NNN Pincer Research Articles

NNN type pincer Pd (II) complexes of pyridine-2,6-dicarboxamides: Catalytic activity and supramolecular formation

Pyridine-2,6-dicarboxamide, NNN pincer type pro-ligands, and their palladium complexes were synthesized. The prepared pro-ligands and complexes were characterized with several characterization techniques (FT-IR, 1H NMR, 13C NMR, and UV–vis analyses). The molecular structure of the acetonitrile-N2,N6-bis(2-bromophenyl)pyridine-2,6-dicarboxamidopalladium(II) complex has been determined by single crystal XRD measurement. This complex contains intramolecular and intermolecular H-bonds, CH⋅⋅⋅π and face-to-face π⋅⋅⋅π interactions. In addition, two synthons were found in the crystal lattice that have been generated through hydrogen-bond interactions. Homo-synthons (R22(12)), which forms through CH⋅⋅⋅O intermolecular interactions (2.816 Å for C15H15⋅⋅⋅O1 and 2.603 Å for C13H13⋅⋅⋅O2) and hetero-synthons (R21(8)), that generated via CH⋅⋅⋅N intermolecular interactions (C21H21C⋅⋅⋅N4, 3.439 Å). Furhermore, homo-synthons (R33(11) and R22(9)) through intermolecular contacts were determined between the palladium complex and the acetonitrile molecules. Furthermore, a quantitative analysis of the noncovalent interactions within the structure was performed using Hirshfeld surface and two-dimensional fingerprint plot analyses. The three-dimensional arrangement of the crystal packing was assessed during the energy-framework calculations, revealing that the electrostatic energy framework had a considerable influence on the dispersion energy framework. The [PdL5] complex provided a conversion of more than 98 % and a yield of more than 98 % in the shortest time among other catalysts, in which the Suzuki–Miyaura CC cross-coupling reaction (SMR) was carried out with the 4-bromotoluene substrate. The activity of [PdL5] complex was then examined in the reactions of two other substrates, 1-bromo-4-isobutylbenzene and 2-bromo-6-methoxynaphthalene. Although a yield of over 97 % and a conversion of over 97 % were observed in the reaction of 1-bromo-4-isobutylbenzene after two hours, the reaction of 2-bromo-6-methoxynaphthalene achieved complete conversion and a yield of over 99 % within just one hour.

Manganese‐Catalyzed α‐Alkylation of Sulfones using Alcohols via a Hydrogen‐Borrowing Strategy: Synthesis of Branched Sulfones

AbstractHerein, we report an efficient and sustainable manganese‐catalyzed α‐C−H bond alkylation methodology to synthesize branched sulfones via a hydrogen borrowing pathway. The air‐stable and phosphine‐free Mn‐catalyst, (NNN)Mn(II)Cl2 was synthesized by using an earth‐abundant, commercially available, and inexpensive precursor MnCl2.4H2O, and a stable NNN pincer i. e. [N‐((benzimidazole‐2‐yl)methyl)quinoline‐8‐amine] ligand system. Taking benzyl phenyl sulfones as substrates, and benzyl alcohol derivatives as alkylating agents, a range of branched sulfones were synthesized in 40–82 % isolated yields using (NNN)Mn(II)Cl2 complex as the catalyst under open‐air conditions. Control experiments and deuterium incorporation studies have also been conducted to investigate the possible reaction mechanism and to provide evidence for the hydrogen borrowing pathway.

Ruthenium NNN‐Based Pincer Complexes with Metal Ligand Cooperation as Catalysts for N‐Methylation of Anilines and Nitroarenes with Methanol as a C1 Source

AbstractA novel phosphine‐free ruthenium pincer complex based on an NNN pincer ligand has been prepared and fully characterized. The complex was subsequently employed as an efficient catalyst for the N‐methylation of amines and the direct N‐methylation of nitroarenes using methanol as a C1 source under mild reaction conditions following the borrowing‐hydrogen approach. Both of the catalytic transformations were performed with only catalytic amounts of base under closed air conditions without using any other additives.

