Search

Organoboron reagents are important synthetic intermediates and have wide applications in synthetic organic chemistry. The selective borylation strategies that are currently in use largely rely on t...

A growing number of organopnictogen redox catalytic methods have emerged-especially within the past 10 years-that leverage the plentiful reversible two-electron redox chemistry within Group 15. The goal of this Perspective is to provide readers the context to understand the dramatic developments in organopnictogen catalysis over the past decade with an eye toward future development. An exposition of the fundamental differences in the atomic structure and bonding of the pnictogens, and thus the molecular electronic structure of organopnictogen compounds, is presented to establish the backdrop against which organopnictogen redox reactivity-and ultimately catalysis-is framed. A deep appreciation of these underlying periodic principles informs an understanding of the differing modes of organopnictogen redox catalysis and evokes the key challenges to the field moving forward. We close by addressing forward-looking directions likely to animate this area in the years to come. What new catalytic manifolds can be developed through creative catalyst and reaction design that take advantage of the intrinsic redox reactivity of the pnictogens to drive new discoveries in catalysis?

Inspired by natural metalloenzymes that efficiently catalyze a variety of transformations, chemists have developed large numbers of dinuclear transition-metal complexes with extraordinary properties and reactivity patterns. For main-group element compounds, however, metal-metal cooperativity is much less explored. Here we present the synthesis and characterization of a room-temperature-stable compound with two separated two-coordinated gallium(I) centers possessing both a lone pair of electrons and a vacant orbital, reminiscent of singlet carbenes. This species displays enhanced reactivity compared to its mononuclear counterpart due to bimetallic cooperativity that allows for the facile activation of strong C-F bonds across the gallium-gallium bond. Two mechanistic scenarios of the cooperative bond activation have been identified by DFT and DLPNO-CCSD(T) calculations.

The development of a photoinduced, highly diastereo- and enantioselective [3 + 2]-cycloaddition of N-cyclopropylurea with α-alkylstyrenes is reported. This asymmetric radical cycloaddition relies o...

All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal Ti2InB2. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of M2AlB2 (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of Mo4/3Y2/3 AlB2 and Mo4/3Sc2/3AlB2 of space group R (3) over barm (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagome ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential twodimensional derivatives. Funding Agencies|Knut and Alice Wallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM16-0004]; Swedish Research councilSwedish Research Council [2019-05047, 201904233, 2016-04412]; Swedish Foundation for Strategic Research (SSF) through the Research Infrastructure Fellow Program [RIF 14-0074]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

As a key component in perovskite solar cells (PVSCs), hole-transporting materials (HTMs) have been extensively explored and studied. Aiming to meet the requirements for future commercialization of PVSCs, HTMs which can enable excellent device performance with low cost and eco-friendly processability are urgently needed but rarely reported. In this work, a traditional anchoring group (2-cyanoacrylic acid) widely used in molecules for dye-sensitized solar cells is incorporated into donor-acceptor-type HTMs to afford MPA-BT-CA, which enables effective regulation of the frontier molecular orbital energy levels, interfacial modification of an ITO electrode, efficient defect passivation toward the perovskite layer, and more importantly alcohol solubility. Consequently, inverted PVSCs with this low-cost HTM exhibit excellent device performance with a remarkable power conversion efficiency (PCE) of 21.24% and good long-term stability in ambient conditions. More encouragingly, when processing MPA-BT-CA films with the green solvent ethanol, the corresponding PVSCs also deliver a substantial PCE as high as 20.52% with negligible hysteresis. Such molecular design of anchoring group-based materials represents great progress for developing efficient HTMs which combine the advantages of low cost, eco-friendly processability, and high performance. We believe that such design strategy will pave a new path for the exploration of highly efficient HTMs applicable to commercialization of PVSCs.

Discovering and constructing novel and fancy structures is the goal of many supramolecular chemists. In this work, we propose an assembly strategy based on the synergistic effect of coordination and covalent interactions to construct a set of octahedral supramolecular cages and adjust their degree of distortion. Our strategy innovatively utilizes the addition of sulfur atoms of a metal sulfide synthon, [Et4N][Tp*WS3] (A), to an alkynyl group of a pyridine-containing linker, resulting in a novel vertex with low symmetry, and of Cu(I) ions. By adjusting the length of the linker and the position of the reactive alkynyl group, the control of the deformation degree of the octahedral cages can be realized. These supramolecular cages exhibit enhanced third-order nonlinear optical (NLO) responses. The results offer a powerful strategy to construct novel distorted cage structures as well as control the degree of distortion of supramolecular geometries.

