Synthesis of Dicarboxylate “C‐Clamp” 1,2‐Diethynylarene Compounds as Potential Transition‐Metal Ion Hosts

Abstract We report an efficient convergent synthesis of a new type of C‐clamp ligand with a 1,2‐diethynylarene scaffold involving a chelate host capable of binding a guest molecule in its endo ‐dicarboxylate pocket. The chemistry involves a combination of palladium‐catalyzed Sonogashira, Heck, and Suzuki cross‐coupling reactions. The compounds 2,3‐bis[2‐(2′‐carboxybiphenyl‐4‐yl)ethynyl]triptycene and 4,5‐bis[2‐(2′‐carboxybiphenyl‐4‐yl)ethynyl]veratrole and their 2′‐carboxy‐ m ‐terphenyl‐4‐yl analogues were designed as dinucleating ligands to assemble carboxylate‐bridged transition‐metal complexes with a windmill geometry. The X‐ray crystal structure of one such C‐clamp compound containing co‐crystallized water molecules reveals strong hydrogen bonds of the aqua guest to the endo ‐oriented carboxylic acid entities of the C‐clamp host. In addition, two syn ‐N‐donor ligands were prepared as a synthetic scaffold to mimic the geometric arrangement of N‐donor atoms in carboxylate‐bridged dinuclear proteins. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)