Coordination-Driven Self-Assemblies with a Carborane Backbone

Theoretical investigations of the Ir-catalyzed direct borylation of B(3,6)–H of o-carborane: the actual catalyst, mechanism, and origin of regioselectivity

The Ir^III species is proved to be the actual catalyst. The electron-delocalized structure and the inductive effects of the carbon centers is account for the regioselectivity.

Synthesis of carborane-fused carbo- and heterocycles via zirconacyclopentane intermediates

Carborane-fused zirconacyclopentane serves as an important synthon for the preparation of a variety of carborane-fused carbo- and heterocycles via insertion and transmetalation reactions.

Structural phase diagrams and isomerism inflexible honeycomb-like 2D hydrogen bonded solid solutions

Solid solutions of hydrogen bonded networks of the formula ((1-2H⁺)_3x(2-2H⁺)_3(1–x)([Fe(CN)₆]₂³⁻))·nH₂O, where (1-2H⁺) and (2-2H⁺) are bisamidinium H bond donor entities, have been prepared and structurally analysed.

Efficient access to amides of the carborane carboxylic acid [1-(COOH)–CB11H11]−

The preparation of the carborane acid chloride [1-(COCl)–CB₁₁H₁₁]⁻ from the carboxylic acid [1-(COOH)–CB₁₁H₁₁]⁻ is reported. This acid chloride exhibits remarkable inertness towards moisture and can be stored under ambient conditions for several months. Reaction with amines affords secondary and tertiary carborane amides [1-(CONR¹R²)–CB₁₁H₁₁]⁻ in moderate to high yields under mild conditions. Two of the amide products were characterized by X-ray crystallography in addition to spectroscopic analysis. Preliminary studies show that the amides can be reduced to the corresponding amines and that the acid chloride has the potential to serve as a starting material for carborane ester formation.

The preparation of the carborane acid chloride [1-(COCl)–CB₁₁H₁₁]⁻ from the carboxylic acid [1-(COOH)–CB₁₁H₁₁]⁻ and subsequent amide formation are reported.

Synthesis of Dicarba-closo-dodecaborane-1-carboxamides

Amide bond formation is one of the most important chemical reactions. In peptide and organic chemistry, the application of amide coupling reagents is a routine strategy, but surprisingly not in carborane chemistry. Thus, we now report a fast, safe, and robust protocol to couple amines to m- and p-dicarba-closo-dodecaborane-1-carboxylic acids. The procedure comprises the activation of carboxylic acid with the coupling reagent (1-cyano-2-ethoxy-2-oxoethylidenaminooxy)(dimethylamino)morpholinocarbenium hexafluorophosphate, extraction of the product using the hydrophobic nature of the cluster, and a straightforward chromatographic purification. The protocol allows access to a variety of carborane-organic hybrid molecules suitable for application in multiple areas.

Iridium-catalysed regioselective borylation of carboranes via direct B-H activation

Carboranes are carbon-boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B-H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)-H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B₂pin₂) as a reagent. Selective cage B(4)-H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)₂-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B-X (X=O, N, C, I and Br) bonds.

Dehydrogenative cross-coupling of o-carborane with thiophenes via Ir-catalyzed regioselective cage B–H and C(sp2)–H activation

Iridium-catalyzed carboxylic acid directed site-selective B–H/C–H dehydrogenative cross-coupling of o-carborane with thiophenes has been achieved for the first time, leading to the preparation of 4-thienyl-o-carboranes in a simple one-pot process for potential applications in materials.

The synthesis and reactivity of 16-electron half-sandwich iridium complexes bearing a carboranylthioamide ligand

The 16-electron complex 2 has been synthesized. It can react with different donor ligands and undergoes M–S bond insertion reactions with DMAD. Complex 2 is shown to react with [Cp*Ir] unit to form a M–M-bound binuclear complex. Interestingly, the metal–metal bond could be broken by HCl to produce the selective B(6)–H activation species.

