Influence of the attachment of a gold(I) phosphine moiety at the upper rim of a calix[4]pyrrole on the binding of tetraalkylammonium chloride salts

Abstract

We report the synthesis of an unprecedent 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 solutions. We describe the results of 1H NMR, UV-vis titrations and isothermal titration calorimetry (ITC) experiments in DCM and acetone solution, aiming at 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.