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En chimie, un adduit est le produit d'une réaction d'addition entre deux unités moléculaires distinctes donnant un produit unique qui contient tous les atomes initiaux mais liés différemment entre eux. Le mot provient du latin adductus, "attiré vers", ou de la contraction des deux termes "addition produit". L'ordre des mots est plus logique en anglais : "addition product" d'où est tiré le terme adduct, traduit ensuite en français par adduit. Un adduit intramoléculaire peut se former par réaction d'addition entre unités disjointes sur une même molécule. Une stœchiométrie différente de 1:1 est par ailleurs possible. Le terme adduit devrait, lorsqu'il s'applique, être préféré au terme plus vague de complexe, qui englobe également les édifices moléculaires unis par des liaisons plus faibles (liaisons coordinatives, ou datives). Exemples d'adduits La réaction du peroxyde d'hydrogène avec le carbonate de sodium donne du percarbonate de sodium . Des adduits se forment souv

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Acides et bases de Lewis

droite|vignette|300x300px|Schéma de quelques et Un acide de Lewis est une espèce chimique qui contient une orbitale électronique vide qui est capable d'accepter une paire d'électrons d'une base de L

Base (chimie)

thumb|Bouteille d'ammoniaque à 25-28%. Une 'base est un produit chimique qui, à l'inverse d'un acide, est capable de capturer un ou plusieurs protons ou, réciproquement, de fournir des électrons. Un m

Ligand (chimie)

Un ligand est un atome, un ion ou une molécule portant des groupes fonctionnels lui permettant de se lier à un ou plusieurs atomes ou ions centraux. Le terme de ligand est le plus souvent utilisé en

Dyes, Radicals and Nitrous Oxide Adducts Derived from N-Heterocyclic Carbenes

Léonard Yannick Maurice Eymann

N-Heterocyclic carbenes are able to form covalent adducts with nitrous oxide (N2O) under ambient conditions. This thesis summarizes the studies of these adducts and their reactivity. A ditopic carbanionic N-heterocyclic carbene was found to react with nitrous oxide, resulting in a stable covalent adduct with two N2O groups attached to the heterocycle. Mesoionic N-heterocyclic carbenes derived from C2-arylated 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, as well as a triazolylidene, also react with N2O. Crystallographic analyses of all complexes reveal bent N2O groups, which can adopt a cis or trans configuration. Resulting complexes of imidazole- or triazole-based mesoionic carbenes and nitrous oxide can be converted into azo dyes by reaction with arenes in the presence of AlCl3 or HCl. The azo coupling can be achieved with electron-rich aromatic compounds such as mesitylene, trimethoxybenzene, azulene, or dibenzo-18-crown-6. The latter coupling reaction allows for an easy preparation of a colorimetric sensor for potassium or sodium ions. The putative intermediate of the reaction with acid, a rare diazohydroxide, has been isolated and structurally characterized. Using imidazolium compounds with two N2O groups, it is possible to prepare amine-substituted azo dyes, or dyes with two azoarene groups attached to the heterocycle. The synthesis and the characterization of a new class of neutral aminyl radicals is also reported. Monoradicals were obtained by the reduction of azoimidazolium dyes with potassium. Structural, spectroscopic and computational data suggest that the spin density is centered on one of the nitrogen atoms of the former azo group. The reduction of a dimeric dye with an octamethylbiphenylene bridge between the azo groups resulted in the formation a biradical with largely independent unpaired electrons. Both, the monoradicals and the biradical were found to display high stability in solution as well as in the solid state.

