Functionalized Tris(anilido)triazacyclononanes as Hexadentate Ligands for the Encapsulation of U(III), U(IV) And La(III) Cations

Tripodal multidentate ligands have become increasingly popular in f-element chemistry 14 for stabilizing unusual bonding motifs and supporting small molecule activation processes; the ste-15 ric and electronic effects of ligand donor atom substituents have proved crucial in both of these 16 applications. Here we functionalize the previously reported tris-anilide ligand {tacn(SiMe2NPh)3} 17 (tacn = 1,3,7-triazacyclononane) to incorporate substituted aromatic rings, with the aim of modifying 18 f-element complex solubility and ligand steric effects. We report the synthesis of two proligands, 19 {tacn(SiMe2NHAr)3} (Ar = C6H3Me2-3,5 or C6H4Me-4), and their respective group 1 transfer agents 20 {tacn(SiMe2NKAr)3}, M(III) complexes [M{tacn(SiMe2NAr)3}] for M = La and U, and U(IV) complexes 21 [M{tacn(SiMe2NAr)3}(Cl)]. These compounds were characterized by multinuclear NMR and FTIR 22 spectroscopy and elemental analysis, with paramagnetic uranium complexes also characterized by 23 solid state magnetic measurements and UV/Vis/NIR spectroscopy; U(III) complexes were addition-24 ally studied by EPR spectroscopy. The solid state structures of all f-block complexes were authenti-25 cated by single crystal X-ray diffraction (XRD), together with a minor byproduct 26 [U{tacn(SiMe2NC6H4Me-4)3}(I)]. Comparisons of the characterization data of f-element complexes 27 herein with similar literature examples containing the {tacn(SiMe2NPh)3} ligand set showed minor 28 changes in physicochemical properties resulted from the different aromatic ring substitution pat-29 terns investigated herein.