Naphthalenide Research Articles

Sodium naphthalenide reduction of 1,3–diphenyl–6–(tert-butyl) fulvene: Stabilizing Eu2+ with a sterically demanding ansa–ligand framework

Stereoselective syntheses of three new rac di–(tert–butyl)ethano bridged metallocene compounds of Yb, Eu and Sm were carried out by a unique strategy involving hydrocarbon radical anion coupling of a trisubstituted pentafulvene followed by incorporation of the metal by K+ salt metathesis reactions. Reductive coupling of 1,3–diphenyl–6–(tert-butyl) fulvene with sodium naphthalenide gave the corresponding bis(cyclopentadiene) ansa–ligand precursor rac–[(CHBut)2(Ph2C5H3)2] HL. Subsequent reaction of HL with KN(SiMe3)2 afforded the corresponding di–potassium salt complex [(CHBut)2(Ph2C5H2)2]K2(THF)31. Reactions of 1 with LnI2 (Ln = Yb, Eu, Sm) afforded new lanthanide ansa–metallocenes, [(CHBut)2(Ph2C5H2)]2Yb(DME) 2, [(CHBut)2(Ph2C5H2)]2Eu(DME)23 and [(CHBut)2(Ph2C5H2)]2Sm(DME)24 in good yields. The ansa–europocene 3 is the first example of a Eu2+ ion complexed by an ethano–bridged cyclopentadienyl ligand. This work underscores the usefulness of hydrocarbon radical anion coupling in the construction of sterically demanding Ph2Cp based ansa–ligand frameworks for d- and f-block metallocenes.

Triaminotriborane(3): A Homocatenated Boron Chain Connected by B-B Multiple Bonds.

A triaminotriborane(3) was isolated as purple crystals through the reduction of (TMP)BCl2 (TMP=2,2,6,6-tetramethylpiperidino) by sodium naphthalenide. Single-crystal X-ray diffraction and computational studies of the obtained triaminotriborane(3) revealed a bent structure of the [B(NR2 )]3 chain. The bond lengths between the central and terminal boron atoms were similar to those observed in neutral diborene species. The multiple-bonding character may be best described by a three-center two-electron π-bond along the B3 chain. The distance between the two terminal boron atoms (2.177 Å) in the solid-state structure implies a weak interaction between them. When an excess amount of Li was used as the reducing agent, the reaction yielded an unusual dianionic species. The isolation and characterization of these two reduction products are reported herein.

Polycarbynes: A new synthetic approach and application to the nucleation of CVD diamond

New methods have been developed for obtaining three preceramic polycarbyne-family polymers. Poly(hydridocarbyne) (PHC) and poly(phenylcarbyne) (PPC) have been synthesized via a mechanically activated reaction between magnesium metal and CRX3 (R=H, Ph; X=Br, Cl). Poly(naphthalene-co-hydridocarbyne) (PNHC) have been obtained by reacting CHBr3 with sodium naphthalide. The efficiencies of PHC, PPC, and PNHC as sources of diamond nuclei in the microwave plasma chemical vapor deposition of diamond films on silicon substrates have been compared. The highest efficiency has been demonstrated by PHC with a high molecular weight, for which the nucleation density has been estimated at ≥109 nuclei per square centimeter of the substrate surface.

Reductive dissolution of supergrowth carbon nanotubes for tougher nanocomposites by reactive coagulation spinning.

Long single-walled carbon nanotubes, with lengths >10 μm, can be spontaneously dissolved by stirring in a sodium naphthalide N,N-dimethylacetamide solution, yielding solutions of individualised nanotubide ions at concentrations up to 0.74 mg mL-1. This process was directly compared to ultrasonication and found to be less damaging while maintaining greater intrinsic length, with increased individualisation, yield, and concentration. Nanotubide solutions were spun into fibres using a new reactive coagulation process, which covalently grafts a poly(vinyl chloride) matrix to the nanotubes directly at the point of fibre formation. The grafting process insulated the nanotubes electrically, significantly enhancing the dielectric constant to 340% of the bulk polymer. For comparison, samples were prepared using both Supergrowth nanotubes and conventional shorter commercial single-walled carbon nanotubes. The resulting nanocomposites showed similar, high loadings (ca. 20 wt%), but the fibres formed with Supergrowth nanotubes showed significantly greater failure strain (up to ∼25%), and hence more than double the toughness (30.8 MJ m-3), compared to composites containing typical ∼1 μm SWCNTs.