We present the development of ligands featuring the unconventional hydrogen bond donor, -CF2H, within a metal's secondary coordination sphere. When metalated with palladium, o-CF2H-functionalized 1,10-phenanthroline provides highly directed H-bonding interactions with Pd-coordinated substrates. Spectroscopic and computational analyses with a series of X-type ligand acceptors (-F, -Cl, -Br, -OR) establish the H-bonding interaction strength for the -CF2H group (∼3 kcal/mol). The synthesis of Pd0/Ni0 complexes and subsequent coupling (Ni) highlight the unique reductive and base compatibility of the -CF2H hydrogen bond donor group.

Racemates have recently received attention as nonlinear optical and piezoelectric materials. Here, a machine-learning-assisted composition space approach was applied to synthesize the missing M = Ti, Zr members of the Δ,Λ-[Cu(bpy)2(H2O)]2[MF6]2·3H2O (M = Ti, Zr, Hf; bpy = 2,2'-bipyridine) family (space group: Pna21). In each (CuO, MO2)/bpy/HF(aq) (M = Ti, Zr, Hf) system, the polar noncentrosymmetric racemate (M-NCS) forms in competition with a centrosymmetric one-dimensional chain compound (M-CS) based on alternating Cu(bpy)(H2O)22+ and MF62- basic building units (space groups: Ti-CS (Pnma), Zr-CS (P1), Hf-CS (P2/n)). Machine learning models were trained on reaction parameters to gain unbiased insight into the underlying statistical trends in each composition space. A human-interpretable decision tree shows that phase selection is driven primarily by the bpy:CuO molar ratio for reactions containing Zr or Hf, and predicts that formation of the Ti-NCS compound requires that the amount of HF present be decreased to raise the pH, which we verified experimentally. Predictive leave-one-metal-out (LOO) models further confirm that behavior in the Ti system is distinct from that of the Zr and Hf systems. The chemical origin of this distinction was probed via fluorine K-edge X-ray absorption spectroscopy. Pre-edge features in the F1s X-ray absorption spectra reveal the strong ligand-to-metal π bonding between Ti(3d - t2g) and F(2p) states that distinguishes the TiF62- anion from the ZrF62- and HfF62- anions.

Azobenzenes are without a doubt the most widely used light-induced switching units, and there is a plethora of application examples ranging from supramolecular chemistry to material science and biological chemistry. Here, we present a smart azobenzene, in which the photoswitching capability of the azobenzene moiety can be reversibly switched on and off using a second unit (redox switch). This second switching unit is based on the variation of the strength of a chalcogen bond between the azo group and a Te-Ph unit in ortho position to the azo group. This allows the selective switching of only one azobenzene unit in the presence of other azobenzene switches. The entire double-switch is a very simple, small system that can also be easily synthesized. As a result, this double-switch can be used as a smarter replacement for the established azobenzene system in the future. For example, in contrast to the latter this double-switch could be employed to store state information analogous to a flip-flop in digital electronic systems.

A class of γ-cyclodextrin-containing hybrid frameworks (CD-HFs) has been synthesized, employing γ-cyclodextrin (γ-CD) as the primary building blocks, along with 4-methoxysalicylate (4-MS-) anions as the secondary building blocks. CD-HFs are constructed through the synergistic exploitation of coordinative, electrostatic, and dispersive forces. The syntheses have been carried out using an organic counteranion co-assembly strategy, which allows for the introduction of 4-MS-, in place of inorganic OH-, into the cationic γ-CD-containing metal-organic frameworks (CD-MOFs). Although the packing arrangement of the γ-CD tori in the solid-state superstructure of CD-HFs is identical to that of the previously reported CD-MOFs, CD-HFs crystallize with lower symmetry and in the cuboid space group P43212-when compared to CD-MOF-1, which has the cubic unit cell of I432 space group-on account of the chiral packing of the 4-MS- anions in the CD-HF superstructures. Importantly, CD-HFs have ultramicroporous apertures associated with the pore channels, a significant deviation from CD-MOF-1, as a consequence of the contribution from the 4-MS- anions, which serve as supramolecular baffles. In gas adsorption-desorption experiments, CD-HF-1 exhibits a Brunauer-Emmett-Teller (BET) surface area of 306 m2 g-1 for CO2 at 195 K, yet does not uptake N2 at 77 K, confirming the difference in porosity between CD-HF-1 and CD-MOF-1. Furthermore, the 4-MS- anions in CD-HF-1 can be exchanged with OH- anions, leading to an irreversible single-crystal to single-crystal transformation, with rearrangement of coordinated metal ions. Reversible transformations were also observed in CD-MOF-1 when OH- ions were exchanged for 4-MS- anions, with the space group changing from I432 to R32. This organic counteranion co-assembly strategy opens up new routes for the construction of hybrid frameworks, which are inaccessible by existing de novo MOF assembly methodologies.

