27 research outputs found

    First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

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    Enantioenriched promethazine and ethopropazine were synthesized through a simple and straightforward four-step chemoenzymatic route. The central chiral building block, 1-(10H-phenothiazin-10-yl)propan-2-ol, was obtained via a lipase-mediated kinetic resolution protocol, which furnished both enantiomeric forms, with superb enantioselectivity (up to E = 844), from the racemate. Novozym 435 and Lipozyme TL IM have been found as ideal biocatalysts for preparation of highly enantioenriched phenothiazolic alcohols (up to >99% ee), which absolute configurations were assigned by Mosher’s methodology and unambiguously confirmed by XRD analysis. Thus obtained key-intermediates were further transformed into bromide derivatives by means of PBr3, and subsequently reacted with appropriate amine providing desired pharmacologically valuable (R)- and (S)-stereoisomers of title drugs in an ee range of 84–98%, respectively. The modular amination procedure is based on a solvent-dependent stereodivergent transformation of the bromo derivative, which conducted in toluene gives mainly the product of single inversion, whereas carried out in methanol it provides exclusively the product of net retention. Enantiomeric excess of optically active promethazine and ethopropazine were established by HPLC measurements with chiral columns

    Dynamic Supramolecular Polymers Based on Zinc Bis(diorganophospate)s: Synthesis, Structure and Transformations in Solid State and Solutions

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    The synthesis, structure and some properties of coordination polymers composed of linear zinc bis(diorganophospate)s (ZnDOPs) with a general formula of Zn[O2P(OR)2]2 (where R = CH3, C2H5, n-C4H9, or 2-ethylhexyl group) are described. Hybrid (co)polymers obtained by different procedures were characterized by means of powder XRD, DSC, SEM, TGA coupled with mass spectrometry of the evolved gases and rheological measurements, as well as FTIR and NMR techniques. The morphology, thermal transformations and solubility of ZnDOPs strongly depend on the type of organic substituent in the O2P(OR)2 ligands and the thermal history of the sample. Because of this, one can obtain highly crystalline rods, semicrystalline powders, as well as rubbery materials exhibiting a second-order transition below −50 °C. Polymeric chains formed by ZnDOPs undergo a reversible dissociation in polar organic solvents (e.g., methanol, DMSO), which allows for easy modification of their composition and physicochemical properties via a simple exchange of diorganophosphate anions. Some of the ZnDOPs were investigated as the latent curing agents for epoxides. On the basis of rheological and DSC studies, it is evident that ZnDOPs catalyze very effectively the cross-linking process within the 130–160 °C temperature range

    Snapshots of the Hydrolysis of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. Impact of Water Molecules on Aggregation Processes in Lithium-Ion Battery Electrolytes

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    Despite that 4,5-dicyano-2-(trifluoromethyl)­imidazole lithium salt (LiTDI) exhibits several interesting features in aprotic solvents such as glymes or carbonate esters, little is known about its structural rearrangement after exposure to water. Since the LiTDI salt has been verified as an effective moisture scavenger able to suppress degradation of the LiPF<sub>6</sub>-based electrolyte, comprehensive knowledge of coordination modes in the LiTDI–H<sub>2</sub>O system, as well as information about the structure of formed hydrates, is desirable. In the present study, we report the impact of water on the LiTDI glyme-based electrolytes investigated by means of the single-crystal X-ray diffraction technique and Raman spectroscopy. We have found that the exposure of lithium 4,5-dicyanoimidazolate–glyme solvates to humid air gives rise to the hydrolysis products arising from stepwise addition of water molecules to the lithium coordination sphere. Several structural motifs have been distinguished as preferred coordination modes in the LiTDI–H<sub>2</sub>O system. A high number of available ether oxygen donor center water molecules cause dissociation of ionic contact pairs and aggregation of cationic species stabilized by crown ethers. Low O:Li molar ratio leads to the formation of LiTDI–glyme–water solvates and LiTDI hydrates. The air-stable LiTDI trihydrate comprises ionic pairs formed by a lithium cation coordinated to an imidazole nitrogen of TDI. A lithium cation coordinated via nitrile groups and bearing water molecules is a basic motif constituting dimeric species of formula [Li­(H<sub>2</sub>O)<sub>2</sub>TDI]<sub>2</sub> which are present in aggregated [Li­(H<sub>2</sub>O)­TDI]<i><sub>n</sub></i> chains making up the structure of a monohydrate. The discovered motifs have been proved to occur in both the solid and melted hydrated systems of LiTDI. They will be helpful for conducting molecular dynamic calculations and for obtaining information how to manipulate the structure of a Li<sup>+</sup>-solvation sheath in both hydrated and liquid aqueous electrolytes based on heterocyclic anions

    Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 2. Ionic Aggregation Modes in Solution and PEO Matrix

