Multinuclear Nuclear Magnetic Resonance Research Articles

Mechanistic Basis of the Cu(OAc)2 Catalyzed Azide-Ynamine (3 + 2) Cycloaddition Reaction.

The Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is used as a ligation tool throughout chemical and biological sciences. Despite the pervasiveness of CuAAC, there is a need to develop more efficient methods to form 1,4-triazole ligated products with low loadings of Cu. In this paper, we disclose a mechanistic model for the ynamine-azide (3 + 2) cycloadditions catalyzed by copper(II) acetate. Using multinuclear nuclear magnetic resonance spectroscopy, electron paramagnetic resonance spectroscopy, and high-performance liquid chromatography analyses, a dual catalytic cycle is identified. First, the formation of a diyne species via Glaser-Hay coupling of a terminal ynamine forms a Cu(I) species competent to catalyze an ynamine-azide (3 + 2) cycloaddition. Second, the benzimidazole unit of the ynamine structure has multiple roles: assisting C-H activation, Cu coordination, and the formation of a postreaction resting state Cu complex after completion of the (3 + 2) cycloaddition. Finally, reactivation of the Cu resting state complex is shown by the addition of isotopically labeled ynamine and azide substrates to form a labeled 1,4-triazole product. This work provides a mechanistic basis for the use of mixed valency binuclear catalytic Cu species in conjunction with Cu-coordinating alkynes to afford superior reactivity in CuAAC reactions. Additionally, these data show how the CuAAC reaction kinetics can be modulated by changes to the alkyne substrate, which then has a predictable effect on the reaction mechanism.

Molecular Insights into Sequence-Specific Protein Hydrolysis by a Soluble Zirconium-Oxo Cluster Catalyst.

The development of catalysts for controlled fragmentation of proteins is a critical undertaking in modern proteomics and biotechnology. {Zr6O8}-based metal-organic frameworks (MOFs) have emerged as promising candidates for catalysis of peptide bond hydrolysis due to their high reactivity, stability, and recyclability. However, emerging evidence suggests that protein hydrolysis mainly occurs on the MOF surface, thereby questioning the need for their highly porous 3D nature. In this work, we show that the discrete and water-soluble [Zr6O4(OH)4(CH3CO2)8(H2O)2Cl3]+ (Zr6) metal-oxo cluster (MOC), which is based on the same hexamer motif found in various {Zr6O8}-based MOFs, shows excellent activity toward selective hydrolysis of equine skeletal muscle myoglobin. Compared to related Zr-MOFs, Zr6 exhibits superior reactivity, with near-complete protein hydrolysis after 24 h of incubation at 60 °C, producing seven selective fragments with a molecular weight in the range of 3-15 kDa, which are of ideal size for middle-down proteomics. The high solubility and molecular nature of Zr6 allow detailed solution-based mechanistic/interaction studies, which revealed that cluster-induced protein unfolding is a key step that facilitates hydrolysis. A combination of multinuclear nuclear magnetic resonance spectroscopy and pair distribution function analysis provided insight into the speciation of Zr6 and the ligand exchange processes occurring on the surface of the cluster, which results in the dimerization of two Zr6 clusters via bridging oxygen atoms. Considering the relevance of discrete Zr-oxo clusters as building blocks of MOFs, the molecular-level understanding reported in this work contributes to the further development of novel catalysts based on Zr-MOFs.