The synthesis of a homologous series containing five new nonionic sulfoxide containing polypeptides was described. Sulfoxide groups bestowed water solubility for all homologues, which allowed their use as a model for study of helix-coil transitions in water while avoiding contributions from charged groups or phase separation. Polypeptides were found to adopt chain conformations in water that were dependent on distance of sulfoxides from chain backbones, overall side-chain lengths, and solvent. These results allow preparation of polypeptide segments with different chain conformations without changing chemical functionality for potential use in structural studies and functional applications.

A novel barium silicon phosphide was synthesized and characterized. Ba2Si3P6 crystallizes in the noncentrosymmetric space group Pna21 (No. 33) and exhibits a unique bonding connectivity in the Si–P...

Rhamnofolane, tigliane, and daphnane diterpenoids are structurally complex natural products with multiple oxygen functionalities, making them synthetically challenging. While these diterpenoids share a 5/7/6-trans-fused ring system (ABC-ring), the three-carbon substitutions at the C13- and C14-positions on the C-ring and appending oxygen functional groups differ among them, accounting for the disparate biological activities of these natural products. Here, we developed a new, unified strategy for expeditious total syntheses of five representative members of these three families, crotophorbolone (1), langduin A (2), prostratin (3), resiniferatoxin (4), and tinyatoxin (5). Retrosynthetically, 1-5 were simplified into their common ABC-ring 6 by detaching the three-carbon units and the oxygen-appended groups. Intermediate 6 with six stereocenters was assembled from four achiral fragments in 12 steps by integrating three powerful transformations, as follows: (i) asymmetric Diels-Alder reaction to induce formation of the C-ring; (ii) π-allyl Stille coupling reaction to set the trisubstituted E-olefin of the B-ring; and (iii) Eu(fod)3-promoted 7-endo cyclization of the B-ring via the generation of a bridgehead radical. Then 6 was diversified into 1-5 by selective installation of the different functional groups. Attachment of the C14-β-isopropenyl and isopropyl groups led to 1 and 2, respectively, while oxidative acetoxylation and C13,14-β-dimethylcyclopropane formation gave rise to 3. Finally, formation of an α-oriented caged orthoester by C13-stereochemical inversion and esterification with two different homovanillic acids delivered 4 and 5 with a C13-β-isopropenyl group. This unified synthetic route to 1-5 required only 16-20 total steps, demonstrating the exceptional efficiency of the present strategy.

We report metal-free bond activation by the carboranyl diphosphine 1-PtBu2-2-PiPr2-C2B10H10. This main group element system contains basic binding sites and possesses the ability to cycle through two-electron redox states. The reported reactions with selected main group hydrides and alcohols occur via the formal oxidation of the phosphine groups and concomitant reduction of the boron cage. These transformations, which are driven by the cooperation between the electron-donating exohedral substituents and the electron-accepting cluster, differ from those of "regular" phosphines and are reminiscent of oxidative addition to transition metal centers, thus representing a new approach to metal-free bond activation.

On a large scale, the dominant method to produce alkyl arenes has been arene alkylation from arenes and olefins using acid-based catalysis. The addition of arene C-H bonds across olefin C═C bonds catalyzed by transition-metal complexes through C-H activation and olefin insertion into metal-aryl bonds provides an alternative approach with potential advantages. This Perspective presents recent developments of olefin hydroarylation and oxidative olefin hydroarylation catalyzed by molecular complexes based on group 10 transition metals (Ni, Pd, Pt). Emphasis is placed on comparisons between Pt catalysts and other group 10 metal catalysts as well as Ru, Ir, and Rh catalysts.

This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure Au

Nitroamino-functionalized 1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (1), when combined with intermolecular hydrogen bonds (HBs) and strong noncovalent interactions between layers, results, for example, in an interlayer distance of 2.9 A for dihydroxylammonium 3,6-dinitramino-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (2c) with a packing coefficient of 0.805. For dihydroxylammonium 6,6′-dinitramino-3,3′-azo-1,2,4-triazolo[4,3-b][1,2,4,5]tetrazine (3b), two fused rings are linked by an azo group, which expands the conjugated system resulting in an even shorter interlayer distance of 2.7 A and a higher packing coefficient of 0.807. These values appear to be the shortest interlayer distances and the highest packing coefficients reported for tetrazine energetic materials. With high packing coefficients, both possess high densities of 1.92 g cm–3 and 1.99 g cm–3 at 293 K, respectively. Compared with its precursor, the hydroxylammonium moiety serves as a buffer chain (H–N–O–H), connecting the anion and cation through...

