A new series of boron substituted cobalt bis(dicarbollide)(1−) ion (1) derivatives of the general formula [(8-CMPO-(CH₂-CH₂O)₂-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co]⁻ (CMPO = Ph₂P(O)-CH₂C(O)NR, R = C₄H₉ (3b), -C₁₂H₂₅ (4b), -CH₂-C₆H₅ (5b)) was prepared by ring cleavage of the 8-dioxane-cobalt bis(dicarbollide) (2) bi-polar compound by the respective primary amines and by subsequent reaction of the resulting amino derivatives (3a–5a) with the nitrophenyl ester of diphenylphosphorylacetic acid. The compounds were synthesized with the aim to develop a new class of more efficient extraction agents for liquid–liquid extraction of polyvalent cations, i.e. lanthanides and actinides, from high-level activity nuclear waste. All compounds were characterized by a combination of ¹¹B NMR, ¹H high field NMR, Mass Spectrometry with Electrospray and MALDI TOF ionisation, HPLC and other techniques. The molecular structure of the supramolecular Ln³⁺ complex of the anion 5b was determined by single crystal X-ray diffraction analysis. Crystallographic results proved that the Ln(III) atom is bonded to three functionalised cobalt bis(dicarbollide) anions in a charge compensated complex. The cation is tightly coordinated by six oxygen atoms of the CMPO terminal groups (two of each ligand) and by three water molecules completing the metal coordination number to 9. Atoms occupying the primary coordination sphere form a tri-capped trigonal prismatic arrangement. Very high liquid–liquid extraction efficiency of all anionic species was observed. Moreover, less polar toluene can be applied as an auxiliary solvent replacing the less environmentally friendly nitro- and chlorinated solvents used in the current dicarbollide liquid–liquid extraction process. The extraction coefficients are sufficiently high for possible technological applications.

Cobalt bisdicarbollides (COSANs) are inorganic boron-based anions that have been previously reported to permeate by themselves through lipid bilayer membranes, a propensity that is related to their superchaotropic character. We now introduce their use as selective and efficient molecular carriers of otherwise impermeable hydrophilic oligopeptides through both artificial and cellular membranes, without causing membrane lysis or poration at low micromolar carrier concentrations. COSANs transport not only arginine-rich but also lysine-rich peptides, whereas low-molecular-weight analytes such as amino acids as well as neutral and anionic cargos (phalloidin and BSA) are not transported. In addition to the unsubstituted isomers (known as ortho- and meta-COSAN), four derivatives bearing organic substituents or halogen atoms have been evaluated, and all six of them surpass established carriers such as pyrenebutyrate in terms of activity. U-tube experiments and black lipid membrane conductance measurements establish that the transport across model membranes is mediated by a molecular carrier mechanism. Transport experiments in living cells showed that a fluorescent peptide cargo, FITC-Arg₈, is delivered into the cytosol.

The reaction of the cobalt bis(dicarbollide)(1−)(1) ion in the presence of t-butylbromide, acting as a potent Lewis acid activator, leads to the clean substitution of 1 by the N-atom of acetonitrile (or benzonitrile), thus resulting in the smooth formation of [(8-RCN)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁰ (R = CH₃ or C₆H₅) (2 and 3). These compounds can serve as versatile precursors for the generation of a variety of other synthetically useful functional groups. The nitrogen atom of the nitrile CN– bond in 2 and 3 is prone to the facile addition of nucleophiles. Thus, alkaline hydrolysis of 2 and 3 in aqueous alcohols furnishes high yields of the corresponding B(8)-N-alkylamides [(8-RC(O)=NH)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁻, where R = CH₃ or C₆H₅ (4 and 5). The reactions with butyl and diethyl amine result in the high-yield formation of 8-alkylamidine derivatives [(8-³R²RNH-¹RCN)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁰, where ¹R = CH₃, ²R = H, ³R = C₄H₉, (6), ¹R = C₆H₅, ²R = ³R = C₂H₅ (7) or ¹R = C₆H₅, ²R = ³R = C₂H₅ (8). Hydrazinolysis of 2 provides a high yield of the zwitterionic [(8-H₃N)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁰ (9), whereas reduction of the nitrile group in 2 and 3 using BH₃·SMe₂ affords the respective alkylammonium derivatives [(8-RH₂N)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁰, where R = –C₂H₅ (10) or –CH₂C₆H₅ (11) in moderate yields. Compound 11 can also be prepared by alkylation of 9 along with dibenzylderivative (12). A further example of alkylation is the ring cleavage of the 3-hydroxypropanesulfonic acid γ-sultone producing a compound with alkyl ammonium sulfonic acid substitution [(8-O₃SC₃H₆NH₂)-1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)-3,3′-Co(III)]⁻ (13) All new compounds were characterized by multinuclear NMR spectroscopy and mass spectrometry and the structures of compounds 2, 6, 7 and 12 were established by X-ray crystallography.