Icosahedral boranes, carboranes, and metallacarboranes are extraordinarily robust compounds with desirable properties such as thermal and redox stability, chemical inertness, low nucleophilicity, and high hydrophobicity, making them attractive for several applications such as medicine, nanomaterials, molecular electronics, energy, catalysis, environmental chemistry, and other areas. The hydrogen atoms in these clusters can be replaced by convenient groups that open the way to a chemical alternative to conventional "organic" or "organometallic" realms. Icosahedral boron cluster derivatives have been reviewed from different perspectives; however, there is a need for a review dedicated to the redox and photophysical characteristics of easily accessible borane and carborane derivatives, which are excellent materials for a wide range of applications. This review deals with the redox properties and photoluminescence behavior of this collection of compounds, as well as their influence on the properties of materials and devices whose working principles are related to electron-transfer or electron-promotion phenomena. We hope that this review will be of great value to boron cluster scientists and researchers working in the photoluminescence and electrochemistry fields who are interested in exploring the possibilities of these unique and promising systems.
Cobaltabisdicarbollide (COSAN) [3,3′-Co(1,2-C2B9H11)2]−, is a complex boron-based anion that has the unusual property of self-assembly into membranes and vesicles. These membranes have similar dimensions to biological membranes found in cells, and previously COSAN has been shown to pass through synthetic lipid membranes and those of living cells without causing breakdown of membrane barrier properties. Here, we investigate the interaction of this inorganic membrane system with living cells. We show that COSAN has no immediate effect on cell viability, and cells fully recover when COSAN is removed following exposure for hours to days. COSAN elicits a range of cell biological effects, including altered cell morphology, inhibition of cell growth and, in some cases, apoptosis. These observations reveal a new biology at the interface between inorganic, synthetic COSAN membranes and naturally occurring biological membranes.
The boron-rich cobaltabisdicarbollide (COSAN) and its 8,8'-I2 derivative (I2-COSAN), both of purely inorganic nature, are shown to accumulate within living cells, where they can be detected using νB-H Raman microspectroscopy. This demonstrates an alternative method for cell labelling and detection.
The anion [3,3'-Co(C2B9H11)2](-) ([COSAN](-)) produces aggregates in water. These aggregates are interpreted to be the result of C-H⋅⋅⋅H-B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN](-) units. The approach is to join two [COSAN](-) anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K(+) selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K(+) from a mixture containing Li(+), Na(+), K(+), Rb(+) and Cs(+); this can be indicative of pseudo-crown ether performance of the dumbbell. One interesting possibility is that the [COSAN](-) anions at the two ends of the linker can act as a hook-and-loop fastener to close the ring. This facet is intriguing and deserves further consideration for possible applications. The distinct affinity towards alkaline metal ions is corroborated by solubility studies and isothermal calorimetry thermograms. Furthermore, cryoTEM micrographs, along with light scattering results, reveal the existence of small self-assemblies and compact nanostructures ranging from spheres to single-/multi-layer vesicles in aqueous solutions. The studies reported herein show that these dumbbells can have different appearances, either as molecules or aggregates, in water or lipophilic phases; this offers a distinct model as drug carriers.
An appealingly wide set of redox couples ranging from -1.74 to -0.35 V based on a metallabisdicarbollide derivative, [M(C2B9H11-yIy)2](-) (M = Co, Fe), each being distinguished from the former by near 0.15 V and all having the same structure have been demonstrated. The redox active methyl viologen moiety ([MV](2+)) has been used as a benchmark.
Pairing lithium and manganese(II) to form lithium manganate [Li2Mn(CH2SiMe3)4] enables the efficient direct Mn–I exchange of aryliodides, affording transient (aryl)lithium manganate intermediates which in turn undergo spontaneous C−C homocoupling at room temperature to furnish symmetrical (bis)aryls in good yields under mild reaction conditions. The combination of EPR with X‐ray crystallographic studies has revealed the mixed Li/Mn constitution of the organometallic intermediates involved in these reactions, including the homocoupling step which had previously been thought to occur via a single‐metal Mn aryl species. These studies show Li and Mn working together in a synergistic manner to facilitate both the Mn–I exchange and the C−C bond‐forming steps. Both steps are carefully synchronized, with the concomitant generation of the alkyliodide ICH2SiMe3 during the Mn–I exchange being essential to the aryl homocoupling process, wherein it serves as an in situ generated oxidant.
Cross-coupling transformations are a powerful tool in organic synthesis. It is known that this kind of transformations undergoes 2-electron redox processes and, for this reason, silver has been nearly forgotten as catalyst for cross-couplings since silver is mainly considered as a 1-electron redox metal. Herein, we disclose effective Ag(I)-catalyzed cross-coupling transformations using bidentate aminoquinoline as a directing group towards different nucleophiles to form CC , C-N and CO bonds. DFT calculations indicate the feasible oxidative addition of L 1-I substrate via Ag(I)/Ag(III) catalytic cycle. Furthermore, ion spectroscopy experiments suggest a highly reactive aryl-Ag(III) that in absence of nucleophiles reacts to form an intermolecular cyclic product [5d-Ag(I)-CH 3 CN], which in solution forms 5a. This work proves that silver can undergo 2-electron redox processes in cross-coupling reactions like Pd and Cu.
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