A Physical‐Inorganic Approach for the Elucidation of Active Iron Species and Mechanism in Iron‐Catalyzed Cross‐Coupling

Carpenter, Stephanie H.; Neidig, Michael L.

doi:10.1002/ijch.201700036

Cited by 24 publications

(10 citation statements)

References 81 publications

(72 reference statements)

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“…This has occurred through operando analysis using physicalinorganic methods including Magnetic Circular Dichroism, EPR and Mössbauer spectroscopies. 71 In particular, operando analysis allowed the active oxidation state of the metal to be determined in several cross-coupling systems. 72 However, at this stage, there is still significant more work required in order to analyse the elementary steps of the coupling mechanism.…”

Section: Contextmentioning

confidence: 99%

Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

et al. 2020

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Section: Contextmentioning

confidence: 99%

Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

et al. 2020

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“…Inspired by bioinorganic studies of systems involving iron, an experimental approach involving the application of these physical-inorganic spectroscopies with an emphasis on the direct correlation of changes in organic product distributions with iron speciation has been utilized and proven to be a powerful technique for studying iron-catalyzed cross-coupling reactions (Figure 1). 30 Central to this approach is the use of 57 Fe Mössbauer spectroscopy as a primary screening tool for determination of the number of iron species present in situ and their relative amounts. 57 Fe Mössbauer spectroscopy is ideally suited for tackling these critical questions because the total number of iron species is readily observable.…”

Section: Mechanistic Studies: Challenges and Approachmentioning

confidence: 99%

Intermediates and Mechanism in Iron-Catalyzed Cross-Coupling

2018

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Iron-catalyzed cross-coupling reactions have attracted significant research interest, as they offer numerous favorable features compared with cross-coupling reactions with precious metal catalysis. While this research has contributed to an empirical understanding of iron-catalyzed cross-coupling, the underlying fundamental mechanisms of reaction and structures of catalytically active species have remained poorly defined. The lack of such detail can be attributed to the difficulties associated with studying such iron-catalyzed reactions, where unstable paramagnetic intermediates abound. Recently, the combined application of physical-inorganic spectroscopic methods, concomitant organic product analysis, and air- and temperature-sensitive inorganic synthesis has yielded the most detailed insight currently available on reactivity and mechanism in iron-catalyzed cross-coupling. This Perspective highlights this approach and the limitations of the contributing techniques as well as some of the key features of the catalytic reactions studied and lessons learned.

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“…The scope of possible bond formations has been extensively studied with various transition metal species, which span almost all 3d-, 4d-, and 5d-block transition metals . However, relatively few studies have been performed to understand the role of the transition metal center at an electronic structural level, while its elucidation would help more systematic development of cross-coupling catalysts for a desired reaction. , The in-situ monitoring of the reaction by employing transition metal-based spectroscopic techniques can provide key insights into this matter, because the metal center is the active site and its electronic structural variation should affect the efficiency of the reaction.…”

Section: Introductionmentioning

confidence: 99%

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

et al. 2020

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High-valent Ni complexes have proven to be good platforms for diverse cross-coupling reactions that are otherwise difficult to be achieved with conventional low-valent catalysts. However, their reductive elimination (RE) activities are still significantly variable by up to 5 orders of magnitude, depending on the supporting ligand and oxidation state of the Ni center. To elucidate frontier molecular orbitals (FMOs) that determine the RE activity of the Ni center, the electronic structures of cycloneophyl (CH2C(CH3)2-o-C6H4) NiIII and NiIV complexes have been characterized by utilizing various transition metal-based spectroscopic techniques such as electronic absorption, magnetic circular dichroism, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopies. In combination with density functional theory computations, the spectroscopic analyses have shown that the energies of the C-to-Ni charge-transfer (CT) electronic transitions are strongly correlated to the rates of C–C bond-forming RE reaction. This correlation suggests that the kinetic barrier of the RE reaction is determined by energy cost for internal CT (ICT) from the coordinated carbon moiety to the Ni center, and that FMOs involved in the RE reaction and the C-to-Ni CT electronic transitions are essentially identical. This FMO determination has led us to discover that photoexcitation to the C-to-Ni CT excited states accelerates the C–C cross-coupling reaction by up to 105 times, as the CT electronic transition can substitute for the rate-determining ICT step of the RE reaction at the ground electronic state.

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A Physical‐Inorganic Approach for the Elucidation of Active Iron Species and Mechanism in Iron‐Catalyzed Cross‐Coupling

Cited by 24 publications

References 81 publications

Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

Intermediates and Mechanism in Iron-Catalyzed Cross-Coupling

Correlation between the C–C Cross-Coupling Activity and C-to-Ni Charge Transfer Transition of High-Valent Ni Complexes

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