate with and dissociate from the TM in response to reaction dynamics. As a proof-of-concept demonstration, an electrocatalyst was developed by dispersing nanoscale ruthenium (Ru) on graphene oxide (GO) and utilizing two-dimensional MXene to compensate for the low electrical conductivity of GO. This electrocatalyst exhibits a maximum NH3 yield of over 5 mg cm−2 h−1, with almost 100 % current-to-NH3 efficiency, far outperforming the performance of most reported Ru-based materials. What's even more remarkable is the achievement of a record-breaking performance: a 200-hour stable electrolysis with a NH3 yield of 40.2 mg cm−2 h−1, using a membrane electrode reactor. Our experimental and theoretical investigations further reveal the non-rigidity of the Ru–O bonds and how they self-regulate to adapt to diverse intermediates involved in NitRR. This work provides an approach to fabricate a high-performance electrocatalyst featuring reversible and non-rigid metal−oxygen bonds, opening new possibilities for practical nitrate electrolysis.

Exploring the anticancer activity of 1-(2-methyl-3-furoyl)-4-phenyl-3-thiosemicarbazide and its Mn(II) complex: Synthesis, spectral, crystal structures, and Hirshfeld surface analysis

The chemistry of mixed ligand transition metal complexes has been of interest of researchers owing to its diverse application and bonding features. Herein, a new thiosemicarbazide derivative namely 1-(2-methyl-3-furoyl)-4-phenyl-3-thiosemicarbazide (HmfpTSC) has been synthesized along with its [Mn(mfpTSC)2(o-phen)] (C1) complex. The prepared ligand (HmfpTSC) and the complex have been confirmed via spectroscopic and single-crystal X-ray data. The HmfpTSC and complex crystallize in a monoclinic crystal system with space group P21/c and P21/n, respectively. HmfpTSC behaves as a uninegative bidentate ligand and its two-unit binds with metal ion along with one unit of o-phen. Using Hirshfeld surface analysis, the weak interactions seen in HmfpTSC and complex have been quantitatively investigated. The MTT assay was used to assess the cytotoxicity of HmfpTSC and [Mn(mfpTSC)2(o-phen)] complex against Dalton's lymphoma cells. Further, the mechanism of anticancer action of ligand and complex was investigated through DAPI, AO/EB staining, and flow cytometry. The both AO/EB and DAPI staining provided compelling evidence of complex-induced cellular and nuclear changes consistent with apoptosis and necrosis.

Imidazopyridine Family: Versatile and Promising Heterocyclic Skeletons for Different Applications.

In recent years, there has been increasing attention focused on various products belonging to the imidazopyridine family; this class of heterocyclic compounds shows unique chemical structure, versatile optical properties, and diverse biological attributes. The broad family of imidazopyridines encompasses different heterocycles, each with its own specific properties and distinct characteristics, making all of them promising for various application fields. In general, this useful category of aromatic heterocycles holds significant promise across various research domains, spanning from material science to pharmaceuticals. The various cores belonging to the imidazopyridine family exhibit unique properties, such as serving as emitters in imaging, ligands for transition metals, showing reversible electrochemical properties, and demonstrating biological activity. Recently, numerous noteworthy advancements have emerged in different technological fields, including optoelectronic devices, sensors, energy conversion, medical applications, and shining emitters for imaging and microscopy. This review intends to provide a state-of-the-art overview of this framework from 1955 to the present day, unveiling different aspects of various applications. This extensive literature survey may guide chemists and researchers in the quest for novel imidazopyridine compounds with enhanced properties and efficiency in different uses.

Electrocatalysis-Enabled Stereoselective Synthesis of Monofluoroalkenes via Hydrodefluorination of gem-Difluoroakenes.

