Structural and Spectroscopic Characterization of a Charge-Separated Uranium Benzophenone Ketyl Radical Complex

Lam, Oanh P.; Anthon, Christian; Heinemann, Frank W.; O’Connor, J. M.; Meyer, Karsten

doi:10.1021/ja801007q

Cited by 111 publications

(147 citation statements)

References 61 publications

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“…Several reports of the isolation of stable, metal-bound ketyl complexes have appeared in the literature 55–59. Of particular relevance here is the work of Wolczanski and coworkers who found that 1e − reduction of di- tert -butyl ketone by the Ti III tris (siloxide) complex Ti(OSi t Bu 3 ) 3 led to a ketyl-Ti IV species capable of thermal dissociation of the neutral ketone to regenerate Ti(OSi t Bu 3 ) 3 60.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)niobium(III) Imido Complexes

2010

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We have investigated both the chemical reduction of (BDI)Nb(V) imido complexes (BDI = HC[C(Me)NAr]2; Ar = 2,6-iPr2-C6H3) to the formal Nb(III) oxidation state and the ability of these Nb(III) complexes to behave as two-electron reductants. The reduction of the Nb(V) species was found to depend heavily on the nature of available supporting ligands, but the chemistry of the reduced compounds proceeded cleanly with a number of unsaturated organic reagents. Accordingly, the novel Nb(V) bis(imido) complexes supported by the monoazabutadiene (mad) ligand (mad)Nb(NtBu)(NAr)(L′) (L′ = py, thf) were formed by either KC8 reduction of (BDI)Nb(NtBu)Cl2(py) in the absence of strong π-acids or by H2 reduction of the Nb(V) dimethyl complex (BDI)Nb(NtBu)Me2 in THF. These products are likely formed though an intramolecular, 2 e− reductive C–N bond cleavage, as has been observed previously for related Group 4 systems, suggesting that transient Nb(III) intermediates were present in both cases. In the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), KC8 reduction of (BDI)Nb(NtBu)Cl2(py) was arrested at the Nb(IV) oxidation state to give (BDI)Nb(NtBu)Cl(dmpe), which was characterized by solution-state EPR spectroscopy as a Nb-centered paramagnet with strong coupling to the two equivalent phosphorus nuclei (Aiso{93Nb} = 120.5×10−4 cm−1, Aiso{31P} = 31.0×10−4 cm−1, giso = 1.9815). When strong π-acids were used to intercept the thermally unstable Nb(III) complex (BDI)Nb(NtBu)(py) prior to reductive cleavage of the ligand C–N bond, the thermally stable Nb(III) species (BDI)Nb(NtBu)(CX)2(L″) (X = O, L″ = py; X = NXyl, L″ = CNXyl; Xyl = 2,6-Me2-C6H3) were obtained in good yields. The Nb(III) complexes (BDI)Nb(NtBu)py, (BDI)Nb(NtBu)(CO)2(py) and (BDI)Nb(NtBu)(CO)2 were subsequently investigated for their ability to serve as two-electron reducing reagents for both metal-ligand multiple bond formation and for the reduction of organic π-systems. The reduction of mesityl azide by (BDI)Nb(NtBu)(py) and diphenylsulfoxide by (BDI)Nb(NtBu)(CO)2 led to the monomeric bis(imido) and dimeric oxo complexes (BDI)Nb(NtBu)(NMes)(py) and [(BDI)Nb(NtBu)]2(μ2-O)2, respectively. MeLi addition to (BDI)Nb(NtBu)(CO)2(py) resulted in the formation of a Nb-acylate via methide addition to one of the carbonyl carbons. The acylate product was revealed to have a short Nb–Cacylate bond distance (2.059(4) Å), consistent with multiple Nb–C bond character resulting from Nb(III) back-bonding into the acylate carbon. The interaction of (BDI)Nb(NtBu)(CO)2 with two equivalents of 4,4′-dichlorobenzophenone resulted in the clean, quantitative formation of the corresponding pinacol coupling product, but introduction of the ketone in 1: 1 molar ratios resulted in mixtures of the pinacol product and the starting material, suggesting that ketone coordination to the Nb(III) complex may be reversible. Relatedly, addition of 1-phenyl-1-propyne to (BDI)Nb(NtBu)(CO)2 formed a thermally unstable 1: 1 Nb/alkyne complex, as characterized by NMR and IR spectroscopies; reaction of this s...

