Ligands For Transition Metals Research Articles

Novel Mixed Ligand Transition Metal Complexes: Synthesis, Characterization, and Biological Evaluation

Novel Mixed Ligand Transition Metal Complexes: Synthesis, Characterization, and Biological Evaluation

Catalytic one-pot three-component synthesis of 3,3′-disubstituted oxindoles and spirooxindole pyrans by mixed ligand transition metal complexes

Catalytic one-pot three-component synthesis of 3,3′-disubstituted oxindoles and spirooxindole pyrans by mixed ligand transition metal complexes

Machine Learning-Assisted Selection of Active Spaces for Strongly Correlated Transition Metal Systems.

Active space quantum chemical methods could provide very accurate description of strongly correlated electronic systems, which is of tremendous value for natural sciences. The proper choice of the active space is crucial but a nontrivial task. In this article, we present a neural network-based approach for automatic selection of active spaces, focused on transition metal systems. The training set has been formed from artificial systems composed of one transition metal and various ligands, on which we have performed the density matrix renormalization group and calculated the single-site entropy. On the selected set of systems, ranging from small benchmark molecules up to larger challenging systems involving two metallic centers, we demonstrate that our machine learning models could predict the active space orbitals with reasonable accuracy. We also tested the transferability on out-of-the-model systems, including bimetallic complexes and complexes with ligands, which were not involved in the training set. Also, we tested the correctness of the automatically selected active spaces on a Fe(II)-porphyrin model, where we studied the lowest states at the DMRG level and compared the energy difference between spin states or the energy difference between conformations of ferrocene with recent studies.

Mixed ligand transition metal(II) complexes: Characterization, spectral, electrochemical studies, molecular docking and bacteriological application

Mixed ligand complexes of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) with N,N'-1,4-phenylene (2-hyboxynaphthaliden imine) (H2L) as primary ligand and 4-aminoantipyrine (4-AAp) as secondary ligand have been prepared. The newly formed complexes were characterized using elemental analysis, magnetic susceptibility, molar conductance, 1H NMR, UV–Vis., FTIR, X-ray diffraction, mass, thermal analysis and ESR techniques. The elemental analysis, data reveal the formation of [2:1:2] [M: H2L: 4-AAP] complexes. The mode of bonding between Cu(II), Ni(II), Co(Il), Mn(II) and Cd(II) and ligands has been studied by IR spectrophotometry. Electronic absorption spectra and magnetic moment measurements of the mixed-ligand complexes suggest a distorted octahedral geometry around the central metal ion and the anions X− are in the axial positions, for all compounds. The ligands are found to behave in a neutral bidentate manner, through nitrogen atom and oxygen atom of carbonyl group (secondary ligand), whereas H2L (primary ligand) coordinated through nitrogen and OH group as a neutral ligand. FT-IR spectral data shows that the ligand acted as bis-bidentate coordination through ON–NO donor system. The XRD patterns of the ligand and its mixed ligand complexes showed the polycrystalline natures. The ligand and its mixed complexes were studied for their microbial activity against some bacteria and fungi. The ligand in comparison to its mixed ligand complexes (1-5) was screened for their antibacterial activity against Klebsiella pneumoniae, Escherichia coli, Pseudomonas sp., Staphylococcus aureus and Bacillus cereus. Antifungal activities of ligand in comparison to its mixed ligand complexes (1-5) were determined against Fusarium oxysporum, Aspergillus niger and Candida albicans. It was found that the mixed ligand complex (5) is more active than other mixed ligand complexes and penicillin G against Bacillus cereus, Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas sp. The mixed ligand complex (5) is more active than the ligand and other mixed ligand complexes and miconazole against Aspergillus niger. The inhibition efficiency of the prepared ligand (H2L) against the corrosion of P355 carbon steel in HCl (2 M) solution was determined by various electrochemical methods are found to be in reasonable agreement. The morphology of protected P355 carbon steel was test by energy dispersive X-ray and scanning electron microscope (EDX–SEM).

