A Strategy for Selective Catalytic B–H Functionalization of o-Carboranes

Accounts of Chemical Research, Journal Year: 2021, Volume and Issue: 54(21), P. 4065 - 4079

Published: Oct. 24, 2021

ConspectusCarboranes are a class of polyhedral carbon-boron molecular clusters featuring three-dimensional aromaticity, which often considered as 3D analogues benzene. Their unique structural and electronic properties make them invaluable building blocks for applications ranging from functional materials to versatile ligands pharmaceuticals. Thus, selective functionalization carboranes has received tremendous research interest. In earlier days, the vast majority works in this area were focused on cage carbon via facile deprotonation CH, followed by reaction with electrophiles. On contrary, B-H activation is very challenging since 10 bonds o-carborane similar, how achieve desired transformation at specific boron vertex long-standing issue.As more electronegative than boron, property results different charges cage, follow order B(3,6)-H ≪ B(4,5,7,11)-H < B(8,10)-H B(9,12)-H. We thought that difference may trigger favorite interaction proper transition metal complex bond carborane, could be utilized solve selectivity issue. Accordingly, our strategy described follows: (1) electron-rich catalysts good most electron-deficient (connected both C-H vertices); (2) relatively B(8,9,10,12)-H (with no bonding either (3) directing-group-assisted catalysis appropriate only one vertex), whose lie middle range bonds. This been successfully applied laboratory other groups development series synthetic routes catalytic carborane resulting synthesis large number cage-boron-functionalized derivatives regioselective fashion. Subsequently, significant progress emerging made.In 2013 we reported tetrafluorination o-carboranes using an Pd(II) salt, [Pd(MeCN)4][BF4], catalyst. 2014 disclosed first example carboxy-directed alkenylation B(4) promoted Ir(III) 2017 presented Ir(I)-catalyzed diborylation also uncovered Pd-catalyzed asymmetric chiral-at-cage 2018. These proof-of-principle studies have greatly stimulated activities enabled catalysts. so far developed toolbox methods B-olefination, -arylation, -alkenylation, -alkynylation, -oxygenation, -sulfenylation, -borylation, -halogenation, -amination. recently expanded base catalysis. As field progresses, expect will invented, detailed Account promote these efforts.

Language: Английский

---

Highly Selective Separation of Benzene and Cyclohexane in a Spatially Confined Carborane Metallacage

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(14), P. 6558 - 6565

Published: March 31, 2022

Separation of light hydrocarbons (C1-C9) represents one the "seven chemical separations to change world". Boron clusters can potentially play an important role in separation, due their unique three-dimensional structures and ability promote a rich array weak noncovalent interactions. Herein, we report rational design metallacages with carborane functionality cooperative dihydrogen binding sites for highly selective capture cyclohexane molecules. The metallacage 1, bearing ligand 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT), produce purity 98.5% single adsorption-desorption cycle from equimolar mixture benzene cyclohexane. In addition, cyclohexene molecules be also encapsulated inside 1. This encapsulation was attributed spatial confinement effects, C-H···π interactions, particularly dihydrogen-bond work suggests exciting future applications cages supramolecular chemistry adsorption separation alkane may open up new research direction host-guest chemistry.

Language: Английский

---

Carboranes as unique pharmacophores in antitumor medicinal chemistry

Molecular Therapy — Oncolytics, Journal Year: 2022, Volume and Issue: 24, P. 400 - 416

Published: Jan. 10, 2022

Carborane is a carbon-boron molecular cluster that can be viewed as 3D analog of benzene. It features special physical and chemical properties, thus has the potential to serve new type pharmacophore for drug design discovery. Based on relative positions two cage carbons, icosahedral closo-carboranes classified into three isomers, ortho-carborane (o-carborane, 1,2-C2B10H12), meta-carborane (m-carborane, 1,7-C2B10H12), para-carborane (p-carborane, 1,12-C2B10H12), all them deboronated generate their nido- forms. Cage compound carborane its derivatives have been demonstrated useful entities in antitumor medicinal chemistry. The applications carboranes field research mainly include boron neutron capture therapy (BNCT), BNCT/photodynamic dual sensitizers, anticancer ligands. This review summarizes progress achieved up October 2021, with particular emphasis signaling transduction pathways, structures, mechanistic considerations using carboranes.

Language: Английский

---

Organocatalytic Asymmetric Synthesis of o-Carboranyl Amines

Journal of the American Chemical Society, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 14, 2025

Carboranyl amines are distinct from typical organic amines. Due to the electronic influence of carborane cage, they have low nucleophilicity and reluctant alkylate. Moreover, asymmetric synthesis chiral carboranes is still in its infancy. Herein we achieved first catalytic N-alkylation o-carboranyl amine, providing general access diverse secondary with high efficiency enantioselectivity under mild conditions. For time, organocatalysis was introduced chemistry. Key success use situ generated (naphtho-)quinone methides as alkylating reagents suitable acid catalysts. This protocol also applicable S-alkylation 1-SH-o-C2B10H11. Control experiments kinetic studies provided important insights into reaction mechanism, which likely involves rate-determining generation quinone methide followed by fast enantio-determining nucleophilic addition.

Language: Английский

---

o-Carborane-Based and Atomically Precise Metal Clusters as Hypergolic Materials

Journal of the American Chemical Society, Journal Year: 2020, Volume and Issue: 142(28), P. 12010 - 12014

Published: June 25, 2020

Atomically precise o-carboranealkynyl-protected clusters [Ag14(C4B10H11)12(CH3CN)2]·2NO3 (CBA-Ag) and [Cu6Ag8(C4B10H11)12Cl]NO3 (CBA-CuAg) have been found to exhibit hypergolic activity, such that they are capable of spontaneous ignition combustion upon contact with the white fuming nitric acid oxidizer. In particular, CBA-CuAg has a short delay time 15 ms, whereas o-carboranealkynyl ligand is hypergolically inert. Systematic investigation revealed metal cluster core catalyzed behavior inert ligand, Cu doping further accelerated catalysis. This work provides new prospective in rational design novel cluster-based fuels for propellant application.

