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Gelation-driven selection in dynamic covalent C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange.

ABSTRACT: Knoevenagel barbiturate derivatives bearing long alkyl chains were proven to form organogels in suitable solvents based on supramolecular interactions. Their reaction with imines allows for component exchange through C[double bond, length as m-dash]C/C[double bond, length as m-dash]N recombination. The effect of various parameters (solvents, chain length, and temperature) on the C[double bond, length as m-dash]C/C[double bond, length as m-dash]N exchange reaction has been studied. Mixing Knoevenagel compound K and imine I-16 in a 1 : 1 ratio generated a constitutional dynamic library containing the four constituents K, I-16, K'-16, and I'. The reversible exchange reaction was monitored by ¹H-NMR, showing marked changes in the fractions of the four constituents on sol-gel interconversion as a function of temperature. The library composition changed from statistical distribution of the four constituents in the sol state to selective amplification of the gel forming K'-16 constituent together with that of its agonist I'. The process amounts to self-organization driven component selection in a constitutional dynamic organogel system undergoing gelation. This process displays up-regulation of the gel-forming constituent by component redistribution through reversible covalent connections.

SUBMITTER: Liang C

PROVIDER: S-EPMC5643956 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Room temperature chemoselective hydrogenation of C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds by using a well-defined mixed donor Mn(i) pincer catalyst.

Project description:Chemoselective hydrogenation of C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and C[double bond, length as m-dash]N bonds in α,β-unsaturated ketones, aldehydes and imines is accomplished at room temperature (27 °C) using a well-defined Mn(i) catalyst and 5.0 bar H2. Amongst the three mixed-donor Mn(i) complexes developed, κ3-(R2PN3NPyz)Mn(CO)2Br (R = Ph, iPr, t Bu); the t Bu-substituted complex ( tBu2PN3NPyz)Mn(CO)2Br shows exceptional chemoselective catalytic reduction of unsaturated bonds. This hydrogenation protocol tolerates a range of highly susceptible functionalities, such as halides (-F, -Cl, -Br, and -I), alkoxy and hydroxy, including hydrogen-sensitive moieties like acetyl, nitrile, nitro, epoxide, and unconjugated alkenyl and alkynyl groups. Additionally, the disclosed method applies to indole, pyrrole, furan, thiophene, and pyridine-containing unsaturated ketones leading to the corresponding saturated ketones. The C[double bond, length as m-dash]C bond is chemoselectively hydrogenated in α,β-unsaturated ketones, while the aldehyde's C[double bond, length as m-dash]O bond and imine's C[double bond, length as m-dash]N bond are preferentially reduced over the C[double bond, length as m-dash]C bond. A detailed mechanistic study highlighted the non-innocent behavior of the ligand in the ( tBu2PN3NPyz)Mn(i) complex and indicated a metal-ligand cooperative catalytic pathway. The molecular hydrogen (H2) acts as a hydride source, whereas MeOH provides a proton for hydrogenation. DFT energy calculations supported the facile progress of most catalytic steps, involving a crucial turnover-limiting H2 activation.

| S-EPMC9710210 | biostudies-literature

Single and double activation of acetone by isolobal B[triple bond, length as m-dash]N and B[triple bond, length as m-dash]B triple bonds.

Project description:B[triple bond, length as m-dash]N and B[triple bond, length as m-dash]B triple bonds induce C-H activation of acetone to yield a (2-propenyloxy)aminoborane and an unsymmetrical 1-(2-propenyloxy)-2-hydrodiborene, respectively. DFT calculations showed that, despite their stark electronic differences, both the B[triple bond, length as m-dash]N and B[triple bond, length as m-dash]B triple bonds activate acetone via a similar coordination-deprotonation mechanism. In contrast, the reaction of acetone with a cAAC-supported diboracumulene yielded a unique 1,2,3-oxadiborole, which according to DFT calculations also proceeds via an unsymmetrical diborene, followed by intramolecular hydride migration and a second C-H activation of the enolate ligand.

| S-EPMC6009441 | biostudies-literature

Hydrodeoxygenation of isocyanates: snapshots of a magnesium-mediated C[double bond, length as m-dash]O bond cleavage.

