A Bidentate Antimony Pnictogen Bonding Host System

Abstract

A bidentate pnictogen bonding host‐system based on 1,8‐diethynylanthracene was synthesized by a selective tin‐antimony exchange reaction and investigated regarding its ability to act as a Lewis acidic host component for the complexation of Lewis basic or anionic guests. In this work, the novel C≡C–Sb(C2F5)2 unit was established to study the potential of antimony(III) sites as representatives for the scarcely explored pnictogen bonding donors. The capability of this partly fluorinated host system was investigated towards halide anions (Cl−, Br−, I−), dimethyl chalcogenides Me2Y (Y = O, S, Se, Te) and nitrogen heterocycles (pyridine, pyrimidine). Insights into the adduct formation behavior as well as the bonding situation of such E⋯Sb–CF moieties were obtained in solution by means of NMR spectroscopy, in the solid state by X‐ray diffraction, by elemental analyses and by computational methods (DFT, QTAIM, IQA), respectively.

Poly-pnictogen bonding: trapping halide ions by a tetradentate antimony(iii) Lewis acid

“…The synthesis of host system 2 was achieved by following a protocol established for the bidentate system 1 : reaction of the corresponding tin compound 3 in a metal exchange reaction with four equivalents of chlorobis(pentafluoroethynyl)stibane ( 4 ) with liberation of chlorotrimethylstannane (Scheme 2). 58,60 After recrystallization, the tetrastibane 2 was obtained in 74% yield. Like the bidentate system 1 , system 2 decomposes on exposure to air by oxidation of Sb( iii ) and hydrolyses on contact with moisture forming pentafluoroethane.…”

“…In pnictogen bonding, this linearity is usually distorted by the presence of the lone pair and falls within a range of 165° to 175°. 48,58,66 When the three adducts are examined in terms of these angles, the iodide adduct has one angle that is strongly out of linearity, while the bromide and chloride adducts each have two strongly deviating angles. The X⋯Sb–C F motifs with these deviating angles correlate with the longest Sb⋯X distances mentioned above.…”

“…, the anions with a higher charge density) are the more stable ones. 58 This is because the Sb⋯X interaction strength increases according to the trend I < Br < Cl < F. Since the enthalpies of formation of the complexes [ 2 ·X] − (X = F, Cl, Br, I) are equal, this stabilizing tendency must somehow be compensated for in host 2 . The reason for this is the different number of strongly attractive Sb⋯X interactions in [ 2 ·X] − , which increases as the halide becomes heavier.…”

Bidentate boron Lewis acids: synthesis by tin boron exchange reaction and host–guest complex formation

“…Second, they prevent steric repulsion between the complexed guest molecule and the backbone, which can occur in some cases, such as with the 1,8-anthracenyl backbone. Finally, the alkynes can be easily substituted with various Lewis acid functions such as boryl 33 and stibanyl 39 groups. Some of these substitution reactions are not accessible for direct functionalization of aromatic systems.…”

“…Since the synthesis and host–guest chemistry with anthracene derivatives is well established in our group, 3,23,30,33,39 we chose the 1,8-diethinylanthracene backbone as a test system for our subsequent work, in which we tried to introduce other boranyl functions by a tin–boron exchange reaction, which offer additional properties such as an easier purification process, less steric repulsion of the substituents, better solubility or a higher Lewis acidity. We then investigated the host–guest chemistry of these new host systems.…”