Palladium-catalyzed asymmetric allylic alkylation (AAA) with alkyl sulfones as nucleophiles

An efficient palladium-catalyzed AAA reaction with a simple α-sulfonyl carbon anion as nucleophiles is presented for the first time. Allyl fluorides are used as superior precursors for the generation of π-allyl complexes that upon ionization liberate fluoride anions for activation of silylated nucleophiles. With the unique bidentate diamidophosphite ligand ligated palladium as catalyst, the in situ generated α-sulfonyl carbon anion was quickly captured by the allylic intermediates, affording a series of chiral homo-allylic sulfones with high efficiency and selectivity. This work provides a mild in situ desilylation strategy to reveal nucleophilic carbon centers that could be used to overcome the pK_a limitation of “hard” nucleophiles in enantioselective transformations.

A variety of “hard” α-sulfonyl carbanions of aryl, heteroaryl and alkyl sulfones were successfully employed as nucleophiles in palladium-catalyzed asymmetric allylic alkylation with excellent enantioselectivities.     

Isolable fluorinated triphenylmethyl cation salts of [HCB11Cl11]−: demonstration of remarkable hydride affinity

Significantly fluorinated triarylmethyl cations have long attracted attention as potentially accessible highly reactive carbocations, but their isolation in a convenient form has proved elusive. We show that abstraction of chloride with a cationic silylium reagent leads to the facile formation of di-, tetra-, and hexafluorinated trityl cations, which could be isolated as analytically pure salts with the [HCB₁₁Cl₁₁]⁻ counterion and are compatible with (halo)arene solvents. The F₆Tr⁺ cation carrying six meta-F substituents was computationally predicted to possess up to 20% higher hydride affinity than the parent triphenylmethyl cation Tr⁺. We report that indeed F₆Tr⁺ displays reactivity unmatched by Tr⁺. F₆Tr⁺ at ambient temperature abstracts hydrides from the C–H bonds in tetraethylsilane, mesitylene, methylcyclohexane, and catalyzes Friedel–Crafts alkylation of arenes with ethylene, while Tr⁺ does none of these.

Hexakis(meta-fluoro)substituted triphenylmethyl cation (F₆Tr⁺) was isolated with a carborane partner anion. Its significantly higher hydride affinity compared to the parent (Tr⁺) allows it to abstract hydrides from a variety of C(sp³)–H bonds.     

Nitride protonation and NH3 binding versus N–H bond cleavage in uranium nitrides

The conversion of metal nitrides to NH₃ is an essential step in dinitrogen fixation, but there is limited knowledge of the reactivity of nitrides with protons (H⁺). Herein, we report comparative studies for the reactions of H⁺ and NH₃ with uranium nitrides, containing different types of ancillary ligands. We show that the differences in ancillary ligands, leads to dramatically different reactivity. The nitride group, in nitride-bridged cationic and anionic diuranium(iv) complexes supported by –N(SiMe₃)₂ ligands, is resistant toward protonation by weak acids, while stronger acids result in ligand loss by protonolysis. Moreover, the basic –N(SiMe₃)₂ ligands promote the N–H heterolytic bond cleavage of NH₃, yielding a “naked” diuranium complex containing three bridging ligands, a nitride (N³⁻) and two NH₂ ligands. Conversely, in the nitride-bridged diuranium(iv) complex supported by –OSi(O^tBu)₃ ligands, the nitride group is easily protonated to afford NH₃, which binds the U(iv) ion strongly, resulting in a mononuclear U–NH₃ complex, where NH₃ can be displaced by addition of strong acids. Furthermore, the U–OSi(O^tBu)₃ bonds were found to be stable, even in the presence of stronger acids, such as NH₄BPh₄, therefore indicating that –OSi(O^tBu)₃ supporting ligands are well suited to be used when acidic conditions are required, such as in the H⁺/e⁻ mediated catalytic conversion of N₂ to NH₃.

Ancillary ligands alter the reactivity of U-nitrides with H⁺, relevant to N₂ conversion to NH₃. The amides lead to complete ligand loss and NH₃ activation, while for siloxides, the nitride is protonated to NH₃ leaving the ancillary ligands intact.     