Project description:Organic isocyanates are readily converted to methyl amine products through their hydroboration with HBpin in the presence of a ?-diketiminato magnesium catalyst. Although borylated amide and N-,O-bis(boryl)hemiaminal species have been identified as intermediates during the reductive catalysis, the overall reduction and C-O activation is metal-mediated and proposed to occur through the further intermediacy of well-defined magnesium formamidato, formamidatoborate and magnesium boryloxide derivatives. Examples of all these species have been identified and fully characterised through stoichiometric reactivity studies and the stability of the borate species leads us to suggest that, under catalytic conditions, the onward progress of the deoxygenation reaction is crucially dependent on the further activation provided by the Lewis acidic HBpin substrate. These deductions have been explored and ratified through a DFT study.

| S-EPMC6092714 | biostudies-literature

U2N@I h(7)-C80: fullerene cage encapsulating an unsymmetrical U(iv)[double bond, length as m-dash]N[double bond, length as m-dash]U(v) cluster.

Project description:For the first time, an actinide nitride clusterfullerene, U2N@I h(7)-C80, is synthesized and fully characterized by X-ray single crystallography and multiple spectroscopic methods. U2N@I h(7)-C80 is by far the first endohedral fullerene that violates the well-established tri-metallic nitride template for nitride clusterfullerenes. The novel U[double bond, length as m-dash]N[double bond, length as m-dash]U cluster features two U[double bond, length as m-dash]N bonds with uneven bond distances of 2.058(3) Å and 1.943(3) Å, leading to a rare unsymmetrical structure for the dinuclear nitride motif. The combined experimental and theoretical investigations suggest that the two uranium ions show different oxidation states of +4 and +5. Quantum-chemical investigation further reveals that the f1/f2 population dominantly induces a distortion of the U[double bond, length as m-dash]N[double bond, length as m-dash]U cluster, which leads to the unsymmetrical structure. A comparative study of U2X@C80 (X = C, N and O) reveals that the U-X interaction in U[double bond, length as m-dash]X[double bond, length as m-dash]U clusters can hardly be seen as being formed by classical multiple bonds, but is more like an anionic central ion X q- with biased overlaps with the two metal ions, which decrease as the electronegativity of X increases. This study not only demonstrates the unique bonding variety of actinide clusters stabilized by fullerene cages, showing different bonding from that observed for the lanthanide analogs, it also reveals the electronic structure of the U[double bond, length as m-dash]X[double bond, length as m-dash]U clusters (X = C, N and O), which are of fundamental significance to understanding these actinide bonding motifs.

| S-EPMC8178745 | biostudies-literature

Gelation-driven Dynamic Systemic Resolution: in situ Generation and Self-Selection of an Organogelator.

Project description:An organogelator was produced and identified from a dynamic imine system, resolved and amplified by selective gelation. The formation of the organogel was monitored in situ by (1)H NMR, showing the existence of multiple reversible reactions operating simultaneously, and the redistribution of the involved species during gelation. The formed organogelator proved effective with a range of organic solvents, including DMSO, toluene, and longer, linear alcohols.

| S-EPMC4462186 | biostudies-literature

(11)C[double bond, length as m-dash]O bonds made easily for positron emission tomography radiopharmaceuticals.

Project description:The positron-emitting radionuclide carbon-11 ((11)C, t1/2 = 20.3 min) possesses the unique potential for radiolabeling of any biological, naturally occurring, or synthetic organic molecule for in vivo positron emission tomography (PET) imaging. Carbon-11 is most often incorporated into small molecules by methylation of alcohol, thiol, amine or carboxylic acid precursors using [(11)C]methyl iodide or [(11)C]methyl triflate (generated from [(11)C]carbon dioxide or [(11)C]methane). Consequently, small molecules that lack an easily substituted (11)C-methyl group are often considered to have non-obvious strategies for radiolabeling and require a more customized approach. [(11)C]Carbon dioxide itself, [(11)C]carbon monoxide, [(11)C]cyanide, and [(11)C]phosgene represent alternative reactants to enable (11)C-carbonylation. Methodologies developed for preparation of (11)C-carbonyl groups have had a tremendous impact on the development of novel PET tracers and provided key tools for clinical research. (11)C-Carbonyl radiopharmaceuticals based on labeled carboxylic acids, amides, carbamates and ureas now account for a substantial number of important imaging agents that have seen translation to higher species and clinical research of previously inaccessible targets, which is a testament to the creativity, utility and practicality of the underlying radiochemistry.

| S-EPMC5000859 | biostudies-literature

A Biobased Vitrimer: Self-Healing, Shape Memory, and Recyclability Induced by Dynamic Covalent Bond Exchange.

