Organic Selenocyanates as Halide Receptors: From Chelation to One-Dimensional Systems

Abstract : Organic selenocyanates were recently identified as strong chalcogen bond donors. They also play an important role in biochemistry. Here, we show that 1,2-bis(selenocyanatomethyl)benzene (1) and 1,2,4,5-tetrakis(selenocyanatomethyl)-benzene (2) crystallize from dimethylformamide (DMF) to afford solvates where two ortho-SeCN moieties act as a chelate toward the carbonyl oxygen atom of DMF through strong Se···O chalcogen bonds. This result led us to explore their ability to also chelate halide anions (Cl–, Br–) in solution as well as in the solid state, an important issue in view of applications in crystal engineering or organocatalysis. NMR titration experiments provide an association constant between 1 and Cl– of 148 M–1. We also observed the recurrent formation of cocrystal salts from the association of the ChB donors 1 and 2 with the onium salts Ph4PCl, Ph4PBr, and Bu4NCl. We demonstrate that not only μ2-halide but also μ4-halide structures can be stabilized though ChB interactions, leading to the formation of complex polymeric anionic networks. Continuous shape measure calculations of these μ4-halide structures demonstrate that seesaw symmetry best describes the μ4-Br– bromide structures, while the smaller chloride anions tend to favor a close-to-tetrahedral μ4-Cl– organization, which is also confirmed by density functional theory calculations. Electrostatic surface potential calculations further demonstrate the efficiency of this chelating ortho-bis(selenocyanatomethyl) motif in 1 and 2, with Vs,max values reaching 50 kcal mol–1, to be compared with the simplest benzyl selenocyanate (36.4 kcal mol–1) or the reference halogen bond donor F5C6–I (35.7 kcal mol–1) in the same conditions.
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Asia Marie S. Riel, Huu-Tri Huynh, Olivier Jeannin, Orion Berryman, Marc Fourmigué. Organic Selenocyanates as Halide Receptors: From Chelation to One-Dimensional Systems. Crystal Growth and Design, American Chemical Society, 2019, 19 (2), pp.1418-1425. ⟨10.1021/acs.cgd.8b01864⟩. ⟨hal-02015955⟩

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