Ambient Stable Trigonal Bipyramidal Copper(III) Complexes Equipped with an Exchangeable Axial Ligand

Chang, Hao-Chen; Lo, Feng Chun; Liu, Wen Chi; Lin, Tsung H.; Liaw, Wen‐Feng; Kuo, Ting Shen; Lee, Way Zen

doi:10.1021/acs.inorgchem.5b00603

Cited by 15 publications

(14 citation statements)

References 64 publications

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“…Compound 2a displayed a 1s → 3d pre-edge transition centered at 8978.1 eV (Figure ), while 2b had an equivalent peak at 8979.4 eV, approximately 1.3 eV higher in energy (Figure S10). − These pre-edge transition energies fall within the expected range for Cu II and Cu III complexes, respectively. DuBois et al showed a shift of 1.0–2.0 eV for Cu II to Cu III pairs and demonstrated that this was the only reliable predictor of oxidation state for Cu XANES .…”

Section: Resultssupporting

confidence: 53%

“…The pre-edge features have the same normalized intensity for both 2a and 2b , suggesting that there has not been a change in geometry or coordination number. Altering the geometry and so the degree of 3d and 4p mixing would change the intensity of this feature. , The 1.3 eV blue shift suggested an integer change in the oxidation state of the metal (thus Cu II to Cu III ). − …”

Section: Resultsmentioning

confidence: 99%

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High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

et al. 2019

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Oxygenases have been postulated to utilize d 4 Fe IV and d 8 Cu III oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal−oxygen adducts, [Ni III (OAc)(L)] (1b) and [Cu III (OAc)(L)] (2b), L = N,N′-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [Ni II (OAc)-(L)] − (1a) and [Cu II (OAc)(L)] − (2a).The complexes 1a/ b−2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, Xray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH 3 , C(CH 3 ) 3 , CH 3 , H, Br, CN, NO 2 ) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d 8 Cu III oxidant displayed a small increase in the rate constant compared to that of the d 7 Ni III oxidant. The d 8 Cu III oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDE C−H ) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.

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Section: Resultssupporting

confidence: 53%

Section: Resultsmentioning

confidence: 99%

High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

et al. 2019

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“…L CuF is, to the best of our knowledge, the first structurally characterized, discrete copper(III) fluoride complex and features the shortest Cu–F distance (1.755(3) Å) reported in the Cambridge Structural Database. Furthermore, L CuCl and L CuBr feature shorter Cu–Cl (2.1085(8) Å) and Cu–Br (2.2562(4) Å) bonds than previously reported five-coordinate copper(III) halide complexes (Cl: 2.2011(18)–2.468(1) Å; Br: 2.3842(5)–2.600(1) Å). ,− …”

Section: Resultsmentioning

confidence: 66%

C(sp³)–H Fluorination with a Copper(II)/(III) Redox Couple

et al. 2020

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Despite the growing interest in the synthesis of fluorinated organic compounds, few methods are able to incorporate fluoride ion directly into alkyl C-H bonds. Here, we report the C(sp 3)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogs, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized. While all three copper(III) halide complexes capture carbon radicals efficiently to afford C(sp 3)-halogen bonds, LCuF is two orders of magnitude more efficient at hydrogen atom abstraction (HAA) than LCuCl and LCuBr. Alongside reported kinetic data for other LCu(III) species, we established a positive correlation between ligand basicity and the rate of HAA. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.

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“…However, given the fidelity between experiment and theory showcased earlier in the prediction of Cu 3d contributions to the LUMOs/SOMOs of formally Cu III complexes, we have extended our calculations to explore the generality of ligand field inversion in a diverse sampling of other formally Cu III complexes (Figure ). ,,,− The calculated LUMOs for each species are shown in Figure along with the corresponding Löwdin orbital compositions. Again, regardless of supporting ligand and geometry, our calculations show that all but one species considered ([CuF 6 ] 3– ) possess LUMOs with <50% Cu 3d-character.…”

Section: Resultsmentioning

confidence: 99%

The Myth of d⁸ Copper(III)

et al. 2019

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Seventeen Cu complexes with formal oxidation states ranging from Cu I to Cu III are investigated through the use of multiedge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Analysis reveals that the metal−ligand bonding in high-valent, formally Cu III species is extremely covalent, resulting in Cu K-edge and L 2,3-edge spectra whose features have energies that complicate physical oxidation state assignment. Covalency analysis of the Cu L 2,3edge data reveals that all formally Cu III species have significantly diminished Cu d-character in their lowest unoccupied molecular orbitals (LUMOs). DFT calculations provide further validation of the orbital composition analysis, and excellent agreement is found between the calculated and experimental results. The finding that Cu has limited capacity to be oxidized necessitates localization of electron hole character on the supporting ligands; consequently, the physical d 8 description for these formally Cu III species is inaccurate. This study provides an alternative explanation for the competence of formally Cu III species in transformations that are traditionally described as metal-centered, 2-electron Cu I /Cu III redox processes.

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Ambient Stable Trigonal Bipyramidal Copper(III) Complexes Equipped with an Exchangeable Axial Ligand

Cited by 15 publications

References 64 publications

High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

C(sp³)–H Fluorination with a Copper(II)/(III) Redox Couple

The Myth of d⁸ Copper(III)

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Ambient Stable Trigonal Bipyramidal Copper(III) Complexes Equipped with an Exchangeable Axial Ligand

Cited by 15 publications

References 64 publications

High-Valent d7 NiIII versus d8 CuIII Oxidants in PCET

High-Valent d7 NiIII versus d8 CuIII Oxidants in PCET

C(sp3)–H Fluorination with a Copper(II)/(III) Redox Couple

The Myth of d8 Copper(III)

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Product

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About

High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

High-Valent d⁷ Ni^III versus d⁸ Cu^III Oxidants in PCET

C(sp³)–H Fluorination with a Copper(II)/(III) Redox Couple

The Myth of d⁸ Copper(III)