Synthesis of unsaturated 7,8- and 7,9-di(hydroxymethyl)decahydro-7,8- and-7,9-dicarba-nido-undecaborate(1−) diethers

Dicarba-nido-undecaborate(1–) anions were obtained by treatment of 1,2-di(hydroxymethyl)-1,2-dicarba-closo-dodecaborane(12) diallyl ether, 1,2-di(hydroxymethyl)-1,2-dicarba-closo-dodecaborane (12), and 1,7-di(hydroxymethyl)-1,7-dicarba-closo-dodecaborane(12) with ethanolic solutions of KOH and subsequent reaction of the products with cesium and tetramethylammonium chlorides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1821–1823, September, 1995.     

Synthesis and deborination of polyhalo-substituted <Emphasis Type="Italic">ortho</Emphasis>-carboranes

Tetraiodo-1,2-dicarba-closo-dodecaborane and 9-bromo-8,10,12-triiodo-1,2-dicarba-closo-dodecaborane were synthesized by oxidative iodination of 1,2-dicarba-closo-dodecaborane and 9-bromo-1,2-dicarba-closo-dodecaborane, respectively, in AcOH using a mixture of nitric and sulfuric acid as an oxidant of iodine. The intermediates in the ortho-carborane iodination were identified. By the action of elemental bromine on 9-iodo-1,2-dicarba-closo-dodecaborane in the presence of aluminum chloride catalyst 9-iodo-8,10,12-tribromo-1,2-dicarba-closo-dodecaborane was obtained. Deborination of the synthesized substances with an alcohol solution of KOH led to formation of 1,5,6,10-tetraiodo-5-bromo-1,6,10-triiodo- and 5-iodo-1,6,10-tribromo-7,8-dicarbaundecaborates methylammonium salts.     

Silicon hydrides and nickel complexes : III. Hydrosilylation of olefins with dichloro[1,2-bis-(dimethylphosphino)-1,2-dicarba-closo-dodecaborane]-nickel(II) as catalyst

The hydrosilylation of olefins catalyzed by nickel(II) chloride complexed with 1,2-bis(dimethylphosphino)-1,2-dicarba-closo-dodecaborane produces terminal and internal adducts in comparable amounts. This unusual feature of the reaction is explained in terms of the electron-accepting nature of the carboranyl group.     

Acidic hydrolysis of N-acyl-1-substituted 3-amino-1,2-dicarba-closo-dodecaboranes

Acidic hydrolysis of N-acyl 1-methyl- and 1-phenyl-3-amino-1,2-dicarba-closo-dodecaboranes has been studied. It has been shown that acidic hydrolysis of diastereomeric amides of 1-methyl-3-amino-1,2-dicarba-closo-dodecaborane results in the partial racemization of the target 3-amino-1-methylcarborane. Under the similar conditions, the hydrolysis of N-acyl-3-amino-1-phenyl-1,2-dicarba-closo-dodecaboranes resulted in amide bond cleavage accompanied by simultaneous deboronation with the removal of boron atom at position 6 of carborane cage and formation of 7,8-dicarba-nido-undecaborane derivative according to ¹¹B and ¹H NMR spectroscopy.     

Lithiacarboranes and 1,2,4-triazine 4-oxides: S N H reactions and ring transformations

The reactions of 1-lithia-1,2- or 1,7-dicarba-closo-dodecaborane with 1,2,4-triazine 4-oxides can follow two competitive pathways: deoxygenative nucleophilic substitution of hydrogen to form 1-(1,2,4-triazin-5-yl)-1,2- or 1,7-dicarba-closo-dodecaboranes and the transformation of the 1,2,4-triazine ring into the triazoline ring giving rise to 1-(2-acetyl-1-aroyl-3-aryl-1,2,4-triazolin-5-yl)-1,2-dicarba-closo-dodecaboranes. Introduction of the electron-withdrawing triazine ring into the carborane cage substantially facilitates deboronation to give 1-(1,2,4-triazin-5-yl)-1,2-1,7-dicarba-nido-undecaboranes.     

