Synthesis of Disubstituted Carboxonium Derivatives of Closo-Decaborate Anion [2,6-B10H8O2CC6H5]-: Theoretical and Experimental Study.

A comprehensive study focused on the preparation of disubstituted carboxonium derivatives of closo-decaborate anion [2,6-B10H8O2CC6H5]- was carried out. The proposed synthesis of the target product was based on the interaction between the anion [B10H11]- and benzoic acid C6H5COOH. It was shown that the formation of this product proceeds stepwise through the formation of a mono-substituted product [B10H9OC(OH)C6H5]-. In addition, an alternative one-step approach for obtaining the target derivative is postulated. The structure of tetrabutylammonium salts of carboxonium derivative ((C4H9)4N)[2,6-B10H8O2CC6H5] was established with the help of X-ray structure analysis. The reaction pathway for the formation of [2,6-B10H8O2CC6H5]- was investigated with the help of density functional theory (DFT) calculations. This process has an electrophile induced nucleophilic substitution (EINS) mechanism, and intermediate anionic species play a key role. Such intermediates have a structure in which one boron atom coordinates two hydrogen atoms. The regioselectivity for the process of formation for the 2,6-isomer was also proved by theoretical calculations. Generally, in the experimental part, the simple and available approach for producing disubstituted carboxonium derivative was introduced, and the mechanism of this process was investigated with the help of theoretical calculations. The proposed approach can be applicable for the preparation of a wide range of disubstituted derivatives of closo-borate anions.

Design, Fabrication and Characterization of Biodegradable Composites Containing Closo-Borates as Potential Materials for Boron Neutron Capture Therapy.

Boron neutron capture therapy (BNCT) has been recognized as a very promising approach for cancer treatment. In the case of osteosarcoma, boron-containing scaffolds can be a powerful tool to combine boron delivery to the tumor cells and the repair of postoperative bone defects. Here we describe the fabrication and characterization of novel biodegradable polymer composites as films and 3D-printed matrices based on aliphatic polyesters containing closo-borates (CB) for BNCT. Different approaches to the fabrication of composites have been applied, and the mechanical properties of these composites, kinetics of their degradation, and the release of closo-borate have been studied. The most complex scaffold was a 3D-printed poly(ε-caprolactone) matrix filled with CB-containing alginate/gelatin hydrogel to enhance biocompatibility. The results obtained allowed us to confirm the high potential of the developed composite materials for application in BNCT and bone tissue regeneration.

Protonation of Borylated Carboxonium Derivative [2,6-B10H8O2CCH3]-: Theoretical and Experimental Investigation.

The process of protonation of [2,6-B10H8O2CCH3]- was investigated both theoretically and experimentally. The most suitable conditions for protonation of the derivative [2,6-B10H8O2CCH3]- were found. The process of protonation was carried out in the presence of an excess of trifluoromethanesulfonic acid CF3SO3H at room temperature in dichloromethane solution. The structure of the resulting complex [2,6-B10H8O2CCH3*Hfac]0 was established using NMR data and the results of DFT calculations. An additional proton atom Hfac was found to be localized on one of the facets that was opposite the boron atom in a substituted position, and which bonded mainly with one apical boron atom. The main descriptors of the B-Hfac bond were established theoretically using QTAIM and NBO approaches. In addition, the mechanism of [2,6-B10H8O2CCH3]- protonation was investigated.

Functionalization of closo-Borates via Iodonium Zwitterions.

A simple method for the functionalization of closo-borates [closo-B10 H10 ](2-) (1), [closo-1-CB9 H10 ](-) (2), [closo-B12 H12 ](2-) (3), [closo-1-CB11 H12 ](-) (4), and [3,3'-Co(1,2-C2 B9 H11 )2 ](-) (5) is described. Treatment of the anions and their derivatives with ArI(OAc)2 gave aryliodonium zwitterions, which were sufficiently stable for chromatographic purification. The reactions of these zwitterions with nucleophiles provided facile access to pyridinium, sulfonium, thiol, carbonitrile, acetoxy, and amino derivatives. The synthetic results are augmented by mechanistic considerations.