Oligomerization of vinyl monomers 20. Carbon-13 NMR of oligomers of 2-vinylpyridine. Studies of labelled end groups

Oligomers of 2-vinylpyridine initiated with Li, Na, K, and Rb salts of ¹³C-labeled or-unlabeled 2-ethylpyridine and terminated with ¹³C-labeled or -unlabeled methyl iodide were separated by liquid chromatography and analyzed by ¹³C-NMR of the initial or terminal CH₃ group. The stereochemistry of the three dyads which flank the initial or terminal methyl group could be determined and this allowed us to evaluate the stereochemistry of both methylation and vinyl addition. The methylation of the Li and Na salts of the oligomer anions is highly (> 95%) stereoselective and independent of chain length, whereas the stereoselectivity of the K and Rb salts is substantially less. These data indicate that the Li and Na oligomer and polymer anions exist in a chelated form in which the metal ion is complexed with the penultimate 2-pyridine group, the other counterions being chelated to a lesser extent. The stereochemistry of monomer addition was found to be less stereoselective than that of methylation for the Li and Na salts. In addition, the apparent meso-stereoselectivity of monomer addition of the Na, K, and Rb systems was greater than that of the Li ion. For the latter system, in particular, the mechanism appeared to be Markoff-like and consistent with different reactivities of anions flanked by a distinct dyad or triad stereochemistry. These data appear to be consistent with the intramolecular coordination that tends to hold the third asymmetric center close to the propagating carbanion.     

Oligomerization of vinyl monomers 18. Stereochemistry of anionic oligomerization of 4-vinylpyridine

Oligomers of 4-vinylpyridine were prepared by reaction in vacuo of 4-vinylpyridine with lithio-4-ethylpyridine at ?78°C, followed by reaction with CH₃I(¹³CH₃I) or CH₃OH. The stereochemistry was studied by NMR and GC. Methylation and the addition of 4-vinylpyridine occurred in a stereochemically nonselective manner. The data also indicated that in contrast to the oligomerization of 2-vinylpyridine the stereoisomeric meso and racemic 4-pyridyl carbanions propagated with equal reaction rates. The stereochemistry was readily explained by an absence of coordination of the Li ion by the nitrogen of the penultimate pyridine ring observed in the corresponding oligomerization of 2-vinylpyridine.     

Structures and Reactivities of Cocrystals Involving Diboronic Acids and Bipyridines: In Situ Linker Reaction and 1D-to-2D Dimensionality Change via Crystal-to-Crystal Photodimerization

Cocrystallizations of diboronic acids [1,3-benzenediboronic acid (1,3-bdba), 1,4-benzenediboronic acid (1,4-bdba) and 4,4’-biphenyldiboronic acid (4,4’-bphdba)] and bipyridines [1,2-bis(4-pyridyl)ethylene (bpe) and 1,2-bis(4-pyridyl)ethane (bpeta)] generated the hydrogen-bonded 1 : 2 cocrystals [(1,4-bdba)(bpe)₂] (1), [(1,4-bdba)(bpeta)₂] (2), [(1,3-bdba)(bpe)₂(H₂O)₂] (3) and [(1,3-bdba)(bpeta)₂(H₂O)] (4), wherein 1,3-bdba involved hydrated assemblies. The linear extended 4,4’-bphdba exhibited the formation of 1 : 1 cocrystals [(4,4'-bphdba)(bpe)] (5) and [(4,4'-bphdba-me)(bpeta)] (6). For 6, a hemiester was generated by an in-situ linker transformation. Single-crystal X-ray diffraction revealed all structures to be sustained by B(O)−H⋅⋅⋅N, B(O)−H⋅⋅⋅O, O_w−H⋅⋅⋅O, O_w−H⋅⋅⋅N, C−H⋅⋅⋅O, C−H⋅⋅⋅N, π⋅⋅⋅π, and C−H⋅⋅⋅π interactions. The cocrystals comprise 1D, 2D, and 3D hydrogen-bonded frameworks with components that display reactivities upon cocrystal formation and within the solids. In 1 and 3, the C=C bonds of the bpe molecules undergo a [2+2] photodimerization. UV radiation of each compound resulted in quantitative conversion of bpe into cyclobutane tpcb. The reactivity involving 1 occurred via 1D-to-2D single-crystal-to-single-crystal (SCSC) transformation. Our work supports the feasibility of the diboronic acids as formidable structural and reactivity building blocks for cocrystal construction.     