Synthesis of new charge-compensated cobalt bis(1,2-dicarbollide) derivatives

New hetero-substituted charge-compensated cobalt bis(1,2-dicarbollide) derivatives were synthesized by the reaction of 8,8′-μ-iodo-3-commo-3-cobalta-bis(1,2-dicarba-closo-dodecaborane) [8,8′-μ-I-3,3′-Co(1,2-C₂B₉H₁₀)₂] with 1,4-thioxane, pyridine N-oxide, and tetrahydropyran. X-ray diffraction studies showed that the 8′-iodo-8-(pyridiniumoxy)eucosahydro-1,1′,2,2′-tetracarba-3-commo-cobalta-closo-tricosaborate molecule has the gauche-conformation (the substituents are turned with respect to each other by 69.2°). The positive charge is predominantly localized on the N(Py) atom.     

Enantioselective synthesis of m-carboranylalanine, a boron-rich analogue of phenylalanine

The enantiomers of the highly lipophilic α-amino acid m-carboranyl-alanine [3-(1,7-dicarba-closo-dodecaborane(12)-1-yl)-2-aminopropanoic acid], a carborane containing analogue of phenylalanine, have been synthesised via hydroxyamination of the N-acyl derivative formed from 3-(m-carboranyl)propionic acid [3-(1,7-dicarba-closo-dodeca-borane(12)-1-yl)-2-propanoic acid] and Oppolzer's camphor sultam. The enantiomeric excess of both enantiomers of the amino acid was >98%. (S)-Configuration was assigned to the (+)-enantiomer (CH₃OH, 589 nm).     

Koordinationseigenschaften von Carbaboranylchlorophosphanen: Synthese und Molekülstruktur von cis-rac-Molybdäntetracarbonyl{1,2-bis(chlorophenylphosphino)-1,2-dicarba-closo-dodecaboran(12)}

Coordination Properties of Carbaboranylchlorophosphines: Synthesis and Molecular Structure of cis-rac -Molybdenumtetracarbonyl{1,2-bis(chlorophenylphosphino)-1,2-dicarba-closo-dodecaborane(12)} Rac-1,2-bis(chlorophenylphosphino)-1,2-dicarba-closo-dodecaborane(12) ( 1 ) reacts with [Mo(CO)₄(NBD)] (NBD = norbornadiene) after several hours at 50–55 °C to yield cis-rac-[Mo(CO)₄{1,2-(PPhCl)₂C₂B₁₀H₁₀}] ( 2 ). 2 was characterised spectroscopically (¹H, ¹³C, ¹¹B and ³¹P NMR) and by crystal structure determination.     

Synthesis,molecular structure and reactivity of the dimethyl sulfide adduct of a 1,3,2-diselenaborolane with an annelated dicarba-closo-dodecaborane(12) unit

The reaction of 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C₂B₁₀H₁₀)Se₂]²⁻ with HBBr₂–SMe₂ affords the dimethyl sulfide adduct of 4,5-[1,2-dicarba-closo-dodecaborano(12)]-1,3-diselena-2-borolane in good yield. The molecular structure was determined by X-ray diffraction, and the solution-state structure was established by NMR spectroscopy (¹H, ¹¹B, ¹³C, ⁷⁷Se NMR). ¹¹B and ⁷⁷Se chemical shifts were reproduced by DFT calculations. Attempts were made to abstract dimethyl sulfide, and the parent donor-free compound could be detected in solution. The reactivity of the title compound was studied towards pyridine, Me₃SnF, [Pt(PPh₃)₂(C₂H₄)], tert-Bu-OH, AlMe₃ and AlH₃-N(Et)Me₂ as well as a hydroborating reagent.     

Water-soluble phosphonium salts containing 1,12-dicarba-closo-dodecaborane(12)

The preparation of new water-soluble phosphonium salts containing 1,12-dodeca-closo-dodecaborane(12) (closo-1,12-carborane) for potential use as tumor-targeting agents in Boron Neutron Capture Therapy (BNCT) is described.     