Covalent Functionalization of Carbon Nanomaterials with Iodonium Salts

Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. Herein, we report an efficient method for the covalent functionalization of carbon nanotubes (CNTs) and graphite. This reaction involves the reduction of carbon nanomaterials with sodium naphthalide, followed by the addition of diaryliodonium salts. CNTs, including single-walled, double-walled, and multi-walled variants (SWCNTs, DWCNTs, and MWCNTs, respectively), as well as graphite, can be efficiently functionalized with substituted arene and heteroarene iodonium salts. The preferential transfer of phenyl groups containing electron-withdrawing groups was demonstrated by reactions with unsymmetrical iodonium salts. The lower reactivity of iodonium salts, relative to the more commonly used diazonium ions, presents opportunities for greater diversity in the selective functionalization of carbon nanomaterials.

Effect of Substituents and Initial Degree of Functionalization of Alkylated Single-Walled Carbon Nanotubes on Their Thermal Stability and Photoluminescence Properties.

Alkylated single-walled carbon nanotubes (SWNTs) have been thermally treated to determine the influence of substituents and the degree of functionalization on their thermal stability and photoluminescence (PL) properties. Alkylated SWNTs were prepared by treating SWNTs with sodium naphthalenide and alkyl bromide. The defunctionalization of the alkylated SWNTs was monitored by absorption and Raman spectra. Selective recovery of the characteristic absorption and radial breathing mode peaks was observed during the thermal treatment, which indicates that the thermal stability of the alkylated SWNTs decreases with increases in SWNT diameter and degree of functionalization. n-Butylated and phenethylated SWNTs showed higher thermal stability than sec-butylated and benzylated SWNTs for a similar degree of functionalization, respectively. The diameter selectivity and effect of substituents on the thermal elimination reaction were confirmed by density functional theory. In addition, it was shown that the initial degree of functionalization of the alkylated SWNTs, with the alkyl group and degree of functionalization being kept constant after thermal treatment, strongly affects their PL properties; Stokes shift, and PL peak intensity.

Wet Chemistry and Peptide Immobilization on Polytetrafluoroethylene for Improved Cell-adhesion.

Endowing materials surface with cell-adhesive properties is a common strategy in biomaterial research and tissue engineering. This is particularly interesting for already approved polymers that have a long standing use in medicine because these materials are well characterized and legal issues associated with the introduction of newly synthesized polymers may be avoided. Polytetrafluoroethylene (PTFE) is one of the most frequently employed materials for the manufacturing of vascular grafts but the polymer lacks cell adhesion promoting features. Endothelialization, i.e., complete coverage of the grafts inner surface with a confluent layer of endothelial cells is regarded key to optimal performance, mainly by reducing thrombogenicity of the artificial interface. This study investigates the growth of endothelial cells on peptide-modified PTFE and compares these results to those obtained on unmodified substrate. Coupling with the endothelial cell adhesive peptide Arg-Glu-Asp-Val (REDV) is performed via activation of the fluorin-containing polymer using the reagent sodium naphthalenide, followed by subsequent conjugation steps. Cell culture is accomplished using Human Umbilical Vein Endothelial Cells (HUVECs) and excellent cellular growth on peptide-immobilized material is demonstrated over a two-week period.

Systematic comparison of conventional and reductive single-walled carbon nanotube purifications

As-synthesised single-walled carbon nanotubes (SWCNTs) are often contaminated with amorphous carbon and residual catalyst particles. These contaminants have a detrimental effect on the effective mechanical and electronic properties, limiting their performance in many applications. A comparative series of SWCNT purifications including acid treatments, gas phase purifications and recently-developed reductive purifications have been conducted using a single commercial SWCNT type (Tuball™). Each of the purification procedures was selected for its potential scalability to bulk quantities and evaluated for the extent of impurity removal, SWCNT damage, and overall yield. Raman spectra confirmed that reductive purification using sodium naphthalide gave the lowest D/G ratio, suggesting that the sp2 carbon framework was most effectively preserved, whilst removing a large proportion (∼74%) of the metal impurities. Conversely, nitric acid treatment was most effective at removing virtually all the metal impurities, but the sp2 carbon framework was most heavily damaged in the process. The development of scalable, one pot, reductive separations provides a useful new approach to SWCNT purification.

