Vertex Differentiation Strategy for Tuning the Physical Properties of closo-Dodecaborate Weakly Coordinating Anions

Abstract

We report the synthesis and characterization of various compounds containing the 1,7,9-hydroxylated closododecahydrododecaborate (B 12 H 9 (OH) 3 2− ) cluster motif. Specifically, we show how the parent compound can be synthesized on the multigram scale and further perhalogenated, leading to a new class of vertex-differentiated weakly coordinating anions. We show that a postmodification of the hydroxyl groups by alkylation affords further opportunities for tailoring these anions' stability, steric bulk, and solubility properties. The resulting dodecaborate-based salts were subjected to a full thermal and electrochemical stability evaluation, showing that many of these anions maintain thermal stability up to 500 °C and feature no redox activity below ∼1 V vs Fc/Fc + . Mixed hydroxylated/halogenated clusters show enhanced solubility compared to their purely halogenated analogs and retain weakly coordinating properties in the solid state, as demonstrated by ionic conductivity measurements of their Li + salts.

The Hammett substituent constant of the dodecaborate dianion inaugurates a non-coordinating, non-basic, and strongly inductively electron-donating group for organic chemistry

“…25,29 Secondly, B 12 H 12 2-, the parent di-anionic dodecahydrido-closo-dodecaborate cluster, which was rst prepared by Pitochelli and Hawthorne, 30 has been described as a non-coordinating anion, which has led to several application lines, for example in electrolytes for batteries. 31,32 Similarly, B 12 H 12 2becomes only protonated below pH 0, in strong or neat inorganic acids. 33,16 It is also stable towards bases and nucleophiles and can be functionalized only by electrophile-induced nucleophilic substitution or by oxidants such as halogens or hydrogen peroxide, which allows the attachment of heteroatoms (S, O, N, P).…”

Redox-Active Boron Clusters

“…(A)–(C) Vertex-differentiated functionalization of dodecaborate-based clusters leads to tunable redox properties. Panel (A) adapted from ref and panel (B) adapted from ref with permission. Copyright 2018 Royal Society of Chemistry and 2023 American Chemical Society, respectively.…”

“…To accomplish this, sodium hypochlorite can be used as an aqueous chlorinating reagent for the [B 12 H 9 (OH) 3 ] 2– anion, producing the [B 12 Cl 9 (OH) 3 ] 2– species (Figure B). Similarly, the perbrominated analogue [B 12 Br 9 (OH) 3 ] 2– can be synthesized from an aqueous solution of [B 12 H 9 (OH) 3 ] 2– and Br 2 in methanol.…”

Alkoxy Substituted Brominated closo-Dodecaborates with Functionalized Aliphatic Spacers

“…1-a, step 2). [12] This one-pot reaction could be conducted on a gram scale and simple purification (removal of volatiles/filtration/precipitation in H2O as the ammonium salt) was sufficient to obtain (NBu4)2•3 in high purity (82%). The obtained product was characterized using 11 B NMR and 1 H NMR spectroscopy and ESI-TOF mass spectrometry.…”