N‐Azidoethyl azoles through N‐alkylation under highly harmonized reaction conditions: Synthesis, characterization, and complexation as energetic coordination compounds

AbstractOrganic azides are universally important in many areas of chemistry, particularly in organic synthesis. The availability of these azides often depends on specific transfer reagents and reaction conditions, or only work with certain substrates. Customizable transfer reagents offer a safe and direct pathway to desired compounds, thereby increasing the availability of N‐alkyl‐azides. In an effort to streamline the synthesis and broaden the scope of N‐azidoethyl‐containing molecules, three different versatile azidoethyl transfer reagents were synthesized and a uniform reaction protocol with azoles as substrates, including imidazole, pyrazole, 1,2,3‐triazole, 1,2,4‐triazole, and tetrazole was established. The resulting azidoethyl‐azoles were further used as ligands for energetic coordination compounds in an effort to create new lead‐free primary explosives. A comprehensive characterization of the transfer reagents, the azidoethyl‐containing products, and energetic coordination compounds was conducted using multinuclear nuclear magnetic resonance (NMR), elemental analysis, mass spectrometry, and infrared spectroscopy (IR). Furthermore, their thermal stability and sensitivity toward friction and impact were determined as well as the detonation properties were calculated by using the EXPLO5 code.

Local Structure in Disordered Melilite Revealed by Ultrahigh Field 71Ga and 139La Solid-State Nuclear Magnetic Resonance Spectroscopy.

Multinuclear Nuclear Magnetic Resonance (NMR) spectroscopy of quadrupolar nuclei at ultrahigh magnetic field provides compelling insight into the short-range structure in a family of fast oxide ion electrolytes with La1+xSr1-xGa3O7+0.5x melilite structure. The striking resolution enhancement in the solid-state 71Ga NMR spectra measured with the world's unique series connected hybrid magnet operating at 35.2 T distinctly resolves Ga sites in four- and five-fold coordination environments. Detection of five-coordinate Ga centers in the site-disordered La1.54Sr0.46Ga3O7.27 melilite is critical given that the GaO5 unit accommodates interstitial oxide ions and provides excellent transport properties. This work highlights the importance of ultrahigh magnetic fields for the detection of otherwise broad spectral features in systems containing quadrupolar nuclei and the potential of ensemble-based computational approaches for the interpretation of NMR data acquired for site-disordered materials.

PI and PIII Ions Supported by BZIMPY Ligands.

We report a class of compounds in which both PIII -X and PI forms featuring the same ligand are stable and readily cycled with each other. A series of PIII -X (X=Cl, Br, I) dicationic triflate salts supported by benzyl- and allyl-substituted 2,6-bis(benzimidazole-2-yl)pyridine (BZIMPY) ligands is synthesized. Surprisingly, treatment of these with R3 PO (R=Et, Oct) results in reduction to BZIMPY-ligated PI monocationic triflate salts while treatment with Ph3 P reduces but also substitutes the compound to produce Ph3 P-BZIMPY-ligated PI dicationic triflate salts. The mechanisms of these surprising reductions are probed experimentally and rationalized computationally. The PIII -X dications are shown to be strong Lewis acids both experimentally and computationally and to readily behave as X+ , PX, and P+ transfer agents in reactions with phosphines, NHCs, and diazabutadienes. The PI mono- and dications are shown to be very effective P+ transfer agents when treated similarly. Oxidation from a monocationic PI salt back to the dicationic PIII -X (X=Cl, Br) salt was achieved by treatment with N-chlorosuccinimide (NCS) or N-bromosuccinimide (NBS). Full characterization is reported using multinuclear nuclear magnetic resonance spectroscopy, elemental analysis, and single-crystal X-ray diffractometry where suitable crystals were isolated.

Synthesis and Characterization of Azido- and Nitratoalkyl Nitropyrazoles as Potential Melt-Cast Explosives.

Desirable advancements in the field of explosive materials include the development of novel melt-castable compounds with melting points ranging from 80 to 110 °C. This is particularly important due to the limited performance and high toxicity associated with TNT (trinitrotoluene). In this study, a series of innovative melt-castable explosives featuring nitratoalkyl and azidoalkyl functionalities attached to the 3-nitro-, 4-nitro-, 3,4-dinitropyrazole, or 3-azido-4-nitropyrazole scaffold are introduced. These compounds were synthesized using straightforward methods and thoroughly characterized using various analytical techniques, including single-crystal X-ray diffraction, IR spectroscopy, multinuclear nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, elemental analysis, and DTA. Furthermore, the energetic properties such as (theoretical) performance data, sensitivities, and compatibilities of the compounds were evaluated and compared among the different structures.

