The synthesis and versatile reducing power of low-valent uranium complexes

Boreen, Michael A.; Arnold, John

doi:10.1039/d0dt03151h

Cited by 45 publications

(31 citation statements)

References 240 publications

(294 reference statements)

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“…Furthermore, three-electron reductions mediated by uranium complexes have been described only rarely. 22,44 To the best of our knowledge, complex 7 is the only reported example of a mononuclear uranium mono(cycloheptatrienyl) species. CHT complexes of uranium are quite rare: only two examples, the U(V) sandwich complex [K(18-crown-6)][U(C 7 H 7 ) 2 ] 45 and the U(IV)−U(IV) inverse sandwich complex [U(BH 4 ) 2 -(THF) 5 ][(U(BH 4 ) 3 ) 2 (μ-η 7 :η 7 -C 7 H 7 )], 46 have been structurally characterized, and few other examples have been reported.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…With the exception of the U(II) tris(amide) [K[2.2.2]cryptand][U(N(SiMe 3 ) 2 ) 3 ], all previously reported examples of U(II) are supported by either cyclopentadienides or tethered arenes capable of engaging in δ-bonding interactions with uranium frontier orbitals. , In contrast to the Zr and Ta examples mentioned above, in which the arene ligands deviate significantly from planarity and display prominent distortions in bond angles and lengths upon binding, δ-bonding interactions from U(II) can lead to more subtle arene distortions. This phenomenon is observed in both U(NH(2,6-(2,4,6- i Pr 3 C 6 H 2 ) 2 C 6 H 3 )) 2 and [K[2.2.2]cryptand][(( Ad,Me ArO) 3 Mes)U], each of which are described as U(II) with neutral arene ligands. , However, none of these previous examples of molecular U(II) contain a formally reduced arene ligand coordinated to the U(II) center; such a ligand system might act as a reservoir of electron density and facilitate new modes of reactivity for U(II) complexes.…”

Section: Introductionmentioning

confidence: 99%

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A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

et al. 2021

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Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 (2) with KC 8 yields the anionic bis(areneEPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a twoelectron reductant toward I 2 to form the dinuclear U(III)−U(III) triiodide species 6) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] ( 7). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] (1-crypt) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)−U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) (8). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 (4) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th-(TDA) 3 (THF)] (5). The C−C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Uranium(II) Arene Complex That Acts as a Uranium(I) Synthon

et al. 2021

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“…One of the recent developments in actinide chemistry was the discovery that the 2+ oxidation state is accessible to uranium. − The initial discovery was made by reduction of the 5f 3 uranium(III) tris(silylcyclopentadienyl) complex Cp′ 3 U (Cp′ = C 5 H 4 SiMe 3 ; eq ). Surprisingly, the [K(crypt)][Cp′ 3 U] (crypt = 2.2.2-cryptand) product was found to have a 5f 3 6d 1 ground state instead of the traditional 5f 4 configuration .…”

Section: Introductionmentioning

confidence: 99%

Density Functional Theory Analysis of the Importance of Coordination Geometry for 5f³6d¹ versus 5f⁴ Electron Configurations in U(II) Complexes

2021

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Density functional theory (DFT) calculations on four known and seven hypothetical U(II) complexes indicate the importance of coordination geometry in favoring 5f 3 6d 1 versus 5f 4 electronic ground states. The known [Cp″ 3 U] − , [Cp tet 3 U] − , and [U(NR 2 ) 3 ] − [Cp″ = C 5 H 3 (SiMe 3 ) 2 , Cp tet = C 5 Me 4 H, and R = SiMe 3 ] anions were found to have 5f 3 6d 1 ground states, while a 5f 4 ground state was found for the known compound (NHAr i Pr 6 ) 2 U. The UV−visible spectra of the known 5f 3 6d 1 compounds were simulated via time-dependent DFT and are in qualitative agreement with the experimental spectra. For the hypothetical U(II) compounds, the 5f 3 6d 1 configuration is predicted for [U(CHR 2 ) 3 ] − , [U(H 3 BH) 3 ] − , [U(OAr′) 4 ] 2− , and [(C 8 H 8 )U] 2− (OAr′ = O-C 6 H 2 t Bu 2 -2,6-Me-4). In the case of [U(bnz′) 4 ] 2− (bnz′ = CH 2 -C 6 H 4t Bu-4), a 5f 3 configuration with a ligand-based radical was found as the ground state.

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“…This example also nicely highlights the high reactivity of U(III), which is the workhorse oxidation state for uranium smallmolecule activation. 11,12,55,56 While the reduction of [U-(NR 2 ) 3 (CNXyl) 2 ] did not result in the intended carbyne product, our results demonstrate that actinide-bound isocyanides can be reduced, suggesting that with the right choice of reducing agent, ancillary ligands, and isocyanide substituent, carbyne formation may be possible. However, the C−C coupling reaction would need to be disfavored, which could possibly be achieved by ensuring that only one isocyanide ligand is coordinated to the uranium center.…”

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confidence: 99%