Experimental and computational studies of the mechanism of iron-catalysed C–H activation/functionalisation with allyl electrophiles

DeMuth, Joshua; Song, Zhihui; Carpenter, Stephanie H.; Boddie, Theresa E; Radović, Aleksa; Baker, Tessa M.; Gutiérrez, Osvaldo; Neidig, Michael L.

doi:10.1039/d1sc01661j

Cited by 14 publications

(12 citation statements)

References 38 publications

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“…Hence, complex 9 , despite being an iron(II) alkoxide similar to 6 , was found to be inert toward allene 2 , with no reaction observed according to an 1 H NMR spectroscopic analysis of an equimolar solution of 2 and 9 in C 6 D 6 . A similar effect has also recently been reported, where the use of strongly chelating diphosphine ligands leads to reduced reaction rates in iron-catalyzed C–H allylations . This striking difference between iron(II) alkoxides 6 and 9 is attributed to the increased coordination strength of dmpe in the latter complex.…”

Section: Results and Discussionsupporting

confidence: 78%

“…Most mechanistic proposals on the mode of operation of iron-catalyzed C–H activation reactions are thus far supported by a limited amount of experimental data. Currently, only a few in-depth studies have been reported, namely on the arylation, alkylation, and allylation of aromatic amides with triazole ,, and quinoline directing groups and on the hydroarylation of allenes enabled by weak O -coordination (Scheme ). In the former studies, the mechanistic manifold proposed was supported by the isolation of iron(II) cyclometallated species combined with Mößbauer spectroscopic studies and stoichiometric experiments (Scheme a). − Subsequently, a low-valent Fe(0)/Fe(II) manifold was proposed by Ackermann and co-workers for the [Fe(PMe 3 ) 4 ]-catalyzed hydroarylation of allenes (Scheme b) .…”

Section: Introductionmentioning

confidence: 99%

“…Currently, only a few in-depth studies have been reported, namely on the arylation, alkylation, and allylation of aromatic amides with triazole ,, and quinoline directing groups and on the hydroarylation of allenes enabled by weak O -coordination (Scheme ). In the former studies, the mechanistic manifold proposed was supported by the isolation of iron(II) cyclometallated species combined with Mößbauer spectroscopic studies and stoichiometric experiments (Scheme a). − Subsequently, a low-valent Fe(0)/Fe(II) manifold was proposed by Ackermann and co-workers for the [Fe(PMe 3 ) 4 ]-catalyzed hydroarylation of allenes (Scheme b) . The proposed mechanism was based on the isolation of a cyclometallated iron hydride complex, which was postulated to be a catalytically active on-cycle species.…”

Section: Introductionmentioning

confidence: 99%

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Cyclometallated Iron(II) Alkoxides in Iron-Catalyzed C–H Activations by Weak O-Carbonyl Chelation

et al. 2022

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Iron catalysts represent an economically attractive tool for C–H activations because of their low costs and low toxicities. Despite an exponential increase of interest in this area, detailed mechanistic understanding remains at a nascent stage. Herein, a detailed investigation of the C–H activation mechanism with [Fe(PMe3)4] unraveled an unexpected iron(II) alkoxide intermediate that was fully characterized and was found to be a more active catalyst in phenone-assisted C–H activations with respect to the previously reported mer-iron hydride cyclometallated counterpart. Mechanistic studies by stoichiometric experimentation, reaction profiling through electron paramagnetic resonance (EPR) and in operando NMR spectroscopy, deuterium labeling, crystallographic analyses, and density functional theory (DFT) calculations provided strong evidence for an oxidative addition of the pivalophenone to a low-valent iron intermediate toward the formation of a transient fac-hydride complex, which very quickly rearranges to an iron alkoxide complex. According to detailed DFT studies, it is proposed that the isolated iron(II) alkoxide is a highly reactive precatalyst, which can easily access the on-cycle fac-hydride complex, thereby translating into highly efficient catalysis. These mechanistic insights form the basis for further developments in iron-catalyzed C–H activation with prospects for stereoselective transformations.