Configurational and Dynamical Heterogeneity in Superionic Li5.3PS4.3Cl1.7−xBrx

AbstractThe correlation between lattice chemistry and cation migration in high‐entropy Li+ conductors is not fully understood due to challenges in characterizing anion disorder. To address this issue, argyrodite family of Li+ conductors, which enables structural engineering of the anion lattice, is investigated. Specifically, new argyrodites, Li5.3PS4.3Cl1.7−xBrx (0 ≤ x ≤ 1.7), with varying anion entropy are synthesized and X‐ray diffraction, neutron scattering, and multinuclear high‐resolution solid‐state nuclear magnetic resonance (NMR) are used to determine the resulting structures. Ion and lattice dynamics are determined using variable‐temperature multinuclear NMR relaxometry and maximum entropy method analysis of neutron scattering, aided by constrained ab initio molecular dynamics calculations. 15 atomic configurations of anion arrangements are identified, producing a wide range of local lattice dynamics. High entropy in the lattice structure, composition, and dynamics stabilize otherwise metastable Li‐deficient structures and flatten the energy landscape for cation migration. This resulted in the highest room‐temperature ionic conductivity of 26 mS cm−1 and a low activation energy of 0.155 eV realized in Li5.3PS4.3Cl0.7Br, where anion disorder is maximized. This study sheds light on the complex structure–property relationships of high‐entropy superionic conductors, highlighting the significance of heterogeneity in lattice dynamics.

Gallium(III)- and Thallium(III)-Encapsulated Polyoxopalladates: Synthesis, Structure, Multinuclear NMR, and Biological Activity Studies.

Three gallium(III)- and thallium(III)-containing polyoxopalladates (POPs) have been synthesized and structurally characterized in the solid state and in solution, namely, the phosphate-capped 12-palladate nanocubes [XPd12O8(PO4)8]13- (X = GaIII, GaPd12P8; X = TlIII, TlPd12P8) and the 23-palladate double-cube [Tl2IIIPd23P14O70(OH)2]20- (Tl2Pd23P14). The cuboid POPs, GaPd12P8 and TlPd12P8, are solution stable as verified by the respective 31P, 71Ga, and 205Tl nuclear magnetic resonance (NMR) spectra. Of prime interest, the spin-spin coupling schemes allowed for an intimate study of the solution behavior of the TlIII-containing POPs via a combination of 31P and 205Tl NMR, including the stoichiometry of the major fragments of Tl2Pd23P14. Moreover, biological studies demonstrated the antitumor and antiviral activity of GaPd12P8 and TlPd12P8, which were validated to be as efficient as cis-platinum against human melanoma and acute promyelocytic leukemia cells. Furthermore, GaPd12P8 and TlPd12P8 exerted inhibitory activity against two herpetic viruses, HSV-2 and HCMV, in a dose-response manner.

Cold, Hot, Dry, and Wet: Locations and Dynamics of CO2 and H2O Co-Adsorbed in an Ultramicroporous MOF.

Climate change from anthropogenic carbon dioxide (CO2) emissions poses a severe threat to society. A variety of mitigation strategies currently include some form of CO2 capture. Metal-organic frameworks (MOFs) have shown great promise for carbon capture and storage, but several issues must be solved before feasible widespread adoption is possible. MOFs often exhibit reduced chemical stabilities and CO2 adsorption capacities in the presence of water, which is ubiquitous in nature and many practical settings. A comprehensive understanding of water influence on CO2 adsorption in MOFs is necessary. We have used multinuclear nuclear magnetic resonance (NMR) experiments at temperatures ranging from 173 to 373 K, along with complementary computational techniques, to investigate the co-adsorption of CO2 and water across various loading levels in the ultra-microporous ZnAtzOx MOF. This approach yields detailed information regarding the number of CO2 and water adsorption sites along with their locations, guest dynamics, and host-guest interactions. Guest adsorption and motional models proposed from NMR data are supported by computational results, including visualizations of adsorption locations and the spatial distribution of guests in different loading scenarios. The wide variety and depth of information presented demonstrates how this experimental methodology can be used to investigate humid carbon capture and storage applications in other MOFs.

