Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis

Abstract

Two series of isostructural tetravalent actinide amidinates [AnX((S)-PEBA) 3 ] (An = Th, U, Np; X = Cl, N 3 ) bearing the chiral (S,S)-N,N′-bis(1-phenylethyl)benzamidinate ((S)-PEBA) ligand have been synthesized and thoroughly characterized in solid and in solution. This study expands the already reported tetravalent neptunium complexes to the lighter actinides thorium and uranium. Furthermore, a rare Ce(IV) amidinate [CeCl((S)-PEBA) 3 ] was synthesized to compare its properties to those of the analogous tetravalent actinide complexes. All compounds were characterized in the solid state using singlecrystal XRD and infrared spectroscopy and in solution using NMR spectroscopy. Quantum chemical bonding analysis including also the isostructural Pa and Pu complexes was used to characterize the covalent contributions to any bond involving the metal cation. Th shows the least covalent character throughout the series, even substantially smaller than for the Ce complex. For U, Np, and Pu, similar covalent bonding contributions are found, but a natural population analysis reveals different origins. The 6d participation is the highest for U and decreases afterward, whereas the 5f participation increases continuously from Pa to Pu.

How 5 f Electron Polarisability Drives Covalency and Selectivity in Actinide N‐Donor Complexes

“…However, in the salen system An bonding was dominated by the strong, hard O ‐donor, which ultimately limits the flexibility of the An−N bond to react to changes in electronic situation, for example, caused by backbonding. Studies of pure N donors remain scarce, especially for the transuranium elements [8–11] . To the best of our knowledge, only two Pu IV complexes exclusively stabilised by N ‐donor ligands are known in the literature: One containing the inorganic NCS − ligands [12] and one with a TREN (tris(2‐aminoethyl)amine)‐type ligand [13] …”

Amidinate Supporting Ligands Influence Molecularity in Formation of Uranium Nitrides

“…Comparison of the U–N amidinate distances in 3 and 4 (2.366(6)–2.502(2) Å), as well as the U–N azide distances (2.340(6) Å in 3 and 2.335(3) Å in 4 ; see Table S3 for full analysis), shows no significant difference in U–N bond lengths for these two ligand systems. The U–N amidinate and U–N azide bond lengths in 1 – 4 are comparable to the analogous U–N distances in the uranium amidinate complexes UCl­(S-PEBA) 3 and U­(N 3 )­(S-PEBA) 3 …”

“…The U−N amidinate and U−N azide bond lengths in 1−4 are comparable to the analogous U−N distances in the uranium amidinate complexes UCl(S-PEBA) 3 and U(N 3 )(S-PEBA) 3 . 42 Reduction of the U(IV) chloride complexes 1 and 2 with metallic sodium in THF gave the dark blue homoleptic U(III) tris(amidinate) complexes U(BCMA) 3 (5) 53 and U(BIMA) 3 (6), respectively, in excellent (95−100%) yields (Scheme 2).…”

“…Our aim in this present work was to develop new nitride precursors with easily tunable supporting ligands to determine whether we could influence the pathways toand composition ofany resulting nitride complexes. We chose amidinate ligands for this purpose because of their well-established steric and electronic tunability and because of their precedent as supporting ligands in actinide chemistry for a variety of chemical transformations. − As recently demonstrated by März and co-workers, careful tuning of uranium coordination using amidate ligands provides new opportunities to isolate and characterize reactive nitride moieties. In addition, amidinate ligands bind to metals only through nitrogen atoms, the latter property being potentially useful in longer term efforts aimed at using these complexes as single-source precursors to uranium nitride materials. − …”

Structure of the {U13} polyoxo cluster U13O8Cl x (MeO)38–x (x = 2.3, MeO = methoxide)

“…Route A: [UCl(S)-PEBA) 3 ] (S)-PEBA: (S,S)-N,N 0 -bis(1phenylethyl)benzamidinate) was prepared according to a reported procedure (Kloditz et al, 2020). A solution containing 10 mg of [UCl(S)-PEBA) 3 ] in 1 mL of methanol was transferred into a quartz cuvette and sealed doubly with a lid and Parafilm in a dry and inert glove box filled with nitrogen gas.…”