Language: Английский

---

Recent Advances in Transition Metal-Catalyzed Selective B-H Functionalization ofo-Carboranes

Bulletin of the Chemical Society of Japan, Journal Year: 2020, Volume and Issue: 94(3), P. 879 - 899

Published: Dec. 18, 2020

Abstract Carboranes are a class of carbon-boron molecular clusters, possessing extraordinary characteristics including three-dimensional aromaticity conjugated by σ-bonds, icosahedral geometry and inherent robustness. They finding growing applications as valuable building blocks in boron neutron capture therapy agents, pharmacophores, nanomaterials, optoelectronic, organometallic/coordination chemistry more. Therefore, the effective controlled functionalization carboranes has attracted enormous research interests, particularly regio- enantio-selective cage BH derivatization among ten chemically similar vertices o-carboranes. Only recent few years, significant progress been made transition metal catalyzed vertex-specific functionalization. This review summarizes advances this realm.

Language: Английский

---

Palladium-Catalyzed Regioselective B(9)-Amination of o-Carboranes and m-Carboranes in HFIP with Broad Nitrogen Sources

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(18), P. 8371 - 8378

Published: May 2, 2022

Amination of carboranes has a good application prospect in organic and pharmaceutical synthesis. However, the current methods used for this transformation suffer from limitations. Herein, we report practical method highly regioselective formation B-N bond by Pd(II)-catalyzed B(9)-H amination o- m-carboranes hexafluoroisopropanol (HFIP) with different nitrogen sources under air atmosphere. The silver salt HFIP solvent play critical roles present protocol. mechanistic study reveals that acts as Lewis acid to promote electrophilic palladation step forming heterobimetallic active catalyst PdAg(OAc)3; strong hydrogen-bond-donating ability low nucleophilicity enhance Pd(II). It is believed these N-containing are potentially great importance synthesis new pharmaceuticals.

Language: Английский

---

“Cage Walking” Synthetic Strategy for Unusual Unsymmetrical Supramolecular Cages

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(15), P. 8569 - 8575

Published: April 6, 2023

Developing novel assembly methods for supramolecular compounds has long been a research challenge. Herein, we describe how to integrate the B-C coupling reaction and "cage walking" process into coordination self-assembly construct cages. In this strategy, dipyridine linkers containing alkynes react with metallized carborane backbone through then resulting in metallacages. However, without alkynyl groups can form only metallacycles. We regulate size of metallacages based on length bipyridine linkers. When tridentate-pyridine participate reaction, new type ravel is formed. The metallization carboranes, especially cages play vital role reaction. This work provides promising principle synthesis opens up opportunity field.

Language: Английский

---

Supramolecular Architectures Bearing Half-Sandwich Iridium- or Rhodium-Based Carboranes: Design, Synthesis, and Applications

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(36), P. 19440 - 19457

Published: Aug. 29, 2023

The utilization of carboranes in supramolecular chemistry has attracted considerable attention. unique spatial configuration and weak interaction forces can help to explore the properties complexes, particularly via host–guest chemistry. Additionally, certain difficulties encountered carborane development─such as controlled B–H bond activation─can be overcome by judiciously selecting metal centers their adjacent ligands. However, few studies are being conducted this nascent research area. With advances field, novel carborane-based complexes will likely prepared, structurally characterized, intrinsically investigated. To expedite these efforts, we present major findings from recent studies, including π–π interactions, associations, steric effects, which have been leveraged implement a regioselective process for activating B(2,9)–, B(2,8)–, B(2,7)–H bonds para-carboranes B(4,7)–H ortho-carboranes. Future should clarify interactions potential enhancing utility complexes. Although exhibit several (such dihydrogen-bond [Bδ+–Hδ−···Hδ+–Cδ−], Bδ+–Hδ−···M+, Bδ+–Hδ−···π interactions), manner they utilized remains unclear. Supramolecular those based on chemistry, platform demonstrating applications interactions. Owing importance alkane separation, related recognition separation isomers primarily summarized. Advances certainly lead more possibilities

Language: Английский

---

B(9)-OH-o-Carboranes: Synthesis, Mechanism, and Property Exploration

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(13), P. 7331 - 7342

Published: March 24, 2023

Herein, we present a chemically robust and efficient synthesis route for B(9)-OH-o-carboranes by the oxidation of o-carboranes with commercially available 68% HNO3 under assistance trifluoromethanesulfonic acid (HOTf) hexafluoroisopropanol (HFIP). The reaction is highly wide scope carboranes, selectivity B(9)/B(8) up to 98:2. success this transformation relies on strong electrophilicity oxidizability HNO3, promoted through hydrogen bonds Brønsted HOTf solvent HFIP. Mechanism studies reveal that o-carborane involves an initial electrophilic attack atom at most electronegative B(9) o-carborane. In transformation, B-H bond nucleophilic site, which different from substitution reaction, where boron site. Therefore, oxidation-reduction mild conditions in N(V) → N(III) H(-I) H(I). derivatization 9-OH-o-carborane was further examined, carboranyl group successfully introduced amino acid, polyethylene glycol, biotin, deoxyuridine, saccharide. Undoubtedly, approach provides selective way rapid incorporation carborane moieties into small molecules application neutron capture therapy, requires targeted delivery boron-rich groups.

Language: Английский

---