Multinuclear 1D and 2D NMR with 19F-Photo-CIDNP hyperpolarization in a microfluidic chip with untuned microcoil

Nuclear Magnetic Resonance (NMR) spectroscopy is a most powerful molecular characterization and quantification technique, yet two major persistent factors limit its more wide-spread applications: poor sensitivity, and intricate complex and expensive hardware required for sophisticated experiments. Here we show NMR with a single planar-spiral microcoil in an untuned circuit with hyperpolarization option and capability to execute complex experiments addressing simultaneously up to three different nuclides. A microfluidic NMR-chip in which the 25 nL detection volume can be efficiently illuminated with laser-diode light enhances the sensitivity by orders of magnitude via photochemically induced dynamic nuclear polarization (photo-CIDNP), allowing rapid detection of samples in the lower picomole range (normalized limit of detection at 600 MHz, nLODf,600, of 0.01 nmol Hz1/2). The chip is equipped with a single planar microcoil operating in an untuned circuit that allows different Larmor frequencies to be addressed simultaneously, permitting advanced hetero-, di- and trinuclear, 1D and 2D NMR experiments. Here we show NMR chips with photo-CIDNP and broadband capabilities addressing two of the major limiting factors of NMR, by enhancing sensitivity as well as reducing cost and hardware complexity; the performance is compared to state-of-the-art instruments.

Platinum(IV) Carbonato Complexes: Formation via the Addition of CO2 to the [Pt(OH)6]2- Anion and Generation of Platinum(IV) Oxide Nanoparticles for the Preparation of Catalysts.

A combination of multinuclear nuclear magnetic resonance spectroscopy and theoretical calculation based on density functional theory was used for a speciation study of Pt in solutions prepared either by the interaction of [Pt(OH)6]2- with gaseous CO2 in an alkaline solution of platinum(IV) hydroxide ([Pt(OH)4(H2O)2]) or by the dissolution of [Pt(OH)4(H2O)2] in an aqueous KHCO3 solution. The formed solutions contained coexisting Pt(IV) carbonato complexes with κ1- and κ2-coordination modes. The gradual condensation of mononuclear Pt species in such bicarbonate solutions resulted in the formation of PtO2 nanoparticles aggregating into a solid precipitate on prolonged aging. The deposition of PtO2 particles from bicarbonate solutions was adapted for the preparation of Pt-containing heterogeneous catalysts: bimetallic Pt-Ni catalysts were prepared using various supporting materials (CeO2, SiO2, and g-C3N4) and tested for the activity in hydrazine-hydrate decomposition. All prepared materials showed high selectivity with respect to H2 production from the hydrazine-hydrate with PtNi/CeO2 showing the highest rate of H2 evolution. In the long-range evaluation, the PtNi/CeO2 catalyst operating at 50 °C showed an exceptional turnover number value of 4600 producing hydrogen at a 97% selectivity level and with a mean turnover frequency value of about 470 h-1. In the case of the PtNi/g-C3N4 catalyst, for the first time, the photodriven decomposition of hydrazine-hydrate was shown to enhance the productivity of the catalyst by 40%.

