Dicarba-closo-dodecaborane(12) derivatives of phosphonium salts: easy formation of nido-carborane phosphonium zwitterions

Charge-Compensated Derivatives of Nido-Carborane

This review summarizes data on the main types of charge-compensated nido-carborane derivatives. Compared with organic analogs, onium derivatives of nido-carborane have increased stability due to the stabilizing electron-donor action of the boron cage. Charge-compensated derivatives are considered according to the type of heteroatom bonded to a boron atom.

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C₂B₆H₈ fragment bridged by the (BH)₂PCl₂⁺ moiety.

In comparison to their neutral or anionic counterparts, examples of cationic boron clusters remain scarce. Here, the authors prepare a variety of cationic polyhedral boranes by reacting closo-10-vertex carboranes with N-heterocyclic carbenes; the resulting open-cage cationic nido- arachno- or closo- derivatives are water soluble, which may enable unprecedented applications.

Selective delivery of remarkably high levels of gadolinium to tumour cells using an arsonium salt

The use of a triphenylarsonium vector for tumour cell-targeting leads to a dramatic increase in Gd³⁺ uptake in human glioblastoma multiforme cells by up to an order of magnitude over the isosteric triarylphosphonium analogue, with significant implications for 'theranostic' applications involving delivery of this important lanthanoid metal ion to tumour cells.

Site-specific synthesis of a hybrid boron-graphene salt

We report the first example of an ionic graphene salt containing boron. An anionic charge is introduced to the graphene surface by means of 7,8-nido-[C2B9H11](-) carborane clusters covalently and electronically bound to the graphene lattice, and this new material was isolated as its Cs(+) salt.

Reversible water activation driven by contraction and expansion of a 12-vertex-closo-12-vertex-nido biscarborane cluster

The metal-free reversible activation of H–OH bonds of water driven by the rearrangement of a boron cluster is presented.

Unprecedented formation of polycyclic diazadiborepine derivatives through cage deboronation of m-carborane

An unprecedented deboronation reaction of icosahedral carboranes is described, in which a BH group of m-carborane is detached from the cage and incorporated into an unusual nido-carborane-anellated diazadiborepine ring system.

Remarkable cage deboronation and rearrangement of a closo-1,12-dicarbadodecaborane to form a neutral nido-7,9-dicarbaundecaborane

Deboronation and cage rearrangement of the closo-1,12-carborane salt [1,12-(PPh2Me)2-1,12-C2B10H10]I2 occurs in refluxing methanol to give the zwitterionic nido-7,9-carborane 7,9-(PPh2Me)2-7,9-C2B9H9. Notably, deboronation and cage substitution of the isomeric closo-1,7-carborane salt [1,7-(PPh2Me)2-1,7-C2B10H10]I2 takes place in methanol to afford the salt [10-OMe-7,9-(PPh2Me)2-7,9-C2B9H9]I.

Extremely Electron-Rich, Boron-Functionalized, Icosahedral Carborane-Based Phosphinoboranes

We have prepared the first examples of B9-connected trivalent aryl and alkyl phosphinoborane species via Pd-catalyzed phosphination of 9-iodo-meta-carborane. Our studies highlight the unique electronic features of the B9-connected meta-carboranyl moiety as compared to its C1-based analogue. This work suggests that the B9-functionalized meta-carboranyl substituent in these ligands exhibits more electron-releasing character than any other known carbon-based substituent, ultimately laying the foundation for a new class of phosphine ligands with extremely electron-rich character.

Synthesis and cellular uptake of boron-rich pyrazolopyrimidines: exploitation of the translocator protein for the efficient delivery of boron into human glioma cells

New 1,2-closo- and 7,8-nido-carboranylpyrazolopyrimidines bind to the translocator protein (TSPO) with high affinity, providing the first evidence of a unique two-site binding profile for the closo-carborane derivative. The boron-rich compounds can also deliver boron to human glioma cells far more effectively than clinical agents used in boron neutron capture therapy (BNCT).

[1,2-Bis(diphenyl-phosphino)-1,2-dicarba-closo-dodeca-borane-κP,P'][7,8-bis-(di-phenyl-phosphino)-7,8-dicarba-nido-undeca-borato-κP,P']gold(I)-dichloro-methane-water (2/1/1)

The title compound, [Au(C₂₆H₃₀B₁₀P₂)(C₂₆H₃₀B₉P₂)]·0.5CH₂Cl₂·0.5H₂O, contains two independent complex mol­ecules in the asymmetric unit. The gold(I) centres display a distorted tetra­hedral geometry. The complex is stablized through weak intra­molecular π–π stacking (Cg⋯Cg = 4.17 Å) and edge-to-face inter­actions (H⋯Cg = 3.21 Å). Adjacent mol­ecules inter­act through C—H⋯π (H⋯Cg = 2.88 Å) and B—H⋯π (H⋯Cg = 3.15 Å) contacts, forming a three-dimensional network, with solvent mol­ecules occupying the cavities. One of the phenyl groups was disordered over two sites with occupancy factors of 0.65 and 0.35.

Mono- and Di-nuclear Gold(I) Complexes Containing 1,12-Dicarba-closo-dodecaborane(12)

The first examples of gold(i) complexes containing monodentate diphenylphosphine-1,12-carborane and bidentate 1,12-bis(diphenylphosphine)-1,12-carborane ligands are reported.