Tetracoordinate Complexes Research Articles

Ligand Variations in Neutral and Cationic Molybdenum Alkylidyne NHC Catalysts

Several neutral and cationic molybdenum alkylidyne complexes bearing mono-, bi-, and tridentate N-heterocyclic carbenes (NHCs) have been prepared. The NHCs were varied in terms of their steric demand, basicity, and the nature of the chelating function. The introduction of a variety of different anionic ligands, such as triflates, halides, and alkoxides, was accomplished by replacing one, two, or three anionic ligands, allowing for substantial variations in the structure of the complexes. tert-Butyl, anisole, and mesityl groups were chosen as alkylidyne substituents. Cationic, tetracoordinate complexes were synthesized, boasting the structure proposed for the active species of molybdenum alkylidyne NHC complexes in alkyne metathesis reactions. The formation of unanticipated structures such as a bis-NHC complex (Mo19) and a complex bearing an alkoxide (Mo16) as a result of the demethylation of 1,2-dimethoxyethane (DME) was observed. The crystal structures of selected complexes are presented. Notably, this work focused exclusively on the syntheses and structures of the complexes; therefore, the reactivity of the complexes in alkyne metathesis reactions was not investigated.

Adsorption performance of silica supported polyamidoamine dendrimers for Cd(II) and Cu(II) in N,N-dimethylformamide

N, N-dimethylformamide (DMF) plays an important role in chemical industry and materials science. The intrusion of metal ions during the production, storage and transportation affects the purity of DMF and brings adverse effects to its practical use. Hence, silica supported polyamidoamine (PAMAM) dendrimers (SG/G1, SG/G2 and SG/G3) were synthesized and recruited for the adsorption of Cd(II) and Cu(II) from DMF solution. The influence factors were determined and the adsorption mechanism was demonstrated base on theoretical calculation. The adsorption amount for the ions decreases by the order of SG/G2 > SG/G3 > SG/G1. Adsorption kinetic can reach equilibrium within 240 min and obeys pseudo-second-order kinetic model. Adsorption isotherm indicates that high temperature and metal ion concentration can promote the adsorption. The adsorption process is spontaneous, endothermic and chemical adsorption in nature and it can be described by Langmuir model. Theoretical calculation reveals that the adsorption mainly took place by forming tetra-coordinated complex via two tertiary amino N and two carbonyl O atoms and metal ions.

The Synthesis of Picolinamide-Supported Tetracoordinated Organoboron Complexes with Aggregation-Induced Emission Property.

The picolinamide-supported tetracoordinated organoboron complexes containing diaryl boronyl segments have been synthesized for the first time. Aryl trifluoroborates were utilized as the BAr2 sources to introduce different aryl motifs with diverse functional groups. The optical experiments discovered these five-membered boron-containing complexes were aggregation-induced emission (AIE) active, thus affording a new class of AIE molecules.

Advances in the Supramolecular Chemistry of Tetracoordinate Boron-Containing Organic Molecules into Organogels and Mesogens.

Boron-containing organic compounds are well accepted as a class of compounds having excellent photophysical properties. In addition to the unique photophysical properties, the ease of synthesis and structural robustness make tetracoordinate boron complexes ideal for a variety of applications. While significant light has been thrown on their luminescence properties, there is no collective attention to their supramolecular chemistry. In this mini review, we discuss the progress made in the supramolecular chemistry of these compounds which includes their utility as building blocks for liquid crystalline materials and gels largely driven by various non-covalent interactions like H-bonding, CH-π interactions, BF-π interactions and Van der Waals forces. The organoboron compounds presented here are prepared from easy-to-synthesize chelating units such as imines, diiminates, ketoiminates and diketonates. Moreover, the presence of heteroatoms such as nitrogen, oxygen and sulfur, and the presence of aromatic rings facilitate non-covalent interactions which not only favor their formation but also helps to stabilize the self-assembled structures.

Electronic and geometric structure of cationic and neutral chromium and molybdenum ammonia complexes.

