Capturing carbon monoxide-Accessing bis(boryl)ketones through direct B-B bond carbonylation.

Carbon monoxide (CO) readily attacks the B-B bonds of the cyclic tetra(amino)tetraborane B(NCy) [cyclohexyl (Cy)], which led to insertion and ring expansion, creating tetraboron analogs of cyclopentanone and cyclohexane-1,3-dione. These intriguing molecules are rare instances of stable CO diborylation products that were made accessible by direct CO capture. While the monocarbonyl product shows remarkable thermal stability, the dicarbonyl product rearranges into a bicyclic tetraborylethylene structure under thermal stress.

Atom-efficient synthesis of BN-heterocycles from oligoboranes and isonitriles.

-Xylyl isonitrile readily inserts into one of the B-B bonds of simple, unactivated linear peraminotri- and tetraboranes. Subsequent thermal rearrangements yield two different types of CBN heterocycles, a 1-azonium-2,4-diboretane-3-ide and a 1,2,4-azadiboretidine, respectively. When heated with a second isonitrile equivalent, these generate 1,3,2-diazaboroles (CBN) and an unsymmetrical 1,4,2,5-diazadiborinine (CBN).

Understanding Twisted Triarylboranes from Single Crystals to Heterojunction Blends and Their Applications in Organic Photovoltaics.

The triarylborane family has expanded rapidly as valuable π electron-accepting moieties in organic materials, yet the performance and application of triarylboranes in organic photovoltaics (OPVs) have thus far been limited. Herein, we present a comprehensive platform of 17 distinct triarylboranes to investigate their structure-property relationships from single crystals to heterojunction blends and further to OPV device performance. We show that twisted triarylboranes exhibit distinct molecular packing behavior in the solid state, characterized by limited π-π stacking and the lack of the face-on orientation required for efficient light-to-electric conversion, in contrast to state-of-the-art OPV materials.

BNB-Modified Perylene, Terrylene, and Quaterrylene Diimides: Introduction of the π-Accepting and Aggregation-Suppressing Diborinic Imide Group in Rylene Dyes.

Rylene diimides are among the most intensively researched classes of functional organic dyes. They are characterized by outstanding photoabsorption and -emission properties in combination with excellent photostability and thermal stability. Due to strong intermolecular π-π interactions, the larger, -extended rylene diimides, in particular, require the complex attachment of solubilizing substituents to enable their handling and processing in the solution phase.

Tuning the emission properties of luminescent 1,2,3-diazaborinates.

B-Aryl-based 1,2,3-diazaborinates (DABates), derived from neutral 1,2,3-diazaborines (DABs), are a promising class of unexplored fluorophores which show an intriguing high optical performance. This work systematically investigates previously unexplored factors that govern their photoluminescence. We strategically designed and synthesized a diverse library of DABate derivatives, modifying the exocyclic boron and N-substituents, the N-lone pair, and the fused π system.

Highly Antiaromatic Naphtho-1,2-Diboretes as Precursors for Tunable, Unsymmetrical 1,4-Diboraanthracenes.

The four-electron reduction of doubly IMes- and SIMes-stabilized 2,3-bis(dibromoboryl)naphthalene (IMes = 1,3-dimesitylimidazol-2-ylidene; SIMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene, mesityl = 2,4,6-trimethylphenyl) yields the first N-heterocyclic carbene (NHC)-stabilized naphtho[2,3-][1,2]diboretes and , which were isolated as dark-blue and red solids, respectively, and analyzed by nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-vis) spectroscopy as well as X-ray crystallography. The synthesis of is systematically accompanied by NHC ring-expanding boron insertion side reactions, absent in that of . Both experimental and computational data show that unlike their biradical cyclic alkyl(amino)carbene (CAAC)-stabilized counterparts, the 1,2-diborete rings in and are closed-shell 4π-antiaromatic compounds.

Spring-Like Behavior in [8]Helicene Diimides: How Helical Pitch Governs Optical Anisotropy and Electronic Conjugation.