Triple-decker complexes comprising heterocyclic middle-deck with coinage metals

Earlier accounts of triple-decker complexes comprising main group elements and transition metals in the middle-deck, motivated us to synthesize triple-decker complexes containing coinage metals in the middle-deck. As a result, we have explored the reactivity of open-cage nido‑ [(Cp*M)2{μ-B2H2E2}], 1–3 (Cp* = η5-C5Me5, 1: M = Co, E = S; 2: M = Co, E = Se; 3: M = Rh, E = Se) with [CuBr(SMe2)]. All the reactions yielded triple-decker complexes, [(Cp*M)2{μ-B2H2E2CuBr}], 4–6 (4: M = Co, E = S; 5: M = Co, E = Se; 6: M = Rh, E = Se) having [CuBr] in the middle-deck. The removal of the SMe2 ligand resulted in the formation of complexes 4–6 as a single product. These complexes are examples of triple-decker species having a planar 5-membered [B2E2Cu] (E = S or Se) middle deck, in which the Cu exists as Cu(I) with an elongated M-Cu bonding interaction. Synthesized complexes have been established by ESI-MS, multinuclear nuclear magnetic resonance (NMR), and IR spectroscopy. The solid-state structures of 5 and 6 were confirmed by single-crystal X-ray diffraction analyses. Density functional theory (DFT) analyses of these complexes have presented a high electron donation from the [B2E2] (E = S or Se) fragment of the middle ring to the axial metals and a weak bonding interaction between group 9 metals and Cu.

Odd-Leg Birdcages for Geometric Decoupling in Multinuclear Imaging and Spectroscopy

The utility of interleaved odd-number leg birdcage coils is demonstrated for decoupling in double- and triple-tuned multinuclear applications. The birdcage was designed to geometrically decouple from a planar double-tuned (1H-23Na) array and from a 31P saddle coil insert to create a triple-tuned configuration. Comparisons between an actively detuned coil and a purely geometrically decoupled architecture were used to demonstrate the capabilities of the design. In particular cases, the simplicity and adaptability of the interleaved nine-leg design for multinuclear nuclear magnetic resonance (NMR) offer a straightforward alternative to the often complex and lossy designs currently available for multinuclear birdcages and volume coils.

Design of a cryogen-free high field dual EPR and DNP probe

We present the design and construction of a cryogen free, dual electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) probe for novel dynamic nuclear polarization (DNP) experiments and concurrent “in situ” analysis of DNP mechanisms. We focus on the probe design that meets the balance between EPR, NMR, and low temperature performance, while maintaining a high degree of versatility: allowing multi-nuclear NMR detection as well as broadband DNP/EPR excitation/detection. To accomplish high NMR/EPR performance, we implement a novel inductively coupled double resonance NMR circuit (1H-13C) in a solid state probe operating at cryogenic temperatures. The components of the circuit were custom built to provide maximum NMR performance, and the physical layout of this circuit was numerically optimized via magnetic field simulations to allow maximum microwave transmission to the sample for optimal EPR performance. Furthermore this probe is based around a cryogen free gas exchange cryostat and has been designed to allow unlimited experiment times down to 8.5 Kelvin with minimal cost. The affordability of EPR/DNP experiment is an extremely important aspect for broader impact with magnetic resonance measurements. The purpose of this article is to provide as complete information as we have available for others with interest in building a dual DNP/EPR instrument based around a cryogen-free cryostat.

Thorium- and Uranium-Mediated C-H Activation of a Silyl-Substituted Cyclobutadienyl Ligand.