Cyclic (alkyl)(amino)carbenes (CAACs) and N-heterocyclic carbenes (NHCs) are widely used as stabilizing ligands in transition metal and main group element chemistry. Variations in their stabilizing properties have been cursorily explained in the literature by the greater π-donating and σ-accepting properties of CAACs relative to NHCs and their differing steric demands; however, a more precise understanding, in particular a disentanglement of steric and electronic effects, is lacking. The recently reported compounds (E)(L)BB(L)(E) (L = NHC (I)/CAAC (II) and E = SPh) present a unique opportunity to investigate the differences between NHC and CAAC donors, as both forms are stable but differ considerably in their geometrical and electronic properties. The NHC systems possess a singlet ground state with a planar central SBBS unit, while their CAAC counterparts show a triplet ground state with a twisted SBBS unit. Steric effects were found to be important in this case; however, it remained unclear how the different forms of twisting in I and II depend on the interplay of steric and electronic effects. In the present work we disentangle both effects. Our investigations explain all of these effects by MO considerations and show that for this kind of system the size of the singlet-triplet gaps are the key determinants of the differences. The different sizes of the S-T gaps result from variations in the antibonding effects within the highest occupied (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). Our explanation seems to contradict the general scientific consensus about variations in the HOMO and LUMO of these two classes of cyclic carbenes; however, comparisons to the Kekulé biradicaloids recently presented by Bertrand and co-workers indicate the generality of our approach.

Despite ample evidence for the unique reactivity offered by hypervalent F-iodanes, mechanistic investigations fall far behind. In order to shed light on the unusual behavior of such F-reagents, we conducted computational and experimental studies on the chemodivergent transformation of styrenes. We identified the spirocyclic F-cyclopropane as the common intermediate for both the C, H-fluorination and C, H-amination pathways. The fate of this key compound is determined by the extent of cationic charge delocalization controlled by the N-substituents. Exploiting this phenomenon, a multitude of different transformations have become available, leading, i.e., to the regiodivergent synthesis of indoles and tryptophans.

Low-dimensional halide perovskites have recently attracted intense interest as alternatives to the three-dimensional (3D) perovskites because of their greater tunability and higher environmental stability. Herein, we present the new homologous 2D series (NH3CmH2mNH3)(CH3NH3)n−1PbnI3n+1 (m = 4–9; n = 1–4), where m represents the carbon-chain number and n equals layer-thickness number. Multilayer (n > 1) 2D perovskites incorporating diammonium cations were successfully synthesized by the solid-state grinding method for m = 4 and 6 and by the solution method for m = 7–9. Structural characterization by single-crystal X-ray diffraction for the m = 8 and m = 9 series (n = 1–4) reveals that these compounds adopt the Cc space group for even n members and Pc for odd n members. The optical bandgaps are 2.15 eV for two-layer (n = 2), 2.01 eV for three-layer (n = 3), and 1.90 eV for four-layer (n = 4). The materials exhibit excellent solution processability, and casting thin-films of the n = 3 members was successfull...

A new state-of-the-art thermoelectric material, Tl2Ag12Te7+δ, which possesses an extremely low thermal conductivity of about 0.25 W m–1 K–1 and a high figure-of-merit of up to 1.1 at 525 K, was obtained using a conventional solid-state reaction approach. Its subcell is a variant of the Zr2Fe12P7 type, but ultimately its structure was refined as a composite structure of a Tl2Ag12Te6 framework and a linear Te atom chain running along the c axis. The super-space group of the framework was determined to be P63(00γ)s with a = b = 11.438(1) A, c = 4.6256(5) A, and that of the Te chain substructure has the same a and b axes, but c = 3.212(1) A, space group P6(00γ)s. The modulation leads to the formation of Te2 and Te3 fragments in this chain and a refined formula of Tl2Ag11.5Te7.4. The structure consists of a complex network of three-dimensionally connected AgTe4 tetrahedra forming channels filled with the Tl atoms. The electronic structures of four different models comprising different Te chains, Tl2Ag12Te7, Tl...

The 2,3-dimethylbutadiene complexes of Group 4 metals with constrained geometry (cg) ligands have been prepared and found to adopt a supine orientation with σ2,π bonding. Treatment of cgTi(2,3-dimethylbutadiene) (1-Ti) with tBuNC leads to the formation of a titana-aziridine (3) with a coordinated cyclopentenimine that arises from the formal [4+1] addition of the diene to the isonitrile. In contrast, the reactions of cgZr(2,3-dimethylbutadiene) (1-Zr) or cgHf(2,3-dimethylbutadiene) (1-Hf) with 2 equiv of tBuNC or XyNC proceeded in a more sophisticated manner to yield unsymmetrical 2,5-diazametallacyclopentane derivatives (4, 6-Zr, and 6-Hf) or symmetrical 2,5-diazametallacyclopentene complexes (7-Zr and 7-Hf). The unsymmetrical products contain coordinated cyclopropanes; the strength of the interaction is measured by the reduction in the 1JCC of the C–C bond that is coordinated. A detailed mechanistic analysis has been possible with the related cgM(Me)2 (M = Ti and Hf) complexes. The first insertion is too...