Aromatic-Exfoliated Transition Metal Dichalcogenides: Implications for Inherent Electrochemistry and Hydrogen Evolution

In the face of rising energy demand and depleting energy resources, energy sustainability has proven to be a formidable environmental and economic challenge, and the search for environmentally friendly energy sources is exigent. To this end, much research has been focused on improving the efficiency of the hydrogen evolution reaction (HER), which generates hydrogen gas, a renewable source of energy carrier. To resolve the steep cost issue of employing Pt, transition metal dichalcogenides (TMDs) have been proposed as emerging HER electrocatalysts, among other electrochemical applications. As the exfoliated TMD exhibits properties distinct from the bulk material, it is prudent to investigate the exfoliation procedure with specific regard to the employed intercalant. Here, we prepared exfoliated MoS2, MoSe2, WS2, and WSe2 from their bulk counterparts using aromatic intercalants, i.e. phenyllithium, sodium naphthalenide, and sodium anthracenide, and characterized them using scanning electron microscopy (SEM),...

Zn0@ZnS Core‐Shell Nanoparticles via Oxidation of Intermediate Zn0 Nanoparticles

AbstractZn0@ZnS core‐shell nanoparticles were prepared via reduction of ZnCl2 to Zn0 nanoparticles and subsequent partial oxidation with elemental sulfur. The intermediate, highly reactive Zn0 nanoparticles were obtained by sodium naphthalenide ([NaNaph]) reduction of ZnCl2 in tetrahydrofuran (THF). After centrifugation, the Zn0 nanoparticles were redispersed in a solution of sulfur in toluene and oxidized by subsequent heating to reflux. According to electron microscopy (HRTEM, HAADF‐STEM), the Zn0@ZnS core‐shell nanoparticles exhibit a mean outer diameter of 12 ± 4 nm, consisting of an inner Zn0 core (8 nm in diameter) and a ZnS shell (2 nm in diameter). HRTEM and XRD confirm the crystallinity of both core and shell. The Zn0@ZnS nanostructure shows synergistic properties of core and shell: the ZnS layer efficiently passivates the reactive Zn0 metal core against oxidation, whereas the optical properties point to dominating metallic behavior of the Zn0 metal core despite of the ZnS shell.

ZnO hollow nanospheres via Laux-like oxidation of Zn0 nanoparticles

Zinc oxide hollow nanospheres were obtained via a Laux-like oxidation of zinc nanoparticles using nitrobenzene as oxidizing agent. The ZnO hollow nanospheres exhibit an outer diameter of 10.4 ± 1.3 nm and a well crystallized sphere wall with a thickness of 2.9 ± 0.4 nm. Laux-like oxidation and formation of the ZnO hollow nanospheres were performed instantaneously after sodium naphthalenide ([NaNaph]) driven reduction of ZnCl2 to Zn0 nanoparticles in the liquid phase without any separation of the intermediate Zn0 nanoparticles. The diameter of the resulting ZnO hollow nanospheres (10.4 ± 1.3 nm) reflects the diameter of the intermediate Zn0 nanoparticles (10.1 ± 2.3 nm). In accordance with the small diameter of the ZnO sphere wall, quantum-size effects occur with a band gap that is blue-shifted by 0.2 eV in comparison to bulk-ZnO.

Origin of exotic ferromagnetic behavior in exfoliated layered transition metal dichalcogenides MoS2 and WS2.

Bulk layered transition metal dichalcogenides (TMDs) show diamagnetic properties. When exfoliated, the materials' band gap increases and changes from an indirect band gap to a direct one. During the exfoliation, the TMDs may undergo a phase transition from 2H to 1T polymorph, which is likely electronically driven and accompanied by a metal-insulator transition. A significantly higher efficiency of the exfoliation was observed using sodium naphthalenide compared to butyllithium. Moreover we demonstrate that the exfoliation has a dramatic influence on the magnetic properties of two TMDs, MoS2 and WS2. These materials become partly ferromagnetic upon exfoliation, which is a highly unexpected behavior. Exotic ferromagnetism is generally observed on samples with a high degree of exfoliation, which indicates the association of this effect with defects formed on the edges of dichalcogenide sheets. Such an exotic ferromagnetic behavior, if properly understood and brought under material engineering control, shall open the door to new applications of these materials.