A (μ-hydrido)diborane(4) anion and its coordination chemistry with coinage metals

A tetra(o-tolyl) (μ-hydrido)diborane(4) anion 1, an analogue of [B₂H₅]⁻ species, was facilely prepared through the reaction of tetra(o-tolyl)diborane(4) with sodium hydride. Unlike common sp²–sp³ diborane species, 1 exhibited a σ-B–B bond nucleophilicity towards NHC-coordinated transition-metal (Cu, Ag, and Au) halides, resulting in the formation of η²-B–B bonded complexes 2 as confirmed by single-crystal X-ray analyses. Compared with 1, the structural data of 2 imply significant elongations of B–B bonds, following the order Au > Cu > Ag. DFT studies show that the diboron ligand interacts with the coinage metal through a three-center-two-electron B–M–B bonding mode. The fact that the B–B bond of the gold complex is much prolonged than the related Cu and Ag compounds might be ascribed to the superior electrophilicity of the gold atom.

A tetra(o-tolyl)(μ-hydrido)diborane(4) anion is facilely prepared via the reaction of tetra(o-tolyl)diborane(4) with NaH. It exhibits a σ-B–B bond nucleophilicity towards NHC-metal halides to give the corresponding η²-B–B bonded metal complexes.     

Nonspherical anion sequestration by C–H hydrogen bonding

Macrocyclic arenes laid the foundations of supramolecular chemistry and their study established the fundamentals of noncovalent interactions. Advancing their frontier, here we designed rigidified resorcin[4]arenes that serve as hosts for large nonspherical anions. In one synthetic step, we vary the host''s anion affinity properties by more than seven orders of magnitude. This is possible by engineering electropositive aromatic C–H bond donors in an idealized square planar geometry embedded within the host''s inner cavity. The hydrogen atom''s electropositivity is tuned by introducing fluorine atoms as electron withdrawing groups. These novel macrocycles, termed fluorocages, are engineered to sequester large anions. Indeed, experimental data shows an increase in the anion association constant (K_a) as the number of F atoms increase. The observed trend is rationalized by DFT calculations of Hirshfeld Charges (HCs). Most importantly, fluorocages in solution showed weak-to-medium binding affinity for large anions like [PF₆]⁻ (10²< K_a <10⁴ M⁻¹), and high affinity for [MeSO₃]⁻ (K_a >10⁶).

Fluorocages: new class of rigidified host utilizing nontraditional C–H hydrogen bonds to capture the nonspherical anions.     

Attaining record-high magnetic exchange,magnetic anisotropy and blocking barriers in dilanthanofullerenes

While the blocking barrier (U_eff) and blocking temperature (T_B) for “Dysprocenium” SIMs have been increased beyond liquid N₂ temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln³⁺ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln₂@C₇₉N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd₂@C_2n (30 ≤ 2n ≤ 80), where an antiferromagnetic J_Gd⋯Gd of −43 cm⁻¹ was found for a stable Gd₂@C₃₈-D_3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd₂@C₆₀ and Gd₂@C₈₀, the formation of two centre-one-electron (2c-1e⁻) Gd–Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln₂@C₅₉N and Ln₂@C₇₉N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm⁻¹ and resultant J_Gd–rad of 869.5 cm⁻¹ for the Gd₂@C₅₉N complex. These parameters are found to be two times larger than the world-record J reported for Gd₂@C₇₉N. Further ab initio calculations reveal an unprecedented U_cal of 1183 and 1501 cm⁻¹ for Dy₂@C₅₉N and Tb₂@C₅₉N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.

Using ab initio calculations, we have made some robust predictions towards lanthanofullerene SMMs exhibiting remarkable characteristics.     

