Aqueous Synthesis of 14‐15‐Membered Crown Ethers with Mixed O, N and S Heteroatoms: Experimental and Theoretical Binding Studies with Platinum‐Group Metals

A series of 14‐15‐membered O, N, and S‐containing crown ethers (CEs) was synthesized by cyclization of bis‐epoxides with aryl‐N or S dinucleophiles using triethylamine as a catalyst and LiCl as a metal template in water. The catalyst dosage, and metal template type and dosage were critical in achieving yields of 56–93 %. Liquid‐liquid extraction (LLE) was performed to evaluate the CE complexation with Pd 2+ and Pt 2+ . Among the CEs, a dioxa‐dithia dibenzo CE exhibited the highest Pd 2+ selectivity even in the presence of other platinum‐group metals (PGMs). Complementary DFT studies reveal that this CE has the most compatible cavity dimension (Ø CE =1.58 Å) with Pd 2+ (Ø Pd 2+ =1.56 Å) forming a square‐planar S 4 geometry. Binding‐energy calculations showed the Pd 2+ complex has the least energy requirement for structural reorientation during complexation. Overall results highlight the importance of CE cavity dimension and presence of S heteroatoms for the structural design of CEs selective towards PGMs such as Pd 2+ .