NMR study of 1-aryl-1,2-dicarba-closo-dodecaboranes: intramolecular C-H?O hydrogen bonding in solution

Dicarba-closo-dodecaborane(12) (carborane) has recently received much attention as a building block for supramolecular assemblies and bioactive compounds. Among carborane isomers, 1,2-dicarba-closo-dodecaborane(12) (o-carborane) has unique chemical properties, including the ability of the o-carborane C-H hydrogens to form hydrogen bonds. To evaluate intramolecular hydrogen bond formation between the o-carborane C-H hydrogen and various hydrogen bond acceptors in solution, we have designed and synthesized 1-aryl-o-carboranes 2. Intramolecular hydrogen bonding ability was evaluated by means of ¹H NMR measurement of the o-carborane C-H hydrogen signal of 2. The 1-(2-methoxyphenyl)-o-carborane derivative 2m appeared to form an intramolecular hydrogen bond between o-carborane C-H hydrogen and the oxygen atom acting as a hydrogen bonding acceptor. In this study, we present evidence for hydrogen bond formation in solution between the o-carborane C-H and hydrogen bond acceptors positioned with appropriate geometry.     

[4+2] Cycloaddition reactions of 1,2,4,5-tetrazines with allylcarboranes

The [4+2] cycloaddition reactions of 3,6-disubstituted 1,2,4,5-tetrazines with 9-allyl-1,7-,9-allyl-1,2-dicarba-closo-dodecaboranes and 1-allyl-2-isopropyl-1,2-dicarba-closo-dodecab-orane have been studied. The pyridazines containing carborane cage have been synthesized for the first time.     

Conjugates of polyhedral boron compounds with carbohydrates 8. Synthesis and properties of nido-ortho-carborane glycoconjugates containing one to three ��-lactosylamine residues

??-Lactosylamine derivatives containing one to three disaccharide residues with the bromine atom at the terminal position of aglycon were synthesized. Conjugation of these derivatives with 1-mercapto-1,2-dicarba-closo-dodecaborane was carried out in DMSO, which was accompanied by deboronation to form nido-ortho-carborane (7,8-dicarba-nido-undecaborate) glycoconjugates in up to 70% yield. The hydrolytic stability of glycoconjugates and the binding efficiency of their triethylammonium salts to castor-bean galectin (Ricinus communis aggluinin, RCA₁₂₀) were estimated. Glycoconjugates are decomposed in an aqueous solution by ??15% at 37 °C in three days. The glycoconjugate salt with one ??-lactosylamine residue binds to galectin analogously to lactose; after indroduction of the second ??-lactosylamine residue into glycoconjugate, the binding efficiency increases ??6-fold due to the cluster effect.     

Synthesis of <Emphasis Type="Italic">ortho</Emphasis>-carboranyl derivatives of (<Emphasis Type="Italic">S</Emphasis>)-asparagine and (<Emphasis Type="Italic">S</Emphasis>)-glutamine

(S)-Asparagine and (S)-glutamine ortho-carboranyl derivatives with free amino and carboxy groups in the α-position were synthesized. By an example of N ^γ-(1,2-dicarba-closo-dodecarboran-3-yl)-(S)-glutamine it was demonstrated that the developed synthetic approach carboranyl derivatives of amino acids allowed the preparation of optically pure isomers.     

Electrochemical study of boron-mercurated derivatives of 3-cyclopentadienyl-3-cobalta-1,2-dicarba-closo-dodecaborane

The cyclic voltammetry and rotating disc electrode methods were used to study the electrochemical reduction and oxidation of boron-mercurated mono- and dimercury derivatives of 3-cyclopentadienyl-3-cobalta-1,2-dicarba-closo-dodecaborane and boron-mercurated dicobaltacarborane on platinum and glassy carbon electrodes in MeCN and DMF solutions. The first reduction step was the reversible electron transfer to the cobalt atom. This process is complicated by adsorption of the reaction product on the electrode, which is especially pronounced when the electrode is coated by metallic mercury evolved at later steps of reduction. The presumptive mechanisms of electroreduction are discussed in detail.     

Structure and properties of 1,2-, 1,7-, and 1,12-dicarba-closo-dodecaboranes(12): A quantum chemical study

The molecular and electronic structures and thermodynamic parameters of 1,2-, 1,7-, and 1,12-dicarba-closo-dodecaborane(12) molecules in the singlet ground state were calculated by the Hartree-Fock, DFT, and MP2 (including B3LYP/6-311G(2d,2p) and MP2/6-311+G(d,2p) methods). The energies and character of spatial localization of the frontier MOs in o-, m-, p-carboranes(12) correlate with the changes in the configuration stabilities and reactivities in the reactions of carboranes with electrophilic and nucleophilic agents and bases. The electrostatic potential distributions in the molecules and the atomic charge distribution of hydrogen atoms correlate with the known chemical properties of carboranes(12). The thermodynamic parameters of two isomerization reactions, o-C₂B₁₀H₁₂ ⇌ m-C₂B₁₀H₁₂ and m-C₂B₁₀H₁₂ ⇌ p-C₂B₁₀H₁₂, calculated for the temperature range 298–1000 K agree with experimental data within the limits of measuring error. The values of the electron density and the Laplacian of the electron density at the (3, −1) critical points of the B-H and C-H bonds correlate with the reactivities of the title compounds. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2074–2080, December, 2006.     

