Axial Donor Effects on Oxidatively Induced Ethane Formation from Nickel–Dimethyl Complexes

Smith, Sofia M.; Rath, Nigam P.; Mirica, Liviu M.

doi:10.1021/acs.organomet.9b00438

Cited by 18 publications

(27 citation statements)

References 42 publications

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“…This superhyperfine pattern clearly indicates the coordination of two 4-MeO-py ligands to the Ni III center. [45][46][47][48][49] Furthermore, the signal produced by the second species strongly resembles EPR data collected for trans-Ni III (salen)(py)2 complexes. 44 The distinction between trans-(py)2 and cis-(py)2 coordination is important in the present case as both are theoretically possible.…”

Section: [Ni III (Dtc)2(l)x] + Formationmentioning

confidence: 56%

Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

Mazumder¹,

Burton²,

Richburg³

et al. 2021

Preprint

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This manuscript describes electrochemical experiments in which a Nickel(III) intermediate is kinetically trapped by the addition of derivatized pyridine ligands to the electrolyte solution. EPR and DFT studies support the conclusion that pyridine coordinates in a trans- configuration and contains a small equilibrium between mono- and bis-pyridine structures. Electrochemical kinetic data provides evidences for decomposition pathways which ultimately result in Ni(IV) complexes.

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Section: [Ni III (Dtc)2(l)x] + Formationmentioning

confidence: 56%

Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

Mazumder¹,

Burton²,

Richburg³

et al. 2021

Preprint

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“…This signal was simulated using superhyperfine coupling to two N atoms with coupling constants A123 = 13.0, 13.0, 18.0 G giving rise to quintet splitting with a 1:2:3:2:1 intensity ratio. This superhyperfine pattern clearly indicates the coordination of two 4-MeO-py ligands to the Ni III center [45][46][47][48][49]. Furthermore, the signal produced by the second species strongly resembles EPR data collected for trans-Ni III (salen)(py)2 complexes 44.…”

mentioning

confidence: 77%

Controlling One-Electron Vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

et al. 2021

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The unique redox cycle of Ni II (dtc)2, where dtcis N,N-diethyldithiocarbamate, in acetonitrile displays 2eredox chemistry upon oxidation from Ni II (dtc)2 → [Ni IV (dtc)3] + but 1eredox chemistry upon reduction from [Ni IV (dtc)3] + → Ni III (dtc)3 → Ni II (dtc)2. The underlying reasons for this cycle lie in the structural changes that occur between four-coordinate Ni II (dtc)2 and sixcoordinate [Ni IV (dtc)3] + . Cyclic voltammetry (CV) experiments show that these 1eand 2e -pathways can be controlled by the addition of pyridine-based ligands (L) to the electrolyte solution. Specifically, the addition of these ligands resulted in a 1eligand-coupled electron transfer (LCET) redox wave which produced a mixture of pyridine-bound Ni(III) complexes, [Ni III (dtc)2(L)] + and [Ni III (dtc)2(L)2] + . Although the complexes could not be isolated, electron paramagnetic resonance (EPR) measurements using a chemical oxidant in the presence of 4-methoxypyridine confirmed the formation of trans-[Ni III (dtc)2(L)2] + . Density functional theory calculations were also used to support the formation of pyridine coordinated Ni(III) complexes through structural optimization and calculation of EPR parameters. The reversibility of the LCET process was found to be dependent on both the basicity of the pyridine ligand and the scan rate of the CV experiment. For strongly basic pyridines (e.g. 4-methoxypyridine) and/or fast scan rates, high reversibility was achieved, allowing [Ni III (dtc)2(L)x] + to be reduced directly back to Ni II (dtc)2 + xL. For weakly basic pyridines (e.g. 3-bromopyridine) and/or slow scan rates, [Ni III (dtc)2(L)x] + decayed irreversibly to form [Ni IV (dtc)3] + . Detailed kinetics studies using CV reveal that [Ni III (dtc)2(L)] + and [Ni III (dtc)2(L)2] + decay by parallel pathways due to a small equilibrium between the two species. The rate constants for ligand dissociation ([Ni III (dtc)2(L)2] + → [Ni III (dtc)2(L)] + + L) along with decomposition of [Ni III (dtc)2(L)] + and [Ni III (dtc)2(L)2] + species were found to increase with 2 the electron-withdrawing character of the pyridine ligand, indicating pyridine dissociation is likely the rate limiting step for decomposition of these complexes. These studies establish a general trend for kinetically trapping 1eintermediates along a 2eoxidation path.

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“…12 For example, the involvement of paramagnetic Ni I and Ni III species has been commonly implicated, yet such intermediates have not been thoroughly investigated, and the key catalytic steps of oxidative addition, transmetalation, and reductive elimination have rarely been observed directly. 10,13,14 Our group has employed tetradentate azamacrocycle N,N'-dialkyl-2,11diaza [3.3](2,6)pyridinophanes ( R N4) ligands to isolate and characterize Ni III species capable of C-C [15][16][17][18] and C-heteroatom 15,19,20 bond formation reactions, and to probe the involvement of highvalent Ni species in these reactions. However, considering that the most ubiquitous ligands in Ni cross-coupling and photocatalytic reactions are the bidentate bipyridine ligands, [8][9][10][11]21 the R N4 ligands were thought to be less effective ligands owing to the crowded environment around the Ni center, which is also expected to disfavor the formation of Ni I species.…”

Section: Introductionmentioning

confidence: 99%

Deciphering the mechanism of the Ni-photocatalyzed C‒O cross-coupling reaction using a tridentate pyridinophane ligand

Mirica

2021

Preprint

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Photoredox nickel catalysis has emerged as a powerful strategy for cross-coupling reactions. Although the involvement of paramagnetic Ni(I)/Ni(III) species as active intermediates in the catalytic cycle has been proposed, a thorough spectroscopic investigation of these species is lacking. Herein, we report a new class of tridentate pyridinophane ligands R N3 that allow for detailed mechanistic studies of the photocatalytic C-O coupling reaction. The derived ( R N3)Ni complexes are active catalysts under mild conditions and without an additional photocatalyst. We also provide direct evidence for the key steps involving paramagnetic Ni species in the proposed catalytic cycle: the oxidative addition of an aryl halide to a Ni(I) species, the ligand exchange/transmetalation at a Ni(III) center, and the C-O reductive elimination from a Ni(III)

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Axial Donor Effects on Oxidatively Induced Ethane Formation from Nickel–Dimethyl Complexes

Cited by 18 publications

References 42 publications

Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

Controlling One-Electron vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

Controlling One-Electron Vs Two-Electron Pathways in the Multi-Electron Redox Cycle of Nickel Diethyldithiocarbamate

Deciphering the mechanism of the Ni-photocatalyzed C‒O cross-coupling reaction using a tridentate pyridinophane ligand

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