S. Heřmánek

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

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.

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.

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.

Electron transfer phenomena in isolated icosahedral borane units

From the experimentally determined charge density at the vertex E-H grouping in eight of the twelve possible positions in the icosahedral carborane family and based on the pK values of particular carborane thiols and on solvent shift differences in the 1H nuclear magnetic resonance signals, the conjugative transfer of electrons between skeletal and exopolyhedral electrons was studied and evidence that the polarizability of the skeletal electrons was due to substituents at the polyhedral cage was found. According to our results we should expect that the polyhedral boron units connected by two-centre bonds should be non-conducting via these bonds and units. The high conductance of the majority of borides cannot be explained by a conductance of the boron framework. It was found that the framework electrons within the polyhedral units were easily polarized. This should be indicated by the dielectric properties, by high refractive indices and by high extinction coefficients for elemental boron and for borides composed of polyhedral boron units.