Favorable molecular interactions between group 16 elements have been implicated in catalysis, biological processes, and materials and medicinal chemistry. Such interactions have since become known as chalcogen bonds by analogy to hydrogen and halogen bonds. Although the prevalence and applications of chalcogen-bonding interactions continues to develop, debate still surrounds the energetic significance and physicochemical origins of this class of σ-hole interaction. Here, synthetic molecular balances were used to perform a quantitative experimental investigation of chalcogen-bonding interactions. Over 160 experimental conformational free energies were measured in 13 different solvents to examine the energetics of O···S, O···Se, S···S, O···HC, and S···HC contacts and the associated substituent and solvent effects. The strongest chalcogen-bonding interactions were found to be at least as strong as conventional H-bonds, but unlike H-bonds, surprisingly independent of the solvent. The independence of the conformational free energies on solvent polarity, polarizability, and H-bonding characteristics showed that electrostatic, solvophobic, and van der Waals dispersion forces did not account for the observed experimental trends. Instead, a quantitative relationship between the experimental conformational free energies and computed molecular orbital energies was consistent with the chalcogen-bonding interactions being dominated by n → σ* orbital delocalization between a lone pair (n) of a (thio)amide donor and the antibonding σ* orbital of an acceptor thiophene or selenophene. Interestingly, stabilization was manifested through the same acceptor molecular orbital irrespective of whether a direct chalcogen···chalcogen or chalcogen···H-C contact was made. Our results underline the importance of often-overlooked orbital delocalization effects in conformational control and molecular recognition phenomena.

Efficient synthesis and catalysis of a series of palladium complexes having a group 13 metalloligand (Al, Ga, In) are reported utilizing 6,6″-bis(phosphino)terpyridine as a new scaffold for Pd–E bonds (E = Al, Ga, In). Systematic investigation revealed unique characteristics of the Al-metalloligand in both structure and reactivity, which exhibited the highest catalytic activity for hydrosilylation of CO2 ever reported (TOF = 19 300 h–1). This study demonstrated fine-tuning of catalyst activity by the precisely designed metalloligand is a promising approach for new catalyst development in synthetic organometallic chemistry.

Aluminum(I) and magnesium(I) compounds are reported for the C-C σ-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C-C σ bond to the main group center either at a single site (Al) or across a metal-metal bond (Mg-Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to α- or β-alkyl migration steps that break the C-C σ bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C-C σ bonds of alkylidene cyclopropanes.

Herein we describe an unprecedented B(C6F5)3-catalyzed cascade reaction of N-allyl-N-furfurylamides involving an initial intramolecular furan Diels–Alder reaction and subsequent ether cleavage. The...

The phosphaaluminirenes HC[(CMe)(NDipp)]2Al[C(R)═P] (Dipp = 2,6-i-Pr2C6H3, R = tBu or adamantyl) 2 and 3, featuring an unsaturated three-membered AlCP ring, have been synthesized as crystalline sol...

The carbon monoxide adduct of an unhindered and highly reactive CAAC-bound arylborylene, [(CAAC)B(CO)Ar] (CAAC = cyclic (alkyl) (amino)carbene), has been prepared using a transfer reaction from the linear iron borylene complex [(PMe3) (CO)3Fe=BAr]. [(CAAC)B(CO)Ar] is a source of the dicoordinate [(CAAC)ArB:] borylene that can be liberated by selective photolytic CO extrusion and that, although highly reactive, is sufficiently long-lived to react intermolecularly. Through trapping of the borylene generated in this manner, we present, among others, the first metal-free borylene(I) species containing a nitrogen-based donor, as well as a new boron-containing radical.

A new nonlinear optical (NLO) material, Bi3TeBO9 (BTBO), is successfully grown from high temperature solution method. BTBO crystallizes in a polar space group of P63 with a framework structure composed of [Bi3O9] blocks, with TeO6 and BO3 interconnection. It is interesting that in the BTBO structure three types of NLO-active units, including stereochemically active lone pair cations (Bi3+ cations), second-order Jahn–Teller distorted octahedra (TeO6 octahedra) and π-orbital planar groups (BO3 groups), simultaneously exist. The additive contribution from these three types of groups results in an extremely large second harmonic generation (SHG) response in BTBO (about 20 times that of KDP), exhibiting the largest SHG effect among the known borate NLO materials. The enhancement of the nonlinear optical property is elucidated by the first-principles analysis.