Synthesis, Characterization and Photo Degradation Studies of New Mixed Ligand Transition Metal Complexes of Mefenamic Acid and Glutamine

Dentate ligands 2-[(2,3-dimethylphenyl)amino]benzoic acid (Mefenamic acid ) and 2,5-diamino-5-oxopentanoic acid(glutamine) were used as bidentate Lewis base to prepare solid complexes with Molybdenum (V), Tungsten (V)) and Lanthanum(III). The Photo degradation study was achieved for the complexes solutions in methanol. The prepared complexes were characterized by using spectroscopy methods like FTIR, UV-visible, Melting points and flame atomic absorption spectroscopy were calculated for all complexes. Furthermore the molar conductance of 0.001 M solutions in acetonitrile and magnetic susceptibility were performed to elucidate the proposed geometry and structures of prepared complexes. Magnetic susceptibility displayed that complexes had not diamagnetic properties. Photo kinetic study was done for La and Mo Complexes to study the photo sensitivity of prepared complexes. Half time of the complexes` photo reaction were achieved and order of reactions were calculated which appear that photo reaction of LaIII complex was from the first order and constant of reaction was calculated (1.62x10-2) min-1 and half time of reaction was (62.112) min. Also, order reaction of Mo (III) complex was from first order too, the value of constant of reaction was (1.88 min-1) and half time of reaction was (26.6) min. TGA analysis of MoIII was done.

Multiconfiguration Pair-Density Functional Theory for Transition Metal Silicide Bond Dissociation Energies, Bond Lengths, and State Orderings.

Transition metal silicides are promising materials for improved electronic devices, and this motivates achieving a better understanding of transition metal bonds to silicon. Here we model the ground and excited state bond dissociations of VSi, NbSi, and TaSi using a complete active space (CAS) wave function and a separated-pair (SP) wave function combined with two post-self-consistent field techniques: complete active space with perturbation theory at second order and multiconfiguration pair-density functional theory. The SP approximation is a multiconfiguration self-consistent field method with a selection of configurations based on generalized valence bond theory without the perfect pairing approximation. For both CAS and SP, the active-space composition corresponds to the nominal correlated-participating-orbital scheme. The ground state and low-lying excited states are explored to predict the state ordering for each molecule, and potential energy curves are calculated for the ground state to compare to experiment. The experimental bond dissociation energies of the three diatomic molecules are predicted with eight on-top pair-density functionals with a typical error of 0.2 eV for a CAS wave function and a typical error of 0.3 eV for the SP approximation. We also provide a survey of the accuracy achieved by the SP and extended separated-pair approximations for a broader set of 25 transition metal–ligand bond dissociation energies.

Bioinspired Brønsted Acid-Promoted Regioselective Tryptophan Isoprenylations.

Tryptophan-containing isoprenoid indole alkaloid natural products are well known for their intricate structural architectures and significant biological activities. Nature employs dimethylallyl tryptophan synthases (DMATSs) or aromatic indole prenyltransferases (iPTs) to catalyze regio- and stereoselective prenylation of l-Trp. Regioselective synthetic routes that isoprenylate cyclo-Trp-Trp in a 2,5-diketopiperazine (DKP) core, in a desymmetrizing manner, are nonexistent and are highly desirable. Herein, we present an elaborate report on Brønsted acid-promoted regioselective tryptophan isoprenylation strategy, applicable to both the monomeric amino acid and its dimeric l-Trp DKP. This report outlines a method that regio- and stereoselectively increases sp3 centers of a privileged bioactive core. We report on conditions involving screening of Brønsted acids, their conjugate base as salt, solvent, temperature, and various substrates with diverse side chains. Furthermore, we extensively delineate effects on regio- and stereoselection of isoprenylation and their stereochemical confirmation via NMR experiments. Regioselectively, the C3-position undergoes normal-isoprenylation or benzylation and forms exo-ring-fused pyrroloindolines selectively. Through appropriate prenyl group migrations, we report access to the bioactive tryprostatin alkaloids, and by C3-normal-farnesylation, we access anticancer drimentines as direct targets of this method. The optimized strategy affords iso-tryprostatin B-type products and predrimentine C with 58 and 55% yields, respectively. The current work has several similarities to biosynthesis, such as—reactions can be performed on unprotected substrates, conditions that enable Brønsted acid promotion, and they are easy to perform under ambient conditions, without the need for stoichiometric levels of any transition metal or expensive ligands.

