Mechanisms for Hydrogen-Atom Abstraction by Mononuclear Copper(III) Cores: Hydrogen-Atom Transfer or Concerted Proton-Coupled Electron Transfer?

Mandal, Mukunda; Elwell, Courtney E.; Bouchey, Caitlin J.; Zerk, Timothy J.; Tolman, William B.; Cramer, Christopher J.

doi:10.1021/jacs.9b08109

Cited by 66 publications

(100 citation statements)

References 56 publications

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“…LCuX results in a lower HAA rate, clearly emphasizing the importance of the proton transfer over electron transfer for the overall rate of HAA by formally LCu III species. In this context, it is informative to compare the HAA rate constants of LCuX with LCuOH 28 and LCu(O2CR) 39 complexes. Despite the different solvents used for HAA kinetic study, a positive correlation of log(k) from HAA by LCu III species with the pKa of the ligand is observed (Fig.…”

Section: Haa and Rc Reactivity Of [Cu III -X]mentioning

confidence: 99%

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

Bower¹,

Cypcar²,

Henriquez³

et al. 2020

Preprint

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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.Carbon-fluorine bonds are becoming increasingly prevalent in pharmaceuticals and agrochemicals. 1 The value of fluorinated compounds in these applications stems from their enhancement of lipophilicity, metabolic stability, and receptor binding affinity. 2

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Section: Haa and Rc Reactivity Of [Cu III -X]mentioning

confidence: 99%

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

Bower¹,

Cypcar²,

Henriquez³

et al. 2020

Preprint

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“…Further studies with different 494 substrates are necessary to decipher how nitrosarene 495 complexes perform this reaction, i.e., in a concerted or 496 sequential manner. 85,86 497 ■ CONCLUSIONS 498 In summary, placing a synthetic handle at the para position of 499 nitrosoarenes enables control over the degree of electron 500 transfer from Cu(I) complexes, from 0e with electron-donating 501 substituents to 1e with electron-neutral substituents and 2e 502 with electron-poor substituents. As the Cu/ArNO adducts are 503 undergoing self-assembly, the geometric preferences of the Cu 504 center will prevail.…”

mentioning

confidence: 99%

Tuning Inner-Sphere Electron Transfer in a Series of Copper/Nitrosoarene Adducts

et al. 2020

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A series of copper/nitrosoarene complexes were created that mimic several steps in biomimetic O 2 activation by copper(I). The reaction of the copper(I) complex of N,N,N′,N′tetramethypropylenediamine with a series of para-substituted nitrosobenzene derivatives leads to adducts in which the nitrosoarene (ArNO) is reduced by zero, one, or two electrons, akin to the isovalent species dioxygen, superoxide, and peroxide, respectively. The geometric and electronic structures of these adducts were characterized by means of X-ray diffraction, vibrational analysis, ultraviolet−visible spectroscopy, NMR, electrochemistry, and density functional theory (DFT) calculations. The bonding mode of the NO moiety depends on the oxidation state of the ArNO moiety: κN for ArNO, mononuclear η 2-NO and dinuclear μ-η 2 :η 1 for ArNO •− , and dinuclear μ-η 2 :η 2 for ArNO 2−. 15 N isotopic labeling confirms the reduction state by measuring the NO stretching frequency (1392 cm −1 for κN-ArNO, 1226 cm −1 for η 2-ArNO •− , 1133 cm −1 for dinuclear μ-η 2 :η 1-ArNO •− , and 875 cm −1 for dinuclear μ-η 2 :η 2 for ArNO 2−). The 15 N NMR signal disappears for the ArNO •− species, establishing a unique diagnostic for the radical state. Electrochemical studies indicate reduction waves that are consistent with one-electron reduction of the adducts and are compared with studies performed on Cu-O 2 analogues. DFT calculations were undertaken to confirm our experimental findings, notably to establish the nature of the charge-transfer transitions responsible for the intense green color of the complexes. In fine, this family of complexes is unique in that it walks through three redox states of the ArNO moiety while keeping the metal and its supporting ligand the same. This work provides snapshots of the reactivity of the toxic nitrosoarene molecules with the biologically relevant Cu(I) ion. 47 usually too oxidative to be stable above −60°C.

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“…For deeper understanding of CO 2 activation by 1 a , we have carried out the intrinsic bond orbital (IBO) analysis scheme developed by Knizia et al [52] . This procedure is extensively applied to understand the bond breaking/bond making process along the reaction coordinate [53–54] . Here, the evolution of IBO along the intrinsic reaction coordinates of the transition states as shown in Figure 3.…”

Section: Resultsmentioning

confidence: 99%

An NHC‐Stabilised Phosphinidene for Catalytic Formylation: A DFT‐Guided Approach

Sreejyothi

Bhattacharyya

Kumar

et al. 2021

Chemistry A European J

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In recent years, the applications of low‐valent main group compounds have gained momentum in the field of catalysis. Owing to the accessibility of two lone pairs of electrons, NHC‐stabilised phosphinidenes have been found to be excellent Lewis bases; however, they cannot yet be used as catalysts. Herein, an NHC‐stabilised phosphinidene, 1,3‐dimethyl‐2‐(phenylphosphanylidene)‐2,3‐dihydro‐1H imidazole (1), for the activation of CO2 is reported.A closer inspection of the CO2 activation process by DFT calculations along with intrinsic bond orbital analysis shows that phosphinidene is associated with phenylsilane through a noncovalent π‐π interaction between two phenyl rings which activates the Si−H bond facilitating hydride transfer to the CO2 molecule. Detailed DFT studies along with spectroscopic experiments were combined to understand the mechanism of CO2 activation and its catalytic reductive functionalisation leading to the formylation of a range of chemically inert primary amides under mild reaction conditions.

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Mechanisms for Hydrogen-Atom Abstraction by Mononuclear Copper(III) Cores: Hydrogen-Atom Transfer or Concerted Proton-Coupled Electron Transfer?

Cited by 66 publications

References 56 publications

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

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

Tuning Inner-Sphere Electron Transfer in a Series of Copper/Nitrosoarene Adducts

An NHC‐Stabilised Phosphinidene for Catalytic Formylation: A DFT‐Guided Approach

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