Synthesis of Differently Substituted tacn‐Based Ligands: Towards the Control of Solubility and Electronic and Steric Properties of Uranium Coordination Complexes

Abstract

Abstract Starting from phenols R1,R2 ArOH ( 5 ) and the anisole derivative 3,5‐di‐ tert ‐butyl‐2‐methoxybenzyl bromide ( 13 ), a series of new tacn‐based ligands ( R1,R2 ArOR 3 ) 3 tacn ( 2 ) have been synthesized with substituents of varying bulkiness and electronic nature at the ortho and para positions with respect to the oxygen coordination site. It was observed that these groups not only determine the steric shielding and solubility properties of 2 , but also deactivate the reactivity of the phenols in the modified Mannich reaction when electron‐withdrawing groups are introduced at the para position in 5 . Treatment of the ligands with UCl 4 in thf led to the isolation of four uranium(IV) chloro complexes [{( R1,R2 ArO) 3 tacn}U IV Cl] ( 14 ), which were characterized by different spectroscopic and physical methods (e.g., 1 H NMR, UV/Vis, SQUID), corroborating the +4 oxidation state in 14 . Single‐crystal X‐ray structure analyses revealed that 14a· CH 2 Cl 2 · CH 3 CN and 14b· 1.25CH 2 Cl 2 crystallize in the chiral, orthorhombic space group P 2 1 2 1 2 1 [ a = 24.934(3), b = 27.941(3), c = 9.045(1) Å, V = 6302(2) Å 3 , Z = 4] and the chiral, hexagonal space group P 6 3 [ a = 22.097(3), c = 17.941(2) Å, V = 7587(2) Å 3 , Z = 4], respectively. Interestingly, complexes 14a , b self‐organize in the solid state into homochiral 1D polymeric superstructures as a result of weak intermolecular C–H ··· Cl contacts.