Monodentate Phosphinoamine Nickel Complex Supported on a Metal-Organic Framework for High-Performance Ethylene Dimerization

Ethylene dimerization is an efficient industrial chemical process to produce 1-butene, with demanding selectivity and activity requirements on new catalytic systems. Herein, a series of monodentate phosphinoamine-nickel complexes immobilized on UiO-66 are described for ethylene dimerization. These catalysts display extensive molecular tunability of the ligand similar to organometallic catalysis, while maintaining the high stability attributed to the metal-organic framework (MOF) scaffold. The highly flexible postsynthetic modification method enables this study to prepare MOFs functionalized with five different substituted phosphines and 3 N-containing ligands and identify the optimal catalyst UiO-66-L5-NiCl2 with isopropyl substituted nickel mono-phosphinoamine complex. This catalyst shows a remarkable activity and selectivity with a TOF of 29 000 (molethyl/molNi/h) and 99% selectivity for 1-butene under ethylene pressure of 15 bar. The catalyst is also applicable for continuous production in the packed column micro-reactor with a TON of 72 000 (molethyl/molNi). The mechanistic insight for the ethylene oligomerization has been examined by density functional theory (DFT) calculations. The calculated energy profiles for homogeneous complexes and truncated MOF models reveal varying rate-determining step as β-hydrogen elimination and migratory insertion, respectively. The activation barrier of UiO-66-L5-NiCl2 is lower than other systems, possibly due to the restriction effect caused by clusters and ligands. A comprehensive analysis of the structural parameters of catalysts shows that the cone angle as steric descriptor and butene desorption energy as thermodynamic descriptor can be applied to estimate the reactivity turnover frequency (TOF) with the optimum for UiO-66-L5-NiCl2. This work represents the systematic optimization of ligand effect through combination of experimental and theoretical data and presents a proof-of-concept for ethylene dimerization catalyst through simple heterogenization of organometallic catalyst on MOF.

Effects of the ligand linkers on stability of mixed-valence Cu(I)Cu(II) and catalytic aerobic alcohol oxidation activity

We synthesized a class of ligands that feature single (L1) and dual amine-bis(triazole) chelates (L2 with a 1,3-phenylene linker and L3 with a 1,5-naphthalene linker). Our findings which were derived from UV-Vis titrations, crystal structure analysis of relevant copper complexes, and DFT calculations indicate the formation of both mononuclear CuBr(L1) and dinuclear (μ-Ln)(CuBr)2 (Ln = L2 and L3) complexes. The catalytic activities of CuBr/Ln, in combination with TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) co-catalyst and NMI (N-methylimidazole) for aerobic alcohol oxidation, reveal the following activity trend: CuBr/L3 > CuBr/L2 > CuBr/L1. Furthermore, electrochemical data from in-situ generated CuBr complexes suggest that the higher catalytic performance of CuBr/L3 is attributed to the presence of less stable mixed-valence and more reducible Cu(I)-L3-Cu(II) species compared to Cu(I)-L2-Cu(II). This difference is a result of weaker σ interactions between Cu-Namine, larger bridging π systems, and a longer Cu···Cu distance in the presence of L3. Additionally, the catalyst system, CuBr/L3/TEMPO/NMI, efficiently promotes the aerobic oxidation of benzyl alcohol to benzaldehyde at room temperature in CH3CN with a high turnover frequency (TOF) of 38 h-1 at 1 h.

Synthesis and Photo/Radiation Chemical Characterization of a New Redox-Stable Pyridine-Triazole Ligand

Photocatalysis using transition-metal complexes is widely considered the future of effective and affordable clean-air technology. In particular, redox-stable, easily accessible ligands are decisive. Here, we report a straightforward and facile synthesis of a new highly stable 2,6-bis(triazolyl)pyridine ligand, containing a nitrile moiety as a masked anchoring group, using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction. The reported structure mimics the binding motif of uneasy to synthesize ligands. Pulse radiolysis under oxidizing and reducing conditions provided evidence for the high stability of the formed radical cation and radical anion 2,6-di(1,2,3-triazol-1-yl)-pyridine compound, thus indicating the feasibility of utilizing this as a ligand for redox active metal complexes and the sensitization of metal-oxide semiconductors (e. g., TiO2 nanoparticles or nanotubes).

