Synthesis of Stable Dodecaalkoxy Derivatives of hypercloso-B₁₂H₁₂

Abstract

The scope and limitations of the alkylation of [closo-B12(OH)12]2- using a series of fourteen alkyl and aralkyl halides and two p-toluenesulfonic acid esters in the presence of N,N-diisopropylethylamine have been investigated. The dodecaalkoxy-closo-dodecaborate products, [closo-B12(OR)12]2-, and their hypercloso two-electron oxidation products have been explored. The species [closo-B12(OR)12]2- containing 26 cage-bonding electrons may undergo two reversible, sequential, one-electron oxidation processes, producing a 25-electron radical anion and a 24-electron neutral species. Several oxidizing reagents were investigated for the chemical oxidation of [closo-B12(OR)12]2- and [hypercloso-B12(OR)12]- to [hypercloso-B12(OR)12]. Both FeCl3.6H2O and K3Fe(CN)6 in 90/5/5 ethanol/acetonitrile/H2O were found to be the reagents of choice. The reverse reaction leading from the neutral species to the radical anion and subsequently to the dianion was achieved using sodium borohydride in ethanol. A variety of alkoxyl derivatives have been synthesized by heating the reactants for extended periods of time in acetonitrile at the reflux temperature. The use of elevated reaction temperatures attained by employing moderate argon pressure (autoclave) over the reaction mixture led to drastic reductions in reaction times and increased efficiency. X-ray diffraction studies of substituted dodecabenzyl ether derivatives proved that 2(2-) has approximate Ih symmetry while hypercloso-2, -3, -9, -11, -12, and -13 have approximate D3d point group symmetry due to Jahn-Teller distortion from Ih.

Synthesis and Applications of Perfunctionalized Boron Clusters

“…75 A variety of other peretherated clusters were also reported using similar conditions. 71 Although these methods were effective, the length of time required for the reactions reduced their utility. To address this issue, our laboratory has reported a rapid microwave-assisted method to prepare peretherated clusters.…”

Multidimensional potential of boron-containing molecules in functional materials

“…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 + . Our focus here will be on the more symmetrical cases, on the compound series [B 6 Hal 6 ] •-(Hal = Cl, Br, I), on well studied [53][54][55][56] [B 9 Br 9 ] •-and on the systems [B 12 X 12 ] •-.…”

“…For non-halide substituted derivatives there were several recent reports by Hawthorne and coworkers describing isolated, slightly Jahn-Teller distorted hypercloso species [B 12 Me 12 ] •-(g = 2⋅0076) and purple [B 12 (OR) 12 ] •-, R = CH 2 Ph and other alkyl groups. [57][58][59] Back-bonding from the electron rich and lone pair-providing alkoxy groups to the electron deficient B 12 cluster was postulated, based on the structural changes such as shrinking B-O distances on oxidation. 58 The alkoxo derivatives were labelled as discrete nanomolecular ions with tunable pseudometallic properties such as metal-like redox reactions 59 while the stable green ion [B 12 (OH) 12 ] •-was structurally analyzed as the Cs + salt, and characterized by EPR (g = 2⋅0042).…”

Boratome als Spinträger in zwei‐ und dreidimensionalen Systemen

“…[62] Für Derivate mit Nicht-Halogen-Substituenten beschrieben Hawthorne und Mitarbeiter isolierte, leicht Jahn-Tellerverzerrte hypercloso-[B 12 Me 12 ]C À -Verbindungen (g = 2.0076) und violette [B 12 (OR) 12 ]C À -Verbindungen (R = CH 2 Ph oder andere Alkylgruppen). [55][56][57] Auf Grundlage von Strukturän-derungen wie den bei der Oxidation kleiner werdenden B-OAbständen wurde eine Rückbindung von elektronenreichen Alkoxygruppen, die Elektronenpaare zur Verfügung stellen, zum elektronenarmen B 12 -Cluster postuliert. [56] Die Alkoxoderivate wurden als diskrete nanomolekulare Ionen mit ein- [57] Während das diamagnetische [B 12 (OH) 12 ] 2À bereits vor längerem beschrieben [58] (14) oder (CH 2 ) 3 ), [64b] einschließlich ihrer strukturellen, [64b] theoretischen [64a] und (spektro)elektrochemischen Charakterisierung, [64] wurde erst vor kürzerer Zeit berichtet.…”

“…[55][56][57] Auf Grundlage von Strukturän-derungen wie den bei der Oxidation kleiner werdenden B-OAbständen wurde eine Rückbindung von elektronenreichen Alkoxygruppen, die Elektronenpaare zur Verfügung stellen, zum elektronenarmen B 12 -Cluster postuliert. [56] Die Alkoxoderivate wurden als diskrete nanomolekulare Ionen mit ein- [57] Während das diamagnetische [B 12 (OH) 12 ] 2À bereits vor längerem beschrieben [58] (14) oder (CH 2 ) 3 ), [64b] einschließlich ihrer strukturellen, [64b] theoretischen [64a] und (spektro)elektrochemischen Charakterisierung, [64] wurde erst vor kürzerer Zeit berichtet. Den Rechnungen zufolge vergrößert sich der C-C-Abstand bei der Reduktion der neutralen Verbindung zum Radikalanion 14 signifikant, was darauf schließen lässt, dass keine C-C-Bindungen im Radikal vorhanden sind.…”