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Section: Results and Discussionsupporting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cyclometallated Iron(II) Alkoxides in Iron-Catalyzed C–H Activations by Weak O-Carbonyl Chelation

et al. 2022

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“…In consequence, computational data are often crucial in this field, and integrated closely with other experimental techniques. 77,78 When exploring double bond isomerization catalysis by an iron(II) β-diketiminate complex (Scheme 7 79 ), we found that we needed to bring a full spectrum of synthetic, computational and spectroscopic insights to bear to develop and assess a mechanistic proposal, as these catalysts can access different spin states along the reaction coordinate. With minimum energy crossing points (MECPs) difficult to determine, experimental data were at times easier to obtain than S C H E M E 5 Proposed mechanistic pathway for Suzuki-Miyaura cross-coupling by a dichloro-bis(aminophosphine) complex.…”

Section: Experimental Approaches Particularly Useful To Computational...mentioning

confidence: 99%

“…In this field, techniques such as Mössbauer, EPR, and related inorganic spectroscopic approaches can also contribute useful experimental insights, although we note that such equipment is less common in research laboratories than NMR, IR, and ESI‐MS while the interpretation of measurements is more involved, often requiring computational input. In consequence, computational data are often crucial in this field, and integrated closely with other experimental techniques 77,78 …”

Section: Experimental Approaches Particularly Useful To Computational...mentioning

confidence: 99%

Computational mechanistic study in organometallic catalysis: Why prediction is still a challenge

Fey

Lynam

2021

WIREs Comput Mol Sci

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Although computational contributions to the understanding of organometallic homogeneous catalysts have become fairly routine, a step-change in the application of computational methods would be to achieve efficient, robust, and reliable prediction of the outcome of catalytic transformations. While we concur that there have been a number of recent promising advances in the interactions between computational and experimental mechanistic studies, the mapping of reactivity space remains incomplete and large-scale studies have to make limiting assumptions which restrict their transferability. Close synergies between characterization and analysis techniques which are integrated with computational data, along with data capture, curation, and exploitation, are vital and develop our understanding of all aspects of the catalytic pathways (including activation and deactivation) and allow the continual refinement of mechanistic understanding, challenged by testing predictions experimentally.Here we review recent examples to formulate a protocol for such interactions.

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Iron‐Catalyzed CH Activation/Functionalization to Form CC Bonds

Neidig¹,

Bhatia²,

DeMuth³

2022

Handbook of CH-Functionalization

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Iron‐catalyzed CH activation has attracted great interest over the past couple of decades as a promising technique to establish CC bond‐forming functionalities for complex molecule design. The motivation behind this trend can be attributed to the low cost, minimal toxicity, and rich oxidation chemistry afforded by iron. The synthetic utility of iron catalysis for CH activation/functionalization was widely recognized following the development of an iron‐catalyzed CH activation system that facilitated the cross‐coupling of a CH bond with an organometallic reagent under oxidative conditions. Following this seminal approach, iron‐catalyzed CH activation has been widely explored to establish CC bonds across a variety of functionalities. This article underscores the evolution of CC bond‐forming iron‐catalyzed CH activation by providing several examples across a broad range of CH functionalizations including alkylation, alkenylation, alkynylation, allylation, arylation, and annulation that involve CH‐activated organoiron species through the reaction of a substrate CH bond with an iron catalyst. An additional section of this article is dedicated to highlighting the key mechanistic insights into iron‐catalyzed CH functionalization, a field that is largely underdeveloped yet invaluable toward the rational development of the next generation of systems in iron‐catalyzed CH activation/functionalization.

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Experimental and computational studies of the mechanism of iron-catalysed C–H activation/functionalisation with allyl electrophiles

Abstract: Experimental and computational studies support an inner-sphere radical pathway for iron-catalysed C–H activation/functionalisation with allyl electrophiles.

Cited by 14 publications

References 38 publications

Cyclometallated Iron(II) Alkoxides in Iron-Catalyzed C–H Activations by Weak O-Carbonyl Chelation

Cyclometallated Iron(II) Alkoxides in Iron-Catalyzed C–H Activations by Weak O-Carbonyl Chelation

Computational mechanistic study in organometallic catalysis: Why prediction is still a challenge

Iron‐Catalyzed CH Activation/Functionalization to Form CC Bonds

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