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

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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

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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

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Synthesis, Characterization, and Density Functional Theory Studies of Three-Dimensional Inorganic Analogues of 9,10-Diboraanthracene—A New Class of Lewis Superacids

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(23), P. 8552 - 8558

Published: May 13, 2021

The three-dimensional inorganic analogues of 9,10-diboraanthracene, B2X2(C2B10H10)2 (X = Cl, 1; X Br, 2), were attained by salt elimination Li2C2B10H10 and trihaloboranes. methyl- phenyl-substituted compounds B2Me2(C2B10H10)2 (3) B2Ph2(C2B10H10)2 (4) obtained treating 1 or 2 with the corresponding Grignard reagents. These fully characterized NMR, cyclic voltammetry (CV), IR, single-crystal X-ray diffraction analyses. Experimental (CV Gutmann–Beckett method) computational (fluoride ion affinity, hydride affinity LUMO energy) results suggest that order Lewis acidity is > 4 3 SbF5. Treatment HSiEt3 gave a rare neutral borane–silane adduct, (Et3SiH)2B2H2(C2B10H10)2 (5). equilibrium 5 in solution was thoroughly investigated spectroscopy quantum calculations.

Language: Английский

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Mechanochemical Iridium(III)-Catalyzed B-Amidation of o-Carboranes with Dioxazolones

Organic Letters, Journal Year: 2021, Volume and Issue: 23(21), P. 8622 - 8627

Published: Oct. 18, 2021

Mechanochemistry was successfully applied to the functionalization of carboranes. The mechanochemical iridium(III)-catalyzed regioselective B(3)- and B(4)-amidation unsubstituted o-carboranes with dioxazolones developed. In addition, substituted demonstrated. Because B-amidation proceeds smoothly without organic solvents or external heating, present method is regarded as a sustainable environmentally friendly surrogate for typical solvent-based reactions.

Language: Английский

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Practical Synthesis of B(9)-Halogenated Carboranes with N-Haloamides in Hexafluoroisopropanol

Inorganic Chemistry, Journal Year: 2022, Volume and Issue: 61(13), P. 5326 - 5334

Published: March 21, 2022

The B(9)-H halogenation of o-carborane and m-carborane was achieved with excellent selectivities in hexafluoroisopropanol (HFIP) under simple reaction conditions: single reagent [trichloroisocyanuric acid (TCCA), tribromoisocyanuric (TBCA) or N-iodosuccinimide (NIS)], catalyst-free, air-/moisture-tolerant, convenient work-up. With this method, a variety 9-halogenated o-carboranes m-carboranes were obtained good to yields broad tolerance functional groups.

Language: Английский

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Iridium-Catalyzed Selective B(4)–H Acylmethylation of o-Carboranes with Sulfoxonium Ylides

Organic Letters, Journal Year: 2022, Volume and Issue: 24(6), P. 1318 - 1322

Published: Feb. 7, 2022

A highly efficient Ir-catalyzed regioselective cage B(4)-H acylmethylation of o-carboranyl acids using sulfoxonium ylides as alkylating regents has been developed, leading to the preparation a large class B(4)-acylmethylated o-carboranes in good excellent yields with broad substrate scope under redox neutral conditions. The -COOH moiety serves traceless directing group and controls regioselectivity monoselectivity.

Language: Английский

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Site‐Selective Functionalization of Carboranes at the Electron‐Rich Boron Vertex: Photocatalytic B−C Coupling via a Carboranyl Cage Radical

Angewandte Chemie International Edition, Journal Year: 2022, Volume and Issue: 61(37)

Published: June 7, 2022

Functionalization of carboranes in a vertex-specific manner is perennial challenge. Here, we report photocatalytic B-C coupling for the selective functionalization at boron site which most distal to carbon. This reaction was achieved by photo-induced decarboxylation carborane carboxylic acids generate vertex-centered carboranyl radicals. Theoretical calculations also demonstrate that more easily occurs bearing higher electron density owing lower energy barrier single-electron transfer radical. By using this strategy, number functionalized could be accessed through alkylation, alkenylation, and heteroarylation under mild conditions. Moreover, both highly efficient blue emitter with solid-state luminous efficiency 42 % drug candidate neutron capture therapy (BNCT) containing targeting fluorine units were obtained.

Language: Английский

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Predicting Dinitrogen Activation by Carborane-Based Frustrated Lewis Pairs

Organometallics, Journal Year: 2022, Volume and Issue: 41(12), P. 1480 - 1487

Published: June 2, 2022

Activation of atmospherically abundant dinitrogen (N2) under mild conditions has been a great challenge in chemistry for decades because the significantly strong N≡N triple bond. The traditional strategy N2 activation was mainly limited to metallic species until ground-breaking achievement by two-coordinated borylenes achieved experimentally 2018. On other hand, carborane derivatives have attracted considerable interest small-molecule activation. Still, utilization remains elusive. Here, we design four types carborane-based frustrated Lewis pairs (FLPs) probe their potential systematical density functional theory calculations. Interestingly, all these FLPs are found become favorable both kinetically and thermodynamically activating with low reaction barriers (ranging from 13.0 25.8 kcal mol–1) high exothermicity, ΔG values ranging −37.5 −51.0 mol–1, indicating metal-free conditions. Our study opens an avenue activation, highlighting importance field

Language: Английский

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Recent Advance in Transition Metal‐Catalyzed Carboxylic Acid Guided B−H Functionalization of Carboranes

Advanced Synthesis & Catalysis, Journal Year: 2022, Volume and Issue: 364(24), P. 4174 - 4188

Published: Dec. 1, 2022

Abstract Carboranes, a three‐dimensional class of carbon‐boron molecular clusters with remarkable electronic, physical, chemical characteristics, have proved as useful building blocks in boron neutron capture therapy agents, supramolecular design, optoelectronics, nanomaterials and organometallic/coordination chemistry. Thus, various organic modifications the B−H C−H functionalities carboranes been developed. These methods great success utilize directing groups, such carboxylic acids, to achieve selective functionalization carboranes. The carboxyl group can be easily introduced then removed after reactions. On other hand, assisted by highly regioselective electrophilic attack at electron‐rich positions B(4) B(5) cage generates five‐membered metallacyclic intermediates, which undergo further transformation. In this review, we show that transition metal‐catalyzed decarboxylation cross coupling reactions offer an opportunity for direct activation magnified image

Language: Английский

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