A. P. Zhdanov

Derivatives of closo-decaborate anion [B10H10]2− with exo-polyhedral substituents

Methods of introducing functional groups into the [B10H10]2− anion based on electrophilic, radical, or nucleophilic substitution for exo-polyhedral hydrogen atoms have been surveyed. Special attention has been focused on nucleophilic substitution reactions promoted by acids, including protonic acids, anhydrous hydrogen halides, metal halides, and carbocations. In addition, methods of tailored functionalization of the substituents in the cluster have been described.

Reactions of nucleophilic addition of primary amines to the nitrilium derivative of the closo-decaborate anion [2-B10H9(N≡CCH3)]−

Compounds (Bu4N)[2-B10H9{NH=C(NHR)CH3}]− are obtained by reactions of the tetrabutylammonium salt of the [2-B10H9(N≡CCH3)]− anion with aliphatic and aromatic primary amines RNH2 (R = n-C3H7, n-C4H9, cyclo-C5H9, C6H5, cyclo-C6H11, n-C6H13, C7H7, C8H8NH2, C6H4NO2, and C18H37) and identified by IR, ESI/MS, and NMR (1H, 11B, and 13C) spectroscopy. The structures of the amidine-type derivatives [2-B10H9{Z-NH=C(NH-cyclo-C5H9)CH3}]− and [2-B10H9{Z-NH=C(NH-C7H7)CH3}]− are determined by X-ray diffraction.

Synthesis of amino-containing meso-aryl-substituted porphyrins and their conjugates with the closo-decaborate anion

Amphiphilic meso-aryl-substituted porphyrins containing an amino group and long-chain hydrophobic substituents were synthesized. Two strategies of the synthesis of asymmetric amino-containing porphyrins using p-acetamidobenzaldehyde and p-nitrobenzaldehyde were developed and investigated. A series of new substituted porphyrin-containing closo-decaborates were prepared based on the synthesized porphyrins and nitrilium derivatives of the closo-decaborate anion [B10H10]2−.

New methods of preparation of hydroxy-closo-decaborates [B10H10 − n(OH)n]2− (n = 1, 2)

New methods of preparation of hydroxy-closo-decaborates [B10H10 − n(OH)n]2− (n = 1, 2) that are based on the reaction of anions [B10H10 − n(OAc)n]2− and alkoxyethylidenoxonio-closo-decaborates [2-B10H9OC(OR)CH3]− with aqueous solution of hydrazine are proposed. The obtained compounds were characterized by IR, ESI/MS, and NMR (1H, 11B, 13C) spectroscopy.

Cobalt(II) and nickel(II) complexes with 1-methyl-2-pyridin-2-yl-1H- and 1-methyl-2-phenyliminomethyl-1H-benzimidazoles and the closo-decaborate anion

Synthesis of cobalt(II) and nickel(II) complexes with the closo-decaborate anion and benzimidazole derivatives (L1 = C13N3H11, L2 = C15N3H13) of the general formula [ML3][B10H10] (M = Co, Ni) is described. Complexes have been characterized by elemental analysis, IR and UV spectroscopy. The structure of a [Ni(L1)3][B10H10] · 1.797CH3CN single crystal has been determined by X-ray diffraction. The imidazole and pyridine N atoms of three L1 molecules, two of which are disordered, form the distorted octahedral environment of the Ni atom. In the crystal, the majority of complexes [Ni(L1)3]2+ have the meridional configuration. The Ni-N bonds with the imidazole nitrogen atoms (2.010(4)–2.076(3) Å) are shorter than those with the pyridine atoms (2.132(4)–2.179(5) Å). This nonequivalence of the Ni-N bonds is responsible for the low magnetic susceptibility of the compound.