Helicenes, with their corkscrew-shaped geometry, have emerged as prototypical molecular springs for engineering chiral functional materials through precise structural modulation. Here we introduce the design and synthesis of [8]helicene diimides ([8]HDIs) and demonstrate that the helical pitch of their backbone can be precisely tuned by bridging the imide nitrogen atoms with alkyl chains of varying lengths (C-C). This approach constrains the molecular geometry to systematically control optical anisotropy, chiroptical response, and electronic communication.

Boron-chalcogen heterocycles and linear tetraboranes from a cyclic tetra(amino)tetraborane.

While small carbocyclic rings have long been recognized as pivotal building blocks in chemistry, their all-boron counterparts have remained largely unexplored. In this work, we present a detailed account of the functionalization reactivity of our cyclic tetraborane B(NCy) (Cy = cyclohexyl) encompassing both ring-expansion and ring-opening reactions. Specifically, diphenyl dichalcogenides effect ring expansion to five-membered BE rings (E = S, Se, Te), while halogenating agents induce ring opening to generate linear tetraboranes with halide end groups.

Synthesis of symmetrical and unsymmetrical cyclic diborenes NHC-directed C-H borylation.

Cyclic diborenes are recognized for their diverse reactivity and properties arising partly due to their ring strain. However, progress in this field has been relatively slow due to the unavailability of suitable synthons for their synthesis. In this study, we describe the synthesis of both symmetrical and unsymmetrical cyclic diborenes using an N-heterocyclic carbene (NHC) as a chelating agent.

N,N-Bis(trifluoromethyl)aminoacetonitrile: A Versatile Building Block for the Introduction of the Bis(trifluoromethyl)amino Group.

N,N-Bis(trifluoromethyl)aminoacetonitrile (CF)NCHCN (1) that is accessible via a simple single-step protocol is established as a building block for the introduction of the (CF)N group. The two reaction sites of 1, the methylene unit and the nitrile (cyano) group, provide access to different organic substance classes. This includes alkenes via Knoevenagel condensations, and N-heterocycles and acid derivatives obtained by addition reactions to the nitrile unit.

Alkali metal salts of 1,2,3-benzodiazaborines: platforms for late-stage -functionalization and metal complexation.

The standard procedure for the preparation of benzoid 1,2,3-diazaborines (DABs) is the condensation of 2-formylphenyl boronic acid with a hydrazine. The choice of hydrazine derivative irreversibly predetermines the -substituent in most cases and is additionally limited by the availability and hazardous nature of the respective hydrazines. Options to subsequently modify the -substituent are scarce.

Insights into topochemical stress-induced high-pressure reactivity of azobenzene by single crystal X-ray diffraction.

This study addresses azobenzene's structural compression and reactivity under hydrostatic high-pressure conditions. Synchrotron X-ray diffraction data of single crystals compressed with neon as the pressure-transmitting medium allowed the refinement of the crystal structure up to 28 GPa, at which the onset of the reaction was observed. Analysis of the pressure-dependent lattice parameters reveals a first-order isostructural phase transition at 13 GPa.

Synthesis and reactivity of a parent phosphathioethynolato-borane and a boraarsaketene.

We present the synthesis and isolation of the first main-group phosphathioethynolates, [LBH(SCP)] (L = SIMes, CAAC; SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene, CAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene), in which phosphathioethynolate coordination occurs exclusively through the sulfur atom, giving rise to a phosphaalkyne-type structural motif. This is reflected in the reactivity of the SIMes derivative towards organic azides and [(η-CH)CoCp] (Cp = CH), which mirrors the behavior of 1-adamantylphosphaalkyne, yielding triazaphospholes and a mixed cyclopentadienyl-(1,3-diphosphete) sandwich complex, respectively. Deviations from typical phosphaalkyne reactivity are observed in reactions with boron-containing heterocycles such as pentaphenylborole (PPB) and a carboranyl-substituted 9-borafluorene, which yield an unprecedented bicyclic structure and a zwitterionic spiro compound, respectively.