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin,proof of oxidation with subvalent Ga+ and silylium catalysis with perfluoroalkoxyaluminate anions

Already 1 mol% of subvalent [Ga(PhF)₂]⁺[pf]⁻ ([pf]⁻ = [Al(OR^F)₄]⁻, R^F = C(CF₃)₃) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe₃ and HSiEt₃ as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiⁱPr₃ are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H₂ and metallic Ga⁰ formed. Without the addition of olefins, the formation of R₃Si–F–Al(OR^F)₃ (R = alkyl), a typical degradation product of the [pf]⁻ anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)₂]⁺[pf]⁻ in weakly coordinating, but polar ortho-difluorobenzene of E_1/2(Ga⁺/Ga⁰; oDFB) = +0.26–0.37 V vs. Fc⁺/Fc (depending on the scan rate). Apparently, subvalent Ga⁺, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)₂]⁺[pf]⁻/HSiEt₃ system also hydrodefluorinates C(sp³)–F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF₃ at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph₃C]⁺[pf]⁻ as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]⁻ anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.

Nobler than expected: subvalent [Ga(PhF)₂][pf] ([pf]⁻ = [Al{OC(CF₃)₃}₄]⁻) oxidizes hydrosilanes to silylium ions, allowing for catalytic hydrosilylation and hydrodefluorination and suggesting that silylium catalysis is possible with the [pf]− anion.     

Heterostructured FeNi hydroxide for effective electrocatalytic oxygen evolution

Hydrogen production technology by water splitting has been heralded as an effective means to alleviate the envisioned energy crisis. However, the overall efficiency of water splitting is limited by the effectiveness of the anodic oxygen evolution reaction (OER) due to the high energy barrier of the 4e⁻ process. The key to addressing this challenge is the development of high-performing catalysts. Transition-metal hydroxides with high intrinsic activity and stability have been widely studied for this purpose. Herein, we report a gelatin-induced structure-directing strategy for the preparation of a butterfly-like FeNi/Ni heterostructure (FeNi/Ni HS) with excellent catalytic performance. The electronic interactions between Ni²⁺ and Fe³⁺ are evident both in the mixed-metal “torso” region and at the “torso/wing” interface with increasing Ni³⁺ as a result of electron transfer from Ni²⁺ to Fe³⁺ mediated by the oxo bridge. The amount of Ni³⁺ also increases in the “wings”, which is believed to be a consequence of charge balancing between Ni and O ions due to the presence of Ni vacancies upon formation of the heterostructure. The high-valence Ni³⁺ with enhanced Lewis acidity helps strengthen the binding with OH⁻ to afford oxygen-containing intermediates, thus accelerating the OER process. Direct evidence of FeNi/Ni HS facilitating the formation of the Ni–OOH intermediate was provided by in situ Raman studies; the intermediate was produced at lower oxidation potentials than when Ni₂(CO₃)(OH)₂ was used as the reference. The Co congener (FeCo/Co HS), prepared in a similar fashion, also showed excellent catalytic performance.

A butterfly-like FeNi/Ni HS featuring a “torso” of Ni-doped FeOOH and two “wings” of Ni₂(CO₃)(OH)₂ showed excellent activity in electrocatalytic oxygen evolution reaction attributable to the increase of higher-valance Ni³⁺ in the heterostructure.     

A small-molecule organic ferroelectric with piezoelectric voltage coefficient larger than that of lead zirconate titanate and polyvinylidene difluoride

Piezoelectric materials that generate electricity when deforming are ideal for many implantable medical sensing devices. In modern piezoelectric materials, inorganic ceramics and polymers are two important branches, represented by lead zirconate titanate (PZT) and polyvinylidene difluoride (PVDF). However, PVDF is a nondegradable plastic with poor crystallinity and a large coercive field, and PZT suffers from high sintering temperature and toxic heavy element. Here, we successfully design a metal-free small-molecule ferroelectric, 3,3-difluorocyclobutanammonium hydrochloride ((3,3-DFCBA)Cl), which has high piezoelectric voltage coefficients g₃₃ (437.2 × 10⁻³ V m N⁻¹) and g₃₁ (586.2 × 10⁻³ V m N⁻¹), a large electrostriction coefficient Q₃₃ (about 4.29 m⁴ C⁻²) and low acoustic impedance z₀ (2.25 × 10⁶ kg s⁻¹ m⁻²), significantly outperforming PZT (g₃₃ = 34 × 10⁻³ V m N⁻¹ and z₀ = 2.54 × 10⁷ kg s⁻¹ m⁻²) and PVDF (g₃₃ = 286.7 × 10⁻³ V m N⁻¹, g₃₁ = 185.9 × 10⁻³ V m N⁻¹, Q₃₃ = 1.3 m⁴ C⁻², and z₀ = 3.69 × 10⁶ kg s⁻¹ m⁻²). Such a low acoustic impedance matches that of the body (1.38–1.99 × 10⁶ kg s⁻¹ m⁻²) reasonably well, making it attractive as next-generation biocompatible piezoelectric devices for health monitoring and “disposable” invasive medical ultrasound imaging.