Copper-catalyzed directed decarboxylative amination of nonactivated aliphatic carboxylic acids is described. This intramolecular C-N bond formation reaction provides efficient access to the synthesis of pyrrolidine and piperidine derivatives as well as the modification of complex natural products. Moreover, this reaction presents excellent site-selectivity in the C-N bond formation step through the use of directing group. Our work can be considered as a big step toward controllable radical decarboxylative carbon-heteroatom cross-coupling.

Designing small-molecule organic redox-active materials, with potential applications in energy storage, has received considerable interest of late. Herein, we report on the synthesis, characterization, and application of two rigid chiral triangles, each of which consist of non-identical pyromellitic diimide (PMDI) and naphthalene diimide (NDI)-based redox-active units. (1)H and (13)C NMR spectroscopic investigations in solution confirm the lower symmetry (C2 point group) associated with these two isosceles triangles. Single-crystal X-ray diffraction analyses reveal their rigid triangular prism-like geometries. Unlike previously investigated equilateral triangle containing three identical NDI subunits, both isosceles triangles do not choose to form one-dimensional supramolecular nanotubes by dint of [C-H···O] interaction-driven columnar stacking. The rigid isosceles triangle, composed of one NDI and two PMDI subunits, forms-in the presence of N,N-dimethylformamide-two different types of intermolecular NDI-NDI and NDI-PMDI π-π stacked dimers with opposite helicities in the solid state. Cyclic voltammetry reveals that both isosceles triangles can accept reversibly up to six electrons. Continuous-wave electron paramagnetic resonance and electron-nuclear double-resonance spectroscopic investigations, supported by density functional theory calculations, on the single-electron reduced radical anions of the isosceles triangles confirm the selective sharing of unpaired electrons among adjacent redox-active NDI subunit(s) within both molecules. The isosceles triangles have been employed as electrode-active materials in organic rechargeable lithium-ion batteries. The evaluation of the structure-performance relationships of this series of diimide-based triangles reveals that the increase in the number of NDI subunits, replacing PMDI ones, within the molecules improves the electrochemical cell performance of the batteries.

Three mononuclear nonheme iron and 2-oxoglutarate dependent enzymes, l-Ile 4-hydroxylase, l-Leu 5-hydroxylase and polyoxin dihydroxylase, are previously reported to catalyze the hydroxylation of l-isoleucine, l-leucine, and l-α-amino-δ-carbamoylhydroxyvaleric acid (ACV). In this study, we showed that these enzymes can accommodate leucine isomers and catalyze regiospecific hydroxylation. On the basis of these results, as a proof-of-concept, we demonstrated that the outcome of the reaction can be redirected by installation of an assisting group within the substrate. Specifically, instead of canonical hydroxylation, these enzymes can catalyze non-native nitrile group installation when an azido group is introduced. The reaction is likely to proceed through C-H bond activation by an Fe(IV)-oxo species, followed by azido-directed C≡N bond formation. These results offer a unique opportunity to investigate and expand the reaction repertoire of Fe/2OG enzymes.

The reaction of (tBu)2ArP (1a–h), where the para position of the Ar group contains electron-donating or electron-withdrawing groups, with sulfated zirconium oxide partially dehydroxylated at 300 °C...

So far the entrapped metals for the isolated endohedral metallofullerenes (EMFs) are primarily limited to rare earth metals, whereas except group-IVB metals, whether it is possible to entrap other d-block transition metals remains unclear. Herein we report the successful entrapment of the group-VB transition metal vanadium(V) into fullerene cage, affording the heretofore unknown V-containing EMFs. Two novel V-containing EMFs--V(x)Sc(3-x)N@C80 (x = 1, 2)--were isolated, and their molecular structures were unambiguously determined by X-ray crystallography to be I(h)(7)-C80 cage entrapping the planar VSc2N/V2ScN clusters. V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) were further characterized by UV-vis-NIR and ESR spectroscopies and electrochemistry, revealing that the electronic and magnetic properties of V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) are tunable upon varying the number of entrapped V atoms (i.e., x value). The molecular structures and electronic properties of V(x)Sc(3-x)N@I(h)(7)-C80 (x = 1, 2) were further compared with those of the reported analogous EMFs based on lanthanide metals and the adjacent group-IVB transition metal Ti, revealing the peculiarity of the group-VB transition metal V-based EMFs.

A new approach for electrooxidative coupling of aromatic compounds and primary alkylamines bearing a functional group such as a hydroxyl group and an amino group was developed. The key to the success of the transformation is heterocyclization of functional primary alkylamines. Treatment of primary alkylamines bearing a functional group with nitriles or their equivalents gives the corresponding heterocycles. The electrochemical oxidation of aromatic substrates in the presence of the heterocycles followed by chemical reaction under nonoxidative conditions gave the desired coupling products.

