"Cage Walking" Synthetic Strategy for Unusual Unsymmetrical Supramolecular Cages.

Developing novel assembly methods for supramolecular compounds has long been a research challenge. Herein, we describe how to integrate the B-C coupling reaction and "cage walking" process into coordination self-assembly to construct supramolecular cages. In this strategy, dipyridine linkers containing alkynes react with the metallized carborane backbone through B-C coupling and then "cage walking" resulting in metallacages. However, dipyridine linkers without alkynyl groups can form only metallacycles. We can regulate the size of metallacages based on the length of the alkynyl bipyridine linkers. When tridentate-pyridine linkers participate in this reaction, a new type of ravel is formed. The metallization of carboranes, the B-C coupling reaction, and especially the "cage walking" process of carborane cages play a vital role in this reaction. This work provides a promising principle for the synthesis of metallacages and opens up a novel opportunity in the supramolecular field.

Synthesis of Carborane-Backbone Metallacycles for Highly Selective Capture of n-Pentane.

The specific recognition and separation of alkanes with similar molecular structures and close boiling points face significant scientific challenges and industrial demands. Here, rectangular carborane-based metallacycles were designed to selectively encapsulate n-pentane from n-pentane, iso-pentane, and cyclo-pentane mixtures in a simple-to-operate and more energy-efficient way. Metallacycle 1, bearing 1,2-di(4-pyridyl) ethylene, can selectively separate n-pentane from these three-component mixtures with a purity of 97%. The selectivity is ascribed to the capture of the preferred guest with matching size, C-H···π interactions, and potential B-Hδ-···Hδ+-C interactions. Besides, the removal of n-pentane gives rise to original guest-free carborane-based metallacycles, which can be recycled without losing performance. Considering the variety of substituted carborane derivatives, metal ions, and organic linkers, these new carborane-based supramolecular coordination complexes (SCCs) may be broadly applicable to other challenging recognition and separation systems with good performance.

Steric-Effects-Directed B-H Bond Activation of para-Carboranes.

The controllable B-H bond activation of carboranes has long been a compelling challenge. However, as the symmetry of para-carborane places the same charge on all of its ten boron atoms, controlling the regiochemistry of B-H bond activation in these molecules has remained out of reach ever since their discovery. Herein, we describe how to use steric effects to achieve a regioselective process for B-H activation of para-carborane. In this strategy, B(2,8)-H or B(2,7)-H activation patterns were achieved by taking advantage of the π-π interactions between pyridine ligands. Interestingly, by employing host-guest interactions in metallacage compounds, B(2,8)-H bond activation could be avoided and exclusive B(2,9)-H bond activation can be achieved. Steric hindrance was also found to be beneficial for regioselective B(2,8)-H bond activation in metallacage species. In this work, we demonstrate that steric effects can be a promising driving force for controllable activation of the B-H bonds of carboranes and open new opportunities in this field.

Metalloradicals Supported by a meta-Carborane Ligand.

In this work, a pincer-type complex [Cp*Ir-(SNPh)(SNHPh)(C2 B10 H9 )] (2) was synthesized and its reactivity studied in detail. Interestingly, molecular hydrogen can induce the transformation between the metalloradical [Cp*Ir-(SNPh)2 (C2 B10 H9 )] (5. ) and 2. A mixed-valence complex, [(Cp*Ir)2 -(SNPh)2 (C2 B10 H8 )] (7.+ ), was also synthesized by one-electron oxidation. Studies show that 7.+ is fully delocalized, possessing a four-centered-one-electron (S-Ir-Ir-S) bonding interaction. DFT calculations were also in good agreement with the experimental results.

Regioselective B(3)-H bond activation based on an o-carboranyl dithiocarboxylate ligand and its derivatives.

Herein, we describe the synthesis of tetraphenylphosphonium o-carboranyl dithiocarboxylate (Ligand 1) and methyldithiocarboxyl-o-carborane (Ligand 2). The complexes [Cp*M(o-C2B10H11CS2)Cl] (M = Ir (3); Rh (4)) and [Cp*M(o-C2B10H11CS2)2] (M = Ir (5); Rh (6)) have been synthesized based on Ligand 1. The selective B-H bond activation of Ligand 2 has also been explored, leading to the synthesis of the B-H activated complex [Cp*Ir(o-C2B10H10CS2CH3)Cl] (7) and four of its substituted derivatives (8, 9, 10 and 11). All of these compounds have been characterised through single-crystal X-ray diffraction, NMR, IR spectroscopy and elemental analysis.

Transition metal-mediated B(4)-H hydroxylation/halogenation of o-carboranes bearing a 2-pyridylsulfenyl ligand.

The introduction of the 2-pyridylsulfenyl directing group to o-carboranes allowed either B(3)-Ir or B(4)-Ir bond formation using a steric effect strategy. Moreover, the reactivity of the B(4)-Rh o-carborane complexes with small molecules was probed by reactions with N-bromosuccinimide, N-iodosuccinimide and O2. Rhodium-mediated B(4)-hydroxylation and B(4)-halogenation which are seldom reported have been achieved under practical and mild conditions.

Regioselective B-H/C-H activation and metal-metal bond formation induced by half-sandwich metals complexes at hydroxy-substituted o-carboranes.

A binuclear iridium complex, (Cp2*Ir2(CH2O)C2B10H8) (6), with a unique metal-metal bond has been synthesized and fully characterized. Importantly, this complex is constructed via selective C-H and B(3)-H bond activation on the carborane precursor. Additionally, when the proligand (2-pyridine)(o-carboranyl)methanol ligand was combined with a half-sandwich iridium complex, selective B(6)-H bond activation or metal-carbon bond formation can be induced by the use of different bases. And the rhodium complex constructed from (2-pyridine)(o-carboranyl)methanol ligand containing a metal-carbon bond has been obtained and fully characterized.

Iridium-induced regioselective B-H and C-H activations at azo-substituted m-carboranes: facile access to polynuclear complexes.

Iridium(iii)-induced selective B(2,3)-H and C-H bond activations at mono- and bi-p-methoxybenzeneazo-substituted m-carboranes have been investigated. A powerful methodology is introduced for the preparation of unique polynuclear complexes featuring m-carboranyl ligands in a single step. The experimental results highlight that the base employed in the reaction plays a key role in the formation and the structures of the complexes.