Photoarylation of Iodocarboranes with Unactivated (Hetero)Arenes: Facile Synthesis of 1,2-[(Hetero)Aryl]n -o-Carboranes (n=1,2) and o-Carborane-Fused Cyclics

Photoarylation of iodocarboranes with unactivated arenes/heteroarenes at room temperature has been achieved, for the first time, thus leading to the facile synthesis of a large variety of cage carbon mono(hetero)arylated and di(hetero)arylated o-carboranes. This work represents a clean, efficient, transition-metal-free, and cheap synthesis of functionalized carboranes, which has significant advantages over the known methods.

Palladium catalyzed regioselective B-C(sp) coupling via direct cage B-H activation: synthesis of B(4)-alkynylated o-carboranes

Pd-catalyzed carboxylic acid guided regioselective alkynylation of cage B(4)-H bonds in o-carboranes has been achieved for the first time using two different catalytic systems. In the presence of 5 mol% Pd(OAc)₂ and 3 equiv. of AgOAc, the reaction of 1-COOH-2-R¹-C₂B₁₀H₁₀ with R₃SiC[triple bond, length as m-dash]CBr in ClCH₂CH₂Cl gives 4-(R₃SiC[triple bond, length as m-dash]C)-2-R¹-o-C₂B₁₀H₁₀ in moderate to high yields. This reaction is compatible with alkynes possessing sterically bulky silyl groups such as ⁱPr₃Si or ^t BuMe₂Si. Meanwhile, another catalytic system of Pd(OAc)₂/AgOAc/K₂HPO₄ can catalyze the direct B(4)-alkynylation of 1-COOH-2-R¹-C₂B₁₀H₁₀ with terminal alkynes R²C[triple bond, length as m-dash]CH in moderate to high yields. The latter has a broader substrate scope from bulky silyl to aromatic to carboranyl substituents. Desilylation of the resultant products affords carboranyl acetylene 4-(HC[triple bond, length as m-dash]C)-2-R¹-o-C₂B₁₀H₁₀ which can undergo further transformations such as Sonogashira coupling, dimerization and click reactions. It is suggested that the above two catalytic systems may proceed via Pd(ii)-Pd(iv)-Pd(ii) and Pd(ii)-Pd(0)-Pd(ii) catalytic cycles, respectively. In addition, the silver salt is found to promote the decarboxylation reaction and thereby controls the mono-selectivity.

Phosphine-catalyzed cage carbon functionalization of o-carborane: facile synthesis of alkenylcarboranes

Phosphines can efficiently catalyze alkenylation of o-carborane with electron-deficient alkynes, which represents the first example of organocatalysis in o-carborane functionalization.

Palladium-Catalyzed Regioselective Diarylation of o-Carboranes By Direct Cage B-H Activation

Palladium-catalyzed intermolecular coupling of o-carborane with aromatics by direct cage B-H bond activation has been achieved, leading to the synthesis of a series of cage B(4,5)-diarylated-o-carboranes in high yields with excellent regioselectivity. Traceless directing group -COOH plays a crucial role for site- and di-selectivity of such intermolecular coupling reaction. A Pd(II)-Pd(IV)-Pd(II) catalytic cycle is proposed to be responsible for the stepwise arylation.

Construction of multiferrocenyl metallacycles and metallacages via coordination-driven self-assembly: from structure to functions

Recently, the construction of discrete multiferrocenyl organometallic structures via coordination-driven self-assembly has attracted considerable attention because of their interesting electrochemical properties and wide range of applications in the areas of organometallic chemistry, electrochemistry, and materials science. Coordination-driven self-assembly has proven to be a simple yet highly efficient approach for the preparation of various multiferrocenyl metallacycles and metallacages with predetermined shapes and sizes as well as the distribution and total number of ferrocenes. This review focuses on the recent progress in the construction of a variety of discrete multiferrocenyl metallacycles and metallacages via coordination-driven self-assembly. The characterization, the structure-related electrochemical properties, and the applications of these multiferrocenyl supramolecular architectures are also discussed.

Palladium-catalyzed regioselective intramolecular coupling of o-carborane with aromatics via direct cage B-H activation

Palladium-catalyzed intramolecular coupling of o-carborane with aromatics via direct cage B-H bond activation has been achieved, leading to the synthesis of a series of o-carborane-functionalized aromatics in high yields with excellent regioselectivity. In addition, the site selectivity can also be tuned by the substituents on cage carbon atom.