Project description:Plant oil-based vitrimer is an innovative and sustainable polymer with wide-ranging potential applications in the field of advanced materials. However, its restricted application is caused by the poor mechanical properties and the need for catalysts during preparation. Using renewable cardanol as the raw material, epoxy cardanol glycidyl ether (ECGE) with an end epoxide group was obtained by the clicking reaction and epoxidation reaction. After the application of citric acid (CA), ECGE was successfully cured, resulting in the production of fully biobased ECGE-CA vitrimers. This material does not require a catalyst, possesses self-healing properties, and exhibits high mechanical strength. On account of the introduction of hydroxyl groups in citric acid, plenty of hydrogen bonds are formed, allowing the topological network rearrangement of the material in the absence of a catalyst. Recyclable adhesives and repairable materials, vitrimer polymers have good shape memory, self-healing, and recyclability since of their dynamic ester and hydroxyl bonds.

| S-EPMC11360019 | biostudies-literature

Discovery of low energy pathways to metal-mediated B[double bond, length as m-dash]N bond reduction guided by computation and experiment.

Project description:This manuscript describes a combination of DFT calculations and experiments to assess the reduction of borazines (B-N heterocycles) by η6-coordination to Cr(CO)3 or [Mn(CO)3]+ fragments. The energy requirements for borazine reduction are established as well as the extent to which coordination of borazine to a transition metal influences hydride affinity, basicity, and subsequent reduction steps at the coordinated borazine molecule. Borazine binding to M(CO)3 fragments decreases the thermodynamic hydricity by >30 kcal mol-1, allowing it to easily accept a hydride. These hydricity criteria were used to guide the selection of appropriate reagents for borazine dearomatization. Reduction was achieved with an H2-derived hydride source, and importantly, a pathway which proceeds through a single electron reduction and H-atom transfer reaction, mediated by anthraquinone was uncovered. The latter transformation was also carried out electrochemically, at relatively positive potentials by comparison to all prior reports, thus establishing an important proof of concept for any future electrochemical B[double bond, length as m-dash]N bond reduction.

| S-EPMC5512141 | biostudies-literature

The third orthogonal dynamic covalent bond.

Project description:Orthogonal dynamic covalent bonds are of interest for the construction of functional systems. The orthogonality of disulfide and hydrazone exchange under basic and acidic conditions, respectively, is well established. However, the integration of boronate esters as the third bond has failed so far because they exchanged too easily, especially under hydrazone exchange conditions. In this report, a collection of bioinspired catechols derived from adhesive natural products from cyanobacteria is screened with phenylboronic acids with proximal alcohols (benzoboroxoles), amines and fluorines to identify the least labile boronate esters. Moreover, Kool's 2-aminophenol catalysts are introduced to selectively accelerate hydrazone exchange without disturbing sufficiently inert boronate esters. Based on these results, we identified three different conditions to selectively exchange disulfides, hydrazones and boronate esters, that is to demonstrate the existence of three orthogonal dynamic covalent bonds. Moreover, their compatibility with functional systems is confirmed by successful hydrazone exchange in multicomponent surface architectures in the presence of intact boronate esters and disulfides.

| S-EPMC6014071 | biostudies-literature

Product distribution and mechanism of the OH- initiated tropospheric degradation of three CFC replacement candidates: CH3CF[double bond, length as m-dash]CH2, (CF3)2C[double bond, length as m-dash]CH2 and (E/Z)-CF3CF[double bond, length as m-dash]CHF.

Project description:The OH radical initiated photodegradation of 2-fluoropropene (CH3CF[double bond, length as m-dash]CH2), 3,3,3-trifluoro-2-(tri-fluoromethyl)propene ((CF3)2C[double bond, length as m-dash]CH2) and (E/Z)-1,2,3,3,3-pentafluoropropene ((E/Z)-CF3CF[double bond, length as m-dash]CHF) has been investigated for the first time using a 1080 L quartz-glass environmental chamber at 298 ± 2 K and atmospheric pressure of synthetic air coupled with in situ FTIR spectroscopy to monitor reactants and products. The major products observed in the OH reaction were CH3C(O)F (98 ± 5)% together with HC(O)H (89 ± 7)% as a co-product, CF3C(O)F (103 ± 8)% together with HC(O)F (96 ± 7)% as a co-product and CF3C(O)CF3 (91 ± 8)% together with HC(O)H (98 ± 12)% as a co-product from the C1-C2 bond cleavage channel of the intermediate hydroxyalkoxy radical, formed by addition of OH to the terminal carbon of the double bond which is designated C1 of 2-fluoropropene, (E/Z)-1,2,3,3,3-pentafluoropropene and 3,3,3-trifluoro-2-(tri-fluoromethyl)propene, respectively. The present results are compared with previous studies for the reaction of OH with the separate isomers (E) and (Z) of 1,2,3,3,3-pentafluoropropene. In addition, atmospheric implications of the reactions studied are discussed.

| S-EPMC9060772 | biostudies-literature

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