Methods to produce B-C, B-P, B-N and B-S bonds in boron clusters

Rapid Synthesis of Redox-Active Dodecaborane B12(OR)12 Clusters Under Ambient Conditions

We have developed a fast and efficient route to obtain perfunctionalized ether-linked alkyl and benzyl derivatives of the closo-[B12(OH)12]2- icosahedral dodecaborate cluster via microwave-assisted synthesis. These icosahedral boron clusters exhibit three-dimensional delocalization of the cage-bonding electrons, tunable photophysical properties, and a high degree of stability in air in both solid and solution states. A series of closo-[B12(OR)12]2-, hypocloso-[B12(OR)12]1- and hypercloso-[B12(OR)12]0 clusters have been prepared with reaction times ranging from hours to several minutes. This method is superior to previously reported protocols since it dramatically decreases the reaction times required and eliminates the need for inert atmosphere conditions. The generality of the new microwave-based method has been further demonstrated through the synthesis of several new derivatives, which feature redox potentials up to 0.6 V more positive than previously known B12(OR)12 cluster compounds. We further show how this method can be applied to a one-pot synthesis of hybrid, vertex-differentiated species B12(OR)11(OR) that was formerly accessible only via multi-step reaction sequence.

Inductive effects of 10 and 12-vertex closo-carborane anions: cluster size and charge make a difference

The inductive effects of 10 and 12-vertex closo-carborane anion ligand substituents are elucidated for the first time. It is found that both of these cluster substituents are potent electron donating groups, which is in contrast to C-functionalized o-carborane. The fact that the 10-vertex cluster displays the strongest electron donating ability can be rationalized by its charge and size.

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/silver tuned selective mono-/tetra-acetoxylation of o-carboranes via B–H activation

Silver tuned the selective mono-/tetra-acetoxylation of o-carboranes via palladium catalyzed B–H activation.

The synthesis, structure and reactivity of an imine-stabilized carboranylphosphorus(i) compound

An imine-stabilized carboranylphosphorus(i) compound has been synthesized, where the imine moiety serves as a σ donor and sterically demanding carboranyl ligand prevents the dimerization, which has been supported by single-crystal X-ray analyses, DFT calculations and reactivity studies.

A carborane-triggered metastable charge transfer state leading to spontaneous recovery of mechanochromic luminescence

Spontaneous recovery of mechanochromic luminescence was realized by carborane-functionalized anthracene derivatives.

Anionic and zwitterionic carboranyl N-heterocyclic carbene Au(i) complexes

The syntheses of the first carboranyl N-heterocyclic carbene complexes with transition metals are reported.

Polyfluorinated carba-closo-dodecaboranes with amino and ammonio substituents bonded to boron

The inner salts x-H3N-closo-1-CB11H11 (x = 12, 2) and 7-H3N-12-F-closo-1-CB11H11 were fluorinated with elemental fluorine in anhydrous hydrogen fluoride to give the B-perfluorinated ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2). Deprotonation of the ammonio group yielded the corresponding amino-functionalized anions [1-H-x-H2N-closo-1-CB11F10](-) (x = 12, 7, 2) that were isolated as [Et4N](+) salts. Hydrolysis of the highly fluorinated inner salts 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) is very slow in acidic aqueous solutions. This stability of the ammonio derivatives is unprecedented because the related fluorinated anion [1-H2N-closo-1-CB11F11](-) is immediately hydrolyzed to simple boron species in the presence of aqueous acids. The ammonio derivatives 1-H-x-H3N-closo-1-CB11F10 (x = 12, 7, 2) are much more acidic compared to their non-fluorinated counterparts as assessed from potentiometric titrations and DFT calculations. The inner salts and the anions were characterized by NMR and vibrational sepectroscopy. Solid-sate structures of 1-H-12-H3N-closo-1-CB11F10·H2O, 1-H-7-H3N-closo-1-CB11F10·diglyme, 1-H-2-H3N-closo-1-CB11F10·0.5H2O, 7-H3N-12-F-closo-1-CB11H10·(CH3)2CO and [Et4N][1-H-12-H2N-closo-1-CB11F10] were determined by single-crystal X-ray diffraction.

