Enantiomerically Pure Tetravalent Neptunium Amidinates: Synthesis and Characterization

Abstract

The synthesis of a tetravalent neptunium amidinate [NpCl(( S )‐PEBA) 3 ] ( 1 ) (( S )‐PEBA=( S , S )‐ N , N′ ‐bis‐(1‐phenylethyl)‐benzamidinate) is reported. This complex represents the first structurally characterized enantiopure transuranic compound. Reactivity studies with halide/pseudohalides yielding [NpX(( S )‐PEBA) 3 ] (X=F ( 2 ), Br ( 3 ), N 3 ( 4 )) have shown that the chirality‐at‐metal is preserved for all compounds in the solid state. Furthermore, they represent an unprecedented example of a structurally characterized metal–organic Np complex featuring a Np−Br ( 3 ) bond. In addition, 4 is the only reported tetravalent transuranic azide. All compounds were additionally characterized in solution using para ‐magnetic NMR spectroscopy showing an expected C 3 ‐symmetry at low temperatures.

Synthesis of Non‐Aqueous Neptunium(III) Halide Solvates from NpO2

“…The Np−Br bond lengths range from 2.8630(10) Å to 2.8990(10) Å, whereas those for Np−O THF range from 2.501(5) to 2.562(5) Å. For comparison, the Np(IV) compound [NpBr((S)‐PEBA) 3 ] ((S)‐PEBA=(S,S)‐N,N’‐bis(1‐phenylethyl)‐benzamidinate) has an Np−Br distance of 2.792(1) Å, which is slightly shorter than 2 due to the smaller ionic radius of the tetravalent ion as compared to the trivalent [22] . NpBr 3 (THF) 4 exhibits axial bromides that are slightly more bent from the expected 180° for a pentagonal bipyramid (165.22(3)°), as compared to NpI 3 (THF) 4 (170.908(16)°), likely due to the larger size of the iodide as compared to bromide [19]…”

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

“…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. − …”