A small-molecule organic ferroelectric (3,3-DFCBA)Cl has high piezoelectric voltage coefficients g₃₃ (437.2 × 10⁻³ V m N⁻¹), a large electrostriction coefficient Q₃₃, and low acoustic impedance z₀, far beyond that of PZT and PVDF.     

Plasmonic O2 dissociation and spillover expedite selective oxidation of primary C–H bonds

Manipulating O₂ activation via nanosynthetic chemistry is critical in many oxidation reactions central to environmental remediation and chemical synthesis. Based on a carefully designed plasmonic Ru/TiO_2−x catalyst, we first report a room-temperature O₂ dissociation and spillover mechanism that expedites the “dream reaction” of selective primary C–H bond activation. Under visible light, surface plasmons excited in the negatively charged Ru nanoparticles decay into hot electrons, triggering spontaneous O₂ dissociation to reactive atomic ˙O. Acceptor-like oxygen vacancies confined at the Ru–TiO₂ interface free Ru from oxygen-poisoning by kinetically boosting the spillover of ˙O from Ru to TiO₂. Evidenced by an exclusive isotopic O-transfer from ¹⁸O₂ to oxygenated products, ˙O displays a synergistic action with native ˙O₂⁻ on TiO₂ that oxidizes toluene and related alkyl aromatics to aromatic acids with extremely high selectivity. We believe the intelligent catalyst design for desirable O₂ activation will contribute viable routes for synthesizing industrially important organic compounds.

Room-temperature O₂ dissociation and spillover, as driven by plasmonic Ru on oxygen-deficient TiO₂, expedite the selective oxidation of primary C–H bonds in alkyl aromatics for synthesizing industrially important organic compounds.     

Uncovering an oxide ion substitution for the OH− + CH3F reaction

Theoretical investigations on chemical reactions allow us to understand the dynamics of the possible pathways and identify new unexpected routes. Here, we develop a global analytical potential energy surface (PES) for the OH⁻ + CH₃F reaction in order to perform high-level dynamics simulations. Besides bimolecular nucleophilic substitution (S_N2) and proton abstraction, our quasi-classical trajectory computations reveal a novel oxide ion substitution leading to the HF + CH₃O⁻ products. This exothermic reaction pathway occurs via the CH₃OH⋯F⁻ deep potential well of the S_N2 product channel as a result of a proton abstraction from the hydroxyl group by the fluoride ion. The present detailed dynamics study of the OH⁻ + CH₃F reaction focusing on the surprising oxide ion substitution demonstrates how incomplete our knowledge is of fundamental chemical reactions.

Reaction dynamics simulations on a high-level ab initio analytical potential energy surface reveal a novel oxide ion substitution channel for the OH⁻ + CH₃F reaction.     

Density functionals with asymptotic-potential corrections are required for the simulation of spectroscopic properties of materials

Five effects of correction of the asymptotic potential error in density functionals are identified that significantly improve calculated properties of molecular excited states involving charge-transfer character. Newly developed materials-science computational methods are used to demonstrate how these effects manifest in materials spectroscopy. Connection is made considering chlorophyll-a as a paradigm for molecular spectroscopy, 22 iconic materials as paradigms for 3D materials spectroscopy, and the V_N⁻ defect in hexagonal boron nitride as an example of the spectroscopy of defects in 2D materials pertaining to nanophotonics. Defects can equally be thought of as being “molecular” and “materials” in nature and hence bridge the relms of molecular and materials spectroscopies. It is concluded that the density functional HSE06, currently considered as the standard for accurate calculations of materials spectroscopy, should be replaced, in most instances, by the computationally similar but asymptotically corrected CAM-B3LYP functional, with some specific functionals for materials-use only providing further improvements.