Thermodynamically Favorable Conversion of Hydrogen Sulfide into Valuable Products through Reaction with Sodium Naphthalenide.

Hydrogen sulfide (H2 S) is an extremely hazardous chemical waste that is generated at large scale in many industries; its abatement has long been an energy-extensive and cost-ineffective liability due to the thermodynamic limitations of the selected approaches and low value of the final products, sulfur and water. Here we introduce an attractive method for H2 S abatement that yields value-added products via a thermodynamically favorable process. Specifically, sodium naphthalenide (Na-NAP) is used to capture H2 S to produce anhydrous Na2 S nanocrystals and 1,4-dihydronaphthalene, which are important materials for batteries and liquid fuels, respectively. This multipurpose process is driven by the acid/base neutralization reaction between hydrogen cations from H2 S and radical anions from naphthalenide. It is spontaneous and irreversible at ambient temperature and pressure, proceeding to completion very rapidly.

Sodium-Naphthalenide-Driven Synthesis of Base-Metal Nanoparticles and Follow-up Reactions.

Mo(0), W(0), Fe(0), Ru(0), Re(0), and Zn(0) nanoparticles—essentially base metals—are prepared as a general strategy by a sodium naphthalenide ([NaNaph])-driven reduction of simple metal chlorides in ethers (1,2-dimethoxyethane (DME), tetrahydrofuran (THF)). All the nanoparticles have diameters ≤10 nm, and they can be obtained either as powder samples or long-term stable suspensions. Direct follow-up reactions (e.g., Mo(0)+S8, FeCl3+AsCl3, ReCl5+MoCl5), moreover, allow the preparation of MoS2, FeAs2, or Re4Mo nanoparticles of similar size as the pristine metals (≤10 nm).

Sodium‐Naphthalenide‐Driven Synthesis of Base‐Metal Nanoparticles and Follow‐up Reactions

AbstractMo0, W0, Fe0, Ru0, Re0, and Zn0 nanoparticles—essentially base metals—are prepared as a general strategy by a sodium naphthalenide ([NaNaph])‐driven reduction of simple metal chlorides in ethers (1,2‐dimethoxyethane (DME), tetrahydrofuran (THF)). All the nanoparticles have diameters ≤10 nm, and they can be obtained either as powder samples or long‐term stable suspensions. Direct follow‐up reactions (e.g., Mo0+S8, FeCl3+AsCl3, ReCl5+MoCl5), moreover, allow the preparation of MoS2, FeAs2, or Re4Mo nanoparticles of similar size as the pristine metals (≤10 nm).

Sequential structural and optical evolution of MoS2 by chemical synthesis and exfoliation

Various types of MoS2 structures are successfully obtained by using economical and facile sequential synthesis and exfoliation methods. Spherically-shaped lumps of multilayer (ML) MoS2 are prepared by using a conventional hydrothermal method and were subsequently 1st-exfoliated in hydrazine while being kept in autoclave to be unrolled and separated into five-to-six-layer MoS2 pieces of several-hundred nm in size. The MoS2 MLs are 2nd-exfoliated in sodium naphthalenide under an Ar ambient to finally produce bilayer MoS2 crystals of ~100 nm. The sequential exfoliation processes downsize MoS2 laterally and reduce its number of layers. The three types of MoS2 allotropes exhibit particular optical properties corresponding to their structural differences. These results suggest that two-dimensional MoS2 crystals can be prepared by employing only chemical techniques without starting from high-pressure-synthesized bulk MoS2 crystals.

Prediction of Boron-Boron Triple-Bond Polymers Stabilized by Janus-Type Bis(N-heterocyclic) Carbenes.

A class of polymeric compounds containing boron-boron triple bonds stabilized by N-heterocyclic biscarbenes is proposed. Since a triply bonded B2 is related to its third excited state, the predicted macromolecule would be composed by several units of an electronically excited first-row homonuclear dimer. Moreover, it is shown that the replacement of biscarbene with N2 or CO as spacers could change the bonding profile of the boron-boron units to a cumulene-like structure. Based on these results, different types of diboryne polymers are proposed, which could lead to an unprecedented set of boron materials with distinct physical properties. The novel diboryne macromolecules could be synthesized by the reaction of Janus-type biscarbenes with tetrabromodiborane, B2 Br4 , and sodium naphthalenide, [Na(C10 H8 )], similarly to Braunschweig's work on the room temperature stable boron-boron triple bond compounds (Science, 2012, 336, 1420).

