J. Plešek

B-Halogen derivatives of the bis(1,2-dicarbollyl)cobalt(III) anion

Abstract The halogenation of (C2B9H11)2Co−Cs+ by elemental halogens in alcohol and γ-radiation-induced halogenation by CHBr3, CH

Liquid chromatographic resolution of enantiomers of deltahedral carborane and metallaborane derivatives

Abstract A successful liquid chromatographic separation of twelve enantiomeric pairs of zwitterionic eleven-vertex nido -carboranes of the type L-R-7,8-C 2 B 9 H 10 (L = Me 2 S, Me 2 SCH 2 , C 6 H 5 N, C 6 H 5 NCH 2 ; R = H, CH 3 , C 6 H 5 , Me = methyl) and of the 4-MeS-3-C 5 H 5 -1,2,3-C 2 CoB 9 H 10 mixed sandwich complex on β-cyclodextrin (CD) chiral stationary phases (CSP) in aqueous-organic mobile phases is described. A comparison of two β-CD CSP columns. Tessek β-CD and Astec Cyclobond I, differing in enantioselectivity and resolution of individual compounds (to some extent), is presented together with a study of the factors controlling retention and enantiomeric resolution.

A new family of stable parent nido-tetracarbaboranes 5,6,8,9-C4B6H10, 2,7,8,11-C4B7H11 and 7,8,9,10-C4B7H11

Abstract The parent tetracarbaboranes, nido-5,6,8,9-C4B8H11 and nido-2,7,8,11-C4B7H11 were isolated via HPLC from the reaction of arachno-4,5-C2B7H13 with acetylene in hexane (120°C, 8 h); thermal decomposition of the arachno-[C4B7H12]− anion at 140°C produced the isomeric nido-7,8,9,10-C4B7H11 species.

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.

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.

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.

Chiral resolution of enantiomers of asymmetric cobaltacarboranes with a monoatomic bridge between ligands by liquid chromatography on a β-cyclodextrin column

Abstract The HPLC resolution on a β-cyclodextrin column is reported of thirteen enantiomeric pairs of racemates of the type 6, 6′-μ-R-E(1,7-C2B9H10)2-2-Co with oxygen, sulphur and nitrogen bridges (E) and with a variety of R substituents differing in size and electronic properties along with structural factors influencing the capacity factors, selectivity and resolution of individual compounds. A semi-preparative method for chiral separations of these racemates is described and circular dichroism (CD) spectra of several pure enantiomers are presented. The CD spectra indicate the same absolute configurations of all enantiomers eluted first or last independent of the nature of the bridging atom and the size of the bridge substituting group R.

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.