Cage-···Cage- Interaction: Boron Cluster-Based Noncovalent Bond and Its Applications in Solid-State Materials

Intercluster B-H and B-B aggregation in iso- and trans-[B20H18]2-. Spherical aromaticity in borane dimers

The formation of molecular-based functional materials is a key step towards the development of technologies at the nanoscale. Recently, it has been shown that after oxidation of closo-[B10H10]2- anions, an induced aggregation of two cluster units is achieved, retaining their parent B10 backbones as persistent building blocks. Such characterization provides an interesting scenario to further understand relevant factors leading to aggregation in a minimal structure involving two units. Here, we explore the interaction between closo-[B10H10]2- units in two isomers, namely, iso- and trans-[B20H18]2-, involving different intercluster contacts based on B-B and B-H interactions, respectively. Our results show that the inherent spherical aromatic characteristics of the parent closo-[B10H10]2- cluster are persistent in both iso- and trans-[B20H18]2- isomers as an interplay between the spherical aromatic properties from both B10 motifs, leading to an overlap of the shielding regions from shielding cone properties, ascribed as a dual spherical-spherical aromatic cluster. From 11B-NMR features, it came out that trans-[B20H18]2- involves larger differences in comparison to closo-[B10H10]2-, owing to the variation of the B10-B10 backbone provided by the intercluster B-interaction, thus resulting in a more effective aggregation connecting such building units, towards boron-based cluster materials.

A Pd-catalyzed route to carborane-fused boron heterocycles

Due to the expanding applications of icosahedral carboranes in medicinal and materials chemistry research, their functionalizations have become one of the central themes in boron-rich cluster chemistry. Although several strategies for incorporating nitrogen-containing nucleophiles on a single boron vertex of the icosahedral carboranes (C2B10H12) have been developed, methods for preparing clusters with vicinal B-N moieties are still lacking. The steric bulk of icosahedral carboranes and disparate electronic and steric nature of the N-containing groups have rendered the vicinal diamination challenging. In this article, we show how a developed Pd-catalyzed process is used to incorporate an array of NH-heterocycles, anilines, and heteroanilines with various electronic and steric profiles onto the vicinal boron vertices of a meta-carborane cluster via sequential or one-pot fashion. Importantly, oxidative cyclizations of the cross-coupling products with indoles and pyrroles appended to boron vertices generate a previously unknown class of all-boron-vertex bound carborane-fused six- and seven-membered ring heterocycles. Photophysical studies of the meta-carborane-fused heterocycles show that these structures can exhibit luminescence with high quantum yields and are amenable to further manipulations.

Carborane-based heteromolecular extended networks driven by directional C-Te⋯N chalcogen bonding interactions

We demonstrate that o-closo-(TeMe)2carborane directs, in the presence of linear ditopic neutral Lewis bases, the formation of co-crystals with 1D extended supramolecular networks. Specifically, the network formation is systematically stabilized by short and quasi-linear C-Te⋯N chalcogen-bonding (ChB) interactions. In sum, we report efficient carborane-based tectons to rationally design high-dimensional neutral heteromolecular networks.

Vertex Differentiation Strategy for Tuning the Physical Properties of closo-Dodecaborate Weakly Coordinating Anions

We report the synthesis and characterization of various compounds containing the 1,7,9-hydroxylated closo-dodecahydrododecaborate (B12H9(OH)32-) cluster motif. Specifically, we show how the parent compound can be synthesized on the multigram scale and further perhalogenated, leading to a new class of vertex-differentiated weakly coordinating anions. We show that a postmodification of the hydroxyl groups by alkylation affords further opportunities for tailoring these anions' stability, steric bulk, and solubility properties. The resulting dodecaborate-based salts were subjected to a full thermal and electrochemical stability evaluation, showing that many of these anions maintain thermal stability up to 500 °C and feature no redox activity below ∼1 V vs Fc/Fc+. Mixed hydroxylated/halogenated clusters show enhanced solubility compared to their purely halogenated analogs and retain weakly coordinating properties in the solid state, as demonstrated by ionic conductivity measurements of their Li+ salts.

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

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