Spectroscopic transitions in materials that involve charge transfer require asymptotically corrected density functionals. As most transitions do have some charge transfer character, use of such methods are generally warranted.     

Anion-coordination-driven single–double helix switching and chiroptical molecular switching based on oligoureas

Synthetic foldamers with helical conformation are widely seen, but controllable interconversion amongst different geometries (helical structure and sense) is challenging. Here, a family of oligourea (tetra-, penta-, and hexa-) ligands bearing stereocenters at both ends are designed and shown to switch between single and double helices with concomitant inversion of helical senses upon anion coordination. The tetraurea ligand forms a right-handed single helix upon chloride anion (Cl⁻) binding and is converted into a left-handed double helix when phosphate anion (PO₄³⁻) is coordinated. The helical senses of the single and double helices are opposite, and the conversion is further found to be dependent on the stoichiometry of the ligand and phosphate anion. In contrast, only a single helix is formed for the hexaurea ligand with the phosphate anion. This distinction is attributed to the fact that the characteristic phosphate anion coordination geometry is satisfied by six urea moieties with twelve H-bonds. Our study revealed unusual single–double helix interconversion accompanied by unexpected chiroptical switching of helical senses.

Two-in-one switching of single–double helical forms and helicities is demonstrated using anion-coordination-driven oligourea foldamers.     

Mutual functionalization of dinitrogen and methane mediated by heteronuclear metal cluster anions CoTaC2−

The direct coupling of dinitrogen (N₂) and methane (CH₄) to construct the N–C bond is a fascinating but challenging approach for the energy-saving synthesis of N-containing organic compounds. Herein we identified a likely reaction pathway for N–C coupling from N₂ and CH₄ mediated by heteronuclear metal cluster anions CoTaC₂⁻, which starts with the dissociative adsorption of N₂ on CoTaC₂⁻ to generate a Ta^δ+–N_t^δ− (terminal-nitrogen) Lewis acid–base pair (LABP), followed by the further activation of CH₄ by CoTaC₂N₂⁻ to construct the N–C bond. The N N cleavage by CoTaC₂⁻ affording two N atoms with strong charge buffering ability plays a key part, which facilitates the H₃C–H cleavage via the LABP mechanism and the N–C formation via a CH₃ migration mechanism. A novel N_t triggering strategy to couple N₂ and CH₄ molecules using metal clusters was accordingly proposed, which provides a new idea for the direct synthesis of N-containing compounds.

A possible N–C bond formation directly from N₂ and CH₄ mediated by heteronuclear metal cluster anions CoTaC₂⁻ at room temperature was identified.     

When SF5 outplays CF3: effects of pentafluorosulfanyl decorated scorpionates on copper

Polyfluorinated, electron-withdrawing, and sterically demanding supporting ligands are of significant value in chemistry. Here we report the assembly and use of a bis(pyrazolyl)borate, [Ph₂B(3-(SF₅)Pz)₂]⁻ that combines all such features, and involves underutilized pentafluorosulfanyl substituents. The ethylene and carbonyl chemistry of copper(i) supported by [Ph₂B(3-(SF₅)Pz)₂]⁻, a comparison to the trifluoromethylated counterparts involving [Ph₂B(3-(CF₃)Pz)₂]⁻, as well as copper catalyzed cyclopropanation of styrene with ethyl diazoacetate and CF₃CHN₂ are presented. The results from cyclopropanation show that SF₅ groups dramatically improved the yields and stereoselectivity compared to the CF₃.

Copper–ethylene and carbonyl complexes of the newly developed [Ph₂B(3-(SF₅)Pz)₂]⁻ enable the study of ligand steric and electronic effects caused by the –SF₅ group (dubbed “super CF₃”), and a comparison to the –CF₃ bearing analogs.     