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    In this paper, we present complementary spectroscopic analyses of lithium 2-trifluoromethyl-4,5-dicyanoimidazole adducts with aprotic solvents like dimethyl ethers of poly­(ethylene glycols) (i.e., glymes) and crown ethers. Comparing the XRD structures with Raman spectra we have found fingerprints of various structural motifs such as ionic pairs, dimers, “free ions”, and higher aggregates. Comprehensive analysis of crystalline materials has been performed to correlate molecular structures with spectroscopic data, which give valuable information about the coordination preferences of substituted 4,5-dicyanoimidazolato anions and provide the basis for further developing a model for poly­(ethylene oxide) electrolytes. Complementary and systematic X-ray studies of glyme adducts enable precise interpretation of the anion–cation and cation–solvent interactions from experimental Raman spectra. This information provides a convenient tool for the characterization of the ionic association interactions within electrolytes

    Chemoenzymatic Synthesis of Optically Active Alcohols Possessing 1,2,3,4-Tetrahydroquinoline Moiety Employing Lipases or Variants of the Acyltransferase from <i>Mycobacterium smegmatis</i> 

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    The enzymatic kinetic resolution (EKR) of racemic alcohols or esters is a broadly recognized methodology for the preparation of these compounds in optically active form. Although EKR approaches have been developed for the enantioselective transesterification of a vast number of secondary alcohols or hydrolysis of their respective esters, to date, there is no report of bio- or chemo-catalytic asymmetric synthesis of non-racemic alcohols possessing 1,2,3,4-tetrahydroquinoline moiety, which are valuable building blocks for the pharmaceutical industry. In this work, the kinetic resolution of a set of racemic 1,2,3,4-tetrahydroquinoline-propan-2-ols was successfully carried out in neat organic solvents (in the case of CAL-B and BCL) or in water (in the case of MsAcT single variants) using immobilized lipases from Candida antarctica type B (CAL-B) and Burkholderia cepacia (BCL) or engineered acyltransferase variants from Mycobacterium smegmatis (MsAcT) as the biocatalysts and vinyl acetate as irreversible acyl donor, yielding enantiomerically enriched (S)-alcohols and the corresponding (R)-acetates with E-values up to 328 and excellent optical purities (>99% ee). In general, higher ee-values were observed in the reactions catalyzed by lipases; however, the rates of the reactions were significantly better in the case of MsAcT-catalyzed enantioselective transesterifications. Interestingly, we have experimentally proved that enantiomerically enriched 1-(7-nitro-3,4-dihydroquinolin-1(2H)-yl)propan-2-ol undergoes spontaneous amplification of optical purity under achiral chromatographic conditions

    Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 1. From Isolated Free Ions to Conductive Aggregated Systems

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    We present complementary series of crystal structures of lithium salts containing 4,5-dicyanoimidazolato anions substituted with perfluoroalkyl groups. Single-crystal X-ray analysis of 10 adducts with aprotic solvents, glymes (dimethyl ethers of poly­(ethylene glycols)) and crown ethers, have been performed to correlate their molecular structures and properties with spectroscopic and thermal data. Comprehensive structure analysis of crystalline materials reveals valuable information about the coordination ability of substituted 4,5-dicyanoimidazolato anions and provides the basis for developing the model of poly­(ethylene oxide) electrolytes and liquid systems. Presented results reveal new aggregation modes at high concentrations of lithium salts involving the release of cations by self-assembly of an anionic subnetwork and provide some insight into the electrochemical performance of TDI anions

    Effect of In–C<sub>NHC</sub> Bonds on the Synthesis, Structure, and Reactivity of Dialkylindium Alkoxides: How Indium Compares to Gallium

