Synthesis and Study of f-Block Complexes Containing Metal-Arene Interactions

The f-block elements are of great interest due to the under explored nature of their chemical bonding interactions and their unique magnetic and electronic properties. For the 5f-orbital elements, such as uranium, the f-orbitals are more readily available for bonding than the contracted, core like, 4f-orbitals of the lanthanides. This makes uranium complexes informative probes into the nature of f-(p/d/f) bonding interactions. Recently, it has been shown that a growing subset of complexes possessing supported uranium-arene interactions have the capability to stabilize unusually low valent U(II) molecular species and support novel catalytic activity. In our laboratory, we have begun to explore avenues for the synthesis of complexes possessing unsupported, as well as tethered, uranium-arene interactions utilizing a range of polyaromatic hydrocarbons or by complexation with the bis(anilide)terphenyl ligand platform [LAr]2- (LAr = {C6H4[(2,6-iPrC6H3)NC6H4]2}2−). For instance, treatment of UI3(dioxane)1.5 with excess [K(18-c-6)(THF)2][C14H10] in DME leads to the formation of the methoxy-bridged dimer [K(18-crown-6)(THF)2]2[U(η6-C14H10)(η4-C14H10)(μ-OMe)]2 (1). Additionally, a series of homoleptic metallate complexes featuring polyaromatic ligands with the general formula [M(L)3]-n (L= perylenide, anthracenide, naphthalenide), can be formed in similar conditions as those of 1, but avoiding the use of DME. These complexes contain a unique type of U-arene bonding and we report their structural, spectroscopic, magnetic, and electronic features. Alternatively, the K2LAr ligand platform has proved to be versatile in binding M(III) f-block ions (M = Ce, U, Np), forming the isostructural complexes [K(X)2][LArM(Cl)2] (X = Et2O or DME) (2), which feature M-η6-arene contacts with the central ring of the terphenyl backbone. Especially rare are these type of bonding interactions for transuranic elements, like neptunium. We report the spectroscopic features and present a structural comparison which highlights the M-C(arene) metrical parameters across the f-metal series