Catalytic Application of Copper Complex Prepared by a NNN Pincer Ligand Supported on Silica Nanoparticles Using first Generation of Polyamidoamine Dendrimers

Catalytic Application of Copper Complex Prepared by a NNN Pincer Ligand Supported on Silica Nanoparticles Using first Generation of Polyamidoamine Dendrimers

NNN pincer palladium(II) complexes with N-(2-(1H-pyrazol-1-yl)phenyl)-picolinamide ligands: synthesis, characterization, and application to heck coupling reaction

NNN pincer palladium(II) complexes with N-(2-(1H-pyrazol-1-yl)phenyl)-picolinamide ligands: synthesis, characterization, and application to heck coupling reaction

Machine Learning-Enabled Predictions of Condensed Fukui Functions and Designing of Metal Pincer Complexes for Catalytic Hydrogenation of CO2.

This research showcases the machine learning (ML)-enabled homogeneous catalyst discovery to be employed in carbon dioxide hydrogenation. To achieve the desired turnover frequency (TOF), the electrophilicity of the central metal atom is a crucial factor in transition metal pincer complexes. The condensed Fukui function is a direct measure of the catalytic performance of these pincer complexes. Herein, we demonstrate that machine learning is a convenient and effiecient method to calculate condensed Fukui functions of the central metal atom. The electrophilicity values of 202 pincer complexes were calculated by using density functional theory (DFT) to train the ML model. The test data of the experimentally established pincer complexes show a direct linkage between calculated electrophilicity and experimental TOF. Further, this data was used to develop an ML protocol to screen 2,84,062 catalyst complexes to get the electrophilicity values of the Mn, Fe, Co, and Ni transition metals encompassing various permutation combinations of PNP, PNN, NNN, and PCP pincer ligands. These findings validate the efficacy of machine learning in the rapid screening of metal pincer catalysts based on condensed Fukui functions.

Preparation of a magnetic copper NNN pincer complex as an efficient catalyst in the synthesis of 4-(phenylethynyl) and 4-(4-phenyl-1H-1,2,3-triazol-5-yl)coumarin derivatives

In this study, a 3-amino-trimethoxysilane-modified magnetic support was prepared and functionalized with furan-2-carbohydrazide through 2,4,6-trichloro-1,3,5-triazine as an organic linker to form a nitrogen rich pincer type ligand for copper coordination. The structure and morphology of the prepared nanocomposite (Fe3O4@SiO2-FCH (NNN pincer)/Cu) was confirmed with various techniques including FT-IR, FE-SEM, VSM, TEM, ICP, XRD, and EDX analysis. The amount of Cu in the nanocomposite was determined to be 9.9%wt. Then, its application in the synthesis of 4-(phenylethynyl)coumarin derivatives through CC bond formation between substituted 4-hydroxycoumarin and phenylacetylene derivatives was evaluated. After functionalizing of 4-position in 4-hydroxycoumarins with phenylacetylene derivatives, sodium azide was added and substituted 4-triazole-coumarins were synthesized in the presence of low amount of Fe3O4@SiO2-FCH (NNN pincer)/Cu nanocatalyst. The nanocatalyst was easy separated using of an external magnet and reused at least four run without reduction in its activity.

Palladium complexes containing NNN pincer type ligands and their activities in Suzuki-Miyaura cross coupling reaction

Five new NNN pincer-type ligands and their palladium complexes were successfully synthesised and characterised by FT-IR, 1H NMR, 13C NMR, and UV–vis analyses. TEM analysis was used to observe the morphological character of the black residues obtained from the fourth cycle of the reusability test. Furthermore, suitable crystals of the N2,N6-bis(2-tert-butylphenyl)pyridine-2,6-dicarboxamide and its palladium complex were elucidated with the X-ray single crystal diffraction method. Both the ligand and its palladium complex crystallise in a monoclinic system with space group P21/c for the H2L4 and C2/c for the palladium complex. The structure of the pincer ligand and its palladium complex were stabilised by intramolecular and intermolecular C–H⋅⋅⋅O, C–H⋅⋅⋅N, and N–H⋅⋅⋅N contacts. A Suzuki-Miyaura cross-coupling reaction between aryl halides and phenylboronic acid was used to assess the catalytic abilities of the palladium pincer complexes. All of the prepared complexes exhibited considerable catalytic activity. However, complexes 4 (Acetonitrile-N2,N6-bis(2-tert-butylphenyl)pyridine-2,6-dicarboxamidopalladium(II)) and 5 (Acetonitrile-N2,N6-bis(2-nitrophenyl)pyridine-2,6-dicarboxamidopalladium(II)) provided almost 100% conversion with nearly 100% yield in the reaction between 4-bromotoluene and phenylboronic acid. Furthermore, these active complexes catalysed the reaction of the sterically hindered and deactivated substrates (1-Bromo-4-izobutylbenzene and 2-bromo-6-methoxynaphthalene) with phenylboronic acid, and complete conversion and yields up to 100% were achieved in a short time with the 2-bromo-6-methoxynaphthalene.