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Section: Resultsmentioning

confidence: 99%

Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)niobium(III) Imido Complexes

2010

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“…from the solvent. These decomposition pathways were observed when the tert‐butyl groups on the ketone were omitted . Additionally, the Bart group isolated the first uranium(III) ketyl radical complex, Tp* 2 U III (OC ⋅ Ph 2 ) (Tp*=hydrotris(3,5‐dimethylpyrazolyl)borate).…”

Section: Introductionmentioning

confidence: 94%

“…In uranium chemistry, the reductive homocoupling of carbonyl functional groups to form pinacols and heterocoupling of carbonyl functional groups are similarly proposed to proceed through radical ketyl intermediates. Recently, two charge‐separated uranium ketyl compounds were isolated and studied . The Meyer group isolated the first uranium ketyl radical complex, [(( t Bu ArO) 3 tacn)U IV (OC ⋅ 4, 4′‐ t Bu Ph 2 )], tacn=1,4,7‐triazacyclononane, which was accomplished using a sterically hindered ketone and supporting ligand to prevent homocoupling or abstraction of H .…”

Section: Introductionmentioning

confidence: 99%

Reduction of Carbonyl Groups by Uranium(III) and Formation of a Stable Amide Radical Anion

Mullane

Cheisson

Nakamaru‐Ogiso

et al. 2017

Chemistry A European J

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Methyl benzoate, N,N-dimethylbenzamide, and benzophenone were reduced by U [N(SiMe ) ] resulting in uranium(IV) products. Reduction of benzophenone lead to U [OC⋅Ph )][N(SiMe ) ] , (1.1) which forms the dinuclear complex, [N(SiMe ) ] U (OCPhPh-CPh O)U [N(SiMe ) ] (1.2), through coupling of the ketyl radical species upon crystallization. Reaction of N,N-dimethylbenzamide with U [N(SiMe ) ] resulted in U [OC⋅(Ph)(NMe )][N(SiMe ) ] (2), a uranium(IV) compound and the first example of a charge-separated amide radical. In the case of methyl benzoate, the reduction resulted in U (OMe)[N(SiMe ) ] (3) and benzaldehyde as the reduced organic fragment. Compound 2 showed the ability to act as a uranium(III) synthon in its reactivity with trimethylsilyl azide, a reaction that yielded U (=NSiMe )[N(SiMe ) ] . Additionally, 2 was reduced with potassium graphite resulting in [U(μ-O)[O=C(NMe )(Ph)][N(SiMe ) ] ] (4), a dinuclear uranium compound bridged by oxo ligands. Reduction of 2 in the presence of 15-crown-5 afforded isolation of the mono-oxo compound, [(15-crown-5) K][UO[N(SiMe ) ] ] (5). The results expand the reduction capabilities of U complexes and demonstrate a strategy for isolating novel metal-stabilized radicals.

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“…The same research group later reported the one-electron reduction of diphenyldiazomethane by trivalent (( t-Bu ArO) 3 tacn)U III (( t-Bu ArO) 3 tacn = 1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane) to produce the uranium radical complex, (( t-Bu ArO) 3 formation of the C H activated product, however, it was too reactive to be isolated. A related trivalent system, (( t-Bu ArO) 3 tacn)U, was found to also singly reduce di-tert-butylbenzophenone affording (( t-Bu ArO) 3 tacn)U IV ( • OC(t-BuPh) 2 ) [368]. The low-temperature range of the eff vs T plot shows a similar trend compared to U CO 2 • and (( Ad ArO) 3 tacn)U IV (Ph 2 CN 2 • ) complexes where an elevated magnetic moment of 1.61 B at 5 K was due to the unpaired spin on the benzophenone ligand.…”

Section: Radical-containing Uranium Complexesmentioning

confidence: 99%

Radical ligand-containing single-molecule magnets

Demir

Jeon

Long

et al. 2015

Coordination Chemistry Reviews

515

386

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Structural and Spectroscopic Characterization of a Charge-Separated Uranium Benzophenone Ketyl Radical Complex

Cited by 111 publications

References 61 publications

Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)niobium(III) Imido Complexes

Synthesis, Characterization, and Reactions of Isolable (β-Diketiminato)niobium(III) Imido Complexes

Reduction of Carbonyl Groups by Uranium(III) and Formation of a Stable Amide Radical Anion

Radical ligand-containing single-molecule magnets

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