The synthesis and structural characterization of carborane oligomers connected by carbon-carbon and carbon-boron bonds between icosahedra

The reaction of dilithiated o-carborane (closo-1,2-Li₂-1,2-C₂B₁₀H₁₀) with CuCl₂ gives 1,1′-bis(o-carborane) (1), 1,3′-bis(o-carborane) (2) and 1,4′-bis(o-carborane) (3). Compound 2 (C₄B₂₀H₂₂) crystallizes in the monoclinic space group P2₁/n with A = 6.9275(6), B = 9.7655(8), C = 12.356(1) Å, β = 90.028(2)° and Z = 2. The structure was solved by direct methods and refined to R = 0.048 and R_w = 0.074. Compound 3 (C₄B₂₀H₂₂) crystallizes in the orthorhombic space group P2₁2₁2₁ with A = 6.8854(5), B = 12.523(1), C = 19.847(1) Å and Z = 4. The structure was solved by direct methods and refined to R = 0.078 and R_w = 0.091. The coupling reaction of dilithiated m-carborane (closo-1,7-Li₂-1,7-C₂B₁₀H₁₀) with CuCl₂ results in the formation of 1,1′-bis(m-carborane) (4) and tetra(m-carborane) (5).     

Novel synthesis of 3-iodo-ortho-carborane

A new and convenient route to 3-iodo-ortho-carborane was developed starting from thallium ortho-dicarbollide. This stable dicarbollide derivative can be isolated and purified thus avoiding undesirable by-product formation observed in a more conventional synthetic approach. Thallium dicarbollide readily reacts with boron triiodide in hexane to give the title compound in 70-80% yield and on a scale ranging from several milligrams to tens of grams of 3-iodo-ortho-carborane.     

Rearrangements in icosahedral boranes and carboranes revisited

The structure, stability, and intermolecular rearrangements between ortho-, meta-, and para-C2B10H12 and were investigated using the hybrid density functional B3LYP/6-31G(d) for vibrational frequencies, as well as B3LYP/6-311+G(2d,p) for single-point electronic energies. The general trends in free energies of rearrangement between ortho-C2B10H12 to meta-C2B10H12 and meta-C2B10H12 to para-C2B10H12 presented here are consistent with experimental reaction temperatures. In addition, the majority of the rearrangements can be viewed in terms of concerted diamond-square-diamond steps and triangular face rotations.     

Is o-carborane photoluminescent?

At 77 K in the solid state and in ethanol glasses, o-carborane (1,2-C₂B₁₀H₁₂) shows a relatively intense (? ∼ 10⁻³ at λ_exc = 260 nm) structured photoluminescence (λ_max = 441 nm).In agreement with the rather slow decay of this emission (τ ∼ 4 s) it is suggested to be a phosphorescence. While it appears to be a genuine property of o-carborane an unknown impurity as origin of this luminescence is not completely excluded.     

Carborane-linked 2′-deoxyuridine 5′-O-triphosphate as building block for polymerase synthesis of carborane-modified DNA

5-[(p-Carborane-2-yl)ethynyl]-2′-deoxyuridine 5′-O-triphosphate was synthesized and used as a good substrate in enzymatic construction of carborane-modified DNA or oligonucleotides containing up to 21 carborane moieties in primer extension reactions by DNA polymerases.     

Porosity tuning of carborane-based metal-organic frameworks (MOFs) via coordination chemistry and ligand design

Two new metal-organic framework (MOF) materials based on boron-rich cluster struts (p-carborane) are reported herein. Cu(I) catalyzed coupling chemistry was used to synthesize carboxylate-based ligands, which are substantially longer than the previously studied dicarboxylated p-carborane, leading to structures with greater porosity. Solvothermal syntheses involving these ligands and Zn salts were used to prepare two new Zn(II)-based MOFs with 2D and 3D open framework structures. Upon thermal activation, these MOFs retain the chemical identity of their frameworks, leading to highly porous materials.