Reactivity of a Strictly T-Shaped Phosphine Ligated by an Acridane Derived NNN Pincer Ligand.

The steric tuning of a tridentate acridane-derived NNN pincer ligand allows for the isolation of a strictly T-shaped phosphine that exhibits ambiphilic reactivity. Well-defined phosphorus-centered reactivity towards nucleophiles and electrophiles is reported, contrasting with prior reports on this class of compounds. Reactions towards oxidants are also described. The latter result in the two-electron oxidation of the phosphorus atom from +III to +V and are accompanied by a strong geometric distortion of the NNN pincer ligand. By contrast, cooperative activation of E-H (HCl, HBcat, HOMe) bonds proceeds with retention of the phosphorus redox state. When using H2 O as a substrate, the reaction results in the full disassembly of H2 O to its constituent atoms, highlighting the potential of this platform for small molecule activation reactions.

Synthesis, crystal structure, DFT calculations, and Hirshfeld surface analysis of an NNN pincer type compound

The novel benzamide derivative NNN pincer type, N,N'-(azanediylbis(2,1-phenylene))bis(3-chlorobenzamide) (H3L), was synthesized from bis(2-nitrophenyl)amine starting material. The pincer ligand was characterized by 1H NMR, 13C NMR, COSY, HMQC, and FT-IR techniques. The geometry of pincer ligand was also confirmed by a single-crystal X-ray diffraction analysis. Structural analysis demonstrate that H3L is monoclinic and space group P21/n with Z = 4. It was find out the molecular conformation of the structure is promoted by intramolecular (NH⋅⋅⋅O, NH⋅⋅⋅N, and CH⋅⋅⋅O) and intermolecular (N(2)-H(2)⋅⋅⋅O(2)i, symmetry code (i) = 1/2 + x, 3/2-y, 1/2 + z) hydrogen bonds. The theoretical study of H3L was performed in the gaseous phase by B3LYP/6-311G(d,p) method to determine the structural properties of the title molecule, as a consequence the obtained data showed that the considerable agreement between the experimental and theoretical results. The reactivity and stability of the molecule were evaluated by calculating the HOMO–LUMO energy gap which was found as 6.5163 eV. In addition, FMO, NBO, NLO, DOS, RDG, MEP surface, and Mulliken atomic charge analyses were carried out. Hirshfeld surface analysis and two-dimensional fingerprint plots were investigated and the obtained data exposed that the most significant contributions to the crystal packing are from C···H/H···C (33.2%), H···H (31.5%), and H···Cl/Cl··H (18.9%) contacts. Furthermore, the molecular docking studies were performed to reveal the binding affinity between the title compound and the main protease (6LU7) of COVID-19 coronavirus.

Sustainable catalysts for efficient triazole synthesis: an immobilized triazine-based copper-NNN pincer complex on TiO2.

The multistep synthesis of a hybrid material based on a TiO2 core with an immobilized triazine-based copper(II)-NNN pincer complex is reported. The formation of the material was confirmed by FT-IR spectroscopy and elemental and thermogravimetric analyses, and the loading by copper ions was quantified by ICP/OES analysis. The properties of the hybrid material were further investigated by X-ray photoelectron spectroscopy (XPS), contiuous wave electron spin resonance (CW-ESR), UV-vis spectroscopy, and argon sorption. Efficient and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles was achieved by employing the hybrid material as a catalyst in a mixture of H2O/EtOH as a green solvent with excellent catalytic activity with a TOF up to 495 h-1 at 50 °C. The reusability of the prepared hybrid material in the catalytic reaction was possible over five consecutive runs without significant loss of catalytic activity. The described method represents an effective way to ensure sustainable use of pincer complexes in catalytic systems by immobilizing them on solid supports, resulting in a hybrid organic-inorganic catalyst platform.