Cyclobutadienyl complexes of the f-elements are a relatively new yet poorly understood class of sandwich and half-sandwich organometallic compounds. We now describe cyclobutadienyl transfer reactions of the magnesium reagent [(η4-Cb'''')Mg(THF)3] (1), where Cb'''' is tetrakis(trimethylsilyl)cyclobutadienyl, toward thorium(IV) and uranium(IV) tetrachlorides. The 1:1 stoichiometric reactions between 1 and AnCl4 proceed with intact transfer of Cb'''' to give the half-sandwich complexes [(η4-Cb'''')AnCl(μ-Cl)3Mg(THF)3] (An = Th, 2; An = U, 3). Using a 2:1 reaction stoichiometry produces [Mg2Cl3(THF)6][(η4-Cb'''')An(η3-C4H(SiMe3)3-κ-(CH2SiMe2)(Cl)] (An = Th, [Mg2Cl3(THF)6][4]; An = U [Mg2Cl3(THF)6][5]), in which one Cb'''' ligand has undergone cyclometalation of a trimethylsilyl group, resulting in the formation of an An-C σ-bond, protonation of the four-membered ring, and an η3-allylic interaction with the actinide. Complex solution-phase dynamics are observed with multinuclear nuclear magnetic resonance spectroscopy for both sandwich complexes. A computational analysis of the reaction mechanism leading to the formation of 4 and 5 indicates that the cyclobutadienyl ligands undergo C-H activation across the actinide center.

Formation of Metallosupramolecular Helicates and Mesocates from Poly-N-Heterocyclic Carbene Ligands.

In this work, a series of poly-NHC-based tetranuclear silver helicates and mesocates were synthesized from the silver-mediated self-assembly of the ligands involving multiple tridentate CNC-type pincer units and NHC coordination sites. The silver helicate was found to be transferred to a gold mesocate upon metal exchange reaction. The metallosupramolecular helicates and mesocates have been fully characterized by single-crystal X-ray crystallography, mass spectrometry, and multinuclear nuclear magnetic resonance spectroscopies. This study provides an example of the selective preparation of poly-NHC-based helicates or mesocates depending on the size of metal ions and the steric effect of ligands.

Order–Disorder Diversity of the Solid State by NMR: The Role of Electrical Charges

The physical explanations and understanding of the order–disorder phenomena in the solid state are commonly inferred from the experimental capabilities of the characterization techniques. Periodicity is recorded according to the averaging procedure of the conventional reciprocal-space techniques (RSTs) in many solids. This approach gives rise to a sharp trimodal view including non-crystalline or amorphous compounds, aperiodic crystals and periodic crystals. However, nuclear magnetic resonance (NMR) spectroscopy offers an alternative approach that is derived from the distinct character of the measurements involved at the local scale. Here, we present a sequence of progressive order–disorder states, from amorphous structures up to fully ordered mineral structures, showing the great diversity existing in the solid state using multinuclear NMR spectroscopy. Some examples in glasses and products of their crystallization are used, as well as several minerals (including beryl-group and feldspar-group minerals) at magnetic fields up to 35.2 T, and some examples from literature. This approach suggests that the solid state is a dynamic medium, whose behavior is due to atomic adjustments from local compensation of electrical charges between similar structural states, which explains Ostwald’s step rule of successive reactions. In fully ordered feldspar minerals, we propose that the electronic structure of the elements of the cavity site is involved in bonding, site morphology and feldspar topology. Furthermore, some implications are derived about what is a mineral structure from the point of view of the NMR experiments. They open the possibility for the development of the science of NMR Mineralogy.

Cluster Growth Reactions: Structures and Bonding of Metal-Rich Metallaheteroboranes Containing Heavier Chalcogen Elements.

