Fluoride ion complexation by a B2/Hg heteronuclear tridentate lewis acid

Abstract

The reaction of [Li(THF)(4)][1,8-mu-(Mes(2)B)C(10)H(6)] with HgCl(2) affords [1,1'-(Hg)-[8-(Mes(2)B)C(10)H(6)](2)] () or [1-(ClHg)-8-(Mes(2)B)C(10)H(6)] (), depending on the stoichiometry of the reagents. These two new compounds have been characterized by (1)H, (13)C, (11)B and (199)Hg NMR, elemental analysis and X-ray crystallography. The cyclic voltammogram of in THF shows two distinct waves observed at E(1/2) -2.31 V and -2.61 V, corresponding to the sequential reductions of the two boron centers. Fluoride titration experiments monitored by electrochemistry suggest that binds tightly to one fluoride anion and more loosely to a second one. Theses conclusions have been confirmed by a UV-vis titration experiment which indicates that the first fluoride binding constant (K(1)) is greater than 10(8) M(-1) while the second (K(2)) equals 5.2 (+/- 0.4) x 10(3) M(-1). The fluoride binding properties of have been compared to those of [1-(Me(2)B)-8-(Mes(2)B)C(10)H(6)] () and [1-((2,6-Me(2)-4-Me(2)NC(6)H(2))Hg)-8-(Mes(2)B)C(10)H(6)] (). Both experimental and computational results indicate that its affinity for fluoride anions is comparable to that of but significantly lower than that of the diborane . In particular, the fluoride binding constants of , and in chloroform are respectively equal to 5.0 (+/- 0.2) x 10(5) M(-1), 1.0 (+/- 0.2) x 10(3) M(-1) and 1.7 (+/- 0.1) x 10(3) M(-1). Determination of the crystal structures of the fluoride adducts [S(NMe(2))(3)][-mu(2)-F] and [S(NMe(2))(3)][-mu(2)-F] along with computational results indicate that the higher fluoride binding constant of arises from a strong chelate effect involving two fluorophilic boron centers.

In silico studies toward the recognition of fluoride ion by substituted borazines

“…These observations indicate the influence of the bulkiness of the substituents toward fluoride ion binding [8]. Further, Lewis acid based bidentate fluoride receptors with B/B and B/Hg as binding sites are also known [27][28][29][30][31]. The fluoride binding constants of bidentate boranes increases 3-4 times than the corresponding monofunctional analogs [9].…”

A class of fascinating optoelectronic materials: Triarylboron compounds

“…Further addition of F  does not lead to additional perturbation of the spectrum, indicating the formation of a 1:1 complex with a binding constant of 5 × 10 9 M 1 , which is remarkably high and by far exceeds that measured for monofunctional borane receptors. In an extension of this research, they have investigated the synthesis of heteronuclear bidentate Lewis acids, such as 37-39 ( Figure 11), which also have high fluoride affinity [34][35][36].…”

“…Owing to the high hydration enthalpy (H° = 504 kJ/mol) of F  , it is problematic to realize the detection in aqueous systems [33,34]. In order to increase the compatibility of these fluoride receptors with aqueous environments, bidentate boranes [34][35][36] whose F  affinity exceeds that of their monofunctional analogs by at least three orders Figure 10 Changes in UV-vis absorption spectra (right) and the color change response of 6 (10 M) at 20 °C in THF upon the addition of F  (adapted from ref. [32]).…”

Tridentate Lewis Acids: Boron‐, Silicon‐ and Gallium‐Functionalised Tris(dimethylsilyl)methanes

“…In most reports, the backbones of these molecules comprise flexible organic frameworks, because only a small number of donor-free rigid organic scaffolds are available. In the majority of cases the rigid backbones used are anthracenes functionalised with boron, [4] aluminium, [5] gallium [5] and indium, [5] but also naphthalenes functionalised with mercury, [6] boron [7,8] and other Lewis acid atoms. [7,9,10] Recently we reported some tridentate Lewis acids based on 1,3,5-trisilacyclohexane and equipped with boron, [11,12] gallium, [11,12] indium [12] and tin [13] functions.…”