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    The investigation of the reactivity of dialkylindium alkoxides toward N-heterocyclic carbenes (NHCs) has shown that both the character of the In–C<sub>NHC</sub> bond and alkyl and alkoxide substituents have a significant effect on the formation of R<sub>2</sub>InOR­(NHC) complexes and the distribution of products. The reactions of simple dimethylindium alkoxides with the N-heterocyclic carbenes 1,3-bis­(2,4,6-trimethylphenyl)­imidazolin-2-ylidene (SIMes) and 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes) lead to the monomeric complexes Me<sub>2</sub>InOR­(NHC), as shown by the isolation of Me<sub>2</sub>InOMe­(NHC) (NHC = IMes (<b>3</b>), SIMes (<b>4</b>)). Compounds Me<sub>2</sub>InOR­(NHC) are unstable in solution and instantly disproportionate, which can be associated with a weaker In–C<sub>NHC</sub> bond in comparison with stable gallium analogues. As a result, Me<sub>3</sub>In­(NHC) (NHC = IMes (<b>1</b>), SIMes (<b>2</b>)) adducts, as well as Mitsubishi-type methylindium alkoxides, are formed. The exchange of a simple alkoxy group with chelating (<i>S</i>)-methyl lactate (<i>S-melac</i>) has resulted in the more stable Me<sub>2</sub>In­(OCH­(Me)­CO<sub>2</sub>Me)­(NHC) complexes. The use of the bulky alkoxide ligand OCPh<sub>2</sub>Me allows for the synthesis of stable Me<sub>2</sub>In­(OCPh<sub>2</sub>Me)­(NHC) (NHC = IMes (<b>6</b>), SIMes (<b>7</b>)) from [Me<sub>2</sub>In­(μ-OCPh<sub>2</sub>Me)]<sub>2</sub> (<b>5</b>). While the strongest In–C<sub>NHC</sub> bond, among the characterized Me<sub>2</sub>In­(OR)­(NHC) complexes, is crucial for the stability of <b>6</b> and <b>7</b>, it is still weaker in comparison with Ga–C<sub>NHC</sub> bonds in the analogous gallium complexes Me<sub>2</sub>Ga­(OCPh<sub>2</sub>Me)­(NHC) (NHC = IMes (<b>8</b>), SIMes (<b>9</b>)). For [<sup><i>t</i></sup>Bu<sub>2</sub>In­(μ-OCH<sub>2</sub>CH<sub>2</sub>OMe)]<sub>2</sub>, the introduction of a bulky <i>tert</i>-butyl group has resulted in a lack of reactivity toward NHCs. However, the structure of <sup><i>t</i></sup>Bu<sub>2</sub>In­(OCPh<sub>2</sub>Me)­(IMes) has confirmed the substantial effect of bulky alkyl substituents on the strength of the In–C<sub>NHC</sub> bond. The structures of <b>1</b>, <b>2</b>, <b>4</b>–<b>6</b>, and <b>8</b> have been determined using both spectroscopic methods in solution and X-ray diffraction studies. Similarly to their gallium analogues, Me<sub>2</sub>In­(OCH­(Me)­CO<sub>2</sub>Me)­(NHC) complexes are highly active in the ring-opening polymerization of <i>rac</i>-lactide already at −20 °C, leading to isotactically enriched PLA (<i>P</i><sub>m</sub> = 0.67–0.76). However, in contrast to the gallium complexes Me<sub>2</sub>GaOR­(NHC), the noninnocent role of an NHC ligand, resulting in the formation of cyclic PLA, has been demonstrated for <b>6</b> and <b>7</b>

    The self-assembly switching of the group 13 tetrahedral Schiff base complexes by changing the character of coordination centre

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    The reaction of Et 3 B with one equivalent of N-substituted salicylideneimine (HsaldR 0 ) yields the monomeric O,N-chelate complexes Et 2 B(saldR 0 ), where R 0 ¼ Me (1) or Ph (2). The crystal structure of the resulting complexes has been determined by X-ray crystallography. The molecular structure of these complexes consists of monomeric four-coordinate chelates and their primary arrangement in the crystal structure is determined by the C-HÁ Á ÁO aryloxide hydrogen bonds. An extended crystal structure analysis reveals that the adjacent monomeric moieties of 1 are interconnected by C-H imino Á Á ÁO hydrogen bridges resulting in a 1-D motif infinite H-bonded chain, whereas the crystalline complex 2 comprises dimeric molecules linked through a pair of intermolecular C-H arom Á Á ÁO interactions. The supramolecular arrangement of both compounds is discussed with relation to the structure of analogous aluminium and gallium complexes, and the role played by the coordination centre on the molecular assembly is analyzed. It is shown that the steric congestion at the hydrogen bond donor and acceptor sites, as a result of changes in the N-alkyl substituents or the coordination centre environment, affect the strength of the intermolecular C-HÁ Á ÁO hydrogen bonds and may lead to the self-assembly switching of the bidentate Schiff base complexes

    Dialkylgallium Alkoxides Stabilized with <i>N</i>‑Heterocyclic Carbenes: Opportunities and Limitations for the Controlled and Stereoselective Polymerization of <i>rac</i>-Lactide