High level quantum chemical approaches are used to study the geometric and electronic structures of M(NH3)n and M(NH3)n + (M = Cr, Mo for n = 1-6). These complexes possess a dual shell electronic structure of the inner metal (3d or 4d) orbitals and the outer diffuse orbitals surrounding the periphery of the complex. Electronic excitations reveal these two shells to be virtually independent of the other. Molybdenum and chromium ammonia complexes are found to differ significantly in geometry with the former adopting an octahedral geometry and the latter a Jahn-Teller distorted octahedral structure where only the axial distortion is stable. The hexa-coordinated complexes and the tetra-coordinated complexes with two ammonia molecules in the second solvation shell are found to be energetically competitive. Electronic excitation energies and computed IR spectra are provided to allow the two isomers to be experimentally distinguished. This work is a component of an ongoing effort to study the periodic trends of transition metal solvated electron precursors.

Highly Reactive Cationic Molybdenum Alkylidyne N-Heterocyclic Carbene Catalysts for Alkyne Metathesis

The tetracoordinated cationic molybdenum alkylidyne N-heterocyclic carbene (NHC) complexes [Mo(≡CC6H4-p-OMe)(IMes)(OCMe(CF3)2)2][BPh4] (Mo5) and [Mo(≡CC6H4-p-OMe)(IMes)(OCMe(CF3)2)2][B(ArF)4] (Mo6, IMes = 1,3-dimesitylimidazol-2-ylidene)) were synthesized from the pentacoordinated progenitor Mo(≡CC6H4-p-OMe)(IMes)(OCMe(CF3)2)2(OTf) (Mo4). Complexes Mo4–Mo6 were evaluated for their ability to catalyze the self-metathesis of several internal alkynes. The presence of a triflate group facilitates formation of a cationic species while preformation of the cationic molybdenum center in molybdenum alkylidyne NHC complexes indeed results in a strong increase in catalyst productivity and activity, also in the presence of functional groups, compared to previously reported neutral congeners. The most striking feature of this class of tetracoordinate cationic complexes is the excellent catalytic activity in the alkyne metathesis of non-protic substrates, thereby supporting our previously published proposal of a tetracoordinate cationic active species in alkyne metathesis formed from the neutral, pentacoordinate molybdenum alkylidyne NHC progenitors. Catalyst productivity, expressed as turnover number, reached 20 000 in the self-metathesis of 1-phenyl-1-propyne (S1) using Mo(≡CC6H4-p-OMe)(1,3-dimesitylimidazol-2-ylidene)(OCMe(CF3)2)2[B(ArF)4] (Mo6) and 5-(benzyloxy)-2-pentyne (S2) at catalyst loadings as low as 0.005 mol %.

A mononuclear copper complex as bifunctional electrocatalyst for CO2 reduction and water oxidation

A tetra-coordinated mononuclear copper complex [Cu II L 2 ](ClO 4 ) 2 ·2CH 3 OH ( 1 ) (L = methoxy-di-pyridin-2-yl-methanol) with planar configuration has been successfully synthesized and characterized, which can serve as an efficient bifunctional molecular electrocatalyst for CO 2 reduction with a FE = ~85% and TOF = 2.99 s −1 in the presence of H 2 O as proton donor, and water oxidation with a FE about ~86% and a high TOF of 9.20 s −1 at the pH of 11.84. • The synthesis and characterization of a tetra-coordinated mononuclear copper complex. • Complex can serve as an efficient electrocatalyst for CO 2 reduction and water oxidation. • This is the first example of copper complex as bifunctional electrocatalyst. To mimic natural photosynthesis, it is still a great challenge to couple catalytic CO 2 reduction and water oxidation in one single system with high activity. In this work, we have successfully synthesized and characterized a tetra-coordinated mononuclear copper complex [Cu II L 2 ](ClO 4 ) 2 ·2CH 3 OH ( 1 ) (L = methoxy-di-pyridin-2-yl-methanol) with planar configuration, which can simultaneously serve as an efficient molecular electrocatalyst for CO 2 reduction and water oxidation. The copper complex displayed electrochemical activity for the reduction of CO 2 to CO in DMF solution with the Faraday efficiency (FE) reached ~85% and a turnover frequency (TOF) of 2.99 s −1 in the presence of proton donor water. Meanwhile, it also can perform electrocatalytic water oxidation with the FE of ~86% and a high TOF of 9.20 s −1 at the pH of 11.84. The high electrochemical activity of complex 1 for the reduction of CO 2 and water oxidation may due to the hydroxyl group on the methoxy-di-pyridin-2-yl-methanol ligand. It represents the first copper complex as homogeneously bifunctional electrocatalyst for CO 2 reduction and water oxidation.

