An Allyl Uranium(IV) Sandwich Complex: Are ϕ Bonding Interactions Possible?

Abstract

A method to explore head-to-head ϕ back-bonding from uranium f-orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single-crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N-((dimethyl)prop-2-enylsilyl)-2,6-diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI 2 (L1) 2 (1), which was synthesized by using the mono-deprotonated ligand [K][N-((dimethyl)prop-2-enyl)silyl)-2,6-diisopropylanilide] (L1). The desired homoleptic sandwich complex U[L2] 2 (2) was prepared from all three ligand precursors, but the most consistent results came from using the dipotassium salt of the doubly deprotonated ligandThis allyl-based sandwich complex was studied by using theoretical techniques with supporting experimental spectroscopy to investigate the potential for phi (ϕ) back-bonding. The bonding between U IV and the allyl fragments is best described as ligand-to-metal electron donation from a two carbon fragment-localized electron density into empty forbitals.

Highly oxidized U(vi) within the smallest fullerene: gas-phase synthesis and computational study of boron-doped U@C27B

“…The nature of the interaction is not very different from that observed in classical organometallic ligands. 31,32,[49][50][51] Finally, we have analysed the hypothetical system Pa@C 27 B, isoelectronic to U@C 27 B + with a closed-shell structure. Protactinium, with a very similar size as U, has the same spatial constraints and it is placed at the centre of the cage interacting with boron and all the carbon atoms in a quite similar way.…”

“…The nature of the interaction is not very different from that observed in classical organometallic ligands. 31,32,49–51…”

Synthesis and comparison of iso-structural f-block metal complexes (Ce, U, Np, Pu) featuring η6-arene interactions

“…24–32 Among this class of molecules, those which feature neutral arene coordinating motifs are of particular interest as these may exhibit covalent participation of the metal in the form of π/ δ / φ type interactions. 31,33–37 Such complexes have potential to provide new key insight into f-block bonding modes as has been the case in other areas of the periodic table; for example, the seminal discovery of bis(benzene)chromium, Cr( η 6 -C 6 H 6 ) 2 , by E. O. Fischer, which revolutionized the understanding of transition metal chemistry. 38…”

“…[24][25][26][27][28][29][30][31][32] Among this class of molecules, those which feature neutral arene coordinating motifs are of particular interest as these may exhibit covalent participation of the metal in the form of p/d/4 type interactions. 31,[33][34][35][36][37] Such complexes have potential to provide new key insight into f-block bonding modes as has been the case in other areas of the periodic table; for example, the seminal discovery of bis(benzene)chromium, Cr(h 6 -C 6 H 6 ) 2 , by E. O. Fischer, which revolutionized the understanding of transition metal chemistry. 38 A challenge to overcome in establishing a suite of analogous metal-arene molecules across the f-block is the "hard" Lewis acidic character of the f-block metal ions that causes interactions with "so" arene donor substituents to be difficult to form and have oen required the use of hard donor atom substituents to act as an "anchor-point" and facilitate binding of the arene to the metal.…”

Thorium- and Uranium-Mediated C–H Activation of a Silyl-Substituted Cyclobutadienyl Ligand

“…This popularity stems largely from the availability of ligand precursors and the ease with which substituents can be introduced, which allows the steric, electronic, and solubility properties of their f-element complexes to be modified for a particular purpose. Other η-bonded ligands are less common in f-element chemistry, although several complexes of cycloheptatrienyl, 21 arene, 22,23 pentadienyl, 24,25 and allyl 26 ligands are known, and the cyclononatetraenyl ligand was recently introduced into lanthanide chemistry. 27,28 Our interest in f-element sandwich compounds was recently extended to incorporate ligands based on the smaller, fourmembered ring η 4 -cyclobutadienyl (Cb).…”