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.

o-Carborane functionalized pentacenes: synthesis, molecular packing and ambipolar organic thin-film transistors

New 6,13-bis[1'-(C≡C)-2'-R-1',2'-C2B10H10]pentacenes (R = H, Me, Et, n-Bu) are synthesized and fully characterized. The results show that the alkyl substituents on the second cage carbon have a significant impact on the molecular packing, and the incorporation of the o-carboranyl moiety into a π conjugated system can lower both LUMO and HOMO energy levels, converting a typical p-type semiconductor into an ambipolar one.

Oxidation of germa- and stanna-closo-dodecaborate

The oxidation of closo-heteroborates [GeB11H11](2-) and [SnB11H11](2-) is presented. Upon oxidation germa-closo-dodecaborate yields a symmetrical dimer exhibiting a Ge-Ge bond between two clusters. This dimer shows sulphur insertion into the Ge-Ge bond at room temperature. In contrast, oxidation of the homologous tin cluster results in an unsymmetrical dimer bearing an Sn-B bond between two clusters. The Sn-B dimer is also the product of the hydride abstraction reaction. In the presence of the donor ligand 2,2'-bipyridine, the oxidation of closo-cluster [SnB11H11](2-) leads to the Sn(IV)-half sandwich coordination compound [bipy-SnB11H11] which dissolves in DMSO to give the Sn(IV)-adduct [bipy(DMSO)-SnB11H11].

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.

The effect of a paramagnetic metal ion within a molecule: comparison of the structurally identical paramagnetic [3,3-Fe(1,2-C2B9H11)2]− with the diamagnetic [3,3-Co(1,2-C2B9H11)2]− sandwich complexes

Effects on the NMR spectra of a paramagnetic metal ion are clearly observed by comparing identical sandwich molecular structures of diamagnetic [3,3′-Co(1,2-C₂B₉H₁₁)₂]⁻ with paramagnetic [3,3′-Fe(1,2-C₂B₉H₁₁)₂]⁻.

Synthesis and chemistry of the open-cage cobaltaheteroborane cluster [{(η5-C5Me5)Co}2B2H2Se2]: a combined experimental and theoretical study

An open cage triple-decker molecule with three planar rings almost parallel to each other (see the picture).

Cation reduction and comproportionation as novel strategies to produce high voltage, halide free, carborane based electrolytes for rechargeable Mg batteries

The chemical reduction of reactive cations and comproportionation are two new strategies reported to produce halide free carborane based electrolytes for rechargeable Mg batteries.

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).

Syntheses and reductions of C-dimesitylboryl-1,2-dicarba-closo-dodecaboranes

An investigation ofC-dimesitylboryl-ortho-carboranes, 1-(BMes₂)-2-R-1,2-C₂B₁₀H₁₀(1and2), reveals that the carborane is the electron-acceptor and the mesityl group is the electron-donor in these dyads.

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).

Synthesis of unsymmetrical N-carboranyl NHCs: directing effect of the carborane anion

The selective synthesis of unsymmetrically substituted anionic C-2 and dianionic C-2/C-5 N-carboranyl NHCs is reported, revealing a directing effect conveyed by the anionic carborane substituent.

Regioselective insertion of o-carborynes into the α-C-H bond of tertiary amines: synthesis of α-carboranylated amines

o-Carboryne can undergo α-CH bond insertion with tertiary amines, thus affording α-carboranylated amines in very good regioselectivity and isolated yields. In this process, the nucleophilic addition of tertiary amines to the multiple bond of o-carboryne generates a zwitterionic intermediate. An intramolecular proton transfer, followed by a nucleophilic attack leads to the formation of the final product. Thus, regioselectivity is highly dependent upon the acidity of α-CH proton of tertiary amines. This approach serves as an efficient methodology for the preparation of a series of 1-aminoalkyl-o-carboranes.