Unsymmetrical PEG-substituted tris(triazolyl)amines as bi-functional surfactants for copper-catalyzed aerobic oxidation of alcohols in water

Amphiphilic tris(triazolyl)amines functionalized with poly(ethylene glycol) 1-(1-R-1H-1,2,3-triazol-4-yl)-N,N-bis((1-benzy-1H-1,2,3-triazol-4-yl)methyl)methanamine [R = PEG200 (NBBT200-OH), mPEG550 (NBBT550), mPEG2000 (NBBT2000)] were investigated as bi-functional surfactants serving as N donor ligands and surfactants for copper-catalyzed aerobic...

[2 × 2] metallo-supramolecular grids based on 4,6-bis((1H-1,2,3-triazol-4-yl)-pyridin-2-yl)-2-phenylpyrimidine ligands: from discrete [2 × 2] grid structures to star-shaped supramolecular polymeric architectures

The self-assembly of bis-tridentate ligands leads to the spontaneous formation of [2 × 2] grid-like metal complexes. However, the synthesis of such ligands is rather cumbersome. In the work, we demonstrate a straightforward synthesis route to prepare bis-tridentate 4,6-bis((1H-1,2,3-triazol-4-yl)-pyridin-2-yl)-2-phenylpyrimidine ligands through double CuAAC click chemistry with 4,6-bis(6-ethynylpyridin-2-yl)-2-phenylpyrimidine as well as their self-assembly into [2 × 2] grid-like metal complexes. In addition, four macromolecular ligands were synthesized starting from azido-end-functionalized poly(2-ethyl-2-oxazoline) (PEtOx) or poly(ethylene glycol) (PEG). These macromolecular ligands were used in the construction of star-shaped supramolecular polymers through complexation with transition metal ions (e.g., Fe2+ or Zn2+). The successful fabrication of complexes and star-shaped polymers was confirmed by UV-vis titration measurements and MALDI-TOF mass spectrometry. However, the chemical structure of the polymer was found to have a strong influence on the [2 × 2] grid formation, which was successful with the PEG-ligands but not with the PEtOx-ligands, while the molecular weight of the PEG did not interfere with grid formation.

Structural and Electronic Control of the Bidentate 1-(2-pyridyl)benzotriazole Ligand in Copper Chemistry with Application to Catalysis in the A3 Coupling Reaction

The hybrid bidentate 1-(2-pyridyl)benzotriazole (pyb) ligand was introduced into 3d transition metal catalysis. Specifically, [Cu^II (OTf)₂ (pyb)₂ ]⋅2 CH₃ CN (1) enables the synthesis of a wide range of propargylamines by the A³ coupling reaction at room temperature in the absence of additives. Experimental and high-level theoretical calculations suggest that the bridging N atom of the ligand imposes exclusive trans coordination at Cu and allows ligand rotation, while the N atom of the pyridine group modulates charge distribution and flux, and thus orchestrates structural and electronic precatalyst control permitting alkyne binding with simultaneous activation of the C-H bond via a transient Cu^I species.

Computational exploration of copper catalyzed vinylogous aerobic oxidation of unsaturated compounds

Selective oxidation is one of the most important and challenging transformations in both academic research and chemical industry. Recently, a highly selective and efficient way to synthesize biologically active γ-hydroxy-α,β-unsaturated molecules from Cu-catalyzed vinylogous aerobic oxidation of α,β- and β,γ-unsaturated compounds has been developed. However, the detailed reaction mechanism remains elusive. Herein, we report a density functional theory study on this Cu-catalyzed vinylogous aerobic oxidation of γ,γ-disubstituted α,β- and β,γ-unsaturated isomers. Our computational study unveils detailed mechanism for each elementary step, i.e. deprotonation, O2 activation, and reduction. Besides, the origin of regioselectivity, divergent reactivities of substrates as well as reducing agents, and the byproduct generation have also been investigated. Notably, the copper catalyst retains the + 2 oxidation state through the whole catalytic cycle and plays essential roles in multiple steps. These findings would provide hints on mechanistic studies and future development of transition metal-catalyzed aerobic oxidation reactions.