The syntheses of imidazolium thiocyanates and imidazolium thioalkynes from dihalo(imidazolium) sulfuranes are reported and their reactivities as CN(+) and R-CC(+) synthons evaluated, respectively. The easy and scalable preparation of these electrophilic reagents, their operationally simple handling, broad substrate scope, and functional group tolerance clearly illustrate the potential of these species to become a reference for the direct electrophilic cyanation and alkynylation of organic substrates.

A highly diastereoselective palladium-catalyzed oxidative carbocyclization–borylation of enallenes assisted by a weakly coordinating hydroxyl group was developed. The reaction afforded functionalized cyclohexenol derivatives, in which the 1,3-relative stereochemistry is controlled (d.r. > 50:1). Other weakly coordinating oxygen-containing groups (ketone, alkoxide, acetate) also assisted the carbocyclization toward cyclohexenes. The reaction proceeds via a ligand exchange on Pd of the weakly coordinating group with a distant olefin group. The high diastereoselectivity of the hydroxyl-directed reaction could be rationalized by a face-selective coordination of the distant olefin. It was demonstrated that the primary coordination of the close-by oxygen-containing functionality was necessary for the reaction to occur and removal of this functionality shut down the reaction.

We report an unexpected rearrangement of a deprotonated picolyl-functionalized N-heterocyclic carbene (NHC) ligand from N,C-chelate to N,N-chelate in three-legged piano-stool Fe(II) and Ru(II) complexes. The reaction mechanism has been explored for one of the Fe(II) complexes. Experimental and computational studies suggest an unusual intermediate featuring a four-membered chelate ring, where the NHC and the α-carbon of one of the N-substituents coordinate to the Fe(II) center. A possible Fe–alkylidene intermediate has also been predicted by computations.

A new niobium oxyfluoride, Nb2O2F3, synthesized through the reaction of Nb, SnO, and SnF2 in Sn flux, within welded Nb containers, crystallizes in a monoclinic structure (space group: I2/a; a = 5.7048(1)Å, b = 5.1610(1)Å, c = 12.2285(2)Å, β = 95.751(1)°). It features [Nb2X10] units (X = O, F), with short (2.5739(1) Å) Nb-Nb bonds, that are linked through shared O/F vertices to form a 3D structure configurationally isotypic to ζ-Nb2O5. Nb2O2F3 undergoes a structural transition at ∼90 K to a triclinic structure (space group: P1̅; a = 5.1791(5)Å, b = 5.7043(6)Å, c = 6.8911(7)Å, α = 108.669(3)°, β = 109.922(2)°, γ = 90.332(3)°). The transition is described as a disproportionation or charge ordering of [Nb2](7+) dimers: (2[Nb2](7+) → [Nb2](6+) + [Nb2](8+)), resulting in doubly (2.5000(9) Å) and singly bonded (2.6560(9) Å) Nb2 dimers. The structural transition is accompanied by an unusual field-independent "spin-gap-like" magnetic transition.

A triad of d10 cobalt dihydrogen complexes was synthesized by utilizing Lewis acidic group 13 metalloligands, M[N((o-C6H4)NCH2PiPr2)3], where M = Al, Ga, and In. These complexes have formal Co(−I) oxidation states, representing the only coordination complexes in which dihydrogen is bound to a subvalent transition metal center. Single-crystal X-ray diffraction and NMR studies support the assignment of these complexes as nonclassical dihydrogen adducts of Co(−I).

The direct application of carboxylic acids as a traceless activation group for radical Michael additions has been accomplished via visible light-mediated photoredox catalysis. Photon-induced oxidation of a broad series of carboxylic acids, including hydrocarbon-substituted, α-oxy, and α-amino acids, provides a versatile CO2-extrusion platform to generate Michael donors without the requirement for organometallic activation or propagation. A diverse array of Michael acceptors is amenable to this new conjugate addition strategy. An application of this technology to a three-step synthesis of the medicinal agent pregabalin (commercialized by Pfizer under the trade name Lyrica) is also presented.

A nitrile-based template that enables meta-selective C-H bond functionalization was developed. The template is applicable to a range of substituted arenes and tolerates a variety of functional groups. The directing group uses a silicon atom for attachment, allowing for a facile introduction/deprotection strategy increasing the synthetic practicality of this template.

