PNNL

Abstract

The potential to explore head-to-head f backbonding from uranium f-orbitals into allyl p* orbitals was pursued. The coordination of allyl groups to uranium was achieved via tethered anilide ligands, the products investigated using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)2-propenylsilyl)2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI2((N-((dimethyl)prop-2-enylsilyl))2,6-diisopropylaniline)2 (1), which was synthesized using the mono-deprotonated ligand [K][N-((dimethyl)propenyl)silyl)2,6-diisopropylanilide] (L1). The desired homoleptic sandwich complex U[N-((dimethyl)prop-2-enidesilyl)2,6-diisopropylanilide]2 (2) was prepared from all three ligand precursors, but most consistent results came from the use of the dipotassium salt of the doubly deprotonated ligand [K]2[N-((dimethyl)propenidesilyl)-2,6-diisopropylanilide] (L2). This allyl-based sandwich complex was studied using theoretical techniques with supporting experimental spectroscopy to investigate the potential for f backbonding. The bonding description between the U(IV) and the allyl fragments is best described as a two-carbon-localized ligand-to-metal electron donation into empty f-orbitals.