In an effort to synthesize cobalt-rich metallaheteroboranes from decaborane(14) analogues, we have studied the reaction of 10-vertex nido-[(Cp*Co)2B6H6E2] (Cp* = η5-C5Me5, 1: E = Se and 2: E = Te) with [Co2(CO)8] under thermolytic conditions. All of these reactions yielded face-fused clusters, [(Cp*Co)2B6H6E2{Co(CO)}(μ-CO){Co3(CO)6}] (3: E = Se and 4: E = Te). Further, when clusters 3 and 4 were treated with [Co2(CO)8], they underwent further cluster buildup reactions leading to the formation of 16-vertex doubly face-fused clusters [(Cp*Co)2B6H6E2{Co2(CO)2}(μ-CO)2{Co4(CO)8}] (5: E = Se and 6: E = Te). Cobaltaheteroboranes 3 and 4 comprise one icosahedron {Co4B6E2} and one square pyramidal {Co3B2} moiety, whereas 5 and 6 are made with one icosahedron {Co4B6E2} and two square pyramidal {Co3B2} cores. In an attempt to generate heterometallic metal-rich clusters, we have explored the reactivity of decaborane(14) analogue nido-[(Cp*Co)2B7TeH9] (7) with [Ru3(CO)12] at 80 °C, which afforded face-fused 13-vertex cluster [(Cp*Co)2B7H7Te{Ru3(CO)8}] (8). Cluster 8 is a rare example of a metal-rich metallaheteroborane in which one icosahedron {Co2Ru2B7Te} and a tetrahedron {Ru2B2} units are fused through a common {RuB2} triangular face. Further, the treatment of nido-[(Cp*Co)2B6S2H4(CH2S2)] (9) with [Fe2(CO)9] afforded 11-vertex nido-[(Cp*Co)2B6S2H4(CH2S2){Fe(CO)3}] (10). The core structure of 10 is similar to that of [C2B9H11]2- with a five-membered pentahapto coordinating face. All of the synthesized metal-rich metallaheteroboranes have been characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy, IR spectroscopy, ESI-MS, and structurally solved by single-crystal X-ray diffraction analysis. Furthermore, theoretical investigations gave insight into the bonding of such higher-nuclearity clusters containing heavier chalcogen atoms.

Highly bioactive novel aryl-, benzyl-, and piperazine-selenoureas: synthesis, structural characterization and in vitro biological evaluation

Selenoureas are widespread as useful elements for constructing important species and biologically active molecules. Finding an efficient and straightforward method to prepare this motif and biologically screen derivatives thereof is crucial. Herein, we demonstrate the effectiveness of using ethanol as a solvent in the preparation of various substituted aryl-, benzyl-, and piperazine-selenoureas from isoselenocyanates and amines. The synthetic method includes mild reaction conditions, large substrate scope, and good isolated yields. Biological evaluation of the prepared products on MDA-MB-231 and MCF-7 cancer cell lines revealed several remarkably active compounds (IC50 < 10 μΜ) with the best one exhibiting IC50 values of 1.8 μΜ and 1.2 μΜ observed against the challenging former triple-negative breast cancer cell line and the latter one, respectively. The chemical structures of all new compounds were fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and high accuracy mass measurements.

Synthesis, Structural Studies, and Application of Aluminum Aryloxides for Ring-Opening Metathesis Polymerization

A series of aluminum aryloxides of types [Al(OAr)3] and [Al(OAr)2Cl] (Ar = 4-CH3C6H4, 4-PhC6H4, 2-iPr-C6H4, 2-tBu-C6H4, 2,6-iPr2C6H3, and 2,6-Cl2C6H3) were synthesized from commercially available reagents and structurally characterized by single X-ray diffraction studies. The structural evaluations for aluminum aryloxides revealed the formation of dinuclear clusters in the solid state. The solution behavior of the synthesized compounds was studied by multinuclear nuclear magnetic resonance (NMR) spectroscopy. The synthesized compounds were applied for the in situ generation of Ziegler–Natta catalyst systems for the ring-opening metathesis polymerization (ROMP) of nonconstrained olefins. The ligand exchange between WCl6 and Al-aryloxides followed by activation with aluminum alkyls resulted in the formation of ill-defined species showing enhanced ROMP reactivity compared to the related systems generated upon the ligand exchange between WCl6 and ArOH or isolated [W(OAr)4Cl2]. The benefits of using newly developed systems for the ROMP of cyclic olefins are their low costs and high molecular weights for polymerization products (Mw > 250 kDa). Moreover, an E/Z stereoselective control over the double C═C bond in the polymeric product was achieved upon tuning the steric volume at the aryloxide ligand framework.