Bipolar Polymeric Protective Layer for Dendrite-Free and Corrosion-Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte

The unstable interface between Li metal and ethylene carbonate (EC)-based electrolytes triggers continuous side reactions and uncontrolled dendrite growth, significantly impacting the lifespan of Li metal batteries (LMBs). Herein, a bipolar polymeric protective layer (BPPL) is developed using cyanoethyl (−CH₂CH₂C≡N) and hydroxyl (−OH) polar groups, aiming to prevent EC-induced corrosion and facilitating rapid, uniform Li⁺ ion transport. Hydrogen-bonding interactions between −OH and EC facilitates the Li⁺ desolvation process and effectively traps free EC molecules, thereby eliminating parasitic reactions. Meanwhile, the −CH₂CH₂C≡N group anchors TFSI⁻ anions through ion-dipole interactions, enhancing Li⁺ transport and eliminating concentration polarization, ultimately suppressing the growth of Li dendrite. This BPPL enabling Li|Li cell stable cycling over 750 cycles at 10 mA cm⁻² for 2 mAh cm⁻². The Li|LiNi_0.8Mn_0.1Co_0.1O₂ and Li|LiFePO₄ full cells display superior electrochemical performance. The BPPL provides a practical strategy to enhanced stability and performance in LMBs application.     

Dramatic effects of the electrolyte cation on the selectivity of electroreductive cycloaddition reactions of bis(enones)

The nature of the electrolyte cation (Li, Na, K, Ag, Mg, Ba) exerts a dramatic effect upon the diastereoselectivity of the intramolecular cyclobutanation reactions of several bis(enones). The formation of cis as against trans cyclobutanes is strongly favored by magnesium ions, presumably via a chelation effect, and becomes exclusive in the case of barium. The latter ion has the additional surprising effect of enhancing the amount of Diels-Alder cycloaddition as opposed to cyclobutanation.     

Theoretical and experimental study on metal(II) halide complexes of 1,3-bis(4-pyridyl)propane

We report the results of detailed experimental and theoretical studies on the molecular structure and vibrational spectra of metal(II) halide complexes of 1,3-bis(4-pyridyl)propane [M(N₂C₁₃H₁₄)X₂, where M represents Zn or Hg, and X represents Cl, Br, or I]. The FT–infrared spectra (FT-IR) and FT-Raman spectra of the metal complexes of the 1,3-bis(4-pyridyl)propane molecule in the powder form were recorded between the 400–4000 and 5–3500 cm^?1 regions, respectively. The molecular geometry and vibrational frequencies of the metal complexes of 1,3-bis(4-pyridyl)propane in the ground state were calculated using density functional theory (B3LYP functional) with LANL2DZ and SDD as basis sets. The total energy distributions (TED) among the symmetry coordinates of the normal modes were computed for the low-energy structure of the molecules. Complete vibrational assignments based on the calculated TED values are given.     

Metal derivatives of 1,3-bis(2-pyridyl)-1,3-propanedione and N,N′-dimethyl-1,3-bis(2-pyridyl)-1,3-propanedione

Complexes of transition metal ions with the oxygen-nitrogen containing ligand 1,3-bis(2-pyridyl)-1,3-propanedione (bpypH) have been synthesized. These present stoichiometries which do not conform with the usual tendency manifested by β-diketones, since molecular formulas with the composition M(bpyp)X are found. A nitrogen methylated ligand N,N′-dimethyl-1,3-bis(2-pyridyl)-1,3-propanedione methyl sulphate [dimebpypH] (MeSO₄)₂ has also been synthesized and its complexes with transition metal ions studied. The stoichiometries now, resemble those of typical β-diketones, namely [dimepyp]₂MX₄ with four anions because of the dicationic nature of the original ligand. This, together with IR evidence suggests a dual type of coordination by bpip via the β-diketone and the pyridyl moieties.     

