Hydroxytricyanoborate Anion: Synthetic Aspects and Structural, Chemical, and Spectroscopic Properties

Abstract

In recent years, salts of the hydridotricyanoborate anion [BH­(CN)3]− (MHB) have become readily available. In spite of the unusually high stability of the MHB anion, it can be used as a valuable starting material for the preparation of selected tricyanoborates, for example, the boron-centered nucleophile B­(CN)3 2–. A further unprecedented example is the hydroxytricyanoborate anion [B­(OH)­(CN)3]− that is accessible by oxidation of (H3O)MHB with elemental bromine in water. The Brønsted acid (H3O)­[B­(OH)­(CN)3] was isolated as a crystalline solid. It serves as a versatile starting material for the synthesis of coordination compounds, metal salts, and ionic liquids. The [B­(OH)­(CN)3]− anion shows a rich coordination chemistry and a high tendency to form hydrogen-bonded motifs as demonstrated by a series of salts with different types of cations. Furthermore, the [B­(OH)­(CN)3]− anion itself serves as starting material for new tricyanoborates such as the unusual trianion [B­{OB­(CN)3}3]3– and the silylated anions [B­(OSiR3)­(CN)3]− (R = Me, Et, Ph). Some of these follow-up products have been characterized by single-crystal X-ray diffraction, e.g., [nBu4N]3[B­{OB­(CN)3}3] and [nBu4N]­[B­(OSiPh3)­(CN)3].

Thermal Decomposition and Hypergolic Reaction of a Dicyanoborohydride Ionic Liquid

“…Presumably, BH­(OH)­(CN) 2 – is formed as an intermediate species by the oxidization of one of the hydrides on the anion. Oxidation of BH 2 (CN) 2 – (or DCBH – ) to yield BH­(OH)­(CN) 2 – is similar to the formation of B­(OH)­(CN) 3 – from BH­(CN) 3 – as described recently . The anion BH­(OH)­(CN) 2 – is observed alongside the final product B­(OH) 3 and unreacted DCBH – .…”

1,3‐Bis(tricyanoborane)imidazoline‐2‐ylidenate Anion—A Ditopic Dianionic N‐Heterocyclic Carbene Ligand

“…[20] The Brønsted acidity of its hydride adduct [BH(CN) 3 ] - [21] was demonstrated by deprotonation to give the B(CN) 3 2À dianion. [22] Furthermore, the large number of chemically stable tricyanoborate ions [RB(CN) 3 ] À with different substituents (R = CN, [19,23] F, [24] perfluoroalkyl, [25] CO 2 H, [22a] OH, [26] …) shows the large stabilization effect of the B(CN) 3 group. The cyano groups attached to boron are the reason for the unprecedented stability of the [B 2 (CN) 6 ] 2À dianion as well.…”

“…[20] The Brønsted acidity of its hydride adduct [BH(CN) 3 ] - [21] was demonstrated by deprotonation to give the B(CN) 3 2À dianion. [22] Furthermore,t he large number of chemically stable tricyanoborate ions [RB(CN) 3 ] À with different substituents (R = CN, [19,23] F, [24] perfluoroalkyl, [25] CO 2 H, [22a] OH, [26] …) shows the large stabilization effect of the B(CN) 3 group.T he cyano groups attached to boron are the reason for the unprecedented stability of the [B 2 (CN) 6 ] 2À dianion as well. [27] Keeping this high thermodynamic and kinetic stability of heteroatomÀB(CN) 3 bonds in mind, we were interested to use tricyanoborane substituents for the preparation of adianionic 1,3-bis(borane)-functionalized NHC and herein, we report its synthesis,s tructural and spectroscopic properties as well as first metal-and non-metal derivatives.…”

Das 1,3‐Bis(tricyanoboran)imidazolin‐2‐ylidenat‐Anion – Ein ditopischer dianionischer N‐heterocyclischer Carben‐Ligand

“…Die Brønsted‐Acidität des korrespondierenden Hydrid‐Addukts [BH(CN) 3 ] −[21] wurde durch die Deprotonierung zum Dianion B(CN) 3 2− nachgewiesen [22] . Auch die große Zahl chemisch stabiler Tricyanoborat‐Anionen [RB(CN) 3 ] − mit unterschiedlichen Substituenten (R=CN, [19, 23] F, [24] Perfluoralkyl, [25] CO 2 H, [22a] OH, [26] …) belegt den großen stabilisierenden Effekt der B(CN) 3 ‐Gruppe. Die Cyanogruppen an Bor sind auch der Grund für die unerwartete Stabilität des [B 2 (CN) 6 ] 2− ‐Dianions [27] .…”

“…[20] Die Brønsted-Aciditätd es korrespondierenden Hydrid-Addukts [BH(CN) 3 ] À [21] wurde durch die Deprotonierung zum Dianion B(CN) 3 2À nachgewiesen. [22] Auch die große Zahl chemisch stabiler Tr icyanoborat-Anionen [RB-(CN) 3 ] À mit unterschiedlichen Substituenten (R = CN, [19,23] F, [24] Perfluoralkyl, [25] CO 2 H, [22a] OH, [26] …) belegt den großen stabilisierenden Effekt der B(CN) 3 -Gruppe.D ie Cyanogruppen an Bor sind auch der Grund fürd ie unerwartete Stabilitätd es [B 2 (CN) 6 ] 2À -Dianions. [27] Die hohe thermodynamische und kinetische Stabilitätv on Heteroatom-B(CN) 3 -Bindungen hat uns dazu bewegt, Tricyanoboran-Substituenten fürd ie Synthese eines dianionischen 1,3-Bis(boran)funktionalisierten NHC einzusetzen.…”