Switching from Transition-State Theory to Solvent-Controlled Adiabatic Charge-Transfer Regime in Bis-Triarylamine Mixed Valence Radical Cations by Modification of the Bridge Electron Density.

For a series of organic intervalence charge-transfer (IVCT) radical cations where two triarylamine redox centers are linked via donor-/acceptor-substituted fluorene bridges, the influence of bridge electron density on the thermally activated hole transfer and the associated energy barrier Δ* was investigated. Comparison of barrier heights obtained from the two-state Mulliken Hush (MH) theory and from potential energy surfaces constructed by the three-state-generalized Mulliken Hush theory (GMH theory) revealed the influence of an accessible bridge-centered hole-transfer state on the activation barrier Δ*. Comparison of these values with averaged barrier heights obtained from temperature-dependent EPR spectroscopy in DCM showed a continuous decrease of barrier height for electron-rich bridges.

A Joyful Journey: Tungsten(VI) and Tungsten(V) Fluorides Meet N-Heterocyclic Carbenes and Cyclic (Alkyl)(Amino)Carbenes.

The first complexation of tungsten(VI) fluoride with N-heterocyclic carbenes (NHCs) and a cyclic (alkyl)(amino) carbene (cAAC) is reported, which led to formation of the complexes [(NHC)WF] (NHC = IiPr, 1; BIiPr, 2; IMes, 3; IDipp, 4; and SIDipp, 5) and [(cAAC)WF] 6. Solid-state structural analysis revealed distorted mono-capped trigonal prismatic geometries for 2 and 3, whereas 6 adopts a pentagonal bipyramidal coordination. Reduction of 1-6 with 0.

Reactivity of Pnictaalumenes Towards 1,3-Dipole Molecules.

Alkynes undergo 1,3-dipolar cyclization reactions with organic azides giving 1,2,3-triazoles. Pnictaalumenes RPn═AlR' are the isoelectronic congeners of alkynes, hence a similar reactivity toward 1,3-dipole molecules is expected. Herein, we report the reactions of TerPn═AlCp* (Ter  =  2,6-(2,6-iPrCH)-CH, Cp*  =  [MeC], Pn  =  P, As) toward aryl azides.

Synthetic access to organyl-substituted 1,2,3-benzodiazaborines with turn-on fluorescence activity.

1,2,3-Benzodiazaborines (DABs), isoelectronic to isoquinoline alkaloids, have attracted considerable interest due to their unique reactivity and promising potential applications, including but not limited to pH sensors, chiral probes or antibacterial agents. Although DABs with hemiboronic acid functionality have been known since the 1960s and were extensively studied since then, a method to convert the borinic acid functionality into a borane moiety with carbon-based substituents has remained elusive and is of interdisciplinary interest. Herein, we present a straightforward and inexpensive two-step synthesis of aryl- and alkyl-substituted DABs starting from established hemiboronic acid derivatives and commercially available reagents.

Formation and Metallomimetic Reactivity of a Transient Dicoordinate Alkylborylene.

While existing literature has primarily focused on carbene-stabilized amino- and arylborylenes of the form [(carbene)BR] (R = substituent), herein we report the generation and metallomimetic reactivity of the first carbene-stabilized alkylborylene [(CAAC)BCy] (CAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene, Cy = cyclohexyl). Furthermore, the transition metal-like decarbonylation reactions of a borylene complex, [(CAAC)BCy(CO)], derived from borylene [(CAAC)BCy] and CO, are described. Additional findings described include i) the identification of the coordination stages of the ligand to boron towards forming complexes [(CAAC)BCyL] in the reduction route from starting material [(CAAC)BCyBr] and in the photolysis route from carbonyl complex [(CAAC)BCy(CO], and ii) insights from quantum-chemical computations regarding the molecular and electronic structure of the borylene at various stages.