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    The structure of a series of Me<sub>2</sub>GaOR­(NHC) complexes with <i>N</i>-heterocyclic carbenes (1,3-bis­(2,4,6-trimethylphenyl)­imidazolin-2-ylidene (SIMes) and 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes)) have been characterized using spectroscopic and X-ray techniques and discussed in view of their reactivity in the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA). Both structure studies and density functional theory (DFT) calculations show the significant influence of NHC and OR on the structure of investigated complexes and has indicated that the Ga–C<sub>NHC</sub> bond (32.6–39.6 kcal mol<sup>–1</sup>) is strong enough to form stable Me<sub>2</sub>GaOR­(NHC) complexes in the form of monomeric species. The reactivity of Me<sub>2</sub>Ga­((<i>S</i>)-OCH­(Me)­CO<sub>2</sub>Me)­(SIMes) (<b>1</b>) and Me<sub>2</sub>Ga­((<i>S</i>)-OCH­(Me)­CO<sub>2</sub>Me)­(IMes) (<b>5</b>) toward Lewis acids such as CO<sub>2</sub> and GaMe<sub>3</sub> has resulted in breaking of the Ga–C<sub>NHC</sub> bond with the formation of (NHC)­CO<sub>2</sub> and Me<sub>3</sub>Ga­(NHC) (<b>8</b> and <b>10</b>) and [Me<sub>2</sub>Ga­(μ-(<i>S</i>)-OCH­(Me)­CO<sub>2</sub>Me)]<sub>2</sub>. Different results have been obtained for l,3-bis­(2,6-diisopropylphenyl)-imidazolin-2-ylidene (SIPr), which coordinates more weakly to gallium, as demonstrated by the Ga–C<sub>NHC</sub> bond strength for model Me<sub>3</sub>GaSIMes, Me<sub>3</sub>GaIMes (<b>8</b>), and Me<sub>3</sub>GaSIPr (<b>10</b>) adducts. The reaction of SIPr with [Me<sub>2</sub>Ga­(μ-OR)]<sub>2</sub> has not allowed for the breaking of Ga<sub>2</sub>O<sub>2</sub> bridges and the formation of monomeric Me<sub>2</sub>GaOR­(SIPr) complexes, contrary to SIMes and IMes. In the case of the reaction with [Me<sub>2</sub>Ga­(μ-(<i>S</i>)-OCH­(Me)­CO<sub>2</sub>Me)]<sub>2</sub>, the ionic compound [Me<sub>2</sub>Ga­(OCH­(Me)­CO<sub>2</sub>)]<sup>−</sup>[SIPrH]<sup>+</sup> (<b>9</b>) has been isolated. The investigated Me<sub>2</sub>GaOR­(NHC) complexes are highly active and stereoselective in the ring-opening polymerization of <i>rac</i>-lactide from −20 °C to room temperature, due to the insertion of <i>rac</i>-LA exclusively into the Ga–O<sub>alkoxide</sub> bond, leading to isotactically enriched polylactide (PLA) (<i>P</i><sub>m</sub> = 0.65–0.78). It has been shown that the polymerization of lactide at low temperature is influenced by the chelate interaction of (<i>S</i>)-OCH­(Me)­CO<sub>2</sub>Me or (OCH­(Me)­C­(O))<sub>2</sub>OR resulting from the primary insertion of <i>rac</i>-LA into the Ga–O<sub>alkoxide</sub> bond, with the Ga center, which can be responsible for the low control over the molecular weight of the obtained PLA. The latter effect can be eliminated by the initial synthesis of Me<sub>2</sub>Ga­((PLA)<sub><i>n</i></sub>OR)­(NHC) with short PLA chains, which allows for controlled polymerization. Although the adverse chelate effect can be also eliminated by the polymerization of <i>rac</i>-LA at room temperature, the stereoselectivity of <i>rac</i>-LA polymerization is strongly affected by transesterification reactions. Out of investigated Me<sub>2</sub>GaOR­(SIMes) and Me<sub>2</sub>GaOR­(IMes) complexes, only the latter allowed for the immortal ring opening polymerization of <i>rac</i>-LA in the presence of <sup><i>i</i></sup>PrOH

    Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure

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    Methods for the synthesis of dialkylgalium compounds with alkoxide or aryloxide ligands possessing N-heterocyclic carbene functionalities have been established. As a result, the synthesis of a series of dialkylgallium complexes Me<sub>2</sub>Ga­(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me<sub>2</sub>Ga­(O,C)·Me<sub>3</sub>Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic carbene functionality. All complexes have been fully characterized using spectroscopic and X-ray techniques. The presence of a strongly basic NHC functionality in alkoxide or aryloxide ligands resulted in the formation of monomeric Me<sub>2</sub>Ga­(O,C) species. The reaction of those complexes with the Lewis acid Me<sub>3</sub>Ga leads to Me<sub>2</sub>Ga­(O,C)·Me<sub>3</sub>Ga adducts (<b>2</b> and <b>6</b>) with a strong Me<sub>3</sub>Ga–O dative bond. The effect of (O,C) ligands with various steric and electronic properties on the structure of obtained Me<sub>2</sub>Ga­(O,C) and Me<sub>2</sub>Ga­(O,C)·Me<sub>3</sub>Ga has been discussed on the basis of spectroscopic data. Finally, the bond valence vector model has been used to estimate the effect of a chelating (O,C) ligand on strains in complexes <b>1</b>–<b>6</b> on the basis of X-ray data
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