Novel ligands for the separation of trivalent lanthanides and actinides-tetrakis(phosphane sulfide) and -(phosphinic acid) cavitands

Cavitands with phosphane sulfide moieties 4 and 8a,b were prepared in good yields from their phosphane oxide analogues, as more stable alternatives for the dithiophosphinic acids used at present. The cavitands 7a and 7b with flexible butoxyphosphane oxide ligating sites are more efficient than cavitand 3 having rigid methylphosphane oxide groups as was studied with EuIII picrate extractions. Due to the absence of an ionic functionality in the phosphane sulfides 4 and 8a,b Am^III and Eu^III are not extracted, not even in the presence of synergents (e.g. TBP, TOPO, HDNNS). Cavitand 10 with phosphinic acid groups efficiently extracts Eu^III in 1:1 or 2:1 complexes, depending on the metal-to-ligand concentration ratio (extraction constants K_ex¹ = 3.9·10^-5M² and K_ex² = 1.9·10²M, respectively). Furthermore, in the case of 10 Eu^III is preferentially extracted over AmIII with a separation factor S_Eu/Am up to 5.