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The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5‐1,2,4‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U‐(η2‐C=C) moiety increases significantly compared to the related ThIV compound [η5‐1,2,4‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low‐valent uranium(II) metallocene [η5‐1,2,4‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero‐unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five‐membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones. [ABSTRACT FROM AUTHOR]

Organic azides that contain naphthyl functional groups were used to prepare uranium(V) imido complexes UV[=NC(2-naph)Ph2][N(SiMe3)2]3 ( 2), UV[=NC(2-naph)3][N(SiMe3)2]3 ( 3), and UV[=N(2-naph)][N(SiMe3)2]3 ( 4), and their properties were compared with UV[=NCPh3][N(SiMe3)2]3 ( 1). The electronic structures of these compounds were investigated by solution electrochemistry studies, which revealed accessible UV/VI, UIV/V, and naphthalene0/naphthalene−1 couples. The uranium(V) naphthylimido complexes were reduced by potassium graphite to yield their uranium(IV) congeners K[UIV[=NC(2-naph)Ph2][N(SiMe3)2]3] ( 2-K), K[UIV[=NC(2-naph)3][N(SiMe3)2]3] ( 3-K), and K[UIV[=N(2-naph)][N(SiMe3)2]3] ( 4-K). The electronic structure of the dianionic compounds were investigated by DFT calculations, and this revealed that the second reduction was ligand-based, which opens the possibility of accomplishing multi-electron redox chemistry by using a tailored multiply-bonded ligand. [ABSTRACT FROM AUTHOR]

After more than 50 years, the synthesis and electronic structure of the first and only reported 'U0 complex' [U(bipy)4] ( 1) has been reinvestigated. Additionally, its one-electron reduced product [Na(THF)6][U(bipy)4] ( 2) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid-to-high-valent uranium ligated by redox non-innocent ligands. [ABSTRACT FROM AUTHOR]

Two new arene inverted-sandwich complexes of uranium supported by siloxide ancillary ligands [K{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 3) and [K2{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 4) were synthesized by the reduction of the parent arene-bridged complex [{U(OSi(O tBu)3)3}2(μ-η6:η6-C7H8)] ( 2) with stoichiometric amounts of KC8 yielding a rare family of inverted-sandwich complexes in three states of charge. The structural data and computational studies of the electronic structure are in agreement with the presence of high-valent uranium centers bridged by a reduced tetra-anionic toluene with the best formulation being UV-(arene4−)-UV, KUIV-(arene4−)-UV, and K2UIV-(arene4−)-UIV for complexes 2, 3, and 4 respectively. The potassium cations in complexes 3 and 4 are coordinated to the siloxide ligands both in the solid state and in solution. The addition of KOTf (OTf=triflate) to the neutral compound 2 promotes its disproportionation to yield complexes 3 and 4 (depending on the stoichiometry) and the UIV mononuclear complex [U(OSi(O tBu)3)3(OTf)(thf)2] ( 5). This unprecedented reactivity demonstrates the key role of potassium for the stability of these complexes. [ABSTRACT FROM AUTHOR]