Controlling Topology within Halogen-Bonded Networks by Varying the Regiochemistry of the Cyclobutane-Based Nodes

The formation of a pair of extended networks sustained by halogen bonds based upon two regioisomers of a photoproduct, namely rctt-1,3-bis(4-pyridyl)-2,4-bis(phenyl)cyclobutane (ht-PP) and rctt-1,2-bis(4-pyridyl)-3,4-bis(phenyl)cyclobutane (hh-PP), that have varied topology is reported. These networks are held together via I⋯N halogen bonds between the photoproduct and the halogen-bond donor 1,4-diiodoperchlorobenzene (C₆I₂Cl₄). The observed topology in each solid is controlled by the regiochemical position of the halogen-bond accepting 4-pyridyl group. This paper demonstrates the ability to vary the topology of molecular networks by altering the position of the halogen bond acceptor within the cyclobutane-based node.     

Scandium-Mediated Formation of a Bis(tetrahydropentalene)

The reactivity of Li[Sc(COT′′)₂] ( 1 ; COT′′=1,4-bis(trimethylsilyl)cyclooctatetraenyl) towards CoCl₂ is considerably different from that of related lanthanide triple-decker sandwich complexes. In addition to the expected triple-decker complex Sc₂(COT′′)₃ ( 2 ), the complex Sc₂{μ-BTHP}(COT′′)₂ ( 3 ) is formed, which comprises the novel BTHP²⁻ ligand (BTHP²⁻=bis(3,5-bis(trimethylsilyl)-1,3a,6,6a-tetrahydropentalene-1-yl)diide or bis(2,7-bis(trimethylsilyl)bicyclo[3.3.0]octa-2,7-dien-4-yl)diide, C₁₆H₁₀(SiMe₃)₄²⁻). The formation of 3 is likely facilitated by the fact that scandium prefers η⁸,η³ coordination rather than highly symmetric η⁸,η⁸ coordination, and the η³-coordinated COT′′ ligand in 1 is activated owing to a loss of aromaticity. Acid hydrolysis of 3 leads to air-stable H₂BTHP ( 4 ).     

Ion equilibria in THF solutions of models of “living” methacrylonitrile oligomers with Li+ counterion

The electro-chemical characteristics of isobutyronitrile lithium (P₁Li) and 2-lithio-4-cyano-2,4-dimethylpentanenitrile (P₂Li) are studied. The dissociation constants K of P₁Li and P₂Li are of the order of 10^?11M and show that in THF mainly contact ion pairs exist. The lower value of K for P²Li is an indication for intramolecular complexation between the counterion and the cyano group, next to the active center. Both compounds tend to form ion triples. The results obtained show that in THF the nitrile group of the second monomer unit participates both in intra- and intermolecular interactions with the counterion.     

Hydroamination of 2-vinylpyridine,styrene, and isoprene with pyrrolidine catalyzed by alkali and alkaline-earth metal complexes

The complexes (dpp-bian)Mg(thf)₃, (dpp-bian)Ca(thf)₄ and (dpp-bian)Mg(pyr)₃ (dpp-bian is the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene dianion; pyr is the pyrrolidine) catalyze the addition of pyrrolidine to 2-vinylpyridine at room temperature. The compound (dppbian)Mg[N(SiMe₃)₂] containing a dpp-bian radical anion catalyzes the addition of pyrrolidine to styrene at 60 °C. The dpp-bian radical anion lithium-sodium salt [(dpp-bian)Li{N-(SiMe₃)₂}][Na(C₇H₈)] is an active catalyst of the addition of pyrrolidine to styrene and isoprene at 60 °C. In all the case, the content of the catalyst was from 1 to 2 mol.%. For styrene and 2-vinylpyridine, the reactions proceeded with the formation of anti-Markovnikov addition product, while 1,4-addition product was obtained in the case of isoprene.     

