Stereoselective radical C–H alkylation with acceptor/acceptor-substituted diazo reagents via Co(<scp>ii</scp>)-based metalloradical catalysis

Cui, Xin; Xue, Xiangxin; Jin, Li‐Mei; Wojtas, Łukasz; Zhang, X. Peter

doi:10.1039/c4sc02610a

Cited by 104 publications

(34 citation statements)

References 68 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Besides cyclopropanation, other catalytic reactions involving carbene radicals have also been reported recently [33,34]. One of them involves formation of ketene intermediates by carbonylation of metal carbene radicals, followed by trapping of the ketene with nucleophiles such as amines or imines, forming amides and b-lactams [42].…”

Section: Carbon-centered Radicals In Catalysismentioning

confidence: 99%

See 1 more Smart Citation

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

View full text Add to dashboard Cite

In the context of homogeneous catalysis, openshell systems are often quite challenging to characterize. Nuclear magnetic resonance (NMR) spectroscopy is the most frequently applied tool to characterize organometallic compounds, but NMR spectra are usually broad, difficult to interpret and often futile for the study of paramagnetic compounds. As such, electron paramagnetic resonance (EPR) has proven itself as a useful spectroscopic technique to characterize paramagnetic complexes and reactive intermediates. EPR spectroscopy is a particularly useful tool to investigate their electronic structures, which is fundamental to understand their reactivity. This paper describes some selected examples of studies where EPR spectroscopy has been useful for the characterization of open-shell organometallic complexes. The paper concentrates in particular on systems where EPR spectroscopy has proven useful to understand catalytic reaction mechanisms involving paramagnetic organometallic catalysts. The expediency of EPR spectroscopy in the study of organometallic chemistry and homogenous catalysis is contextualized in the introductory Sect. 1. Section 2 of the review focusses on examples of C-C and C-N bond formation reactions, with an emphasis on catalytic reactions where ligand/substrate non-innocence plays an important role. Both carbon and nitrogen centered radicals have been shown to play an important role in these reactions. A few selected examples of catalytic alcohol oxidation proceeding via related N-centered ligand radicals are included in this section as well. Section 3 covers examples of the use of EPR spectroscopy to study important commercial ethylene oligomerization and polymerization processes. In Sect. 4 the use of EPR spectroscopy to understand the mechanisms of Atom Transfer Radical Polymerization is discussed. While this review focusses predominantly on the application of EPR spectroscopy in mechanistic studies of C-C and C-N bond formation reactions mediated by organometallic catalysts, a few selected examples describing the application of EPR spectroscopy in other catalytic reactions such as water splitting, photo-catalysis, photo-redox-catalysis and related reactions in which metal initiated (free) radical formation plays a role are included as well. EPR spectroscopic investigation in this area of research are dominated by EPR spectroscopic studies in isotropic solution, including spin trapping experiments. These reactions are highlighted in Sect. 5. EPR spectroscopic studies have proven useful to discern the correct oxidation states of the active catalysts and also to determine the effective concentrations of the active species. EPR is definitely a spectroscopic technique that is indispensable in understanding the reactivity of paramagnetic complexes and in conjunction with other advanced techniques such as X-ray absorption spectroscopy and pulsed laser polymerization it will continue to be a very practical tool.

show abstract

Section: Carbon-centered Radicals In Catalysismentioning

confidence: 99%

“…As a result several examples of reactions in which C-C and C-H bonds are formed have been shown to involve carbene radicals [32][33][34]. The most representative examples are cyclopropanation reactions mediated by metallo-radical cobalt(II) porphyrin complexes.…”

Section: Carbon-centered Radicals In Catalysismentioning

confidence: 99%

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

View full text Add to dashboard Cite

show abstract

“…We reason that this porphyrin byproduct is formed by coordination of 2 endo to the macrocyclic cavity of 9 to produce the carbenoid fragment, which further reacts with the thread component by insertion reactions into the CÀHbonds of the cyclopropane moiety or those on the benzylic position (for proposed structures of the rotaxane byproduct, see Figure S5). [7] Those CÀHi nsertions are not observed in the cyclopropanation reactions promoted by acyclic Co II /porphyrinates [4] because the cyclopropane product diffuses away from the Co II /porphyrinate catalyst after the carbene-transfer reaction occurs.Inthe case of rotaxanes,the mechanical bond always keeps the thread component near the Co II active center, thereby facilitating this follow up intercomponent Scheme 1. Proposed mechanism for the active-metal-template synthesis of rotaxanes using the radical-carbene transfer reaction to olefins promoted by Co II /porphyrinates.…”

mentioning

confidence: 99%

Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes

et al. 2018

View full text Add to dashboard Cite

show abstract

“…20 The group of Zhang has developed a variety of different porphyrins with chiral substituents enabling them to perform these reactions with high enantioselectivity (Figure 4). 19,21 Next to cyclopropanation, cobalt porphyrins have also been used for C-H activation. 15a Here the challenge lies in the chemoselectivity, since most organic molecules contain many very similar C-H bonds.…”

Section: Figure 3 Examples Of Complexes Used For Carbene and Nitrene mentioning

confidence: 99%

Radical-type Reactions Controlled by Cobalt: From Carbene Radical Reactivity to the Catalytic Intermediacy of Reactive o-Quinodimethanes

Grotenhuis

Bruin

2018

Synlett

View full text Add to dashboard Cite

In this account, we summarize our recent efforts in the fields of ‘open-shell organometallic chemistry’ and ‘metalloradical catalysis’. We focus in particular on the use of so-called ‘carbene radicals’ for the synthesis of a variety of useful synthons for organic chemistry. We further show that unexpected reactivity arises from catalytic synthesis of unusual o-quinone methide and o-quinodimethane intermediates that undergo subsequent rearrangements to uncommon products.1 Introduction2 General (Fischer-Type) Carbene and Nitrene Reactivity and Their Relation to Carbene and Nitrene Radical Reactivity3 Carbene and Nitrene (Radical) Precursors4 Formation and Intrinsic Radical-Type Reactivity of Carbene and Nitrene Radicals5 Types of Cobalt Catalysts Used in Reactions Involving Carbene and Nitrene Radicals6 Applications of Cobalt-Catalyzed Ring-Closure Reactions via Carbene Radicals7 Intermediacy of o-Quinone Methide and o-Quidodimethanes in Carbene Ring-Closing Reactions8 Conclusion

show abstract

Stereoselective radical C–H alkylation with acceptor/acceptor-substituted diazo reagents via Co(ii)-based metalloradical catalysis

Cited by 104 publications

References 68 publications

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes

Radical-type Reactions Controlled by Cobalt: From Carbene Radical Reactivity to the Catalytic Intermediacy of Reactive o-Quinodimethanes

Contact Info

Product

Resources

About