Electronic Structures of Reduced Manganese, Iron, and Cobalt Complexes Bearing Redox‐Active Bis(imino)pyridine Pincer Ligands

Chirik, Paul J.

doi:10.1002/9783527681303.ch7

Cited by 13 publications

(7 citation statements)

References 77 publications

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“…Tridentate, mer pincer-type ligands are now ubiquitous in catalysis, and the [OCO] pincer appears to be well positioned to take a place alongside "privileged" ligands for base-metal catalysis, such as bis(imino)pyridine [NNN] pincers. 60 The factors that make this system particularly attractive as a platform for new reaction chemistry include the capacity to stabilize Co over three or more formal oxidation states at relatively modest potentials, along with an impressive flexibility in coordination number and geometry. All of these are predicated on the capacity of the [OCO] ligand to persist in oxidation states that span multiple electrons.…”

Section: ■ Conclusionmentioning

confidence: 99%

“…For instance, the redox-active bis(imino)pyridine [NNN] pincer ligands 58,59 were termed "privileged" because of their utility in Fe and Co catalysis. 60 Accordingly, elaborating a library of ligands that stabilize low-coordinate, later 3d metals across two or more formal oxidation states is a first step toward designed base-metal complexes for sustainable catalysis.…”

Section: ■ Introductionmentioning

confidence: 99%

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Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States

et al. 2017

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A new family of low-coordinate Co complexes supported by three redox-noninnocent tridentate [OCO] pincer-type bis(phenolate) N-heterocyclic carbene (NHC) ligands are described. Combined experimental and computational data suggest that the charge-neutral four-coordinate complexes are best formulated as Co(II) centers bound to closed-shell [OCO] dianions, of the general formula [(OCO)CoL] (where L is a solvent-derived MeCN or THF). Cyclic voltammograms of the [(OCO)CoL] complexes reveal three oxidations accessible at potentials below 1.2 V vs Fc/Fc, corresponding to generation of formally Co(V) species, but the true physical/spectroscopic oxidation states are much lower. Chemical oxidations afford the mono- and dications of the imidazoline NHC-derived complex, which were examined by computational and magnetic and spectroscopic methods, including single-crystal X-ray diffraction. The metal and ligand oxidation states of the monocationic complex are ambiguous; data are consistent with formulation as either [(OCO)Co(THF)] containing a closed-shell [OCO] diphenolate ligand bound to a S = 1 Co(III) center, or [(OCO)Co(THF)] with a low-spin Co(II) ion ferromagnetically coupled to monoanionic [OCO] containing a single unpaired electron distributed across the [OCO] framework. The dication is best described as [(OCO)Co(THF)], with a single unpaired electron localized on the d Co(II) center and a doubly oxidized, charge-neutral, closed-shell OCO ligand. The combined data provide for the first time unequivocal and structural evidence for [OCO] ligand redox activity. Notably, varying the degree of unsaturation in the NHC backbone shifts the ligand-based oxidation potentials by up to 400 mV. The possible chemical origins of this unexpected shift, along with the potential utility of the [OCO] pincer ligands for base-metal-mediated organometallic coupling catalysis, are discussed.

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Section: ■ Conclusionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States

et al. 2017

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“…Due to the important catalytic properties of iron-pincer complexes, electronic structure studies of these systems have been widely explored, − particularly where ligand redox noninnocence can occur such as in iron complexes containing bis(imino)pyridine ligands (also known as pyridyl diimine, or PDI, ligands). By contrast, detailed electronic structure studies of NHC-containing pincer complexes of iron have been less common.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Circular Dichroism and Density Functional Theory Studies of Iron(II)-Pincer Complexes: Insight into Electronic Structure and Bonding Effects of Pincer N-Heterocyclic Carbene Moieties

et al. 2016

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Iron complexes containing pincer ligands that incorporate N-heterocyclic carbene (NHC) moieties are of significant interest in organometallic catalysis in order to generate more oxidatively robust complexes that may exhibit novel catalytic properties. In order to define the effect that introducing NHC moieties into pincer ligands has on electronic structure and bonding in iron(II)-pincer complexes, MCD and DFT studies of (iPrCDA)FeBr2, (iPrPDI)FeBr2, and (iPrCNC)FeBr2 were performed. These studies quantify the electronic structures and bonding interactions as a function of pincer ligand variation. They also demonstrate that the observed ligand fields (and, hence, spin states) directly correlate to the increased Fe–C bonding and pincer-donating abilities that result from introducing NHC moieties into the pincer ligand. However, the net donor abilities of the pincers and the strength of the Fe-pincer interaction do not directly correlate to the number of NHC moieties present, but instead are determined to be due to differences in Fe–C and overall Fe-pincer bonding as a result of the position of the NHC moieties in the pincer ligand and the overall geometric constraints of the pincer architecture.

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“…Intrigued by the reactivity and electronic structure of the pyridinediimine (PDI) complexes, we prepared a series of iron–metal complexes based on bipyridine (Figure A). It was previously demonstrated that earth-abundant metal complexes with bipyridine or phenanthroline ligands are outstanding catalysts in a variety of organic transformations .…”

Section: Results and Discussionmentioning

confidence: 99%

Extensive Redox Non-Innocence in Iron Bipyridine-Diimine Complexes: a Combined Spectroscopic and Computational Study

et al. 2021

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Metal–ligand cooperation is an important aspect in earth-abundant metal catalysis. Utilizing ligands as electron reservoirs to supplement the redox chemistry of the metal has resulted in many new exciting discoveries. Here, we demonstrate that iron bipyridine-diimine (BDI) complexes exhibit an extensive electron-transfer series that spans a total of five oxidation states, ranging from the trication [Fe(BDI)] 3+ to the monoanion [Fe(BDI] −1 . Structural characterization by X-ray crystallography revealed the multifaceted redox noninnocence of the BDI ligand, while spectroscopic (e.g., 57 Fe Mössbauer and EPR spectroscopy) and computational studies were employed to elucidate the electronic structure of the isolated complexes, which are further discussed in this report.

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Electronic Structures of Reduced Manganese, Iron, and Cobalt Complexes Bearing Redox‐Active Bis(imino)pyridine Pincer Ligands

Cited by 13 publications

References 77 publications

Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States

Redox-Active Bis(phenolate) N-Heterocyclic Carbene [OCO] Pincer Ligands Support Cobalt Electron Transfer Series Spanning Four Oxidation States

Magnetic Circular Dichroism and Density Functional Theory Studies of Iron(II)-Pincer Complexes: Insight into Electronic Structure and Bonding Effects of Pincer N-Heterocyclic Carbene Moieties

Extensive Redox Non-Innocence in Iron Bipyridine-Diimine Complexes: a Combined Spectroscopic and Computational Study

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