A highly efficient red-emitting luminescent paper-based chemosensor for hydrogen sulfide

The first discrete bimetallic europium(iii)/copper(ii) complex for the fast, sensitive and selective luminescent detection of both aqueous and gaseous hydrogen sulfide has been developed. The chemosensor displayed an impressive response time of 30 seconds and a low theoretical limit of detection (100 ppb) for gaseous hydrogen sulfide.

Influence of catalyst nuclearity on copper-catalyzed aerobic alcohol oxidation

Reactions of CuX with the bis(triazolyl) ligand Hbtm [bis(1-benzyl-1H-1,2,3-triazol-4-yl)phenylmethanol] in CH2Cl2 afforded trinuclear copper(ii) complexes with a core structure (μ-X)Cu3(μ-κ3-N,O,N-btm)3(L)2+ [X = Cl, L = CH3OH (1); X = Br, L = H2O (2)], while a similar reaction of [Cu(CH3CN)4](PF6) with the mono(triazolyl) ligand HPhtm [(1-benzyl-1H-1,2,3-triazol-4-yl)diphenylmethanol] resulted in the mononuclear complex [Cu(κ2-N,O-Phtm)(κ2-N,O-HPhtm)(κ1-N-HPhtm)][PF6] (3). The structural characterization of these complexes was made by single-crystal X-ray crystallography in combination with elemental and ESI mass analyses. Catalytic studies toward aerobic oxidation of benzyl alcohol to benzaldehyde revealed that the trinuclear 1 and 2 exhibited higher activities than the mononuclear 3 in both CH3CN and EtOH/H2O solvent systems.

Computational investigations of click-derived 1,2,3-triazoles as keystone ligands for complexation with transition metals: a review

In recent years, metal complexes of organo 1,2,3-triazole click-derived ligands have attracted significant attention as catalysts in many chemical transformations and also as biological and pharmaceutical active agents. Regarding the important applications of these metal-organo 1,2,3-triazole-based complexes, in this review, we focused on the recently reported investigations of the structural, electronic, and spectroscopic aspects of the complexation process in transition metal complexes of 1,2,3-triazole-based click ligands. In line with this, the coordination properties of these triazole-based click ligands with transition metals were studied via several quantum chemistry calculations. Moreover, considering the complexation process, we have presented comparative discussions between the computational results and the available experimental data.

Functional metal complexes from CuAAC “click” bidentate and tridentate pyridyl-1,2,3-triazole ligands

This Frontiers article examines the use of “click” complexes for the development of catalysts, anti-cancer and anti-bacterial agents and emissive materials.

Effects of appended hydroxyl groups and ligand chain length on copper coordination and oxidation activity

The effects of appended hydroxyl groups and the chain length of a series of (imino)pyridine ligands on copper coordination and copper-catalyzed aerobic oxidation of alcohols were investigated.

Benzimidazole–triazole ligands with pendent triazole functionality: unexpected formation and effects on copper-catalyzed aerobic alcohol oxidation

Benzimidazole–triazole based ligands, prepared from cyclization of amine–triazoles, produce active Cu catalysts for aerobic alcohol oxidation.

Enhanced product selectivity promoted by remote metal coordination in acceptor-free alcohol dehydrogenation catalysis

A bimetallic [Ir³⁺]₂ complex was synthesized based on a bridging 1,2,3-triazole ligand that coordinates to one Cp*Ir unit as N,N-bidentate chelate, and to the other as a C,C-bidentate ligand.

Synthesis and structural studies of 1,4-di(2-pyridyl)-1,2,3-triazole dpt and its transition metal complexes; a versatile and subtly unsymmetric ligand

Structural analysis of the 1,4-di(2-pyridyl)-1,2,3-triazole ligand and its transition metal complexes of varying lability demonstrate the coordination chemistry selectivity of this subtly unsymmetric ligand.

The N-silylation of sulfoximines

The copper-catalyzed N-silylation of sulfoximines was achieved in good to moderate yields in the presence of di-tert-butyl peroxide.