Cisoid Conformation Research Articles

Conformation-assisted solid-solid phase transition of LiTFSI electrolyte salt and the lithium ion coordination

Single crystal growth and characterization of the lithium bis(trifluoromethyl sulfonyl)imide (LiTFSI), the most common electrolyte salt for lithium-ion batteries, have been performed and succeeded in unraveling the atomic structures of its different crystalline phases. The structures of two crystalline phases (phase I: orthorhombic, Pccn; phase II: monoclinic, P21/c) have been determined through temperature-dependent X-ray crystallography of the LiTFSI single crystal on heating, and the solid-solid phase transformation between phase I and phase II has been dictated. Interestingly, a conformational change of TFSI⁻ from transoid to cisoid has been discovered during the transition from phase I to phase II, which has been further confirmed by the temperature-dependent Raman spectroscopy. The coordination of Li⁺ with the TFSI⁻ ions of different conformations has been also elucidated in the polymorphic crystalline structures. The solid-solid phase transformation of the first-order leads to the cracking of the LiTFSI crystal, probably along the lithium-ion or the fluorine-rich layer in phase II. In the molten state, the coexistence of the transoid conformation and the cisoid conformation is found in the TFSI⁻ ions, affirming the recent observation in the concentrated non-crystalline state. This work is anticipated to shed light on the (de)solvation and the transport of lithium ions in complex fluids encompassing LiTFSI electrolyte solutions from the structural aspects.

Formation of a Metallomacrocycle Possessing Nitrogen Donors Assembled in the Cavity and Unique Water Clusters.

2,2'-Bipyridyl (bpy) is widely used as a chelating unit for metal complexation but is not usually considered as a hydrogen-bonding unit. This is because the metal-free bpy units are usually in a transoid conformation, and the two nitrogen lone pairs are pointed to the opposite sides. We now report a metallomacrocycle whose three metal-free bpy units are in a cisoid conformation and are fixed in the cavity. The complexation of nickel(II) only at the salen units of the triangular bpytrisalen ligand produced this rigid and planar macrocycle. Its cavity is surrounded by hydrogen-bond acceptors (N of bpy and O of salen), and it was found that unique pentagonal prism clusters of water molecules templated by the cavity were formed in the crystal. This study has not only increased the variation of the synthetic methodologies of multinuclear complexes but has also provided the structural platform on which multiple bpy units exert hydrogen-bonding functions.

Crystal structures and conformational effects in bis-fluorenyl based ligands and related ruthenium nitrosyl complexes

Four crystal structures (two ruthenium complexes and two ligands) are presented containing a bis-fluorene fragment on which alkyl chains (methyl and hexyl) are grafted. The possibility to get both cisoid and transoid conformations in the bis-fluorene units is discussed. A computational investigation using the density functional theory indicates a tendency for a gradual stabilization of the cisoid form, as the length of the chains increases. The effect of the conformation on the charge transfer electronic properties of bis-fluorene based materials is discussed computationally at one-photon absorption (OPA) level and tentatively at two-photon absorption (TPA) levels, but it is found to be modest.

New copper(I) complexes of bulky 5-substituted-2-iminopyrrolyl ligands as catalysts for azide-alkyne cycloaddition.

