An N-Tethered Uranium(III) Arene Complex and the Synthesis of an Unsupported U-Fe Bond

Amination of 2,2 ''-dibromo-p-terphenyl with 2,6-diisopropylaniline, through Pd mediated cross coupling, yields the p-terphenyl bis(aniline) ligand H2LAr. Deprotonation of H2LAr with excess KH generates the dianion [K(DME)(2)](2)L-Ar as a dark red solid. Treatment of [K-(DME)(2)](2)L-Ar with UI3(dioxane)(1.5) produces the mononuclear U(III) complex (LU)-U-Ar(I)(DME) (1). Subsequent addition of the nucleophilic metal anion [CpFe(CO)(2)](-) (Fp(-)) gives the bimetallic U(III) compound (LU)-U-Ar(Fp) (2) in modest yield which features a rare instance of an unsupported U-M bond. Inspection of the metrical parameters of the solid-state structures of 1.DME and 2.0.5DME from X-ray crystallographic analyses show a seemingly eta(6)-interaction between the uranium and the terphenyl ligand (1: U1-C-centroid = 2.56 angstrom; 2: U1-C-centroid = 2.45 angstrom), spatially imposed as a consequence of the anilide N-donor atom coordination. Furthermore, the U-Fe bond length in 2 (U1-Fe1 = 2.9462(3) angstrom) is consistent with a metal-metal single bond. Notably, electronic structure analyses by CASPT2 calculations instead suggest that electrostatic, and not covalent, interactions dominate between the U-arene systems in 1 and 2 and between the U-Fe bond in the latter.