(Benzylideneamino)thioureas – Chromogenic Interactions with Anions and N–H Deprotonation

A family of neutral N ‐(R 1 ‐substituted‐benzylideneamino)‐ N′ ‐(R 2 ‐substituted‐phenyl)thioureas (LH) were designed as anion receptors, and their interactions with anions in MeCN solution were investigated through spectrophotometric and 1 H NMR titration experiments. While oxo anions (e.g., CH 3 COO – , H 2 PO 4 – ) form genuine H‐bond complexes based on complementary N–H ··· O interactions with LH receptors, the fluoride ion undergoes a two‐step interaction, involving (i) formation of the [LH ··· F] – complex, and (ii) release of an HF molecule to give [HF 2 ] – and the deprotonated form of the receptor (L – ). Deprotonation takes place at the N–H fragment closer to the R 2 ‐substituted phenyl ring, as indicated by 1 H NMR spectroscopy. The log  K values for the formation of the [LH ··· CH 3 COO] – H‐bond complexes vary over the 3.1–3.8 range and are scarcely affected by the natures of the R 1 and R 2 substituents. The investigated systems may be of interest in the design of molecular devices in which the optical properties of different and distant substituents are modulated through the interaction of a chosen anion at the thiourea site.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)