Ekaterina V. Bogdanova

The crystal molecular structure of the co-crystal of boric acid (BA) with triphenylphosphine oxide (TPO) 1:2, H₃BO₃∙2Ph₃PO, was determined by single-crystal X-ray diffraction. In the crystal, pairs of the boric acid molecules are connected to each other by hydrogen bonds, and each acid molecule forms two hydrogen bonds with the oxygen atoms of two triphenylphosphine oxide molecules. The crystal packing of the new complex was compared with the crystal packings of the known 1:1 complex of boric acid and triphenylphosphine oxide, and boric acid and triphenylphosphine oxide themselves. Also, the energetic preferences and densities of the co-formers (BA and TPO) were compared for their pure forms and co-crystals. It is shown that more tight crystal packing is not necessarily accompanied by higher stability.

The interaction of bis(dioxane) and bis(tetrahydropyran) derivatives of iron(II) bis(dicarbollide) [8,8'-{O(CH₂CH₂)₂Х}₂-3,3'-Fe(1,2-C₂B₉H₁₀)₂] (Х = O, CH₂) with pyridine in an inert atmosphere has been studied. It has been found that the ring-opening of oxonium cycles proceeds stepwise, with the formation of the corresponding mono- and dipyridinium iron(II) complexes. Using the bis(dioxane) dipyridinium derivative as an example, it was found that, when in solution, oxidation of the resulting products to the corresponding paramagnetic complexes of iron(III) is possible. This approach opens the way to obtain bifunctional iron bis(dicarbolide) derivatives with different substituents. The obtained compounds have been characterized by multinuclear NMR and IR spectroscopies, as well as high-resolution mass spectrometry. The structure of the symmetrical dipyridinium iron(II) complex [8,8'-(C₅H₅NCH₂CH₂OCH₂CH₂O)₂-3,3'-Fe(1,2-C₂B₉H₁₀)₂] was determined by single crystal X-ray diffraction.

A zwitterionic N-bridged cobalt bis(dicarbollide) compound [8,8'-μ-NH2-3,3'-Co(1,2-C2B9H10)2] was prepared by the reaction of [8,8'-μ-Et(HO)C=N-3,3'-Co(1,2-C2B9H10)2] with triethylamine in acetone. The complex obtained was characterized by NMR, IR, UV-Vis spectroscopy as well as high-resolution mass spectrometry.

The addition reactions of water, alcohols, and primary and secondary amines to the 10-acetonitrilium derivative of nido-carborane were studied. Hydrolysis of 10-MeC≡N-7,8-C₂B₉H₁₁ results in iminol 10-MeC(OH)=HN-7,8-C₂B₉H₁₁, which, on treatment with a base, gives amide [10-MeC(=O)HN-7,8-C₂B₉H₁₁]⁻. The reactions of 10-MeC≡N-7,8-C₂B₉H₁₁ with alcohols lead to imidates 10-ROC(Me)=HN-7,8-C₂B₉H₁₁ (R = Me, Et) as mixtures of E- and Z-isomers. In the solid state, 10-MeOC(Me)=HN-7,8-C₂B₉H₁₁ adopts E-configuration. The reactions of 10-MeC≡N-7,8-C₂B₉H₁₁ with primary amines result in amidines 10-RNHC(Me)=HN-7,8-C₂B₉H₁₁ (R = Me, Et) as mixtures of E- and Z-isomers. In the solid state 10-EtNHC(Me)=HN-7,8-C₂B₉H₁₁ was found to have the Z-configuration, which is stabilized by intramolecular N-H⋯H-B interactions between the NH group originating from the primary amine and the BH group of the carborane cage. These interactions are rather strong (3.7 kcal/mol) and are likely to persist in solution. The reactions of 10-MeC≡N-7,8-C₂B₉H₁₁ with secondary acyclic (Me₂NH, Et₂NH) and cyclic (piperidine, morpholine) amines result in amidines 10-R₂NC(Me)=HN-7,8-C₂B₉H₁₁ (R = Me, Et; R₂ = N(CH₂)₅, N(CH₂CH₂)₂O) as single isomers, which, according to single crystal X-ray diffraction data, have the E-configuration.

Iron( ii ) bis(dicarbollide) amidinium [8,8′-(RNHC(Et)HN) ₂ -3,3′-Fe(1,2-C ₂ B ₉ H ₁₀ ) ₂ ] and oxonium [8,8′-(RR′O) ₂ -3,3′-Fe(1,2-C ₂ B ₉ H ₁₀ ) ₂ ] derivatives were synthesized and studied by NMR spectroscopy, single crystal X-ray diffraction and cyclic voltammetry.

To combine the neutron-capturing and photodynamic properties of boron nanoclusters and derivatives of natural chlorins, respectively, in one molecule, conjugate of chlorin e6 methyl ester with cyclen and dioxane and nitrile derivatives of cobalt bis(dicarbollide) were synthesized. The conditions for the purification of compounds by HPLC were selected since the work with natural compounds is complicated by the production of closely related impurities.

A series of novel cobalt bis(dicarbollide) based amidines were synthesized by the nucleophilic addition of primary and secondary amines to highly activated B-N⁺≡C–R triple bond of the propionitrilium derivative [8-EtC≡N-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)]. The reactions with primary amines result in the formation of mixtures of E and Z isomers of amidines, whereas the reactions with secondary amines lead selectively to the E-isomers. The crystal molecular structures of E-[8-EtC(NMe₂)=HN-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)], E-[8-EtC(NEt₂)=HN-3,3′-Co(1,2- C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] and E-[8-EtC(NC₅H₁₀)=HN-3,3′-Co(1,2-C₂B₉H₁₀)(1′,2′-C₂B₉H₁₁)] were determined by single crystal X-ray diffraction.