Dismutation of Tricyanoboryllead Compounds: The Homoleptic Tetrakis(tricyanoboryl)plumbate Tetraanion

Abstract

A series of unprecedently air‐stable (tricyanoboryl)plumbate anions was obtained by the reaction of the boron‐centered nucleophile B(CN)32− with triorganyllead halides. Salts of the anions [R3PbB(CN)3]− (R=Ph, Et) were isolated and found to be stable in air at room temperature. In the case of Me3PbHal (Hal=Cl, Br), a mixture of the anions [Me4−nPb{B(CN)3}n]n− (n=1, 2) was obtained. The [Et3PbB(CN)3]− ion undergoes stepwise dismutation in aqueous solution to yield the plumbate anions [Et4−nPb{B(CN)3}n]n− (n=1–4) and PbEt4 as by‐product. The reaction rate increases with decreasing pH value of the aqueous solution or by bubbling O2 through the reaction mixture. Adjustment of the conditions allowed the selective formation and isolation of salts of all anions of the series [Et4−nPb{B(CN)3}n]n− (n=2–4) including the homoleptic tetraanion [Pb{B(CN)3}4]4−.

Alkylcyanoborate Anions: Building Blocks for Fluorine‐Free Low‐Viscosity, Electrochemically and Thermally Stable Ionic Liquids

“…[32] In addition, further related tetrahedral cyanoborate anions that are unusually stable have been reported, for example with fluorinated and non-fluorinated aryl and pyridyl substituents [ArB(CN) 3 ] À , [33] the cyanotris(trifluoromethyl)borate anion [(CF 3 ) 3 B(CN)] À , [34] and tricyanoborate anions with functional groups such as [B(OH)(CN) 3 ] À [35] and [B{C(O)OH}(CN) 3 ] À . [36] The general, unusual stability of tetrahedral cyanoborate anions is additionally emphasized by the formation of [Hg{B(CN) 3 } 2 ] 2À and related mercury(II) complexes, [37] by isolation of salts of the dianion [B 2 (CN) 6 ] 2À , [38] of the lead(IV) anions [(C 2 H 5 ) 4À x Pb{B-(CN) 3 } x ] xÀ (x = 1À 4), [39] and by the preparation of anionic NHCs [40] such as the 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion. [40a] Perfluoroalkyltrifluoroborate anions [R F BF 3 ] À [41] and alkyltrifluoroborate anions [RBF 3 ] À [42] have been employed as building blocks for ILs and the influence of the alkyl chain length on some properties of the ILs was elucidated.…”