Five dinuclear copper(I) complexes of the type [Cu{κN,κN'-5-R-NC4H2-2-C(H)N(2,6-iPr2C6H3)}]2 (1a-e; R = 2,4,6-iPr3C6H2 (a), R = 2,6-Me2C6H3 (b), R = 3,5-(CF3)2C6H3 (c), R = 2,6-(OMe)2C6H2 (d), R = CPh3 (e)) were prepared by the reaction of the respective 5-R-2-iminopyrrolyl potassium salts KLa-e and [Cu(NCMe)4]BF4 in moderate yields. These new copper(I) complexes were characterized by NMR spectroscopy, elemental analysis and, in selected cases, by single crystal X-ray diffraction and their structural and electronic features further analyzed by DFT calculations and cyclic voltammetry, respectively. X-ray diffraction studies reveal dimeric Cu structures assembled by 2-iminopyrrolyl bridging ligands adopting a transoid conformation (complexes 1a and 1d), while complexes 1c and 1e displayed a cisoid conformation of those moieties, with respect to the Cu(I) centers. Additionally, VT-1H NMR and 1H-1H NOESY NMR experiments on complexes 1a-e exhibited complex fluxional processes in solution, assigned to a conformational inversion of the respective Cu2N4C4 metallacycles in all complexes but 1c, accompanied by a cisoid-transoid isomerization in the cases of complexes 1d,e. The Cu(I) complexes were also analyzed by cyclic voltammetry, where all complexes exhibit two oxidation processes, where the first oxidation is reversible, with the exception of 1b and 1c, which also show the highest oxidation potentials. The oxidation potentials follow clear trends related to the structural parameters of the complexes, in particular the Cu⋯Cu distance and the Cu2N4C4 macrocycles torsion angles. All new 5-substituted-2-iminopyrrolyl Cu(I) complexes 1a-e served as catalysts for azide-alkyne cycloaddition (CuAAC) reactions, being able to generate the respective 1,2,3-triazole products in yields as high as 82% and turnover frequencies (TOFs) as high as 859 h-1, after optimizing the conditions. The activity, as measured by the TOF, is in accordance with the oxidation potential of the corresponding complexes, the easier the oxidation, the higher the TOF value. Complex 1-H, where R = H, proved to be a poor catalyst for the same reactions, indicating that the 5-substitution in the ligand framework is crucial in stabilizing any potential catalytic species.

Reactivity studies of cycloplatinated triarylguanidinato complexes, [Pt(TAG-κC,κN)(X)(S(O)Me2)] (X = Cl and OC(O)CF3) towards Lewis bases, and structural aspects of the products⊕

Reactions of six-membered cycloplatinated 2-anisyl- and 2-tolyl-guanidinato complexes, cis-[Pt(TAG-κC,κN)(X)(S(O)Me2)] (X = Cl (1) and OC(O)CF3 (2)) with two equiv of 3,5-dimethylpyrazole (3,5-dmpzH) and 3,5-diphenylpyrazole (3,5-dppzH) afforded the corresponding platinacycles, cis-[Pt(TAG-κC,κN)(PzH)2]X (3 − 5) in ≥ 69% yields. The reactions of 1 with one equiv of 3,5-dmpzH and 3,5-dppzH in the presence of excess of Et3N afforded [Pt(TAG-κC,κN)(μ-Pz)]2 (6 and 7) in 71% and 73% yields, respectively. Reactions of 1 with one equiv of 3,5-lutidine and 2,6-xylylisocyanide, L afforded cis-[Pt(TAG-κC,κN)Cl(L)] (8 and 9) in 84% and 75% yields, respectively. Reactions of 1 and 2 with two equiv of 2,6-xylylisocyanide, L in the presence of one equiv of AgBF4 afforded the corresponding cationic complexes [Pt(TAG-κC,κN)(L)2]BF4 (10 and 11) in 81% and 77% yields, respectively. The new complexes were characterised by elemental analyses, IR, multinuclear NMR spectroscopies while for 5, 10 and 11, 195Pt NMR spectroscopic data are also reported. Molecular structures of 3, 4⋅3 toluene, 5, 6, 7⋅0.5 n-hexane and 10 were determined by single crystal X-ray diffraction. Platinacycles 3 and 4⋅3 toluene revealed an α-out conformation while 5 revealed a β-out conformation. Further, 6 and 7⋅0.5 n-hexane revealed transoid in-in and cisoid in-out conformations, respectively.

Synthesis and Single Crystal X-ray Studies of Dimesityl Ditelluride: [2,4,6-Me3C6H2Te

The reaction of freshly prepared mesityl magnesium bromide with tellurium powder in anhydrous THF provided the dimesityl ditelluride: [2,4,6-Me3C6H2Te]2. A suitable needle-shaped crystal of dimesityl ditelluride was developed by evaporation of a solution in chloroform. The Te compound was developed with the orthorhombic space group Iba2 with a = 15.2916(7) Å, b = 15.7225(7) Å, c = 14.5272(7) Å and α,□β,□γ = 90°. The geometry about the central tellurium atoms adopt a bent-shaped geometry with torsion angle C10–Te2–Tel–C1 = 87.0(3)°□ and this may be considered a cisoid conformation. Intermolecular C–H….Te interactions give rise to a two-dimensional supramolecular synthons in its crystalline state. The crystal packing diagram shows Te….H [Te1….H5A, 3.2557(5) Å & Te1….H8C, 3.2578(5) Å] hydrogen-bonding interactions which are responsible for associative forces.