Intramolecular hydrogen bonding stabilizes the nuclearity of complexes. A comparative study based on the H-carborane and Me-carborane framework

The H– on the adjacent carbon of the carboranylcarboxylate ligand is responsible for intramolecular interactions that stabilize the nuclearity of Cu(ii) complexes.

Energy transfer within self-assembled cyclic multichromophoric arrays based on orthogonally arranged donor–acceptor building blocks

We herein present the coordination-driven supramolecular synthesis and photophysics of a [4+4] and a [2+2] assembly, built up by alternately collocated donor–acceptor chromophoric building blocks based, respectively, on the boron dipyrromethane (Bodipy) and perylene bisimide dye (PBI). In these multichromophoric scaffolds, the intensely absorbing/emitting dipoles of the Bodipy subunit are, by construction, cyclically arranged at the corners and aligned perpendicular to the plane formed by the closed polygonal chain comprising the PBI units. Steady-state and fs time-resolved spectroscopy reveal the presence of efficient energy transfer from the vertices (Bodipys) to the edges (PBIs) of the polygons. Fast excitation energy hopping – leading to a rapid excited state equilibrium among the low energy perylene-bisimide chromophores – is revealed by fluorescence anisotropy decays. The dynamics of electronic excitation energy hopping between the PBI subunits was approximated on the basis of a theoretical model within the framework of Förster energy transfer theory. All energy-transfer processes are quantitatively describable with Förster theory. The influence of structural deformations and orientational fluctuations of the dipoles in certain kinetic schemes is discussed.

Palladium catalyzed selective mono-arylation of o-carboranes via B–H activation

Palladium catalyzed selective mono-arylation of o-carborane on B(8) and B(9).

Palladium catalyzed regioselective mono-alkenylation of o-carboranes via Heck type coupling reaction of a cage B–H bond

Palladium catalyzed electrophilic B–H activation for regioselective mono-alkenylation of o-carborane on B(8) and B(9).

Directed flexibility: self-assembly of a supramolecular tetrahedron

Self-assembly of 4 terpyridine-modified, flexible crown ether ligands with 12 Zn²⁺ ions results in high yield tetrahedron construction.

Carba-closo-dodecaborate anions with two functional groups: [1-R-12-HC≡C-closo-1-CB₁₁H₁₀]⁻ (R = CN, NC, CO₂H, C(O)NH₂, NHC(O)H)

Disubstituted carba-closo-dodecaborate anions with one functional group bonded to the cluster carbon atom and one ethynyl group bonded to the antipodal boron atom were synthesized from easily accessible {closo-1-CB11} clusters. [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b) was prepared starting from Cs[12-Et3SiC≡C-closo-1-CB11H11] (Cs1c) via salts of the anions [1-HO(O)C-12-HC≡C-closo-1-CB11H10](-) (2b) and [1-H2N(O)C-12-HC≡C-closo-1-CB11H10](-) (3b). In a similar reaction sequence [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b) was obtained from Cs[1-H2N-12-HC≡C-closo-1-CB11H10] (Cs5b) by formamidation to yield [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b) and successive dehydration. In addition, the synthesis of the isonitrile [Et4N][1-CN-closo-1-CB11H11] ([Et4N]7a) is presented. The {closo-1-CB11} derivatives were characterized by multinuclear NMR as well as vibrational spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of [Et4N][1-HO(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]2b), [Et4N][1-H2N(O)C-12-HC≡C-closo-1-CB11H10] ([Et4N]3b), [Et4N][1-NC-12-HC≡C-closo-1-CB11H10] ([Et4N]4b), [Et4N][1-H(O)CHN-12-HC≡C-closo-1-CB11H10] ([Et4N]6b), [Et4N][1-CN-12-HC≡C-closo-1-CB11H10] ([Et4N]7b), and K[1-H(O)CHN-closo-1-CB11H11] ([Et4N]6a) were determined. The transmission of electronic effects through the carba-closo-dodecaboron cage was studied based on (13)C NMR spectroscopic data, by results derived from density functional theory calculations, and by a comparison to the data of related benzene and bicyclo[2.2.2]octane derivatives.