Nucleophilic addition of aromatic amide oximes to [2-B10H9NCC2H5]– anion

A series of closo-decaborate anions containing an O-iminoacylamide oxime fragment were synthesized by nucleophilic addition of aromatic amide oximes to 2-propionitrilium closo-decaborate anion. The isolated compounds were characterized by IR, 1H, 13C–{1H}, and 11B–{1H} NMR, and mass spectra. The structure of (Ph4P)[2-B10H9NH=C(Et)ON=C(NH2)C6H4Me-2] was determined by single-crystal X-ray analysis.

Synthesis of carbocation salts of boron cluster anions [B10H10]2− and [B12H12]2−

A series of closo-decaborates and closo-dodecaborates as carbocation salts was obtained by the reaction of Kat2[BnHn] (n = 10, 12; Kat = Na, K, Ag) with tertiary alkyl halides tC4H9Cl, 1-AdBr, and (C6H5)3CCl. The prepared compounds were identified by IR and 1H, 11B, 13C NMR spectroscopy.

Mechanism of generation of closo-decaborato amidrazones. Intramolecular non-covalent B–H⋯π(Ph) interaction determines stabilization of the configuration around the amidrazone CN bond

Three types of N(H)-nucleophiles, viz. hydrazine, acetyl hydrazide, and a set of hydrazones, were used to study the nucleophilic addition to the CN group of the 2-propanenitrilium closo-decaborate cluster (Ph3PCH2Ph)[B10H9NCEt], giving N-closo-decaborato amidrazones. A systematic mechanistic study of the nucleophilic addition is provided and included detailed synthetic, crystallographic, computational and kinetic work. As a result, two possible mechanisms have been proposed, which consist of firstly a consecutive incorporation of two Nu(H) nucleophiles, with the second responsible for a subsequent rapid proton exchange. The second possible mechanism assumes a pre-formation of a dinuclear [Nu(H)]2 species which subsequently proceeds with the nucleophilic attack on the boron cluster. The activation parameters for hydrazones indicate a small dependence on bond formation [ΔH‡ = 6.8–15 kJ mol−1], but significantly negative entropies of activation [ΔS‡ ranges from −139 to −164 J K−1 mol−1] with the latter contributing some 70–80% of the total Gibbs free energy of activation, ΔG‡. In the X-ray structure of (Z)-(Ph3PCH2Ph)[B10H9N(H)C(Et)NHNCPh2], very rare intramolecular non-covalent B–H⋯π(Ph) interactions were detected and studied by DFT calculations (M06-2x/6-311++G** level of theory) and topological analysis of the electron density distribution within the framework of Baders theory (QTAIM method). The estimated strength of these non-covalent interactions is 0.8–1.4 kcal mol−1.

Hydrolysis of nitrilium derivatives of the closo-decaborate anion [2-B10H9(N≡CR)]– (R = CH3, C2H5, C(CH3)3, or C6H5)

Reaction of tetrabutylammonium salts of [2-B10H9(N≡CR)]– (R = CH3, C2H5, C(CH3)3, or C6H5) anions with water results in N-borylated iminols (Bu4N)[2-B10H9NH=C(OH)R], and in the presence of an alkali, corresponding N-substituted amides (Bu4N)2[2-B10H9NH-C(=O)R] are formed. The compounds obtained are identified by IR, ESI/MS, and 1H, 11B, and 13C NMR spectroscopy. The crystal structure of compound (Bu4N)[2-B10H9(Z-{NHC(OH)C2H5})] is studied by X-ray diffraction.

A new method for the synthesis of carboxonium derivatives of the closo-decaborate anion [2,6-B10H8(O2CR)]–, where R = CH3, C2H5

A single-stage scheme for the synthesis of carboxonium derivatives of the closo-decaborate anion by the reaction between the [B10H11]– anion and carboxylic acids was proposed. Target compounds were separated and characterized by IR and 1H, 11B, 13C NMR spectroscopy. In addition to the target compounds, closo-decaborate cluster opening products ere formed, and in the reaction between the closo-decaborate anion and acetic acid, a polymeric product was observed. The polymeric product (Ph4P)n[2,6,3,7-B10H6O2CCH3]n was characterized by X-ray diffraction.