Ethynylmonocarba-closo-dodecaborates: M[12-HCC-closo-1-CB11H11] and M[7,12-(HCC)2-closo-1-CB11H10] (M = Cs, [Et4N])

Cesium and tetraethylammonium salts of the ethynyl functionalized monocarba-closo-dodecaborate anions [12-HCC-closo-1-CB₁₁H₁₁]⁻ and [7,12-(HCC)₂-closo-1-CB₁₁H₁₀]⁻ were obtained by desilylation of [Et₄N][12-Me₃SiCC-closo-1-CB₁₁H₁₁] and [Et₄N][7,12-(Me₃SiCC)₂-closo-1-CB₁₁H₁₀], respectively. Their thermal properties were examined by differential scanning calorimetry. The compounds were characterized by multi-NMR, IR, and Raman spectroscopy, (−)-MALDI mass spectrometry, and elemental analysis. Single-crystals of Cs[12-HCC-closo-1-CB₁₁H₁₁] and [Et₄N][7,12-(HCC)₂-closo-1-CB₁₁H₁₀] were studied by X-ray diffraction. The discussion of the spectroscopic and structural properties is supported by data derived from theoretical calculations using density functional theory as well as perturbation theory.     

The crystal and molecular structures of three germatrane derivatives

The molecular and crystal structure of three germatrane compounds: 1-(1-bromobicyclo[4.1.0]hept-7-yl)germatrane, l-(1-trimethylsilanyl-cyclopropyl)-germatrane and 1-(1-Methyl-1,2-dicarba-closo-dodecaboranyl)germatrane has been determined by X-ray diffraction method in order to investigate main geometrical regularities of the germatrane molecules. There were established all values of the main structural parameters above-mentioned molecules.     

Chiral functionalized bisphosphine ligands: Transition metal complexes of 1,2-bis(tert-Butylchlorophosphino)-1,2-dicarba-closo-dodecaborane(12)

When rac- or meso-1,2-bis(tert-butylchlorophosphino)-1,2-dicarba-closo-dodecaborane(12) (1a or 1b) is reacted with [M(CO)₄(NBD)] (M = Cr, Mo, NBD = norbornadiene), [Mo(CO)₄(EtCN)₂] or [W(CO)₆], rac-[Cr(CO)₄{1,2-(P^tBuCl)₂C₂B₁₀H₁₀}] (2), rac- or meso-[Mo(CO)₄{1,2-(P^tBuCl)₂C₂B₁₀H₁₀}] (3a or 3b) and rac-[W(CO)₄{1,2-(P^tBuCl)₂C₂B₁₀H₁₀}] (4) could be isolated as pure diastereomers. UV irradiation of 1 with [Cr(CO)₆] in moist THF proceeds with hydrolysis and formation of [Cr(CO)₄{1,2-(P(OH)^tBu)₂C₂B₁₀H₁₀}] (5) which contains the metal complex-stabilized phosphinous acid. Compounds 2–5 were characterized spectroscopically (¹H, ³¹P, ¹¹B, ¹³C NMR), by mass spectrometry and by X-ray structure determination.     

Conjugates of polyhedral boron compounds with carbohydrates. 2. Unexpected easy closo- to nido-transformation of a carborane-carbohydrate conjugate in neutral aqueous solution

A novel 1,2-dicarba-closo-dodecaborane-lactose conjugate 4c, when dissolved in water or methanol, is subject to unexpected deboronation in neutral conditions leading to the formation of the corresponding nido-counterpart (5) as detected by ¹¹B NMR spectroscopy. After heating the aqueous solution of the conjugate 4c at 60 °C for 17 h pure 1,2-dicarba-nido-undecaborane-lactose conjugate 5 was obtained.