The Sixteen CB₁₁H_nMe_12-n^- Anions with Fivefold Substitution Symmetry:  Anodic Oxidation and Electronic Structure

Abstract

The 15 symmetrically methylated derivatives of the CB11H12(-) anion (1a) have been synthesized and found to vary greatly in ease of oxidation. Cyclic voltammetry in liquid SO2 yielded fully reversible oxidation potentials for five of those that have no adjacent unsubstituted vertices in positions 7-12; three others showed some indication of reversibility. The anions 1a-16a and the Jahn-Teller distorted neutral radicals 1r-16r have been characterized by ab initio and density functional theory calculations. In the state average CASSCF(13,12)/6-31+G* approximation, the ground state potential energy surface of 1r contains five symmetry-related pairs of minima. The computational results account for the reversible redox potentials very well when the solvent is included explicitly (RI-DFT(BP)/TZVP, COSMO). For display and for a semiquantitative understanding of methyl substituent effects in terms of perturbation theory, the molecular orbitals of 1a have been expressed in the symmetry-adapted cluster basis. The results serve as an underpinning for a set of additive empirical increments for redox potential prediction. Relative to the usual hydrogen standard, a single methyl group facilitates oxidation by approximately 50, 70, 70, and 10 mV in positions 1, 2, 7, and 12, respectively. This electron donor effect on the redox potential is due to a contribution, whereas those of (inductive and direct field) type are negligible.

Metal Complexes with Very Large Dipole Moments: the Anionic Carborane Nitriles 12-NC–CB11X11– (X = H, F, CH3) as Ligands on Pt(II) and Pd(II)

“…1 H NMR (600.1 MHz, acetone-d 6 ) δ 2.24 (dt, J = 9.5, 7.5 Hz, 12H, P−CH 2 ), 1.60 (bs, 2H, C carb −H), 1.28 (dt, J = 18.3, 7.6 Hz, 18H, CH 3 ), −0.10 (s, 60H, B−CH 3 ). 11 cis-Chlorobis(triethylphosphine)-(12-cyano-1-carba-closododecaborate)platinum(II) (21). The binuclear complex 22 (60 mg, 0.054 mmol) was dissolved in MeOH (10 mL), and MeOH (2 mL) solution of 2 (38 mg, 0.125 mmol, 2.3 equiv) was added.…”

Chemistry of the Carba-closo-dodecaborate(−) Anion, CB11H12-

“…We shall describe in section 8.6 the complexity that was involved in the preparation of all 15 symmetrically methylated CB 11 H 12 -anions. 13 Specific synthesis of most of the vast number of unsymmetrically methylated ones would be a much harder proposition.…”

“…What is most needed at present is a high-yield one-step or two-step synthesis from cheap bulk chemicals. As we shall see in section 7, starting with bulk chemicals, at this time some 29 Ph H H I 162 36 Me Me Me OMe 196 13 TIPS H H I 163 36 Me Me Me OH 197 44 Me H Cl Cl 164 21 HS H H H 198 44 Me H Br Br 165 21 MeS H H H 199 14 Me H I I 166 21 Me2S + H H H 200 40 Me F F F 167 21 H H H M e 2S 201 45 Me Cl Cl Cl 168 21 H H H X g 202 41 Me Br Br Br 169 37 F H H H 203 41 Me Me 179 39 H H I I 213 15 Me Me Me F 180 40 H F F F 214 47 Me Me Me I 181 41 H C l C l C l 215 13 Me Me I Me 182 41 H B r B r B r 216 13 Me I Me Me 183 41 H I I I 217 13 Me Me I I 184 41 Br Br Br Br 218 48 F H Me Me 185 42 Me3N + H H I 219 48 Cl H Me Me 186 31 X d H H I 220 48 Cl Me Me Me 187 43 NH3 + H I I 221 48 Br Me Me Me 188 43 NH3 + I I I 222 48 I M e M e M e 189 14 H B r C l C l 223 49 H O H B r B r 190 14 H I Cl Cl 224 16 H H H X h 191 14 H C l B r B r 225 16 H H H X i 192 …”

Preparation of undecamethylated and hexamethylated 1‐halocarba‐closo‐dodecaborate anions

“…Depending on the property examined, its −E effect may dominate its +I effect, as reflected for instance in the much lower oxidation potential of CB 11 Me − 12 [10] and other methylated derivatives [25] relative to 1, and in the reduction of the acidity of the CH vertex in 1 upon methylation.…”

“…This involves treatment with an alkyl triflate in the presence of a base that removes triflic acid, which is formed as a byproduct of alkylation. This reaction has been used for the preparation of the undecamethylated anion HCB 11 (CH 3 ) − 11 [13,24] and many other polymethylated derivatives of the CB 11 H − 12 anion [25]. A cheaper methylation procedure using an alkyl bromide in a pressure vessel instead of triflate has been described [26], but we have not been able to reproduce the results.…”