Diborabutatriene: an electron-deficient cumulene.

The complexation of two equivalents of a cyclic (alkyl)(amino)carbene (CAAC) to tetrabromodiborane, followed by reduction with four equivalents of sodium naphthalide, led to the formation of the CAAC-stabilized linear diboracumulene (CAAC)2B2. The capacity of the CAAC ligand to facilitate B2 →CAAC donation of π-electron density resulted in important differences between this species and a previously reported complex featuring a B≡B triple bond stabilized by cyclic di(amino)carbenes, including a longer B-B bond and shorter B-C bonds. Frontier orbital analysis indicated sharing of valence electrons across the entire linear C-B-B-C unit in (CAAC)2B2, which is supported by natural population analysis and cyclic voltammetry.

The Stannylphosphide Anion Reagent Sodium Bis(triphenylstannyl) Phosphide: Synthesis, Structural Characterization, and Reactions with Indium, Tin, and Gold Electrophiles

Treatment of P4with in situ generated [Na][SnPh3] leads to the formation of the sodium monophosphide [Na][P(SnPh3)2] and the Zintl salt [Na]3[P7]. The former was isolated in 46% yield as the crystalline salt [Na(benzo-15-crown-5)][P(SnPh3)2] and used to prepare the homoleptic phosphine P(SnPh3)3, isolated in 67% yield, as well as the indium derivative (XL)2InP(SnPh3)2 (XL = S(CH2)2NMe2), isolated in 84% yield, and the gold complex (Ph3P)AuP(SnPh3)2. The compounds [Na(benzo-15-crown-5)][P(SnPh3)2], P(SnPh3)3, (XL)2InP(SnPh3)2, and (Ph3P)AuP(SnPh3)2 were characterized using multinuclear NMR spectroscopy and X-ray crystallography. The bonding in (Ph3P)AuP(SnPh3)2 was dissected using natural bond orbital (NBO) methods, in response to the observation from the X-ray crystal structure that the dative P:→Au bond is slightly shorter than the shared electron-pair P-Au bond. The bonding in (XL)2InP(SnPh3)2 was also interrogated using (31)P and (13)C solid-state NMR and computational methods. Co-product [Na]3[P7] was isolated in 57% yield as the stannyl heptaphosphide P7(SnPh3)3, following salt metathesis with ClSnPh3. Additionally, we report that treatment of P4 with sodium naphthalenide in dimethoxyethane at 22 °C is a convenient and selective method for the independent synthesis of Zintl ion [Na]3[P7]. The latter was isolated as the silylated heptaphosphide P7(SiMe3)3, in 67% yield, or as the stannyl heptaphosphide P7(SnPh3)3 in 65% yield by salt metathesis with ClSiMe3 or ClSnPh3, respectively.

Reversible Switching of Coordination Mode of ansa bis(Amidinate) Ligand in Ytterbium Complexes Driven by Oxidation State of the Metal Atom

Reaction of bisamidine C6H4-1,2-{NC(t-Bu)NH(2,6-Me2C6H3)}2 (1) and [(Me3Si)2N]2Yb(THF)2 (THF = tetrahydrofuran) (toluene; room temperature) in a 1:1 molar ratio afforded a bis(amidinate) Yb(II) complex [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]Yb(THF) (2) in 65% yield. Complex 2 features unusual κ(1)amide, η(6)-arene coordination of both amidinate fragments to the ytterbium ion, resulting in the formation of a bent bis(arene) structure. Oxidation of 2 by Ph3SnCl (1:1 molar ratio) or (PhCH2S)2 (1:0.5) leads to the Yb(III) species [C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]YbCl(1,2-dimethoxyethane) (3) and {[C6H4-1,2-{NC(t-Bu)N(2,6-Me2C6H3)}2]Yb(μ-SCH2Ph)}2 (4), performing "classic" κ(2)N,N'-chelating coordination mode of ansa bis(amidinate) ligand. By the reduction of 3 with equimolar amount of sodium naphthalide [C10H8(•-)][Na(+)] in THF, complex 2 can be recovered and restored to a bent bis(arene) structure. Complex 3 was also synthesized by the salt metathesis reaction of equimolar amounts of YbCl3 and the dilithium derivative of 1 in THF.