Synthesis and Characterization of Pyridine Dipyrrolide Uranyl Complexes

[Image: see text] The first actinide complexes of the pyridine dipyrrolide (PDP) ligand class, ((Mes)PDP(Ph))UO(2)(THF) and ((Cl2Ph)PDP(Ph))UO(2)(THF), are reported as the U(VI) uranyl adducts of the bulky aryl substituted pincers ((Mes)PDP(Ph))(2–) and ((Cl2Ph)PDP(Ph))(2–) (derived from 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H(2)(Mes)PDP(Ph), Mes = 2,4,6-trimethylphenyl), and 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H(2)(Cl2Ph)PDP(Ph), Cl(2)Ph = 2,6-dichlorophenyl), respectively). Following the in situ deprotonation of the proligand with lithium hexamethyldisilazide to generate the corresponding dilithium salts (e.g., Li(2)(Ar)PDP(Ph), Ar = Mes of Cl(2)Ph), salt metathesis with [UO(2)Cl(2)(THF)(2)](2) afforded both compounds in moderate yields. The characterization of each species has been undertaken by a combination of solid- and solution-state methods, including combustion analysis, infrared, electronic absorption, and NMR spectroscopies. In both complexes, single-crystal X-ray diffraction has revealed a distorted octahedral geometry in the solid state, enforced by the bite angle of the rigid meridional ((Ar)PDP(Ph))(2–) pincer ligand. The electrochemical analysis of both compounds by cyclic voltammetry in tetrahydrofuran (THF) reveals rich redox profiles, including events assigned as U(VI)/U(V) redox couples. A time-dependent density functional theory study has been performed on ((Mes)PDP(Ph))UO(2)(THF) and provides insight into the nature of the transitions that comprise its electronic absorption spectrum.