Two-Electron-Transfer Redox Systems, Part 7: Two-Step Electrochemical Oxidation of the Boron Subhalide Cluster Dianions (X = Cl, Br, I)

Abstract

Boron subhalide cluster dianions B6X 2- 6 (X = Cl, Br, I) are electrochemically oxidized in two steps. According to cyclic voltammograms, the first step is chemically reversible and yields the corresponding radical anions B6X .- 6. The electron transfer is nearly diffusion controlled. The second, slower electron-transfer step leads to a species which we assume to be the hitherto not yet described neutral compounds B6X 2- 6. The voltammograms indicate a coupled fast catalytic reaction, producing the radical anions in a reduction by an electrolyte component. Computer simulations of the cyclic voltammograms reveal mechanistic details of the redox reactions, as well as quantitative values for formal potentials, rate constants, and diffusion coefficients. The results are compared to other BnXn redox systems.

Synthesis and Applications of Perfunctionalized Boron Clusters

“…The perfunctionalization chemistry of closo -[B 10 H 10 ] 2– was developed somewhat in parallel with that of the closo -[B 12 H 12 ] 2– dodecaborate cluster in the early 1960s, − with several routes to diverse functionalized derivatives resulting in partial substitutions of the cage-bound hydrogen atoms . Despite this early progress, in the subsequent decades, only halogenation resulted in the successful substitution of all B–H vertices to achieve perfunctionalization of the B n H n 2– ( n = 7–11) clusters to form species of the type B n X n 2– (X = Cl, Br, or I). ,,− …”

Electronic structures of two kinds of oligoborane radical anions: mixed-valence description of a reducedp-phenylenediborane and spin density distributions in distorted octahedral clusters [B6Hal6]•−, Hal = Cl, Br, I

“…Geometry optimization leads to two closely lying geometries corresponding to trigonal and tetragonal distortion of the octahedron in the case of [B 6 Cl 6 ] Á7 (2a) and [B 6 Br 6 ] Á7 (2b); for [B 6 I 6 ] Á7 (2c), only one geometry minimum with trigonal distortion was obtained. Comparable calculations on neutral [B 6 X 6 ] systems yield higher bonding energies of the neutral species, by about 4 eV, relative to the corresponding anions, which indicates that solvent stabilisation is needed in order to oxidize the radical anions [30].…”

“…The hyperfine information as well as the g factor anisotropy were reproduced for two well-documented cases, a p-phenylene bridged diborane radical anion 1 [13,19 -22] and hexanuclear clusters 2a -c [17,[28][29][30]. Both kinds of compounds reflect the capability of boron to act as spin-bearing centre of mixedvalent systems, which may be a description complementary to the usual formulation of these and related species as electron-deficient clusters [31] or B-containing radicals [8,32].…”

Multidimensional potential of boron-containing molecules in functional materials

“…X = H, n = 8). 43,44 Several theoretical studies have appeared later for species with X = H 45,46 and the attention was also extended to perhalide compounds (X = Hal, n = 6, 8, 9, 10), [47][48][49][50][51][52][53][54][55][56] to peralkylated species such as [B 12 Me 12 ] •-, 57 and to related OR substituted derivatives (R = CH 2 Ph, H). [58][59][60] The substituted 'hypercloso' compounds, typically generated by one-electron oxidation from dianionic closo precursors, are stabilized with electronegative substituents because neither Hal + nor R + or RO + are good leaving groups such as H + .…”