Harnessing transient CAAC-stabilized mesitylborylenes for chalcogen activation.

Newly synthesized adducts of CAAC-bound mesitylborylene with carbon monoxide (CO) and trimethylphosphine (PMe) are established as efficient precursors for the generation of the dicoordinate borylene [(CAAC)BMes] (CAAC = cyclic(alkyl)(amino)carbene), as demonstrated by their ability to activate elemental chalcogens. Upon thermal or photolytic activation, these precursors readily react with sulfur and selenium, yielding boron chalcogenides characterized by terminal boron-chalcogen double bonds. In contrast, the reaction with tellurium leads to the formation of an unusual diradical ditelluride species with a Te-Te bond.

Azolium-2-dithiocarboxylates as redox active ligands in nickel chemistry.

The coordination chemistry of carbene-CS adducts of selected NHCs and cAACs and their redox active nature in nickel complexes is reported. These azolium-2-dithiocarboxylate ligands can be considered as 1,1-isomeric dithiolene analogues bearing a 2π electron reservoir. Depending on the co-ligands attached to nickel, square planar mono- or bis-(carbene-CS) complexes of the types [Ni(IPr)(carbene-CS)] (2a-g) (carbene = cAAC, IDipp, IMes, BIMe, BIPr, IPr, and IPr) and [Ni(carbene-CS)] (3a-c) (carbene = cAAC, IDipp, and IMes) are accessible by alkene substitution using [Ni(IPr)(ƞ-CH)] or [Ni(COD)] as the starting material (cAAC = 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene, IR = 1,3-diorganylimidazolin-2-ylidene, IR = 1,3-diorganyl-4,5-dimethylimidazolin-2-ylidene, and BIR = 1,3-diorganylbenzimidazolin-2-ylidene).

A fully conjugated meso-boron-substituted porphyrinoid combining Lewis acidity with redox-switchable aromaticity.

The structural motif of porphyrin is relevant for many essential biological processes and has emerged as a versatile component of functional materials. Here, we introduce a thiophene-based porphyrinogen having electron-deficient boron atoms in all four meso-positions. Its fully π-conjugated backbone exhibits effectively concealed antiaromaticity, with locally confined aromaticity to the thiophene units.

A BNAlP-heterocycle.

We report the [2+2]-cyclization reaction of a phosphaalumene with its lighter analog, an iminoborane, to give a species with a four-membered BNAlP-heterocycle with alternating Lewis basic and acidic centers in the ring. The reactivity of this heterocycle towards alkenes and alkynes is described, giving chain molecules and ring-expanded species.

Poly(Ferrocenylene Iminoborane) and the Merging of 1,1'-Ferrocenylene with p-Phenylene Iminoborane Building Blocks into Alternating Copolymers, Oligomers, and Macrocycles.

The combination of redox-active ferrocene moieties, conjugated B=N units, and p-phenylene building blocks in linearly concatenated architectural arrangements has been explored. Oligo- and poly(ferrocenylene iminoborane)s have been successfully prepared, whereby in the latter case, the formation of linear polymers vs. discrete molecular macrocycles could be largely influenced by the polymerization conditions applied.

Synthesis of base-free boriranes and their conversion to borirenes using strong reductant.

Boriranes, highly strained three-membered cyclic organoboron heterocycles, have emerged as potential synthons for the synthesis of many organoboron species. However, the synthesis of boriranes with tricoordinate, sp-hybridised boron and tetracoordinate, sp-hybridised carbon atoms is very challenging owing to their high Lewis acidity. Herein we describe the isolation of base-free triaminoboriranes from the room-temperature reaction of diaminoalkynes with an aminodistannylborane.

Straightforward Formation of Borirenes from Boroles and Dialkynes.

We report a selective one-step synthesis of perarylated borirenes by reaction of antiaromatic boroles with 1,4-diarylbuta-1,3-diynes. Mechanistic studies, both experimental and computational, reveal key intermediates, including boranorbornadiene and 7-borabicyclo[4.1.