We report a simple and economical method to synthesize monofluoroalkenes via the electrochemical hydrodefluorination of gem-difluoroalkenes. This reaction proceeds efficiently at room temperature, eliminating the requirement for a costly transition metal catalyst, ligand, and external reducing agent. The monofluoroalkene products can be obtained in medium to good yields and up to 99:1 E/Z selectivity. The reaction is easily scalable to gram scale.

Deracemization of Atropisomeric Biaryls Enabled by Copper Catalysis.

Atropisomeric biaryls have found crucial applications in versatile chiral catalysts as well as in ligands for transition metals. Herein, we have developed an efficient crystallization-induced deracemization (CID) method to access chiral biaryls from their racemates with a chiral ammonium salt under copper catalysis including BINOL, NOBIN, and BINAM derivatives. After being significantly accelerated by its bidentate diamine ligand, the copper catalyst exhibits high efficiency and selectivity in racemizing biaryl skeletons, and the cocrystal complex would be enantioselectively formed together with chiral ammonium salt, which on acid-quenching would directly deliver chiral biaryl without further chromatographic purification. This CID process is easily scalable, and the chiral ammonium salt was nicely recoverable. Ligand effect studies showed that bulky alkyl substitution was an indispensable element to ensure efficient racemization, which probably proceeds via a radical-cation intermediate and further allows axial rotation by forming a delocalized radical.

Chiral arylsulfinylamides as reagents for visible light-mediated asymmetric alkene aminoarylations.

Two- or one-electron-mediated difunctionalizations of internal alkenes represent straightforward approaches to assemble molecular complexity by the simultaneous formation of two contiguous Csp3 stereocentres. Although racemic versions have been extensively explored, asymmetric variants, especially those involving open-shell C-centred radical species, are much more limited both in number and scope. Here we describe enantioenriched arylsulfinylamides as all-in-one reagents for the efficient asymmetric, intermolecular aminoarylation of alkenes. Under mild photoredox conditions, nitrogen addition of the arylsulfinylamide onto the double bond, followed by 1,4-translocation of the aromatic ring, produce, in a single operation, the corresponding aminoarylation adducts in enantiomerically enriched form. The sulfinyl group acts here as a traceless chiral auxiliary, as it is eliminated in situ under the mild reaction conditions. Optically pure β,β-diarylethylamines, aryl-α,β-ethylenediamines and α-aryl-β-aminoalcohols, prominent motifs in pharmaceuticals, bioactive natural products and ligands for transition metals, are thereby accessible with excellent levels of regio-, relative and absolute stereocontrol.

A Powerful P-N Connection: Preparative Approaches, Reactivity, and Applications of P-Stereogenic Aminophosphines.

For more than five decades, P-stereogenic aminophosphine chalcogenides and boranes have attracted scientific attention and are still in the focus of ongoing research. In the last years, novel transition metal-based synthesis methods have been discovered, in addition to the long-known use of chiral auxiliaries. Enantiomerically pure compounds with N-P+-X- (X=O, S, BH3) motifs served as valuable reactive building blocks to provide new classes of organophosphorus derivatives, thereby preserving the stereochemical information at the phosphorus atom. Over the years, intriguing applications in organocatalysis and transition metal catalysis have been reported for some representatives. Asymmetric reductions of C=C, C=N, and C=O double bonds were feasible with selected P-stereogenic aminophosphine oxides in the presence of hydrogen transfer reagents. P-stereogenic aminophosphine boranes could be easily deprotected and used as ligands for various transition metals to enable catalytic asymmetric hydrogenations of olefins and imines. This review traces the emergence of a synthetically and catalytically powerful functional compound class with phosphorus-centered chirality in its main lines, starting from classical approaches to modern synthesis methods to current applications.

Synthesis of enantiopure 1,2,3-triazolylidene-type mesoionic carbene (MIC) conjugate acids featuring a rigid bicyclic scaffold

Chiral NHCs have found numerous applications as ligands for transition metals and in their own right for asymmetric catalysis. We report a synthetic route from l-malic acid to enantiopure 1,2,3-triazoliums with the chiral center in a fused ring.