Initiation of rare earth metal-mediated vinylphosphonate polymerization with unbridged rare earth metallocenes (Cp2LnX) follows a complex reaction pathway. Depending on the nature of X, initiation can proceed either via abstraction of the acidic α-CH of the vinylphosphonate (e.g., for X = Me, CH2TMS), via nucleophilic transfer of X to a coordinated monomer (e.g., for X = Cp, SR) or via a monomer (i.e., donor)-induced ligand-exchange reaction forming Cp3Ln in equilibrium (e.g., for X = Cl, OR), which serves as the active initiating species. As determined by mass spectrometric end group analysis, different initiations may also occur simultaneously (e.g., for X = N(SiMe2H)2). A general differential approach for the kinetic analysis of living polymerizations with fast propagation and comparatively slow initiation is presented. Time-resolved analysis of monomer conversion and molecular weights of the formed polymers allow the determination of the initiator efficiency throughout the whole reaction. Using this normalization method, rare earth metal-mediated vinylphosphonate GTP is shown to follow a Yasuda-type monometallic propagation mechanism, with an SN2-type associative displacement of the polymer phosphonate ester by a monomer as the rate-determining step. The propagation rate of vinylphosphonate GTP is mainly determined by the activation entropy, i.e. the change of rotational and vibrational restrictions within the eight-membered metallacycle in the rate-determining step as a function of the steric demand of the metallacycle side chains and the steric crowding at the metal center.

n-Alkyl arenes were prepared in a one-pot tandem dehydrogenation/olefin metathesis/hydrogenation sequence directly from alkanes and ethylbenzene. Excellent selectivity was observed when ((tBu)PCP)IrH2 was paired with tungsten monoaryloxide pyrrolide complexes such as W(NAr)(C3H6)(pyr)(OHIPT) (1a) [Ar = 2,6-i-Pr2C6H3; pyr = pyrrolide; OHIPT = 2,6-(2,4,6-i-Pr3C6H2)2C6H3O]. Complex 1a was also especially active in n-octane self-metathesis, providing the highest product concentrations reported to date. The thermal stability of selected olefin metathesis catalysts allowed elevated temperatures and extended reaction times to be employed.

Fe-based superconductors have attracted research interest because of their rich structural variety, which is due to their layered crystal structures. Here we report the new-structure-type Fe-based superconductors CaAFe4As4 (A = K, Rb, Cs) and SrAFe4As4 (A = Rb, Cs), which can be regarded as hybrid phases between AeFe2As2 (Ae = Ca, Sr) and AFe2As2. Unlike solid solutions such as (Ba(1-x)K(x))Fe2As2 and (Sr(1-x)Na(x))Fe2As2, Ae and A do not occupy crystallographically equivalent sites because of the large differences between their ionic radii. Rather, the Ae and A layers are inserted alternately between the Fe2As2 layers in the c-axis direction in AeAFe4As4 (AeA1144). The ordering of the Ae and A layers causes a change in the space group from I4/mmm to P4/mmm, which is clearly apparent in powder X-ray diffraction patterns. AeA1144 is the first known structure of this type among not only Fe-based superconductors but also other materials. AeA1144 is formed as a line compound, and therefore, each AeA1144 has its own superconducting transition temperature of approximately 31-36 K.

We developed a 1,3-dipolar cycloaddition reaction of azomethine imines with terminal alkynes catalyzed by group 11 metal amides to provide N,N-bicyclic pyrazolidinone derivatives. This reaction afforded the cycloadducts in a unique 5,7-disubstituted manner. Furthermore, we succeeded in applying this catalysis to asymmetric reactions, and the desired heterocycles were produced in high yields with exclusive regioselectivity and high enantioselectivity. Mechanistic studies elucidated a stepwise reaction pathway and critical features that determine the regioselectivity.

The number of Zintl phases containing polyhedral clusters of tetrel elements that are accessible for chemical reactions of the main-group element clusters is rather limited. The synthesis and structural characterization of two novel ternary intermetallic phases A14ZnGe16 (A = K, Rb) are presented, and their chemical reactivity is investigated. The compounds can be rationalized as Zintl phases with 14 alkali metal cations A+ (A = K, Rb), two tetrahedral [Ge4]4– Zintl anions, and one anionic heterometallic [(Ge4)Zn(Ge4)]6– cluster per formula unit. The Zn–Ge cluster comprises two (Ge4) tetrahedra which are linked by a Zn atom, with one (Ge4) tetrahedron coordinating with a triangular face (η3) and the other one with an edge (η2). [(η3-Ge4)Zn(η2-Ge4)]6– is a new isomer of the [(Ge4)Zn(Ge4)]6– anion in Cs6ZnGe8. The phases dissolve in liquid ammonia and thus represent rare examples of soluble Zintl compounds with deltahedral units of group 14 element atoms. Compounds with tetrahedral [E4]4– species have previ...