Tricarboranyl pentaerythritol-based building block

A new tricarborane building block based on pentaerythritol was prepared for applications in boron neutron capture therapy (BNCT). Its X-ray single-crystal structure revealed a high degree of steric congestion. To enable the attachment of the building block to other moieties, a succinimidyl linker has been introduced at the focal point, and a generation-2 hexacarborane-containing dendron carrying 60 boron atoms has been prepared using a 2,2-bis(hydroxymethyl)propionic acid core.     

Preparation, crystallographic characterization and theoretical study of two isomers of C70(CF3)12

Two isomers of C70(CF3)12 have been isolated from a mixture obtained by trifluoromethylation of C70 with CF3I; their molecular structures determined by X-ray crystallography are in good agreement with the results of theoretical DFT calculations for the most stable C70(CF3)12 isomers.     

Captured at last: a catalyst-substrate adduct and a Rh-dihydride solvate in the asymmetric hydrogenation by a Rh-monophosphine catalyst

The mechanism of asymmetric hydrogenation catalyzed by [Rh(NBD)((R)-PhenylBinepine)(2)]SbF(6)1 has been studied by NMR experiments and DFT computations. Either the low-temperature hydrogenation of the catalyst-substrate adduct 4 or the reaction of solvate dihydride 6 with MAC produced the hydrogenation product with over 99% ee (S).     

Polymerization of ethylene oxide with potassium-graphite inclusion compounds

The polymerization of ethylene oxide (EO) in tetrahydrofuran (THF) initiated by inclusion compounds of potassium in graphite (C₂₄K) at 50°C was studied. During the initial slow stage of the polymerization the catalyst efficiency increases, while during the second rapid stage the reaction proceeds at a constant concentration of the active centers. The influence of the catalyst and monomer concentrations on the concentration of the active centers and on the catalyst efficiency was studied. The existence of the slow stage is explained by diffusion of ethylene oxide between the graphite planes, where both initiation and initial chain growth take place. The diffusion of the growing chains from the catalyst into the solution brings about the formation of a necessary concentration of active centers in the solution, which ensures the rapid growth of the polymer chains under homogeneous conditions. An x-ray study of the catalyst after polymerization shows a strongly disturbed crystal structure of the graphite. Poly-(ethylene oxide) obtained at a higher degree of conversion, does not contain low molecular weight fractions.     

Structures of Chlorinated Fullerenes,IPR C96Cl20 and Non‐classical C94Cl28 and C92Cl32: Evidence of the Existence of Three New Isomers of C96

Chlorination of various HPLC fractions of C₉₆ with a mixture of VCl₄ and SbCl₅ at 340–360 °C and single‐crystal X‐ray diffraction study of the products led to the identification of three new IPR isomers of C₉₆. The C₉₆(175) isomer forms a stable chloride, C₉₆(175)Cl₂₀, while chlorides of two other new isomers, C₉₆(114) and C₉₆(80), undergo cage shrinkage yielding C₉₄(NC1)Cl₂₈ and C₉₆(NC2)Cl₃₂ with non‐classical (NC) cages. These two NC chlorides contain, respectively, one and two heptagons flanked by pairs of fused pentagons and are stabilized by chlorine attachment to the emerging pentagon–pentagon junctions. Thus, the number of the experimentally confirmed C₉₆ isomers has reached nine, which corroborates the empirical rule that the C_6n fullerenes exhibit particularly rich isomerism.     

Facile Separation,Spectroscopic Identification,and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene

We survey the structure and electronic properties of the family of higher trifluoromethylated C₇₀(CF₃)_n molecules with n=14, 16, 18, and 20. Twenty‐two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π‐system topologies, which enabled us to study the interplay between the CF₃ addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed‐shell cyclopentadienyl anions C₇₀(CF₃)_{n? 1} ^? through CF₃ detachment upon electron transfer. A detailed study of the process is presented for a SPP‐C₇₀(CF₃)₁₆ where potentiostatic electrolysis at the second reduction potential gives C₇₀(CF₃)₁₅^? oxidizable to a persistent C₇₀(CF₃)₁₅^· radical. Together with the literature data for the lower C₇₀(CF₃)_n compounds with n=2–12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO–LUMO gaps within the ranges of ?4.3 to ?3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of ?5.6 to ?6.9 eV and show linear correlation with the number of addends.     

A novel polybromide complex of bismuth – (Et4N)3{[Bi2Br9](Br2)}: synthesis and structural features

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To turn the tide in the Soviet scientific instrumentation: in memoriam Erlen I. Fedin (1926–2009)

Structural Chemistry - A brief account of Soviet magnetic resonance (MR) scientific instrumentation in the 1970s–1980s is given. The impact of Erlen Ilyich Fedin (1926–2009), the head...