Synthesis, computational, anticancerous and antiproliferative effects of some copper, manganese and zinc complexes with ligands derived from symmetrical 2,2’-diamino-4,4’-dimethyl-1,1’-biphenyl-salicylaldehyde

Abstract Four new symmetrical Schiff bases derived from 2,2’-diamino-4,4’-dimethyl-1,1’-biphenyl-salicylaldehyde have been synthesized and characterized by elemental analysis and different spectroscopic techniques. The reaction of 2,2’-diamino-4,4’-dimethyl-1,1’-biphenyl with two equivalents of 5-tert-butyl-, 3,5-dinitro-, 3,5-dibromo- and 3-tert-butyl-salicylaldehyde yielded 2,2’-bis(5-tert-butyl-salicylideneamino)-4,4’-dimethyl-1,1’-biphenyl (A1) as well as the 3,5-dinitro- (A2), 3,5-dibromo- (A3) and 3-tert-butyl- (A4) substituted derivatives. The tetradentate ligands were then reacted with copper-, manganese- and zinc-acetate producing the tetra-coordinate metal complexes which were characterized by FTIR, UV-Visible spectroscopy, magnetic susceptibility and elemental analysis. Zinc complexes were characterized by 1H-NMR spectroscopy. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level of theory were carried out to fully optimize and examine the molecular geometries of complexes. Subsequently, IR vibrational and UV-Vis absorption spectra were computed and correlated with the observed values and the results are in good agreement with the experimental data. The anticancerous and antiproliferative activity of the A3 ligand and its metal complexes were determined.

New luminescent tetracoordinate boron complexes: an in-depth experimental and theoretical characterisation and their application in OLEDs

New luminescent 2-iminopyrrolyl boron complexes with different BX2moieties are extensively studiedviacomplementary experimental and theoretical methodologies, including application in OLEDs.

Cobalt Corroles: From Monomolecular Binding to Porous Organic Polymers (POPs) for the Selective Detection of Carbon Monoxide (CO)

Detection of carbon monoxide (CO) at few ppm levels is a critical point for quality control of domestic and industrial environment. CO is responsible for thousands of intoxications and hundreds of deaths per year in the world. Moreover, CO is a residual gas found in the industrial dihydrogen used for Proton Exchange Membrane fuel cell, and deactivates the fuel cell prematurely. Corroles have beenlargely used in sensing applications.[1] Cobalt corroles display high binding affinity for carbon monoxide even in the presence of nitrogen and dioxygen.[2] The affinity of the Co(III) metallocorroles for CO is directly correlated with the Lewis acid character of the metal center. Therefore, structural modifications on the aromatic ring have a direct influence on the reactivity of the metal complex. We have recently obtained very low CO detection level (ppm) using SAW devices functionalized by cobalt corrole deposited as a film on a guiding layer of silica or a gold surface.[3] Tetra-coordinated cobalt corroles were found to be not so stable over time. A new approach was developed, using labile axial ligands as a protective group of the tetra-coordinated metal complexes. We will present the e-chem and spectro e-chem properties of the cobalt complexes with different axial ligands. As our previous work on the synthesis of porous sol-gel materials functionalized by cobalt corroles gave us also encouraging results for CO sorption and detection[4], we have prepared new porous structured materials functionalized by corrole complexes for gas detection applications. Among all the methods of synthesis of porous architectures, organic materials belonging to the POP (Porous Organic Polymer) family are an appealing and original approach in this research field.[5] We will thus describe the synthesis of new POPs functionalized by cobalt corroles (Fig. 1). Their selective sorption properties for CO over N2, O2and CO2will be also presented.Authors would like to acknowledge the ANR program (CO3SENS project), the FEDER and the “Région Bourgogne” for financial support, and for the allocation of a PhD grant (JCE Program). REFERENCES:[1] Paolesse, R.; Nardis,S.; Monti, D.; Stefanelli, M.; Di Natale, C., Chem. Rev. 2017, 117, 2517–2583;[2] J.-M. Barbe, G. Canard, S. Brandès, F. Jerôme, G. Dubois, R. Guilard, Dalton Trans. 2004, 1208-1214; [3] M. Vanotti, C. Theron, S. Poisson, V. Quesneau, M. Naitana, V. Soumann, S. Brandès, N. Desbois, C. Gros, T.-H. Tran-Thi, V. Blondeau-Patissier, Proceedings 2017, 1, 444-447; [4] J. M. Barbe, G. Canard, S. Brandès, R. Guilard, Chem. Eur. J. 2007, 13, 2118-2129; [5] S. Brandès, V. Quesneau, O. Fonquernie, N. Desbois, V. Blondeau-Patissier, C. P. Gros, Dalton Trans. 2019, 48, 11651-11662 (Cover). Figure 1