Optimization of crystal packing in semiconducting spin-crossover materials with fractionally charged TCNQδ− anions (0 < δ < 1)

Co-crystallization of the prominent Fe(ii) spin-crossover (SCO) cation, [Fe(3-bpp)₂]²⁺ (3-bpp = 2,6-bis(pyrazol-3-yl)pyridine), with a fractionally charged TCNQ^δ− radical anion has afforded a hybrid complex [Fe(3-bpp)₂](TCNQ)₃·5MeCN (1·5MeCN, where δ = −0.67). The partially desolvated material shows semiconducting behavior, with the room temperature conductivity σ_RT = 3.1 × 10⁻³ S cm⁻¹, and weak modulation of conducting properties in the region of the spin transition. The complete desolvation, however, results in the loss of hysteretic behavior and a very gradual SCO that spans the temperature range of 200 K. A related complex with integer-charged TCNQ⁻ anions, [Fe(3-bpp)₂](TCNQ)₂·3MeCN (2·3MeCN), readily loses the interstitial solvent to afford desolvated complex 2 that undergoes an abrupt and hysteretic spin transition centered at 106 K, with an 11 K thermal hysteresis. Complex 2 also exhibits a temperature-induced excited spin-state trapping (TIESST) effect, upon which a metastable high-spin state is trapped by flash-cooling from room temperature to 10 K. Heating above 85 K restores the ground-state low-spin configuration. An approach to improve the structural stability of such complexes is demonstrated by using a related ligand 2,6-bis(benzimidazol-2′-yl)pyridine (bzimpy) to obtain [Fe(bzimpy)₂](TCNQ)₆·2Me₂CO (4) and [Fe(bzimpy)₂](TCNQ)₅·5MeCN (5), both of which exist as LS complexes up to 400 K and exhibit semiconducting behavior, with σ_RT = 9.1 × 10⁻² S cm⁻¹ and 1.8 × 10⁻³ S cm⁻¹, respectively.

Co-crystallization of the cationic complex [Fe(3-bpp)2]²⁺ with fractionally charged TCNQ^δ− anions (0 < δ < 1) affords semiconducting spin-crossover (SCO) materials. The abruptness of SCO is strongly dependent on the interstitial solvent content.     

From a nanoparticular solid-state material to molecular organo-f-element-polyarsenides

A convenient pathway to new molecular organo-lanthanide-polyarsenides in general and to a f-element complex with the largest polyarsenide ligand in detail is reported. For this purpose, the activation of the solid state material As⁰_nano (nanoscale gray arsenic) by the multi electron reducing agents [K(18-crown-6)][(Ln^+II)₂(μ-η⁶:η⁶-C₆H₆)] (Ln = La, Ce, Cp′′ = 1,3-bis(trimethylsilyl)cyclopentadienyl anion) and [K(18-crown-6)]₂[(Ln^+II)₂(μ-η⁶:η⁶-C₆H₆)] (Ln = Ce, Nd) is shown. These non-classical divalent lanthanide compounds were used as three and four electron reducing agents where the product formation can be directed by variation of the applied reactant. The obtained Zintl anions As₃³⁻, As₇³⁻, and As₁₄⁴⁻ were previously not accessible in molecular 4f-element chemistry. Additionally, the corresponding compounds with As₁₄⁴⁻-moieties represent the largest organo-lanthanide-polyarsenides known to date.

Reaction of non-classical divalent lanthanide compounds with nanoparticulate gray arsenic via three- and four-electron reduction led to a series of new f-element polyarsenides, including the largest f-element polyarsenide known to date.     

Trimacrocyclic hexasubstituted benzene linked by labile octahedral [X(CHCl3)6]− clusters

Crystalline supramolecular architectures mediated by cations, anions, ion pairs or neutral guest species are well established. However, the robust crystallization of a well-designed receptor mediated by labile anionic solvate clusters remains unexplored. Herein, we describe the synthesis and crystalline behaviors of a trimacrocyclic hexasubstituted benzene 2 in the presence of guanidium halide salts and chloroform. Halide hexasolvate clusters, viz. [Cl(CHCl₃)₆]⁻, [Br(CHCl₃)₆]⁻, and [I(CHCl₃)₆]⁻, were found to be critical to the crystallization process, as suggested by the single-crystal structures, X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and NMR spectroscopy. This study demonstrates the hitherto unexpected role that labile ionic solvate clusters can play in stabilizing supramolecular architectures.