Unique Octupolar 2D-Polymer Frameworks as Mixed Conductors and Metal-Free Catalysts for Dual-Promoted Li and S Electrochemistry: Multi-regulation Role of Ethoxylation Chemistry

Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li⁺ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li−S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li−S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm⁻² at high sulfur loading of 8.7 mg cm⁻². Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored −CN/C−O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li₂S conversion.     

Molecular Engineering on Solvation Structure of Carbonate Electrolyte toward Durable Sodium Metal Battery at −40 °C

Carbonate electrolytes have excellent chemical stability and high salt solubility, which are ideally practical choice for achieving high-energy-density sodium (Na) metal battery at room temperature. However, their application at ultra-low temperature (−40 °C) is adversely affected by the instability of solid electrolyte interphase (SEI) formed by electrolyte decomposition and the difficulty of desolvation. Here, we designed a novel low-temperature carbonate electrolyte by molecular engineering on solvation structure. The calculations and experimental results demonstrate that ethylene sulfate (ES) reduces the sodium ion desolvation energy and promotes the forming of more inorganic substances on the Na surface, which promote ion migration and inhibit dendrite growth. At −40 °C, the Na||Na symmetric battery exhibits a stable cycle of 1500 hours, and the Na||Na₃V₂(PO₄)₃ (NVP) battery achieves 88.2 % capacity retention after 200 cycles.     

Sodium‐ and Potassium‐Hydrate Melts Containing Asymmetric Imide Anions for High‐Voltage Aqueous Batteries

Aqueous Na‐ or K‐ion batteries could virtually eliminate the safety and cost concerns raised from Li‐ion batteries, but their widespread applications have generally suffered from narrow electrochemical potential window (ca. 1.23 V) of aqueous electrolytes that leads to low energy density. Herein, by exploring optimized eutectic systems of Na and K salts with asymmetric imide anions, we discovered, for the first time, room‐temperature hydrate melts for Na and K systems, which are the second and third alkali metal hydrate melts reported since the first discovery of Li hydrate melt by our group in 2016. The newly discovered Na‐ and K‐ hydrate melts could significantly extend the potential window up to 2.7 and 2.5 V (at Pt electrode), respectively, owing to the merit that almost all water molecules participate in the Na⁺ or K⁺ hydration shells. As a proof‐of‐concept, a prototype Na₃V₂(PO₄)₂F₃|NaTi₂(PO₄)₃ aqueous Na‐ion full‐cell with the Na‐hydrate‐melt electrolyte delivers an average discharge voltage of 1.75 V, that is among the highest value ever reported for all aqueous Na‐ion batteries.     

Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B−B Bond

Deprotonation of the doubly arylene-bridged diborane(6) derivative 1 H₂ with (Me₃Si)₃CLi or (Me₃Si)₂NK gives the B−B σ-bonded species M[ 1 H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4′-di-tert-butyl-2,2′-biphenylylene). With nBuLi as the base, the yield of Li[ 1 H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[ 2 H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[ 2 H] are linked by a μ-H bridge. In the closely related molecule Li[ 3 H], the corresponding μ-H atom can be abstracted with (Me₃Si)₃CLi to afford the B−B-bonded conjugated base Li₂[ 3 ] (THF, 150 °C; 15 %). Li[ 1 H] and Li[ 2 H] were characterized by NMR spectroscopy and X-ray crystallography.     

Coordination polymers derived from gallium and zinc metal–metal bonded species

The reaction of (dpp-bian)Ga–Zn(dpp-bian) (dpp-bian is 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with 1,3-di(4-pyridyl)propane results in 1D coordination polymer [(dpp-bian)Ga–Zn(dpp-bian)(μ²-1,3-Py₂(CH₂)₃)]_n with the retained Ga–Zn bond. In contrast, the coordination of 1,3-di(4-pyridyl)propane to Zn atoms in the (dpp-bian)Zn–Zn(dpp-bian) complex induces the cleavage of the Zn–Zn bond which is accompanied by reduction of dpp-bian radical anions to dianions. The reaction product represents 1D coordination polymer [{(dpp-bian)Zn}(μ²-1,3-Py₂(CH₂)₃)]_n.     