Structural Evidence for Pnictogen-Centered Lewis Acidity in Cationic Platinum-Stibine Complexes Featuring Pendent Amino or Ammonium Groups.

As part of our continuing interest in the chemistry of cationic antimony Lewis acids as ligands for late transition metals, we have now investigated the synthesis of platinum complexes featuring a triarylstibine ligand substituted by an o-[(dimethylamino)methyl]phenyl group referred to as ArN. More specifically, we describe the synthesis of the amino stibine ligand Ph2SbArN (L) and its platinum dichloride complex [LPtCl]Cl which exists as a chloride salt and which shows weak coordination of the amino group to the antimony center. We also report the conversion of [LPtCl]Cl into a tricationic complex [LHPt(SMe2)]3+ which has been isolated as a tris-triflate salt after reaction of [LPtCl]Cl with SMe2, HOTf and AgOTf. Finally, we show that [LHPt(SMe2)][OTf]3 acts as a catalyst for the cyclization of 2-allyl-2-(2-propynyl)malonate.

Anti-Bacterial and Anti-Fungal Study of Schiff Bases and their Metal Co (II)& Zn (II) Complexes

Synthesis of Schiff bases from different types of aromatic aldehyde and 3-amino-2- napthol-4-sulphonic acid and then prepared the Co (II), Zn (II) complexes. Metal complexes of Schiff bases have occupied a central role in the development of coordination Chemistry. A number of verities of stable chemical species have been synthesized, containing transition metal and multifarious ligand. Metal complexes of Schiff base shows the strong anti fungicidal, anti bacterial activity, anti viral infection, anticancer, herbicides, plant growth regulators and anti covulsants . Metal complexes also find a wide applications in the field of industrial chemistry, analytical chemistry, pharmaceutical chemistry, agricultural chemistry and bioorganic chemistry. Recently hetrocyclic such as 2 ‘al’ pyrrol, 2 ‘al’ furan, 2 ‘al’ thiophen and aromatic aldehyde, there metal Zn (II), Co (II) complexes have also gained a focal position in bioinorganic field and frequently used as antifungal, plant growth regulators and anticancer.

Cover Feature: Recent Progress of Two‐Dimensional Metal‐Organic Frameworks and Their Derivatives for Oxygen Evolution Electrocatalysis (ChemElectroChem 23/2020)

The Cover Feature shows two-dimensional (2D) metal-organic frameworks (MOFs) that emerge as electrocatalysts for the oxygen evolution reaction (OER). The transition metal nodes and ligands can be feasibly adjusted for improved performance. 2D MOF derivatives are also promising. More information can be found in the Review by W. Huang et al.

Direct Electrochemical Defluorinative Carboxylation of gem-Difluoroalkenes with Carbon Dioxide.

We report a facile and economical synthesis of α-fluoroacrylic acids via direct electrochemical defluorinative carboxylation of gem-difluoroalkenes with CO2. By using a platinum plate as the working cathode and a cheap nickel plate as the anode in a user-friendly undivided cell under constant current conditions, the reactions proceed smoothly under room temperature, without the use of expensive transition metal catalysts, ligands, external base or reductant, affording the desired adducts in up to 83% yield and 20:1 Z/E ratio, with good functional group tolerance. A cyclic voltammetry study was conducted and suggested a novel ECEC process.

(N),C,N-Coordinated Heavier Group 13-15 Compounds: Synthesis, Structure and Applications.

The aim of this review is to summarize recent achievements in the field of (N),C,N-coordinated group 13-15 compounds not only regarding their synthesis and structure, but mainly focusing on their potential applications. Relevant compounds contain various types of N-coordinating ligands built up on an ortho-(di)substituted phenyl platform. Thus, group 13 and 14 derivatives were used as single-source precursors for the deposition of semiconducting thin films, as building blocks for the preparation of high-molecular polymers with remarkable optical and chemical properties or as compounds with interesting reactivity in hydrometallation processes. Group 15 derivatives function as catalysts in the Mannich reaction, in the allylation of aldehydes or activation of CO2 . They were used as transmetallation reagents in transition metal catalysed coupling reactions. The univalent species serve as ligands for transition metals, activate alkynes or alkenes and are utilized as catalysts in the transfer hydrogenation of azo-compounds.