Isolation, characterization and semi-synthesis of natural products dimeric amide alkaloids

Isolation, characterization and semi-synthesis of natural products dimeric amide alkaloids

Bis(dicarbollide) Complexes of Transition Metals as a Platform for Molecular Switches. Study of Complexation of 8,8'-Bis(methylsulfanyl) Derivatives of Cobalt and Iron Bis(dicarbollides).

Complexation of the 8,8′-bis(methylsulfanyl) derivatives of cobalt and iron bis(dicarbollides) [8,8′-(MeS)2-3,3′-M(1,2-C2B9H10)2]− (M = Co, Fe) with copper, silver, palladium and rhodium leads to the formation of the corresponding chelate complexes, which is accompanied by a transition from the transoid to the cisoid conformation of the bis(dicarbollide) complex. This transition is reversible and can be used in design of coordination-driven molecular switches based on transition metal bis(dicarbollide) complexes. The solid-state structures of {(Ph3P)ClPd[8,8′- (MeS)2-3,3′-Co(1,2-C2B9H10)2-κ2-S,S′]} and {(COD)Rh[8,8′-(MeS)2-3,3′-Co(1,2-C2B9H10)2-κ2-S,S′]} were determined by single crystal X-ray diffraction.

Conformation and Aromaticity Switching in a Curved Non-Alternant sp2 Carbon Scaffold.

A curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd‐catalyzed [5+2] annulation from a 3,9‐diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly‐like motion. Stepwise oxidation produced radical cation 1 .+ and dication 1 2+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π‐overlap between the enantiomers. For the radical cation 1 .+, a less curved cisoid conformation is observed with a π‐dimer‐type arrangement. 1 2+ adopts a more planar structure with transoid conformation and slip‐stacked π‐overlap with closest neighbors. We also observed an intermolecular mixed‐valence complex of 1⋅(1 .+)3 that has a huge trigonal unit cell [(1)72(SbF6)54⋅(hexane)101] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

Conformation and Aromaticity Switching in a Curved Non‐Alternant sp2 Carbon Scaffold

AbstractA curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd‐catalyzed [5+2] annulation from a 3,9‐diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly‐like motion. Stepwise oxidation produced radical cation 1.+ and dication 12+. In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π‐overlap between the enantiomers. For the radical cation 1.+, a less curved cisoid conformation is observed with a π‐dimer‐type arrangement. 12+ adopts a more planar structure with transoid conformation and slip‐stacked π‐overlap with closest neighbors. We also observed an intermolecular mixed‐valence complex of 1⋅(1.+)3 that has a huge trigonal unit cell [(1)72(SbF6)54⋅(hexane)101] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

Transoid and cisoid Conformations in Silver-Mediated Cytosine Base Pairs: Hydrogen Bonding Dictates Argentophilic Interactions in the Solid State.

We have synthesized and structurally characterized examples of the well-known silver-mediated DNA base pair in its simplest possible form, as [AgI-bis-(N3-cytosine)]+. The compounds show differences such as variable coordination geometry, conformation with cisoid and transoid arrangements, and, in one case, intramolecular base pairing. Collectively, these compounds represent three of five permutations of linear/bent coordination geometry and cisoid/transoid arrangement of the cytosine ligands and contain the global minimum conformation as determined by DFT calculations: bent-transoid. Furthermore, these compounds show no argentophilic intercomplex interactions in the solid state, in marked contrast to alkylated and nucleoside analogues, and so do not form the supramolecular 1D "metallo-DNA" duplex observed in those cases but instead form hydrogen-bonded sheets. This marked difference may be attributed, in part, to the additional hydrogen bond donor site at N1 of the nucleobase that ubiquitously participates in intermolecular interactions.

Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3‐Triazole‐based Liquid Crystal

AbstractThe 1,2,3‐triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials—though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3‐triazolyl linkages. The molecule assembles into a double‐stranded helical columnar LC structure (Colhel). The X‐ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non‐zero dipole moment. The helical columns in the Colhel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105–115 °C in the Colhel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field.

Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3-Triazole-based Liquid Crystal.

