Single-crystal cryogenic X-ray diffraction at 6 K, electron paramagnetic resonance spectroscopy, and correlated electronic structure calculations are combined to shed light on the nature of the metal−tris(aryloxide) and η 2 −H, C metal−alkane interactions in the [(( t•Bu ArO) 3 tacn)U III ( Me cy-C6)]•( Me cy-C6) adduct. An analysis of the ligand field experienced by the uranium center using ab initio ligand field theory in combination with the angular overlap model yields rather unusual U−O ArO and U−N tacn bonding parameters for the metal−tris(aryloxide) interaction. These parameters are incompatible with the concept of σ and π metal−ligand overlap. For that reason, it is deduced that metal− ligand bonding in the [(( t•Bu ArO) 3 tacn)U III ] moiety is predominantly ionic. The bonding interaction within the [(( t•Bu ArO) 3 tacn)-U III ] moiety is shown to be dispersive in nature and essentially supported by the upper-rim t Bu groups of the ( t•Bu ArO) 3 tacn 3− ligand.Our findings indicate that the axial alkane molecule is held in place by the guest−host effect rather than direct metal−alkane ionic or covalent interactions.

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We present the synthesis and reactivity of a newly developed, cyclen-based tris-aryloxide ligand, namely cyclen(Me)(t-Bu,t-BuArOH)3, and its coordination chemistry to uranium. The corresponding uranium(III) complex [UIII((OArt-Bu,t-Bu)3(Me)cyclen)] (1) was characterized by...

The activation of chalcogen–chalcogen bonds using organometallic uranium complexes has been well documented for S–S, Se–Se, and Te–Te bonds. In stark contrast, reports concerning the ability of a uranium complex to activate the O–O bond of an organic peroxide are exceedingly rare. Herein, we describe the peroxide O–O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that the oxidative addition occurs in two sequential, single-electron oxidations of the metal center, including rebound of a terminal oxygen radical. This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light, in solution, releases 9,10-diphenylanthracene to generate a cyclic uranyl trimer through formal two-electron photooxidation. Analysis of the mechanism of this photochemical oxidation via density functional theory (DFT) calculations indicates that the formation of this uranyl trimer occurs through a fleeting uranium cis-dioxo intermediate. At room temperature, this cis-configured dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands from the complex, which then goes on to form the isolated uranyl trimer complex.

We report a series of uranium complexes stabilized by the pentakis-benzyl-derivatized cyclopentadienyl ligand, Cp Bn5 . Treatment of [UCl 4 ] and [UI 3 (1,4-dioxane) 1,5 ] with 2 equiv of the potassium salt, Cp Bn5 K, yielded the corresponding complexes [(Cp Bn5 ) 2 U IV (Cl) 2 ] (1) and [(Cp Bn5 ) 2 U III (I)] (4). Subsequently, tetravalent 1 is either methylated to give [(Cp Bn5 ) 2 U IV (Me) 2 ] (2) or reduced to form trivalent [(Cp Bn5 ) 2 U III (μ-Cl) 2 K(OEt 2 ) 3 ] (3). Oxidation of 4 with AgI yields [(Cp Bn5 ) 2 U IV (I) 2 ] (5), which was found to generate rarely observed, linear uranium metallocenes [(Cp Bn5 ) 2 U IV (NCMe) 5 ][X] 2 (X = PF 6 − (6), BPh 4 − (7)) upon abstraction of the iodide ligands with thallium salts in acetonitrile. All complexes were characterized by 1 H NMR spectroscopy, CHN elemental analysis, UV−vis−NIR spectroscopy, and SQUID magnetization measurements. The solid-state molecular structures of 1−7 were determined by single-crystal X-ray diffraction analysis. An in-depth computational analysis revealed the peculiar electronic structure of the linearly coordinated title complex 7 and its closely related, parent [(Cp*) 2 U IV (NCMe 3 ) 5 ] 2+ dication.