Recent Developments in Enantioselective Transition Metal Catalysis Featuring Attractive Noncovalent Interactions between Ligand and Substrate.

Enantioselective transition metal catalysis is an area very much at the forefront of contemporary synthetic research. The development of processes that enable the efficient synthesis of enantiopure compounds is of unquestionable importance to chemists working within the many diverse fields of the central science. Traditional approaches to solving this challenge have typically relied on leveraging repulsive steric interactions between chiral ligands and substrates in order to raise the energy of one of the diastereomeric transition states over the other. By contrast, this Review examines an alternative tactic in which a set of attractive noncovalent interactions operating between transition metal ligands and substrates are used to control enantioselectivity. Examples where this creative approach has been successfully applied to render fundamental synthetic processes enantioselective are presented and discussed. In many of the cases examined, the ligand scaffold has been carefully designed to accommodate these attractive interactions, while in others, the importance of the critical interactions was only elucidated in subsequent computational and mechanistic studies. Through an exploration and discussion of recent reports encompassing a wide range of reaction classes, we hope to inspire synthetic chemists to continue to develop asymmetric transformations based on this powerful concept.

A Novel Bisoxazoline‐Imidazolium Salt in Ytterbium‐Catalyzed Asymmetric Reduction of Ketone

Chiral N‐heterocyclic carbene (NHC), a privileged ligand for transition metals, has had a profound impact on organometallic chemistry. The monodentate and bidentate chiral carbenes have been developed significantly, while the tridentate ones have been less exploited. Herein, we designed and synthesized a new bisoxazoline‐imidazolium salt as a carbene precursor, which owns three chelating sites and two kinds of chiral information centers. A preliminary investigation on the asymmetric ketone reduction was also studied.

Charge-transfer processes in metal complexes enable luminescence and memory functions

Molecular transition-metal–ligand complexes are emerging as useful paradigms in materials science. Transition metal complexes have diverse metal d electron configurations, oxidation states, coordination numbers and geometries such that they can undergo a diverse array of electronic transitions. Metal-to-ligand charge-transfer transitions and their associated excited states are especially attractive given their rich redox properties and robustness. This chemistry is accessible by appropriate choice of low-valence metal centres and strong π-acceptor ligands. An in-depth fundamental understanding of their charge-transfer, assembly and structure–property relationships is important to allow us to rationally design complexes and tune their characteristics for an intended application. In addition to their attractive light-harvesting and photocatalytic applications, this Perspective describes recent developments in the use of transition metal complexes as materials in phosphorescent organic light-emitting diodes and resistive memory devices. Metal–ligand complexes undergo diverse charge-transfer processes when stimulated by light or electric fields. This Perspective describes how these processes can be exploited in photosensitizers, luminophores and resistive memory materials.

Base-promoted selective O-phosphorylation of aryl triflates with P(O)-H compounds

Compared to previous transition metal-catalyzed C-phosphorylation reactions for constructing C–P bonds, in the absence of transition metal catalysts and ligands, a direct O-phosphorylation of aryl triflates selectively occurred with P(O)-H compounds in the presence of a base via the construction of O–P bonds. This transformation proceeds under simple and mild conditions, and provides a new method for the preparation of valuable organophosphoryl compounds from readily available P(O)-H compounds and triflates.

Synthesis and Antibacterial Studies of new mixed ligand transition metal complexes of thioester (1, 3, 4-Oxadiazole) derivative (phozbt) and dppe Ligands.