The 1,2,3-triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials-though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3-triazolyl linkages. The molecule assembles into a double-stranded helical columnar LC structure (Colhel ). The X-ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non-zero dipole moment. The helical columns in the Colhel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105-115 °C in the Colhel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field.

Ab Initio Force Fields for Organic Anions: Properties of [BMIM][TFSI], [BMIM][FSI], and [BMIM][OTf] Ionic Liquids.

Room-temperature ionic liquids (ILs) composed of organic anions bis(trifluoromethanesulfonyl)imide (TFSI), bis(fluorosulfonyl)imide (FSI), and trifluoromethanesulfonate (OTf) exhibit interesting physical properties and are important for many electrochemical applications. TFSI and FSI form "hydrophobic" ILs, immiscible with water but miscible with many organic solvents and polymers; for computer simulation studies, it is thus essential to develop force fields for these anions that are transferable among this wide variety of chemical environments. In this work, we develop entirely ab initio force fields for the TFSI, FSI, and OTf anions and predict the properties of corresponding 1-butyl-3-methylimidazolium ILs. We discuss important subtleties in the force field development related to accurately modeling conformational flexibility, that is, relaxed torsional profiles and intramolecular electrostatic interactions. The TFSI anions have notable conformational flexibility in the IL, and we predict approximately 70% cisoid and 20% transoid conformations, which is largely driven by cation/anion ion-pair interactions and is opposite to the trend expected from the anion ab initio potential energy surface. The favorable interactions between the cation and cisoid TFSI conformations result in a shoulder in the cation/anion radial distribution function at short distances, whereas interconversion between cisoid and transoid conformations occurs on a commensurate time scale as ion diffusion processes. In addition to this physical insight on anion effects, we expect that these force fields will have important applications for studying a variety of complex electrolyte systems.

A comparison of pseudoproline substitution effects on cyclisation yield in the total syntheses of segetalins B and G

AbstractThe total syntheses of the naturally occurring cyclic pentapeptides, segetalins B and G, using a traceless pseudoproline‐mediated cyclization reaction is reported. The incorporation of a cysteine‐derived gem‐dimethyl pseudoproline [Cys(ΨMe,MePro)] residue in the linear precursors to induce a cisoid amide bond prior to the head‐to‐tail cyclization resulted in improved cyclization yields in both cases. Cysteine‐derived pseudoproline residues lacking the gem‐dimethyl substituents [Cys(ΨH,HPro)] were not as effective at inducing cisoid conformations of the amide bonds and resulted in lower cyclization yields with a concomitant increase in the formation of cyclodimers. The Cys(ΨMe,MePro) containing cyclic peptides were subject to deprotection and desulfurization to give the alanine containing natural products in high overall yields. In contrast, deprotection of cyclic peptides containing Cys(ΨH,HPro) residues upon treatment with trifluoroacetic acid removed other side chain‐protecting groups but left the Cys(ΨH,HPro) residues intact.

(Indenyl)rhodacarboranes. Electronic versus steric effects on the conformation of cyclic ligands

(Indenyl)rhodacarboranes 1,2-R2-3-(η5-indenyl)-3,1,2-RhC2B9H9 (2a: R = H; 2b: R = Me) and 3-(η5-indenyl)-4-SMe-3,1,2-RhC2B9H10 (3) were synthesized by reactions of the iodide complex [(η5-indenyl)RhI2]n (1b) with Tl[Tl(η-7,8-R2-7,8-C2B9H9)] or Tl[9-SMe2-7,8-C2B9H10]. The formation of 3 is accompanied by monodemethylation of the SMe2 substituent. The structures of rhodacarboranes 2b, 3 and the half-sandwich complex (η5-indenyl)RhBr2(dmso) were determined by X-ray diffraction. Rhodacarborane 2b has the sterically unfavorable eclipsed cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged close to the carborane cage carbon atoms. The thermal stability of conformers for 2b was analyzed by the DFT calculations.