We report the synthesis and robust crystallization of a trimacrocyclic hexasubstituted benzene and guanidium mediated by unprecedented labile halide hexasolvate clusters, viz. [Cl(CHCl₃)₆]⁻, [Br(CHCl₃)₆]⁻, [I(CHCl₃)₆]⁻, and [Br(CHBr₃)₆]⁻.     

Isolation of the elusive bisbenzimidazole Bbim3−˙ radical anion and its employment in a metal complex

The discovery of singular organic radical ligands is a formidable challenge due to high reactivity arising from the unpaired electron. Matching radical ligands with metal ions to engender magnetic coupling is crucial for eliciting preeminent physical properties such as conductivity and magnetism that are crucial for future technologies. The metal-radical approach is especially important for the lanthanide ions exhibiting deeply buried 4f-orbitals. The radicals must possess a high spin density on the donor atoms to promote strong coupling. Combining diamagnetic ⁸⁹Y (I = 1/2) with organic radicals allows for invaluable insight into the electronic structure and spin-density distribution. This approach is hitherto underutilized, possibly owing to the challenging synthesis and purification of such molecules. Herein, evidence of an unprecedented bisbenzimidazole radical anion (Bbim³⁻˙) along with its metalation in the form of an yttrium complex, [K(crypt-222)][(Cp*₂Y)₂(μ-Bbim˙)] is provided. Access of Bbim³⁻˙ was feasible through double-coordination to the Lewis acidic metal ion and subsequent one-electron reduction, which is remarkable as Bbim²⁻ was explicitly stated to be redox-inactive in closed-shell complexes. Two molecules containing Bbim²⁻ (1) and Bbim³⁻˙ (2), respectively, were thoroughly investigated by X-ray crystallography, NMR and UV/Vis spectroscopy. Electrochemical studies unfolded a quasi-reversible feature and emphasize the role of the metal centre for the Bbim redox-activity as neither the free ligand nor the Bbim²⁻ complex led to analogous CV results. Excitingly, a strong delocalization of the electron density through the Bbim³⁻˙ ligand was revealed via temperature-dependent EPR spectroscopy and confirmed through DFT calculations and magnetometry, rendering Bbim³⁻˙ an ideal candidate for single-molecule magnet design.

The long sought-after bisbenzimidazole radical was isolated through complexation to two rare earth metallocenes followed by reduction, and analysed through crystallography, VT EPR spectroscopy, electrochemistry, magnetometry, and DFT computations.     

An electrically conductive metallocycle: densely packed molecular hexagons with π-stacked radicals

Electrical conduction among metallocycles has been unexplored because of the difficulty in creating electronic transport pathways. In this work, we present an electrocrystallization strategy for synthesizing an intrinsically electron-conductive metallocycle, [Ni₆(NDI-Hpz)₆(dma)₁₂(NO₃)₆]·5DMA·nH₂O (PMC-hexagon) (NDI-Hpz = N,N′-di(1H-pyrazol-4-yl)-1,4,5,8-naphthalenetetracarboxdiimide). The hexagonal metallocycle units are assembled into a densely packed ABCABC… sequence (like the fcc geometry) to construct one-dimensional (1D) helical π-stacked columns and 1D pore channels, which were maintained under the liberation of H₂O molecules. The NDI cores were partially reduced to form radicals as charge carriers, resulting in a room-temperature conductivity of (1.2–2.1) × 10⁻⁴ S cm⁻¹ (pressed pellet), which is superior to that of most NDI-based conductors including metal–organic frameworks and organic crystals. These findings open up the use of metallocycles as building blocks for fabricating conductive porous molecular materials.

Intrinsically electron-conductive metallocycle was synthesized. π-Radicals play a key role in constructing π-stacked columns among molecular hexagons and achieving high electrical conductivity over 10⁻⁴ S cm⁻¹ in polycrystalline pellet.