 Complexes of transition  palladium(II) and platinum(II) metals that possessing two kinds of ligands: S-5-phenyl -1, 3, 4-oxadiazole-2-yl benzothioate (phozbt) and tertiary diphosphine (dppe), were synthesized. The thioester (phozbt) ligand was synthesized by reaction between 2-mercapto-5-phenyl-1,3,4-oxadiazole (PhozSH) with benzoyl chloride and using sodium hydroxide. The synthesized ligand and complexes were described by C, H, N, S analysis, infrared spectra, molar conductivity, UV-visible and magnetic susceptibility measurements.  The (dppe) act as bidentate chelate that linked to the metals on both P-donor atoms. According to the spectral analysis of the complexes, a square planer structure were suggested for both metal complexes. The ligand and complexes were studied for antibacterial activity by using agar diffusion method. This study showed positive inhibition zone results, for both ligand and complexes with S. aureus and P. aeruginosa bacteria.&nbsp

Evaluation of Octaethyl-7,17-dioxobacteriochlorin as a Ligand for Transition Metals

The propensity of octaethyl-7,17-dioxobacteriochlorin toward the formation of transition metal complexes was evaluated. A variety of MII ions (M = Co, Ni, Cu, Zn, Pd, Ag, and Cd) and Fe(III) could be inserted using standard methodologies or, more often, using more forcing conditions. The stable products were spectroscopically characterized. The solid-state structures of the Ni(II), Cu(II), Pd(II), and Ag(II) complexes could also be determined by single crystal X-ray diffractometry, whereby the [7,17-dioxobacteriochlorinato] chromophore was found to be largely planar in all cases. The rate of Zn(II) insertion into octaethyl-7,17-dioxobacteriochlorin was less than half that into the corresponding 7-oxochlorin, which itself was about half the rate into the parent octaethylporphyrin. These rate differences reflect the relative decreased basicity of the β-oxo-substituted chromophores and possibly also their decreased conformational flexibility. We compare the basicity of the dioxobacteriochlorin to that of a range of related products of varying reduction state (porphyrin, chlorin, bacteriochlorin), an isomer, and the absence or presence of oxo-functionality, like oxochlorin, chlorin, oxobacteriochlorins, and bacteriochlorin, quantifying the effects of these macrocycle modifications. The work rationalizes earlier reports of the inability of tolyporphin A, a natural product possessing a 7,17-dioxobacteriochlorin chromophore, to form metal complexes and provide a more quantitative understanding of the degree of modulation that β-oxo groups have on the coordination properties of porphyrinoids.

(para‐Cymene)Ru(II) Complexes with Chelating Benzotriazole Ligands: Application in Oxidation and Reduction Catalysis

Abstract1‐Heteroaryl‐substituted benzotriazole motifs represent a new class of bidentate chelating ligands for several transition metals. Although metal complexes having such ligands in tris‐ and bis‐chelated binding have been extensively studied, investigation of mono‐chelated metal complexes, especially their structural and catalytic properties, is rarely explored. In this work, two such complexes – [(para‐cymene)Ru(BTZ‐2P)Cl]PF6 and [(para‐cymene)Ru(BTZ‐2Q)Cl]PF6, (BTZ‐2P=1‐(pyridine‐2‐yl)‐1H‐benzo[d][1,2,3]triazole; BTZ‐2Q=1‐(quinoline‐2‐yl)‐1H‐benzo[d][1,2,3]triazole) have been synthesized and characterized through various spectroscopic method and X‐ray crystallography. Their electronic spectra and electrochemical properties have also been explored. Both the complexes have been successfully applied in two types of important catalytic processes – (a) oxidation of aryl olefins to corresponding aromatic carbonyl compounds, and (b) transfer hydrogenation of aromatic carbonyl compounds to the corresponding alcohols.

Cascade and multicomponent synthesis of structurally diverse 2-(pyrazol-3-yl)pyridines and polysubstituted pyrazoles.

The cascade reaction between N-tosylhydrazones and 2-alkynylpyridines leads to 2-(pyrazol-3-yl)pyridines, important structural motifs in ligands for transition metals and bioactive molecules. When the reaction is conducted with 2,6-diethynylpyridine, the important 2,6-bis(pyrazolyl)pyridines are obtained, featuring the arrangement of tridentate and also pentadentate ligands. A novel three-component version of the reaction has been designed, which involves the use of α-bromo-N-tosylhydrazones, alkynylpyridines and NH-azoles. The generality of the multicomponent reaction is further illustrated by the preparation of different polysubstituted pyrazoles by employing an array of terminal alkynes. In these multicomponent reactions, complex molecules featuring three different heterocycles are assembled in a single step from commercial materials, enabling the fast generation of molecular diversity.