Photoluminescent properties of three lanthanide compounds of formulae LnCl3(diphenyl((5-phenyl-1H-pyrazol-3-yl)methyl)phosphine oxide)2, Ln = Sm, Eu and Tb: X-ray structural, emission and vibrational spectroscopies, DFT and thermogravimetric studies

Abstract The synthesis and properties of a new sensitizing bidentate ligand, diphenyl((5-phenyl-1H-pyrazol-3-yl)methyl)phosphine oxide, 2, capable of demonstrating the emissive properties of lanthanide elements, is described. Two ligands are attached to LnCl3 moieties, Ln = Sm, Eu and Tb, resulting in complexes of formulae LnCl3(2)2. These complexes were structurally characterized by single-crystal X-ray crystallography and have geometries that are pentagonal bipyramidal with the two bidentate ligands in a cisoid conformation on the equatorial plane and the three chloride ligands in a mer-configuration. The coordination bond distances decrease from Sm to Tb paralleling the decrease in lanthanide ionic radii. The photoluminescent properties of these complexes were examined and, one of them, TbCl3(2)2, was assessed a ΦF of ca. 1.00. DFT calculations were conducted to understand the mechanism of proton transfer in ligand 2 for a hydrogen atom hopping between nitrogen atoms on the pyrazolyl moiety and, to assess aspects of the coordination sphere of the lanthanide complexes.

Phase Transitions of the Ionic Liquid [C2C1im][NTf2] under High Pressure: A Synchrotron X-ray Diffraction and Raman Microscopy Study

The interplay between crystallization and glass transition in the archetypal ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C2C1im][NTf2], has been studied as a function of pressure up to ca. 12 GPa. Besides heterogeneous crystal nucleation, homogeneous nucleation in the sample inside the diamond anvil cell was also observed depending on compression/decompression rate. Amorphization of the crystal and glass formation under pressure has been followed by synchrotron X-ray diffraction. The characteristic Raman bands of the [NTf2]− anion provide a microscopic probe of the different phases. The crystalline phase is composed of the [NTf2]− cisoid conformer, but moisture implies formation of crystal with the transoid conformer. Raman spectra show that crystalline phases might become microscopically heterogeneous because of [NTf2]− conformational disorder. Raman mapping reveals the order–disorder evolution from crystal to glass. Crystals of [C2C1im][NTf2] formed under high pressure and room temperature are similar to previously reported low temperature and atmospheric pressure crystals. Thus, it is concluded that density is the main factor controlling crystallization and glass formation under high pressure of [NTf2]− based ionic liquids due to hindrance of efficient ion packing. The results highlight that ionic liquids are good models to understand fundamental questions related to the mechanism of crystallization and glass transition.

(Indenyl)iridacarborane (η5-indenyl)Ir(η-7,8-C2B9H11): synthesis, structure, and bonding

A reaction of iodide [(η5-indenyl)IrI2]n (1) with thallium dicarbollide Tl[Tl(η-7,8-C2B9H11)] leads to (indenyl)iridacarborane (η5-indenyl)Ir(η-7,8-C2B9H11) (2) in 32% yield. The X-ray diffraction study showed that in the structure of 2, the five-membered rings C5 and C2B3 have a cisoid conformation, in which the bridgehead carbon atoms of the indenyl ligand are arranged opposite to the carborane cage carbon atoms. The DFT calculations showed that the Ir—indenyl bond in compound 2 is weaker than the Ir—Cp bond in the complex (η-7,8-C2B9H11)IrCp.

Piperazine-Based N4-Type 16-Membered Macroheterocycles and Their Nickel(II) Complexes

Square-planar diamagnetic nickel(II) complexes 5a and 5b containing 16-membered diamino-diimino ligands were prepared from the corresponding open-chain complexes 2a and 2b via condensation with o-phthalic dialdehyde in methanol. The solid-state structure of the starting complex 2b revealed the cisoid conformation of aryl groups compared to the transoid one found in the case of 2a. At the same time, the cisoid conformation is not retained in acetone solution: rather, the tert-Bu-substituted complex 2b was fully transformed into the trans form whereas its analogue 2aexhibits both cis and transforms in acetone solution. The cisoid conformation was also observed for the cyclic structures 5a and 5b by X-ray analysis and VT NMR experiments. The borohydride reduction of 5a with subsequent cyanide-assisted removal of nickel led to a new 16-membered tetraazamacrocycle 6. Its X-ray structure showed a cisoid conformation supported by two intramolecular hydrogen bonds that was also sustained in solution. VT NMR experiments revealed the degenerative interconvertion of a macrocycle with activation energy ca. 41.9±0.8 kJ/mol.