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

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 of the BÀ H and CÀ H functionalities in carboranes have been developed. These methods with great success utilize directing groups, such as carboxylic acids, to achieve a selective BÀ H functionalization of carboranes. The carboxyl group can be easily introduced to carboranes and then be removed after reactions. On the other hand, assisted by the carboxyl group a highly regioselective electrophilic attack at the electron-rich positions B(4) and B(5) of the cage generates five-membered metallacyclic intermediates, which then undergo further transformation. In this review, we show that transition metal-catalyzed decarboxylation cross coupling reactions offer an opportunity for the selective and direct BÀ H activation of carboranes. 1. Introduction 2. Formation of BÀ C(sp 2 ) Bonds 3. Formation of BÀ C(sp) Bonds 4. Formation of BÀ C(sp 3 ) Bonds 5. Formation of BÀ N Bonds 6. Formation of BÀ O Bonds 7. Formation of BÀ X Bonds 8. Formation of BÀ N Bonds and BÀ C(sp 2 ) Bonds 9. Formation of CÀ N Bonds 10. Conclusions and Outlooks

Iridium(III)-catalyzed remote B(9)−H alkylation of o-carboranes with nitrile template

“…Although electrophilic substitution reactions at electron-rich cage boron have been previously accomplished [15][16][17][18][19] , there are signi cant regioselectivity issues due to the small difference in electron density among the similar B − H bonds 20,21 . Accordingly, the development of e cient and site-selective cage boron functionalization merits considerable attention [22][23][24][25][26][27] .…”

Asymmetric synthesis of metallacarboranes using a traceless chiral auxiliary

“…Carboranes are a class of boron-rich cage-like molecular clusters possessing three-dimensional aromaticity. Due to their unique properties in chemical bonding, electronic regulation, thermal stability, shape, lipophilicity etc., 1 in the past decades, great efforts have been made to functionalize [2][3][4] and employ carboranes as the key structural units in polymers, 5,6 optoelectronic materials, [7][8][9] pharmaceuticals, [10][11][12] coordination chemistry 13 and catalysis. 14 Among the known carboranes, o-carborane (o-C 2 B 10 H 12 ), has been the most easily accessible and most studied precursor.…”

Site- and enantioselective B−H functionalization of carboranes

“…1b) 18,19 . However, signi cant advances in the synthesis of chiral molecules possessing carborane moieties have only recently achieved despite of recent progress for the functionalization of carboranes [20][21][22][23][24] . For the rst time, Kalinin and co-workers carried out the direct asymmetric synthesis (up to 32% e.e.)…”