EPFL2018

Chargement

A Two Step Postsynthetic Modification Strategy: Appending Short Chain Polyamines to Zn-NH2-BDC MOF for Enhanced CO2 Adsorption

Mehrdad Asgari, Jordi Espin Marti, Anita Justin, Ilia Kochetygov, Wendy Lee Queen, Olga Trukhina

Functionalizing metal–organic frameworks (MOFs) with amines is a commonly used strategy to enhance their performance in CO2 capture applications. As such, in this work, a two-step strategy to covalently functionalize NH2-containing MOFs with short chain polyamines was developed. In the first step, the parent MOF, Zn4O(NH2-BDC)3, was exposed to bromoacetyl bromide (BrAcBr), which readily reacts with pendant -NH2 groups on the 2-amino-1,4-benzenedicarboxylate (NH2-BDC2–) ligand. 1H NMR of the digested MOF sample revealed that as much as 90% of the MOF ligands could be functionalized in the first step. Next, the MOF samples 60% of the ligands functionalized with acetyl bromide, Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, was exposed to several short chain amines including ethylenediamine (ED), diethylenetriamine (DETA), and tris(2-aminoethyl)amine (TAEA). Subsequent digested 1H NMR analysis indicated that a total of 30%, 28%, and 19% of the MOF ligands were successfully grafted to ED, DETA, and TAEA, respectively. Next, the CO2 adsorption properties of the amine grafted MOFs were studied. The best performing material, TAEA-appended-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8, exhibits a zero-coverage isosteric heat of CO2 adsorption of −62.5 kJ/mol, a value that is considerably higher than the one observed for the parent framework, −21 kJ/mol. Although the boosted CO2 affinity only leads to a slight increase in the CO2 adsorption capacity in the low-pressure regime (0.15 bar), which is of interest in postcombustion carbon dioxide capture, the CO2/N2 (15/85) selectivity at 313 K is 143, a value that is ∼35 times higher than the one observed for Zn4O(NH2-BDC)3, 4.1. Such enhancements are attributed to accessible primary amines, which were grafted to the MOF ligand. This hypothesis was further supported via in situ DRIFTS measurements of TAEA-Ac-Zn4O(NH2-BDC)1.2(BrAcNH-BDC)1.8 after exposure to CO2, which revealed the chemisorption of CO2 via the formation of hydrogen bonded carbamates/carbamic acid and CO2δ- species; the latter are adducts formed between CO2 and [amineH]+Br– salts that are produced during the amine grafting step.

2021

Chargement

Development of metal-organic frameworks based on N-heterocyclic ligands

Ilia Kochetygov

Metal-organic frameworks (MOFs) have firmly established in the field of porous materials since their early discovery in the 1990s. With a plethora of applications, these materials offer endless possibilities owing to their tunable, modular nature. The vast amount of synthesized MOFs indicates an utmost interest in this topic among researchers in academia and industry. However, bulk scale uses of MOFs for gas storage, catalysis, water purification and complex separations require such MOFs to have a definite, large pore size in the nanometer range. As MOFs are modular, the production of such large pore materials requires a separate synthesis of particular building blocks called ligands. Most pathways to obtain large ligands rely on the use of palladium-catalyzed coupling chemistry, thus incurring enormous costs and low scalability of the corresponding MOFs. In this thesis, we explore metal-organic frameworks based on N-heterocyclic ligands. We show how the use of these heterocycles has allowed us to easily construct ligands and new MOFs with them, and we showcase various applications of these materials. In Chapter 1, we briefly overview the existing state of the art in ligand design for metal-organic frameworks and define thesis aims. In Chapter 2, we show how a new ligand forms a Cu-Sp5 MOF, which has one of the highest CO2/N2 adsorption selectivities in flue gas conditions reported to date. We investigate the origins of such remarkable performance via multiple characterization techniques. Chapter 3 reports a new MOF Cu-Sp5-BF4. We for the first time access N-heterocyclic carbene (NHC) adduct chemistry in a MOF via ligand post-synthetic modification. We then reveal how this process alters the dimensionality of the material and how it improves the accessibility of NHC sites for a second-step iridium grafting. We finally shed light on iridium speciation in the final material using a combination of EXAFS and XPS methods, and how it changes upon a catalytic reaction of stilbene hydrogenation. Chapter 4 illustrates a new approach for ligand synthesis for large pore MOFs. We show the development of a new concept in ligand design that we call LigX. Using the LigX approach, we simplify large pore MOF ligand synthesis by avoiding time- and cost-intensive Pd-based chemistry. We show the synthesis of structurally diverse MOFs using this methodology.

EPFL2022

Chargement

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