Photoredox B-H functionalization to selective B-N(sp3) coupling of nido-carborane with primary and secondary amines

Organocatalytic Asymmetric Synthesis of o-Carboranyl Amines

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

Charge-Compensated Derivatives of Nido-Carborane

This review summarizes data on the main types of charge-compensated nido-carborane derivatives. Compared with organic analogs, onium derivatives of nido-carborane have increased stability due to the stabilizing electron-donor action of the boron cage. Charge-compensated derivatives are considered according to the type of heteroatom bonded to a boron atom.

Selective Labeling of Peptides with o-Carboranes via Manganese(I)-Catalyzed C-H Activation

A robust method for the selective labeling of peptides via manganese(I) catalysis was devised to achieve the C-2 alkenylation of tryptophan containing peptides with 1-ethynyl-o-carboranes. The manganese-catalyzed C-H activation was accomplished with high catalytic efficiency, and featured low toxicity, high functional group tolerance and excellent E-stereoselectivity. This approach unravels a promising tool for the assembly of o-carborane with structurally complex peptides of relevance to applications in boron neutron capture therapy.

Pd-Catalyzed Selective B(6)-H Phosphorization of nido-Carboranes via Cascade Deboronation/B-H Activation from closo-Carboranes

Efficient Pd-catalyzed regioselective B(6)-H phosphorization of nido-carboranes via cascade deboronation/B-H activation of readily available C-substituted o-carboranes with various phosphines using 3-methylpyridine or isoquinoline as a directing group in combination with pyridine ligands has been developed, affording unprecedented B(6)-phosphinated nido-carborane derivatives with high selectivity in a simple one-pot process.

Cyclic Carbonate Synthesis from Epoxides and CO2 Catalyzed by Aluminum-Salen Complexes Bearing a nido-C2B9 Carborane Ligand

The active and well-designed Schiff base ligands are considered "privileged ligands". The so-called salen ligands, i.e., the tetradentate [O, N, N, O] bis-Schiff base ligands, have also found broad applications in many homogeneous catalytic reactions. Modification of the salen ligands has concentrated on altering the substituents in the phenolate rings and variations in the diamine backbones. Herein, o-carborane-supported salen ligands (2) were designed and prepared. A series of aluminum-salen complexes (3·(sol)₂), which were supported by the nido-C₂B₉ carborane anions, were synthesized. These Al(III) complexes showed high activities (TOF up to 1500 h^-1) in catalyzing the cycloaddition of epoxides and CO₂ at atmospheric pressure and near room temperature. Complexes 3·(sol)₂ are one of the rare examples of Al-based catalysts capable of promoting cycloaddition at 1 bar pressure of CO₂. Density functional theory (DFT) studies combined with the catalytic results reveal that the catalytic cycles occur on two axial sites of the Al(III) center.

Synthesis and Reactivity of Cyclic Oxonium Derivatives of nido-Carborane: A Review

Nucleophilic ring-opening reactions of cyclic oxonium derivatives of anionic boron hydrides are a convenient method of their modification which opens practically unlimited prospects for their incorporation into various macro- and biomolecules. This contribution provides an overview of the synthesis and reactivity of cyclic oxonium derivatives of nido-carborane as well as half-sandwich complexes based on it.