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showing 10 items of 17345 documents
Effect of Guest Molecules on Spin Transition Temperature in Loaded Hofmann‐Like Clathrates with Improved Porosity
2020
The synthesis, crystal structure, magnetic and calorimetric studies of a new clathrate compound of the Hofmann-type spin crossover (SCO) metal-organic framework (MOF) {Fe(bpb)[MII(CN)4]}·xGuest (bpb = bis(4-pyridyl)butadiyne, and MII = Ni, Pt) with characteristic fsc topology is reported. The framework {Fe(bpb)[MII(CN)4]} can host up to 1.5 guest molecules of (trifluoromethyl)benzene and display complete one-step cooperative SCO behavior. Our systematic study on {Fe(bpb)[Pt(CN)4]}·xGuest shows a general reciprocal correlation between the SCO temperature with the volume of the guest molecules.
Theoretical Investigation of the Low-Energy States of CpMoCl(PMe 3 ) 2 and Their Role in the Spin-Forbidden Addition of N 2 and CO
2003
International audience; A recent computational investigation of Jahn−Teller effects in unsaturated 16-electron d4d6 [CpMLn] complexes (Abu-Hasanayn, F.; Cheong, P.; Oliff, M. Angew. Chem.2002, 41, 2120) highlighted the typical presence of two spin-triplet and two singlet states of competing stability in these complexes and pointed out the necessity to account for more than one electronic state in studies thereof. Consequently, we have reinvestigated the addition of N2 to all the four low-energy states of CpMoCl(PH3)2, a reaction for which previously only one singlet and one triplet state have been considered (Keogh, D. W.; Poli, R. J. Am. Chem. Soc.1997, 119, 2516). The present study was pe…
Copper(I)-catalysed regioselective synthesis of pyrazolo[5,1-c]-1,2,4-triazoles: A DFT mechanistic study
2017
Abstract Formation of pyrazolo[5,1-c]-1,2,4-triazoles by means of Cu(I)-catalysed [3+2] cycloaddition (32CA) reactions of C,N-cyclic azomethine imines with phenylacetylene, experimentally reported by Katritzky et al. (JOC 2012, 77, 5813), was studied using the density functional theory (DFT) method. Comparison with the uncatalysed 32CA reaction indicates that the Cu(I) catalyst provides new reaction pathways with lower electronic energy barriers in dichloromethane as solvent. The mechanism proposed by Katritzky for the Cu(I) catalysed reaction is compared with that proposed by Sharpless et al. (JACS 127, 2005, 210). The major difference between these two mechanisms lies in the coordination …
Oxoanion binding to a cyclic pseudopeptide containing 1,4-disubstituted 1,2,3-triazole moieties
2016
A macrocyclic pseudopeptide 3 is described featuring three amide groups and three 1,4-disubstituted 1,2,3-triazole units along the ring. This pseudopeptide was designed such that the amide NH groups and the triazole CH groups converge toward the cavity, thus creating an environment well suited for anion recognition. Conformational studies in solution combined with X-ray crystallography confirmed this preorganisation. Solubility of 3 restricted binding studies to organic media such as 5 vol% DMSO/acetone or DMSO/water mixtures with a water content up to 5 vol%. These binding studies demonstrated that 3 binds to a variety of inorganic anions in DMSO/acetone including chloride, nitrate, sulfat…
Regio- and Stereoselective Synthesis of 3-Pyrazolylidene-2-oxindole Compounds by Nucleophilic Vinylic Substitution of (E)-3-(Nitromethylene)indolin-2…
2019
[EN] A highly regio- and stereoselective synthesis of 3-alkylidene-2-oxindoles has been described through a nucleophilic vinylic substitution (SNV) of (E)-3-(nitromethylene)indolin-2-one using pyrazol-3-ones as nucleophiles and Et3N as a base. The reaction affords selectively the Z-isomer when pyrazol-3-ones without substituents at the 4 position are used. While the reaction is E-selective with 4- substituted pyrazolones. The stereoselectivity (up to >20:1) and the yields (up to 98%) are very high under mild reaction conditions.
Supramolecular open-framework architectures based on dicarboxylate H-bond acceptors and polytopic cations with three/four N–H+donor units
2015
International audience; Supramolecular assemblages based on anionic H-acceptors and cationic H-donors have been envisioned to elaborate open frameworks maintained by ionic H-bonds. Combinations of di-anionic chloranilate (CA2-), oxalate (Ox2-), or terephthalate (BDC2-) and trisimidazolium or tetrapyridinium derivatives (three and four N-H+ donors, respectively) yielded five architectures of formulae [(H3TrIB)(CA)1.5[middle dot]2DMF[middle dot]2.5H2O] (1), [(H4Tetrapy)(CA)2[middle dot]3DMF] (2), [(H3TrIB)(HOx)(Ox)[middle dot]5H2O] (3), [(H4Tetrapy)(Ox)2[middle dot]5H2O] (4), and [(H4Tetrapy)(BDC)2(H2O)[middle dot]1DMF[middle dot]3H2O] (5) (with TrIB = 1,3,5-trisimidazolylbenzene and Tetrapy …
Half-sandwich complexes of molybdenum-(III), -(IV) and -(V) with P–O and P–N bifunctional ligands Ph2PCH2X (X = 2-oxazolinyl, or C(O)NPh2)
2000
International audience; The reaction of the ligands Ph2PCH2X (X = 2-oxazolinyl, I; or C(O)NPh2, II) with the half-sandwich molybdenum(III) precursors [Mo(η-C5R5)(μ-Cl)2]2 (R = H or Me) has been investigated. Ligand I reacts with both complexes to form the corresponding adducts [Mo(η-C5R5)Cl2(Ph2PCH2C3H4NO)] (R = H, 1; or Me, 2). The reaction between I and [MoCp*Cl4] (Cp* = η-C5Me5) affords [MoCp*Cl4(Ph2PCH2C3H4NO-κ1P)] as a kinetic isomer, which then transforms quantitatively to [MoCp*Cl3(Ph2PCH2C3H4NO-κ2P,N)]+Cl−, 3. Ligand II reacts with [MoCp(μ-Cl)2]2 (Cp = η-C5H5) to afford the adduct [CpMoCl2{Ph2PCH2C(O)NPh2-κ2P,O}], 4, as an equilibrium mixture of two isomers. Longer reaction times in…
Probing the guest-binding preference of three structurally similar and conformationally adaptive macrocycles.
2019
A hybrid macrocycle was synthesized by combining the repeat units in oxatub[4]arene and zorb[4]arene, and its recognition behavior and conformational analysis were studied. Three structurally similar and conformationally adaptive macrocycles show different guest-binding selectivities and preferences even in a complex mixture containing three macrocycles and three guests.
Total Synthesis of Stemoamide, 9a-epi-Stemoamide, and 9a,10-epi-Stemoamide: Divergent Stereochemistry of the Final Methylation Steps
2020
Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.
Proline-Modified Porphyrin Catalysts for Enantioselective Epoxidations: Design, Synthesis, and Reactivity
2004
International audience; The syntheses of various strapped and −picket-fence× chiral porphyrins are described, and their reactivities towards the enantioselective epoxidation of alkenes are reported. Four L-proline residues provide the chiralityfor the various meso-substituted catalysts, which differ by either the spatial arrangement of the stereogenic centers or the nature and length of the straps. The resulting bridged structures possess four amide linkages ineach strap, leading to highly rigid molecules with well-defined geometries whereas the strapped Fe catalysts gave rise to only moderate enantioselectivities, the C2-symmetrical ones being superior to the D2-symmetrical compounds. The …