Synthesis and Structural Investigation of a Complete Series of Brightly Colored Alkali Metal 1,3-Dimethylviolurates

A complete series of alkali metal 1,3-dimethylviolurates M(Me₂Vio) was synthesized and fully characterized. The title compounds M(Me₂Vio)(H₂O) [M = Li ( 3 ), Na ( 4 )], K(Me₂Vio)(H₂O)_0.5 ( 5 ) and M(Me₂Vio) [M = Rb ( 6 ), Cs ( 7 )] were prepared by neutralizing 1,3-dimethylvioluric acid (= HMe₂Vio; 2 ) with 1 equiv. of the corresponding metal hydroxides MOH. The resulting salts exhibit striking colors ranging from orange-red ( 3 ) through purple ( 4 , 5 ) to bright blue ( 6 , 7 ). In contrast to the monohydrate 4 , the classical synthesis of sodium 1,3-dimethylviolurate from 1,3-dimethylbarbituric acid and NaNO₂ afforded the purple trihydrate Na(Me₂Vio)(H₂O)₃ ( 4a ). All new compounds have been fully characterized by their IR and NMR (¹H, ¹³C) spectra as well as elemental analyses. X-ray crystal structure determination revealed that the title compounds exist as one- (Li, Na), two- (K, Cs), or three-dimensional (Rb) coordination polymers in the solid state.     

Metal complexes of C2-symmetric chiral bipyridine ligands. X-ray structure of [bis(nitrato)(4S,5S)-2,2-dimethyl-4,5-bis(2-pyridyl)-1,3-dioxolane cobalt(II)]

Chelating properties of C₂-symmetric chiral bipyridine ligands are discussed. In particular we report the syntheses of the cobalt(II), nickel(II), zinc(II) and copper(II) complexes of (4S,5S)-2,2-dimethyl-4,5-bis(2-pyridyl)-1,3-dioxolane. All compounds have been characterized by IR spectroscopy, and an X-ray diffraction analysis has been carried out on one of them: Co(L)(NO₃)₂. The ligand coordinates the cobalt atom by the two nitrogen donors N(1) and N(2). A seven-membered chelation ring is formed, presenting a remarkable non-crystallographic twofold pseudosymmetry around the axis connecting Co and the midpoint of the C(6)–C(7) bond. The metal also binds two monodentate nitrates, thus completing a distorted coordination tetrahedron.     

Mononuclear and one-dimensional manganese(II) complexes constructed by dithioethers: Effect of flexibility and positional isomerism

Interactions of dithioether ligands L², L⁴ and L⁵ (L² = 1,3-bis(4-(3-pyridyl) pyrimidin-2-ylthio) propane; L⁴ = 1,3-bis[4-(3-pyridyl) pyrimidinyl thiomethyl]benzene; L⁵ = 1,4-bis[4-(3-pyridyl)pyrimidinylthiomethyl] benzene) with Mn(II) ions and NH₄SCN in an analogous way led to the formation of two discrete mononuclear complexes and a one-dimensional chain, respectively, which may be attributed to the different flexibility and positional isomerism of the ligands.     

Theoretical and experimental studies of the diketene system: Product branching decomposition rate constants and energetics of isomers

The kinetics and mechanism for the thermal decomposition of diketene have been studied in the temperature range 510–603 K using highly diluted mixtures with Ar as a diluent. The concentrations of diketene, ketene, and CO₂ were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene (k₁) and CO₂ (k₂) have been determined and compared with the values predicted by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the branching reaction. The first-order rate constants, k₁ (s⁻¹) = 10^{15.74 ± 0.72} exp(−49.29 (kcal mol⁻¹) (±1.84)/RT) and k₂ (s⁻¹) = 10^{14.65 ± 0.87} exp(−49.01 (kcal mol⁻¹) (±2.22)/RT); the bulk of experimental data agree well with predicted results. The heats of formation of ketene, diketene, cyclobuta-1,3-dione, and cyclobuta-1,2-dione at 298 K computed from the G2M scheme are −11.1, −45.3, −43.6, and −40.3 kcal mol⁻¹, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 580–590, 2007