Fischer Carbene Pentannulation with Alkynes Having Adjacent Carbonate or Acyloxy Groups: Synthesis of 3-Substituted 1-Indanones.

Various aryl Fischer carbenes reacted with alkynes having adjacent acyloxy or carbonate groups to regioselectively deliver 3-substituted 1-indanones. The acyloxy or carbonate group probably coordinates with the Cr metal to give a tetra-coordinated chromium complex forming a six-membered ring that retards CO insertion for ketene formation, which is required for benzannulation. Alternatively, the ortho position aryl ring attack results in pentannulation, providing regioselectively 3-substituted 1-indanones. The method is extended to the synthesis of the core structure of 3-epi-mutisianthol.

Generation of two-dimensional spectrochemical series in tetrahedral complexes

The physical properties of metal complexes that exist in many places are due to the ligand field splitting and electronic configuration of the d-orbital of the central transition metal, so changing the ligand field splitting of the d-orbital allows to control the physical properties. The arrangement of metals and ligands in order of the ligand field splitting is called a spectrochemical series. There is already a spectrochemical series only in the case of octahedral hexa-coordination complexes, but no equivalent index is shown for any other symmetry such as tetrahedral tetra-coordination complexes. In this study, we have investigated the creation of spectrochemical series in tetrahedral tetra-coordinated metal complexes. As a result, it is possible to accurately grasp the ligand field splitting of a tetrahedral tetra-coordinated metal complex, and to more effectively apply energy for expressing a spin crossover phenomenon in which the magnetism reversibly changes.

Homoleptic and heteroleptic Zn(ii) selone catalysts for thioetherification of aryl halides without scrubbing oxygen

Tetra-coordinated zinc imidazoline selone complexes were synthesized and utilized as potential catalysts in the thioetherification of aryl halides without scrubbing oxygen.

Collisional dynamics simulations revealing fragmentation properties of Zn(ii)-bound poly-peptide.

Chemical dynamics simulations are performed to study the collision induced gas phase unimolecular fragmentation of a model peptide with the sequence acetyl-His1-Cys2-Gly3-Pro4-Tyr5-His6-Cys7 (analogue methanobactin peptide-5, amb5) and in particular to explore the role of zinc binding in reactivity. Fragmentation pathways, their mechanisms, and collision energy transfer are discussed. The probability distributions of the pathways are compared with the results of the experimental IM-MS, MS/MS spectrum and previous thermal simulations. Collisional activation gives both statistical and non-statistical fragmentation pathways with non-statistical shattering mechanisms accounting for a relevant percentage of reactive trajectories, becoming dominant at higher energies. The tetra-coordination of zinc changes qualitative and quantitative fragmentation, in particular the shattering. The collision energy threshold for the shattering mechanism was found to be 118.9 kcal mol-1 which is substantially higher than the statistical Arrhenius activation barrier of 35.8 kcal mol-1 identified previously during thermal simulations. This difference can be attributed to the tetra-coordinated zinc complex that hinders the availability of the sidechains to undergo direct collision with the Ar projectile.

