Bohumil Štíbr

Improved synthesis of arachno-6,9-C2B8H14 and its halogenation under electrophilic conditions

Abstract A convenient synthesis of arachno -6,9-C 2 B 8 H 14 , based on the reduction of nido -5,6-C 2 B 8 H 12 with sodium tetrahydroborate, is reported. Electrophilic halogenation of the former carborane produced a series of 1-X-6,9-C 2 B 8 H 13 (X = Cl, Br and I) derivatives whose constitution was established on the basis of their 1 H and 11 B NMR spectra.

A 11B NMR study of 5,6-dicarba-nido-decaborane (12)

Abstract Final assignment of all eight signals in the 11 B NMR spectrum (64.2 MHz) of 5,6-dicarba-nido-decaborane (12) is reported on the basis of its substituted derivatives.

Reversed-phase ion-pair liquid chromatographic separations of some heteroborane anions

Abstract Separation of 23 heteroborane anions by reversed-phase ion-pair liquid chromatography on C1-bonded-phase columns using C12 or C6 n-alkylamine pairing ion is reported. The elution was monitored with a UV detector at 235, 254 or 280 nm well below microgram sensitivity level. The effects of the concentrations of the pairing ion and the inert salt, the pH, the pairing ion length, the stationary phase material and the methanol—water ratio on retention and selectivity were investigated.

The Preparation and Structures of New Nido-Platinaheteroboranes

Abstract Treatment of 4-XB8H12 (X=CH2, NH and S) hetero-boranes1–3 with Pt(PPh3)4 produced new ten-vertex platinaheteroboranes, 9,9-(PPh3)2-6,9-XPtB8H10 which are isoelectronic with nido-6-CB9H13. Their molecular structures were determined by single crystal X-ray studies. ESCA spectra were measured to estimate the influence of heteroborane ligands on central Pt atoms.

Some electrophilic substitution reactions of closo-[1-CB11H12]− and one-boron insertion into nido-7-L-7-CB10H12 (L = H− or Me3N) compounds. Isolation of all three B-substituted closo-Me3N-1-CB11H11 derivatives

Abstract Electrophilic deuteration of closo -[1-CB 11 H 12 ] − in the DCl/D 2 O system confirmed the expected order of reactivity on individual skeletal atoms, decreasing in the series B(12) > B(7–11) > B(2–6) > C(1). In contrast, electrophilic B-substitution of closo -[1-CB 11 H 12 ] − with H 2 NOSO 3 H is consistent with the preference of the B(7)-substitution to suggest a different mechanism for almost exclusive formation of 7-H 3 N- closo -1-CB 11 H 11 . 7-Me 3 N- closo -1-CB 11 H 11 was isolated along with the remaining 2- and 12-Me 3 N-1-CB 11 H 11 isomers as side products of the thermal decomposition of [BH 2 (NMe 3 ) 2 ] + [ nido -7-CB 10 H 13 ] − at 270°C, which is inconsistent with a specific insertion of the BNMe 3 fragment into the open face of nido -[7-CB 10 H 13 ] − . Nevertheless, clean 10 B-insertion was observed in the reactions of Et 3 N 10 BH 3 with both nido -[7-CB 10 H 13 ] − and 7-Me 3 N- nido -7-CB 10 H 12 to give respectively closo -[1-CB 11 H 12 ] − and [1-Me 2 N-1-CB 11 H 11 ] − labelled by 10 B exclusively at the B(2) site. Cage rearrangement was observed, however, in the reaction of 7-Me 3 N-8-PhCH 2 - nido -7-CB 10 H 11 with Et 3 NBH 3 under similar conditions to produce only the 1-Me 3 N-7-PhCH 2 -1-CB 11 H 10 closo -isomer.

High-performance liquid chromatographic separations of some boranes and their derivatives

Abstract The high-performance liquid chromatographic conditions required for the liquid-solid separation of about 20 higher boranes, heteroboranes and their derivatives were established. The separations were carried out on silica gel using n -heptane and methylene chloride as mobile phases. Except for several closo -boranes, spectrophotometric detection at 254 nm was used for borane compounds. Instead of water, acetonitrile and in some instances isopropanol were used as silica gel modifiers.

Steric and metal-centre control of two-, three- and four-orbital carborane-metal interaction in tin and platinum complexes of the {C2B8H9X} ligand, where X H and Ph

Abstract The cluster 11B and 1H NMR properties of the cluster species [1,1-Me2-1,2,3-SnC2B8H10] (compound 1), [1,1-{P(OMe)3}2-1,2,3-PtC2B8H10 (compound 2) and [1,1-{P(OMe)3}2-1,2,3-PtC2B8H9-2-Ph] (compound 3), together with single-crystal X-ray diffraction analyses of the platinum compounds, show that the metal-to-cluster bonding is substantially different for each of these three species, occurring predominantly via two, three and four orbitals respectively. The differences between compounds 2 and 3 constitute a rare example of a sterically induced change in metal oxidation state.

Charge distribution in icosahedral carboranes: A UV photoelectron spectroscopic study

Abstract The UV photoelectron (PE) investigation of dicarba- closo -dodecaboranes 1,12-C 2 B 10 H 12 , 1-SH-1,12-C 2 B 10 H 11 , 2-SH-1,12-C 2 B 10 H 11 , 1-X-1,2-C 2 B 10 H 11 (X=SH, phenyl), 3-phenyl-1,2-C 2 B 10 H 11 , 4-X-1,2-C 2 B 10 H 11 , 8-X-1,2-C 2 B 10 H 11 , 9-X-1,2-C 2 B 10 H 11 , 9-X-1,7-C 2 B 10 H 11 , (X = SH,CH 3 S) and 1-SH-1,7-C 2 B 10 H 11 is reported. The first two band systems in the PE spectrum of 1, 12-C 2 B 10 H 11 are assigned to cluster π-bonding orbitals and σBH(CH)-bonding orbitals, respectively. The interaction between exo-substituent and cluster π-orbitals is weak and the sulphur lone pair ionization energy depends simply on the mutual position of substituent and carbon atoms. The electron density at particular vertices in 1,2-C 2 B 10 H 12 decreases in the order 9 > 8 > 4 > 3 > 1.

Substitution of arachno-4,6-c2b7h13 carborane

Abstract Substitution of the 4,6-C2B7H13 cluster yields a series of 3-X-4,6-C2H7H12 (X = Cl, Br, I or HS), 5-X-4,6-C2B7H12 (X = Br, I, HS or Bu), and 3,5-X2-4,6-C2B7H11 (X = D, Cl, Br or I) derivatives whose 1H and 11B NMR spectra are reported and discussed.

Halogenation of 4,5-dicarba-arachno- nonaborane(13),4,5-C2B7H13

Abstract The AlX3-catalyzed (X = Cl, Br, and I) halogenation of arachno-4,5-C2B7H13 with anhydrous hydrogen halides produces a series of 6-substituted derivatives, 6-X-4,5-C2B7H12. The same compounds along with 6,8-I2-4,5-C2B7H11 are obtained in non-catalyzed reactions with elemental halogens. The electrophile-induced nucleophilic substitution concept (EINS) of the substitution with hydrogen halides is suggested. The constitution of all compounds isolated was unambiguously determined via 1H, 13C, 11B, and two-dimensional (2-D) 11B-11B NMR spectra.