Themed collection Boron Chemistry in the 21st Century: From Synthetic Curiosities to Functional Molecules

Boranes are effective catalysts for bespoke siloxane synthesis via (modified) Piers–Rubinsztajn reactions, enabling complex macromolecular architectures with novel functionality, through careful selection of reaction components and conditions.

This article discusses in a big-picture manner popular boron chemistries that are a focus in multidisciplinary applications.

BODIPYs provide tunable electronic properties key to many applications. This article highlights structural modification at boron.

This feature article highlights our recent study on new organoboron compounds and boron-mediated reactions, developed based on the concept of vacant boron p-orbital engineering in combination with peripheral space design for boron.

A straightforward, one-step MCR yields visible light-absorbing, viscosity-responsive BOSPYR dyes with tunable emissions and inherent chirality at-boron, which open doors for potential applications in biological imaging and chiroptical sensing.

Metal-free direct C7-alkenylation of N-propargylindoles without directing groups is described. C7-Alkenylation products could further convert into the fused indoles by deprotonation and finally polyaromatic N-heterocycles by hydride abstraction.

Using nucleophilic, boron-based –CF₂Ar reagents, we demonstrate three methods to form C–C_F bonds: (1) nucleophilic aromatic substitution, (2) palladium catalyzed cross-coupling, and (3) nucleophilic substitution.

An electron counting rule for borophenes based on graphene and MgB₂ helps to design metallated borophenes and borophanes, and suggests strategies to release 2D-borophenes from metal surfaces.

Herein, we use α-boryl iminium intermediates to access progressively depeptidized branched β-aminoboronic acids. We show the interaction of these compounds with carbohydrates and demonstrate their potential as synthetic building blocks.

An unstable azidoborole derivative was prepared and indirectly identified through trapping in the form of neutral Lewis adducts and, quite surprisingly, in the form of the diazidoborolate complex anion.

Upon electrophilic initiation, difunctional aminoboranes underwent either B–N coupling or an unexpected Cl/Me exchange reaction.

A series of photochromic four-coordinate spirocyclic boron(III) compounds that display thermally activated upconversion processes from the lower-lying unreactive excited state to the higher-lying photoreactive excited state is reported.

The zinc hydride compound, [Bptm]ZnH, is a catalyst for hydroboration of CO₂ and carbonyl compounds.

Metallacarboranes are electrochemical analogs to ferrocene. Here the potential advent of metallacarboranes as internal reference systems is studied in various electrochemical conditions and aqueous and organic solvents with no need for derivatization.

C–H functionalization of undecahalogenated carborane anions, [HCB₁₁X₁₁⁻] (X = Cl, Br, I), is performed with Cs₂CO₃ in acetonitrile.

A particular fluorene-derivative-based o-carborane π-conjugated system exhibits a strong solid-state luminescence efficiency, while preserving the luminescent properties as nanoparticles homogeneously dispersed in water.

Two new approaches to the functionalization of the 1-carba-closo-decaborate anion resulting in the formation of B–O and B–N bonds were developed.

An enantioselective and regioselective dearomative borylation of 4-quinolinols was developed for synthesis of unprecedented heterocyclic α-amino boronates, a new class of compounds potentially relevant to drug discovery.

Photoelectron spectroscopy and quantum chemistry studies are used to investigate the structure and bonding of AuB₈⁻.

The successful synthesis and first structural characterization by single crystal X-ray crystallography of a highly strained benzoborirene motif, as well as its reactivity towards selected electrophiles and nucleophiles are reported.

This report describes the incorporation of BODIPY dyes into the ligand framework of a borane to generate a family of molecular boranes that are capable of exhibiting tunable Lewis acidities through BODIPY-based redox events.

The present work demonstrated the hitherto unknown biological activity of metallacarboranes.

A reaction sequence for an easy coupling of the conformationally restrained cobalta bis(dicarbollide)(1⁻) ion with organic molecules is presented along with electrochemical studies and resolution of enantiomers.

Na₂B₁₂I₁₂ is a candidate X-ray contrast agent, but produces rapid hemolysis at the concentrations needed for medical imaging. Encapsulation within 2-hydroxypropyl-γ-cyclodextrin effectively protects red blood cells at substoichiometric levels.

Structure–activity relationships of dodecaborate-substituted nitroanilines as hosts in cyclodextrins have been elucidated.

Atom transfer radical addition of alkyl halides to alkenes was developed using a low amount of a stable initiator, amine borane complexes.

Isoxazoloazaborines have been synthesized from 4-N-propargylaminoisoxazole via gold(I)-catalyzed propargyl aza-Claisen rearrangement followed by electrophilic borylative cyclization in 27–86% yields.

The direct access to (mesityl)(alkyl)haloboranes (Mes(Alk)BX) (X = Br, Cl) from mesitylborane dimer and vinyl halides is presented, revealing two accessible pathways, one of which being kinetically favoured.

Regiocontrolled cross-coupling of an optically enriched dehydropiperidinyl boronate with cinnamyl carbonates affords 2-allylated 3,4-dehydropiperidines exclusively with enantiospecificity up to 99%.