New NNN pincer copper complexes as potential anti-prostate cancer agents

Eleven novel NNN Cu(II) complexes supported by a tridentate bis(imidazo[1,2-α]pyridin-2-yl)pyridine ligand were synthesized and characterized by elemental analysis, HRMS, and X-ray determination. Target prediction and docking studies indicated that these pincer complexes formed hydrogen bonds with Asp33 and Gly35 of Cathepsin D protein, which is highly associated with prognosis of advanced prostate cancer. Furthermore, they exhibited anti-proliferation activity in both androgen-sensitive and androgen-insensitive prostate cancer cells according to WST-1 assay results. Mechanistic study showed that pincer complexes arrested cell cycle progression at G0/G1 phase and inhibited Cathepsin D regulated signaling pathways. Most importantly, new pincer copper complexes significantly inhibited xenograft prostate cancer growth along with a promising in vivo safety profile. In summary, these results suggest the applicability of the developed novel pincer copper complexes as promising anticancer agents for prostate cancer treatment.

Synthesis and structural characterization of a series of Co(II) NNN pincer complexes

Several new Co(II) complexes supported by CztBu(PyriPr)2– ligand(s) in various ligand-to-metal ratios are reported. The synthesis and characterization of CztBu(PyriPr)2Co (1) completes a series of analogous compounds (CztBu(PyriPr)2M, M = Fe(II), Co(II), Ni(II)), offering insights into chemical trends across late first-row transition metal complexes. Additionally, chemical oxidation of (CztBu(PyriPr)2)2Co (2) gave complex 5, in which unprecedented, cobalt-facilitated CC coupling of pyrazole moieties has occurred.

Dual Reactivity of a Geometrically Constrained Phosphenium Cation

A geometrically constrained phosphenium cation in bis(pyrrolyl)pyridine based NNN pincer type ligand (1+) was synthesized, isolated and its preliminary reactivity was studied with small molecules. 1+ reacts with MeOH and Et2NH, activating the O−H and N−H bonds via a P-center/ligand assisted path. The reaction of 1+ with one equiv. of H3NBH3 leads to its dehydrogenation producing 5. Interestingly, reaction of 1+ with an excess H3NBH3 leads to phosphinidene (PI) species coordinating to two BH3 molecules (6). In contrast, [1+][OTf] reacts with Et3SiH by hydride abstraction yielding 1-H and Et3SiOTf, while [1+][B(C6F5)4] reacts with Et3SiH via an oxidative addition type reaction of Si−H bond to P-center, affording a new PV compound (8). However, 8 is not stable over time and degrades to a complex mixture of compounds in matter of minutes. Despite this, the ability of [1+][B(C6F5)4] to activate Si−H bond could still be tested in catalytic hydrosilylation of benzaldehyde, where 1+ closely mimics transition metal behaviour.

Dual Reactivity of a Geometrically Constrained Phosphenium Cation.

A geometrically constrained phosphenium cation in bis(pyrrolyl)pyridine based NNN pincer type ligand (1+ ) was synthesized, isolated and its preliminary reactivity was studied with small molecules. 1+ reacts with MeOH and Et2NH, activating the O−H and N−H bonds via a P‐center/ligand assisted path. The reaction of 1+ with one equiv. of H3NBH3 leads to its dehydrogenation producing 5. Interestingly, reaction of 1+ with an excess H3NBH3 leads to phosphinidene (PI) species coordinating to two BH3 molecules (6). In contrast, [1+ ][OTf] reacts with Et3SiH by hydride abstraction yielding 1‐H and Et3SiOTf, while [1+ ][B(C6F5)4] reacts with Et3SiH via an oxidative addition type reaction of Si−H bond to P‐center, affording a new PV compound (8). However, 8 is not stable over time and degrades to a complex mixture of compounds in matter of minutes. Despite this, the ability of [1+ ][B(C6F5)4] to activate Si−H bond could still be tested in catalytic hydrosilylation of benzaldehyde, where 1+ closely mimics transition metal behaviour.