Mononuclear zinc(II) Schiff base complexes as catalysts for the ring-opening polymerization of lactide

Materials combining bio-based resource and degradability aspects such as polylactide (PLA) can represent a sustainable alternative to commercially used oil-based plastics. With tin octanoate (Sn(Oct)2) as the catalyst of choice for industrial scale PLA production, traces of the toxic heavy metal can be released into the environment, rendering PLA unsuitable for specific applications. Herein we present four new homoleptic zinc Schiff base complexes that offer facile synthesis and can be handled under aerobic conditions. These robust, tetra-coordinated complexes have been tested as catalysts for the ring-opening polymerization (ROP) of lactide and are well suited under industrially relevant conditions. In situ Raman spectroscopy has been used to determine the apparent reaction rate constant (kapp) for all complexes at 150 °C in bulk. For the fastest complex a kp of 3.66 ± 0.14 × 10–2 L mol−1 s−1 was additionally determined. For this catalyst, 71% conversion and a number-averaged molar mass of above 90000 g mol−1 has been reached within less than 30 min at a monomer-to-initiator ratio ([M]/[I]) of 1000:1. The good polydispersity (Ð = 1.7) indicates a controllable ROP via the coordination-insertion mechanism (CIM).

New sulfonamide complexes with essential metal ions [Cu (II), Co (II), Ni (II) and Zn (II)]. Effect of the geometry and the metal ion on DNA binding and nuclease activity. BSA protein interaction

Mixed divalent Cu, Co, Ni and Zn complexes containing the new sulfonamide ligand N–(2–(pyridin–2–yl)ethyl)quinoline–8–sulfonamide (HQSEP) were prepared and characterized by physico-chemical techniques. The tetracoordinate [Cu(QSEP)X] [X = Br (1), Cl (2)] compounds present a seesaw geometry (τ4 = 0.56 (1) and 0.50 (2)). The Cu(II) in the [Cu(QSEP)(NO3)(MeOH)] (3) complex is five coordinate with a slightly distorted SP geometry (τ = 0.11). The [M(QSEP)(benz)] [M = Cu(II) (4), Ni(II) (5), Co(II) (6) and Zn(II) (7); benz = benzoate] compounds are configurationally isotypic. The coordination geometries of the M(II) ions can be best described as distorted SP (τ = 0.29, 0.15, 0.34 and 0.18 for 4, 5, 6 and 7, respectively). The interaction of the compounds with CT–DNA was studied by different techniques. Notably, these studies indicated that the tetracoordinate complexes (1 and 2) present higher DNA affinity than pentacoordinate compounds (3–7). In line with the Irving–Williams order of stability, 5 presented higher propensity for DNA binding than 6. Interestingly, the cleavage activity of 1–4 in the presence of ascorbate/H2O2 follows the same trend as that found for DNA binding affinity, being the tetracoordinate 1 and 2 more effective as nucleases than the five coordinate 3 and 4. Also, the DNA cleavage reaction mechanism was investigated. DNA cleavage experiments upon irradiation indicated the important role of the aromatic nature of the coligand in the photocleavage activity of 1–4. Finally, the interaction of the compounds with bovine serum albumin (BSA) was studied and the binding constants were calculated.

Cyclic(alkyl)(amino) Carbene-Promoted Ring Expansion of a Carbodicarbene Beryllacycle.

Recent synthetic efforts have uncovered several bond activation pathways mediated by beryllium. Having the highest charge density and electronegativity, the chemistry of beryllium often diverges from that of its heavier alkaline earth metal congeners. Herein, we report the synthesis of a new carbodicarbene beryllacycle (2). Compound 2 converts to 3 via an unprecedented cyclic(alkyl)(amino) carbene (CAAC)-promoted ring expansion reaction (RER). While CAAC activates a carbon-beryllium bond, N-heterocyclic carbene (NHC) coordinates to beryllium to give the tetracoordinate complex 4, which contains the longest carbeneC-Be bond to date at 1.856(4) Å. All of the compounds were fully characterized by X-ray crystallography, Fourier transform infrared spectroscopy, and 1H, 13C, and 9Be NMR spectroscopy. The ring expansion mechanism was modeled with both NHC and CAAC using density functional theory calculations. While the activation energy for the observed beryllium ring expansion with CAAC was found to be 14 kJ mol-1, the energy barrier for the hypothetical NHC RER is significantly higher (199.1 kJ mol-1).

