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

Abstract

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]2LAr as a dark red solid. Treatment of [K(DME)2]2LAr with UI3(dioxane)1.5 produces the mononuclear U(III) complex LArU(I)(DME) (1). Subsequent addition of the nucleophilic metal anion [CpFe(CO)2]- (Fp-) gives the bimetallic U(III) compound LArU(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 η6-interaction between the uranium and the terphenyl ligand (1: U1-Ccentroid = 2.56 Å 2: U1-Ccentroid = 2.45 Å), 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) Å) 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.