Investigation of NNN Pincer Ruthenium(II) Complexes with a Pendant Hydroxyl Group for N‐Monomethylation of amines and Nitroarenes by Methanol

AbstractA family of air‐ and moisture‐stable NNN pincer ruthenium(II) complexes with a pendant OH were developed, which exhibit unprecedented high reactivity and selectivity in N‐monomethylation of amines and nitroarenes using methanol. The investigation reveals adopting the combination of 1H‐pyrazole‐1‐yl and 3,5‐dimethyl‐4‐hydroxyethyl‐1H‐pyrazol‐1‐yl as the two assistant arms of the pyridyl‐backbone is a suitable choice. The mechanism study discloses that, during the catalytic cycle, dehydrogenation of methanol to form formaldehyde is a fast and reversible step.

Synthesis, characterization, and reactivity of a novel magnetically recyclable triazine‐based Cu–NNN–pincer complex

AbstractA new heterogeneous catalytic system containing triazine‐based copper(II) tridentate–NNN–pincer complex, covalently anchored to the amine‐functionalized silica‐coated Fe3O4 magnetic nanoparticles, Fe3O4@SiO2–NH–CCl–AT–Cu(II), was synthesized. Its structure was studied through the standard methods of FT‐IR, NMR, EDX, TGA, FE‐SEM, MAP images, XRD, ICP, and N2 adsorption–desorption isotherm analysis and utilized for the production of propargylamines by one‐pot A3 coupling of phenylacetylene, aldehydes, and secondary amines, attaining TOF values of up to 40,000 h−1. The impact of various solvents, reaction time, temperature, catalyst amount, and recyclability of the catalyst were studied to optimize reaction conditions. The catalyst was re‐examined five times, and no noteworthy reduction in activity was observed.

Synthesis, antibiofilm activity and molecular docking study of new water-soluble copper(II)-pincer complexes

Bacteria in biofilms exhibited higher resistance to immune system and antibiotic treatment compared to their free living/planktonic counterparts. Hence there is a strong interest for developing new compounds with good antibiofilm activity. Herein three new Cu(II) complexes (CuL1, CuL2 and CuL3) with NNN pincer type ligands (L1-L3) were synthesized and the structures were confirmed by FT-IR, UV–Vis spectroscopy and single crystal X-ray analysis. Structural studies revealed the formation of five coordinate Cu(II) complexes with square-pyramidal geometry. All three compounds were investigated for antibiofilm activity against ESKAPE pathogens, such as Klebsiella pneumoniae, Enterococcus faecium, Acinetobacter baumanii, Pseudomonas aeruginosa, Enterobacter cloacae and Escherichia coli. Antibiofilm studies revealed that CuL1 was more effective against gram positive bacteria whereas CuL3 was more effective against gram negative bacteria. CuL2 showed least effective against all the bacteria stains. Computational docking studies of complexes with biomolecular targets revealed preferential binding with 5FCA (Enterococcus faecium).

Catalytic reduction of nitroarenes and degradation of dyes at room temperature by an efficient NNN pincer palladium catalyst based on the magnetic amino-triazole-modified chitosan

In this study, a magnetic chitosan biosupport was synthesized and functionalized with a NNN pincer ligand to facilitate palladium immobilization. FT-IR, FE-SEM, EDX, XRD, VSM, ICP, BET, and TGA analyses were used to characterize the synthesized nanocomposite (Fe3O4@Triazole-CS@NNN-Pd). Then, its catalytic activity in the reduction of a wide variety of nitroaromatic compounds at room temperature was investigated using sodium borohydride as a reducing agent, as well as the degradation of three hazardous dyes, including Methylene Blue (MB), Methyl Orange (MO), and Rhodamine B (RhB). This technique is feasible due to its ease of purification, environmental friendliness, and high yield of product generation in a relatively short response time. The nanocatalyst is easily separated, recovered, and reused for numerous cycles without significantly degrading catalytic activity.

Synthesis and Characterization of a Series of Co(Ii) Nnn Pincer Complexes

Synthesis and Characterization of a Series of Co(Ii) Nnn Pincer Complexes