CHITOSAN-SUPPORTED MERCURY(II) ACETATE AS A CATALYST FOR TRANSVINYLATION REACTIONS OF AZOLES

The application of homogeneous catalysts - transition metal complexes - on organic polymers is of a great interest among researchers. Heterogeneous catalysts often have a long life span and are easy to separate from the reactants and reaction products, and they can also be reused. A homogeneous catalyst on a heterogeneous support acts as if it were in solution, but simultaneously it is a separate stationary phase. In this study we tried to use chitosan as a carrier for metal ions (particularly mercury(II), knowing in advance that chitosan is a good ligand for transition metals). Interest in chitosan is associated with their unique physiological and environmental properties, such as biocompatibility, biodegradation, and chelating ability. Here, an efficient and easy method of vinylation of azoles in the presence of chitosan-supported mercury(II) acetate heterogenous catalytic system is reported. As a result, several products were synthesized in high yields. The developed procedure is easy to perform, requires less amount of catalyst, shortens reaction time, excludes the formation of side products, and provides higher selective yields of vinylated products, reduces water contamination with mercury salts. Furthermore, it is possible to recover the catalyst from the reaction mixture and recycle this catalytic system more than four times.

Chemoselective reduction of aromatic nitro compounds (o-nitrophenol derivatives) using simple borane-THF without transition metal catalysts, additives, or ligands

Chemoselective reduction of aromatic nitro compounds (ortho-nitrophenol derivatives) using Borane in THF (BH3-THF) at room temperature, without using an additional metal catalyst is reported. Interestingly, nitroarenes containing two or three groups, a selective reduction of the nitro group adjacent to the hydroxy group is observed which happens to be the first Chemoselective reduction protocol for nitro groups using BH3-THF. The presence of the phenolic hydroxyl group is found to be the key that aids in hydrogen transfer to the nitro group through a cyclic transition step.

Thioxobimanes.

Dioxobimanes, colloquially known as bimanes, are a well-established family of N-heterobicyclic compounds that share a characteristic core structure, 1,5-diazabicyclo[3.3.0]octadienedione, bearing two endocyclic carbonyl groups. By sequentially thionating these carbonyls in the syn and anti isomers of the known (Me,Me)dioxobimane, we were able to synthesize a series of thioxobimanes, representing the first heavy-chalcogenide bimane variants. These new compounds were extensively characterized spectroscopically and crystallographically, and their aromaticity was probed computationally. Their potential role as ligands for transition metals was demonstrated by synthesizing a representative gold(I)-thioxobimane complex.

Photothermal Aza‐Michael Addition of Divergent Amines to Vinyl Sulfones: A Method Towards Transition Metal‐ and Base‐Free Medium

AbstractA highly efficient and versatile method has been developed for the photothermal aza‐Michael addition, producing β‐amino sulfones with excellent yields. The protocol uses mild and simple conditions under the batch and continuous flow process and is suitable for synthesis, without the need for transition metal catalysts, ligands, strong acids, or bases. This sustainable approach offers a significant breakthrough in organic synthesis with potential applications in medicinal chemistry and materials science.

Photophysical, electrochemical and electrochromic behavior of transition metal complexes with 1,10-phenanthroline ligands