Aryl(Mes)iodonium salts, which are multifaceted aryl transfer reagents, are synthesized via boron-iodane exchange.

Salts of the anions [RB(CN)₃]⁻ and [RBF(CN)₂]⁻ (R = ethyl, vinyl, ethynyl) provide high thermal and electrochemical stabilities. The EMIm-salts are low viscosity room temperature ionic liquids with a wide liquid range.

A ruthenium tris(pyridyl)borate complex is subjected to electrophilic and nucleophilic reactions at the bridgehead borons. These transformations allow for facile tuning of the properties and open up new pathways to functional scorpionate complexes.

A non-protic surrogate that contains two molecules of HCl for the synthesis of alkenyl chlorides from internal alkynes is reported. The HCl transfer is catalyzed by B(C₆F₅)₃ and driven by release of strain and aromatization.

This study shows for the first time the catalytic activity in amine-borane dehydrogenation for lanthanide(II) species and unveils the step-by-step transformations of the starting complexes into active catalytic intermediates.

A new cyclic diborylamide ligand has been developed and successfully employed to synthesize low-coordinate iron(II) complexes.

A convenient synthesis of [closo-B₁₀H₈-1,10-(COOH)₂]²⁻ leads to a new class of stable diaminocarbonium ylides.

Novel symmetric and unsymmetric diboranes with sp³-hybridized boron atoms and especially electron-donating bridging guanidinate substituents are synthesized and their properties analysed. Moreover, dismutation equilibria are disclosed.

A Rh-catalyzed one-pot trifunctionalization of o-carboranes with three different substituents via sequential B(3)–, B(4)–, and B(5)–H activation has been developed.

A series of trans-alkenyl MIDA boronates have been prepared by palladium-catalyzed cross-coupling reaction of N-methyliminodiacetyl boronate (BMIDA)-substituted N-tosylhydrazone and benzyl bromides.

Borylation of cyclic aryl–alkyl sulfones gives boronate esters by selective cleavage of C(sp²)–SO₂ or C(sp³)–SO₂ bonds via Cu-mediated or Cu-free processes.

The rotation of iron bis(dicarbollide) complexes was characterized by Mössbauer spectroscopy and computational methods. Unexpected Fe^II-like character in the 8-dioxane iron bis(dicarbollide) adduct was discovered.

The synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described.

Two challenging but rewarding topics in chemical synthesis are C–F-bond activation and development of B-centered nucleophiles. We have now tackled both subjects by forming aryl–B bonds via S_NAr-type reactions on fluorobenzenes under mild conditions.

The transformation of C,C′-bound bis(ortho-carborane) to C,B′-bound is reported for the first time.

Transmetalation is a key method for the construction of element–element bonds.

Aryl amino borinium cation can serve as the catalyst for hydrosilylation of ketones and aldehydes.

The oxidation of cyclic alkyl(amino)carbene-stabilised closed-shell 1,4-diborabenzene and the related open-shell singlet biradical 9,10-diboraanthracene with elemental chalcogens yields bicyclic compounds with different lengths of chalcogen bridges.

Exchange of boryl moieties is possible between alkenylboranes and diboron reagents as a stereospecific cross-metathesis with formation of mixed diboron reagents. DFT calculations propose a mechanism with both symmetric and non-symmetric diboron reagents.

Selective reduction of aldehydes and ketones to alcohols using KB₃H₈ was achieved in water and THF.

The interaction of carbon monoxide with an intramolecular FLP and a strong electrophile leads to rapid cleavage of the CO triple bond and enables the formation of new B/N heterocycles via selective incorporation of single carbon atoms.

I(III) reagent [PhI(Pyr)₂]²⁺ (Weiss’ reagent) can be activated with borane Lewis acids in which a pyridine ligand is abstracted giving a more reactive derivative of the reagents.

A general frustrated Lewis pair chelation approach was used to access the parent iminoborane isomers HBNH and NBH₂.

Carboxyboranylamino ethanol is cell membrane permeable and has low cytotoxicity. It shows high molecular docking scores and improved antitumor efficacy in vitro.

Photoactive thiophene-fused boracycle analogues of diboraanthracenes.

A new ambiphilic phosphine-xanthylium ligand is described, along with its ability to stabilize a catalytically competent Au–μ(OH)–BF₃ complex via anion-π⁺ interactions.

A fluorescent, strongly Lewis-acidic borenium cation (Gutmann–Beckett acceptor number >100) was created using a tridentate formazanate ligand. This cation shows a potential utility as a colourimetric reactivity probe.

The borane-catalysed hydrocyanation of enones has been developed and applied across a series of substrates including those being functional groups susceptible to reduction.

A dithienylethene molecule involving carborane clusters shows remarkable fatigue resistance and high contrast visual colour changes when irradiated with alternating ultraviolet and visible light.

B–N(sp³) coupling of nido-carborane with organic amines by photoredox catalysis leads to nitrogen-containing nido-carboranes in moderate to good yields.

The site-selective N¹-alkylation of benzotriazoles with diazoalkanes is achieved using 10 mol% of B(C₆F₅)₃ as a catalyst.

Coordination induced bond weakening (CIBW) leads to facile PCET at various E–H bonds.