Ligands for Eu III , Fe III , Sr II , and UO 2 II Based on CMPO‐Functionalized Resorcinarene Cavitands; Synthesis and Extraction

Partially functionalized cavitands ( 7a–d ) have been synthesized starting from the tetrakis(bromomethyl)cavitand 6 . New cavitand‐based cation ligands, with one to three carbamoylmethylphosphane oxide (CMPO) moieties ( 11a–d ), were prepared in good (66–90%) yields. The ligands 11a–d extract Eu III , but do so less effectively than the tetra‐CMPO cavitand 1 . The decreasing number of CMPO groups which result in decreasing extraction percentages for Eu III , also decrease the selectivity of Eu III over that of Fe III , Sr II , and UO   2 II . There is a difference in extraction behavior, determined by radio‐tracer experiments, between the distal and proximal disubstituted ligands, 11b and 11c , respectively. The extraction constants for the 1:1 complex of 11b and 11c with Eu(picrate) 3 are K ex = 6.7 · 10 8 M −4 and 3.7 · 10 9 M −4 , respectively.