Palladium catalyzed/counter ion tuned selective methylation of o-carboranes

Advances in the selective functionalization of B(3,6)-H of o-carboranes

This review summarizes the methodologies for the selective functionalization of the B(3,6) vertices of o-carboranes, including the deboration-capitation reaction, the coupling reaction of B-X (X = I, Br) bonds, reactions of 1,3-dehydro-o-carborane and [3-N2-o-C2B10H11][BF4] as well as transition-metal-catalyzed B-H activation. These works offer a versatile toolbox for synthesizing B(3,6)-substituted o-carborane derivatives and will promote their applications in material science, pharmaceutical chemistry, and related disciplines.

Iridium-catalyzed selective arylation of B(6)-H of 3-aryl-o-carboranes with arylboronic acid via direct B-H activation

This work discloses an iridium-catalyzed selective arylation of B(6)-H of 3-Ar-o-carboranes with arylboronic acid via direct B-H activation for the first time. A series of unsymmetric and symmetric 3,6-diaryl-o-carboranes decorated with diverse active groups have been synthesized with moderate to excellent yields under mild conditions. This work offers an efficient approach for selective arylation of B(6)-H with arylboronic acid and has important value for selective functionalization of o-carboranes.

Theoretical calculation of regioselectivity and solvation effects on B-H activation of O-carborane guided by directing group

This study focuses on uncovering the regioselectivity, directing group, ligand, and solvation effect in B-H activation, which was investigated by DFT calculations. The reaction mechanism was investigated in vacuum, and the advantageous reaction pathway and rate-determining step were determined. Furthermore, the solvation effects and the ligand that coordinated with Pd were studied. The results showed that in neutral and cationic pathways, the anion (OTf)/ligand (1,10-phenanthroline) exerted significant influence on the transition metal catalytic center Pd, thus affecting B-H activation at different sites. The solvation effects also exerted significant influence on the reaction. The greater the polarity of the solvent, the greater the influence on the energies of all stationary points.

The in Situ NHC-Palladium Catalyzed Selective Activation of B(3)-H or B(6)-H Bonds of o-Carboranes for Hydroboration of Alkynes: An Efficient Approach to Alkenyl-o-carboranes

An in situ Pd-NHC catalyzed selective B(3,6)-H activation for hydroboration of internal alkynes has been accomplished under mild conditions. This work offers a facile approach for the synthesis of alkenyl-o-carboranes and has important reference for selective functionalization of B(3,6)-H bonds.

Palladium Catalyzed Selective B(3)-H Activation/Oxidative Dehydrogenative Coupling for the Synthesis of Bis(o-carborane)s

A palladium catalyzed selective B(3)-H activation/oxidative dehydrogenative coupling for the synthesis of bis(o-carborane)s connected with B(3)-B(3') and B(3)-B(6') bonds has been developed for the first time. A plausible mechanism involving stepwise activation of B(3)-H and B(3'/6')-H bonds by Pd^II and Pd^IV was proposed. This work is the first example and the most efficient protocol for synthesis of bis(o-carborane)s connected with B(3)-B(3') and B(3)-B(6') bonds, which has important reference for design, synthesis, and application of bis(o-carborane)s in related fields.

Synthesis of Polyhedral Borane Cluster Fused Heterocycles via Transition Metal Catalyzed B-H Activation

Aromatic heterocycles are ubiquitous building blocks in bioactive natural products, pharmaceutical and agrochemical industries. Accordingly, the carborane-fused heterocycles would be potential candidates in drug discovery, nanomaterials, metallacarboranes, as well as photoluminescent materials. In recent years, the transition metal catalyzed B-H activation has been proved to be an effective protocol for selective functionalization of B-H bond of o-carboranes, which has been further extended for the synthesis of polyhedral borane cluster-fused heterocycles via cascade B-H functionalization/annulation process. This article summarizes the recent progress in construction of polyhedral borane cluster-fused heterocycles via B-H activation.