The effect of locking π-conjugation in organoboron moieties in the structures of luminescent tetracoordinate boron complexes.

A series of 8 luminescent borafluorene complexes were extensively studied both experimentally and theoretically in order to elucidate the effect of organoboron moiety rigidification on the physicochemical properties of these compounds. Due to the spiro geometry of the boron atom, borafluorene and ligand units are perpendicularly aligned, which considerably affects the flexibility of the molecule as well as its solid-state structure. Through comparative analysis with close diphenyl analogues, we show how these structural features influence the thermal, photoluminescent and charge mobility behaviour of the studied compounds. Crystal structural analysis revealed that the molecules are connected mostly through C-HO and C-Hπ interactions formed between perpendicularly aligned borafluorene and ligand moieties from neighboured molecules, serving as a complementary donor and acceptor of electron density, respectively. This also efficiently prevents molecules from engaging in unfavoured π-stacking contact. Furthermore, structural analysis suggests that borafluorene complexes possess a considerable degree of flexibility due to OBN heterocycle distortions and mutual borafluorene-ligand plane movements. The magnitude of these effects strictly depends on the ligand structure and may lead either to enhancing or lowering the quantum yield value with respect to BPh2 analogues, while the absorption and emission wavelength are slightly affected. The measured photophysical parameters for solid-state samples showed that the studied complexes are much better emitters in their crystalline states that in amorphous films. The TD-DFT and NTO calculations revealed a significant change in frontier molecular distribution, with the HOMO localized on the borafluorene moiety. However, as the HOMO-LUMO transition is geometrically not favoured, excitation occurred from HOMO-1 localized on the ligand. Finally, aggregation effects were discussed based on supramolecular arrangements in crystal structures and charge transfer rates obtained from theoretical calculations in the framework of the Marcus-Hush approximation. They suggest that borafluorene complexes are much better electron carriers with respect to non-annulated BPh2 complexes.

Catalytic Aerobic Oxidation of Alcohols by Copper Complexes Bearing Redox-Active Ligands with Tunable H-Bonding Groups.

In this research article, we describe the structure, spectroscopy, and reactivity of a family of copper complexes bearing bidentate redox-active ligands that contain H-bonding donor groups. Single-crystal X-ray crystallography shows that these tetracoordinate complexes are stabilized by intramolecular H-bonding interactions between the two ligand scaffolds. Interestingly, the Cu complexes undergo multiple reversible oxidation-reduction processes associated with the metal ion (CuI, CuII, CuIII) and/or the o-phenyldiamido ligand (L2-, L•-, L). Moreover, some of the CuII complexes catalyze the aerobic oxidation of alcohols to aldehydes (or ketones) at room temperature. Our extensive mechanistic analysis suggests that the dehydrogenation of alcohols occurs via an unusual reaction pathway for galactose oxidase model systems, in which O2 reduction occurs concurrently with substrate oxidation.

Computational modeling of mixed-ligand cobalt complexes with o-quinone derivative of corannulene

The structure and energy characteristics of isomers of electrically neutral adducts of tetracoordinate cobalt complexes with o-quinone derivative of corannulene were studied quantum chemically within the density functional theory (DFT) in the UB3LYP*/6-311++G(d,p) approximation. It was shown that the framework rigidity of the redox-active ligand favors convergence of the energy levels of the high-spin and low-spin isomers of the complexes under study as compared to the o-benzoquinone-containing analogues. At the same time, steric strain in the corannulene moiety causes the stability of the adducts to reduce. A compound characterized by high stabilization energy and the ability to switch its spin states via valence tautomeric rearrangements was found by systematic variation of structural parameters of cobalt bis(chelate).