We report the synthesis of an unprecedented mono-gold(I) phosphine complex based on a "two-wall" aryl-ethynyl extended calix[4]pyrrole. We describe and compare the binding properties of the parent 10α,20α-bis-aryl-ethynyl calix[4]pyrrole ligand and the prepared organometallic compound as receptors for tetraalkylammonium chloride salts in dichloromethane and acetone. We describe the results of H NMR, UV-Vis titrations and isothermal titration calorimetry (ITC) experiments in dichloromethane and acetone, aiming to thermodynamically characterize the formed complexes. The obtained results indicate a noticeable decrease in the binding affinity of the chloride for the mono-gold(I) receptor 1 compared to the parent ligand 2. The increase in the negative value of the electrostatic surface potential at the center of the aromatic ring of the gold(I) meso-aryl-ethynyl substituent serves to explain the observed results and the presence in solution of the chloride complex of 1 as a mixture of two conformers.
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