A series of non-noble transition metal complexes were synthesized by coordinating Fe2+, Co2+, and Ni2+ with ligands having a parent structure of 4,7-diphenyl-1,10-phenanthroline (L1 and L2) and dipyrido[3,2-a:2′,3′-c]phenazine (L3–L5), and their photophysical, electrochemical, and electrochromic properties were studied. Both transition metal ions and ligands produce more or less influence on these properties. Electrochromic properties such as color, optical contrast, response time, coloration efficiency and switching stabilities can be tuned by selecting proper metal ions, parent structure of ligands, and substituent groups. Theory calculation results indicate that electrons flow from the metallic center to the ligands. The UV–vis spectra of all five Fe(II) complexes showed a broad and strong MLCT band at ca. 530 nm. The UV–vis spectra of Fe(II), Co(II) and Ni(II) complexes with L2 ligand showed a strong LC (π–π*) band at ca. 325 nm. Electrochromic process caused a change in the intensity of LC and MLCT absorption. The ligands produced little effect on the bleached and colored states of Fe(II) complexes, all of them showed a bleached state of red and a colored state of purple-red probably due to the reversible Fe(II)/Fe(III) transition. Both Co(II) and Ni(II) complexes showed a bleached state of pale yellow, however, the ligands produced significant effect on their colored states probably due to the partially electron density displacement between the metal ions and the ligands. When the parent structure of ligand is 4,7-diphenyl-1,10-phenanthroline, electron-donating substituent such as –OCH3 is beneficial to electrochromic properties, and Fe(II) complexes have higher optical contrast and coloration efficiency compared to Co(II) and Ni(II) complexes. When the parent structure of ligand is dipyrido[3,2-a:2′,3′-c]phenazine, –CN substituent markedly enhances the optical contrast and coloration efficiency of Fe(II), Co(II) and Ni(II) complexes.

Tris(3-nitropentane-2,4-dionato-κ2 O,O′) Complexes as a New Type of Highly Energetic Materials: Theoretical and Experimental Considerations

Decreasing the sensitivity towards detonation of high-energy materials (HEMs) is the ultimate goal of numerous theoretical and experimental studies. It is known that positive electrostatic potential above the central areas of the molecular surface is related to high sensitivity towards the detonation of high-energy molecules. Coordination compounds offer additional structural features that can be used for the adjustment of the electrostatic potential values and sensitivity towards detonation of this class of HEM compounds. By a careful combination of the transition metal atoms and ligands, it is possible to achieve a fine-tuning of the values of the electrostatic potential on the surface of the chelate complexes. Here we combined Density Functional Theory calculations with experimental data to evaluate the high-energy properties of tris(3-nitropentane-2,4-dionato-κ2 O,O′) (nitro-tris(acetylacetonato)) complexes of Cr(III), Mn(III), Fe(III), and Co(III). Analysis of the Bond Dissociation Energies (BDE) of the C-NO2 bonds and Molecular Electrostatic Potentials (MEP) showed that these compounds may act as HEM molecules. Analysis of IR spectra and initiation of the Co(AcAc-NO2)3 complex in the open flame confirmed that these compounds act as high-energy molecules. The measured heat of combustion for the Co(AcAc-NO2)3 complex was 14,133 J/g, which confirms the high-energy properties of this compound. The results also indicated that the addition of chelate rings may be used as a new tool for controlling the sensitivity towards the detonation of high-energy coordination compounds.

Synergistic effect of Polydopamine incorporated Copper electrocatalyst by dopamine oxidation for efficient hydrogen production

Tuning the metal-support interaction in electrocatalysts has been proposed as a viable method for manipulating the electronic structure and catalytic activity. In this work, inspired by natural hydrogenase enzyme, electrocatalysts with a hybrid metal-matrix complex using polydopamine (PDA) as a supporting matrix were synthesized for efficient green hydrogen production. Among the various Metal-PDA electrocatalysts, Cu-PDA shows outstanding catalytic activity (low overpotential (ƞ) of 104 mV at 10 mA cm−2 and small Tafel slope of 60.67 mV dec-1) with high stability at neutral pH. Also, the electrochemical impedance spectroscopy analysis verified the fast charge transfer properties of Cu-PDA (2.8 Ω cm2) than PDA (26 Ω cm2), indicating a faster proton-coupled electron transfer process in Cu-PDA electrocatalyst. Therefore, emerging nature inspired organic ligand-transition metal ion complexes can be extensively encouraged as a prospective HER electrocatalyst under neutral conditions.