Bromoporphyrins as Versatile Synthons for Modular Construction of Chiral Porphyrins:  Cobalt-Catalyzed Highly Enantioselective and Diastereoselective Cyclopropanation

Chen, Ying; Fields, Kimberly B.; Zhang, X. Peter

doi:10.1021/ja044889l

Cited by 207 publications

(112 citation statements)

References 17 publications

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“…A particularly interesting set of reactions proceeds through metal-carbenoid intermediates that had never been exploited for catalysis by heme proteins. The synthetic porphyrin systems relied on synthetic activated reagents such as ethyldiazoacetate (EDA) to generate the metal carbenoid, which could then react with olefins or insert the carbene into various N-H, C-H, or O-H bonds (Baumann et al 2007;Chen et al 2004;Wolf et al 1995). That the metal-carbenoid intermediate resembles compound I in the native P450 catalytic cycle (Fig.…”

Section: New Enzymes From Old: Adding To the Cytochrome P450's (Alreamentioning

confidence: 99%

The nature of chemical innovation: new enzymes by evolution

Arnold

2015

Quart. Rev. Biophys.

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Abstract. I describe how we direct the evolution of non-natural enzyme activities, using chemical intuition and information on structure and mechanism to guide us to the most promising reaction/enzyme systems. With synthetic reagents to generate new reactive intermediates and just a few amino acid substitutions to tune the active site, a cytochrome P450 can catalyze a variety of carbene and nitrene transfer reactions. The cyclopropanation, N-H insertion, C-H amination, sulfimidation, and aziridination reactions now demonstrated are all well known in chemical catalysis but have no counterparts in nature. The new enzymes are fully genetically encoded, assemble and function inside of cells, and can be optimized for different substrates, activities, and selectivities. We are learning how to use nature's innovation mechanisms to marry some of the synthetic chemists' favorite transformations with the exquisite selectivity and tunability of enzymes.

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Section: New Enzymes From Old: Adding To the Cytochrome P450's (Alreamentioning

confidence: 99%

The nature of chemical innovation: new enzymes by evolution

Arnold

2015

Quart. Rev. Biophys.

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“…Hence, substrate redox non-innocence is not just a chemical curiosity, and the cyclopropanation reactions mediated by cobalt porphyrins provided prime examples of catalytic reactions proceeding via carbene radicals behaving as (Fig. 4) [36][37][38] led to unprecedented reactivity and selectivity, which was explained by the increased nucleophilic character of the carbene radical compared to an unreduced Fischer-type carbene, allowing the pursuit of more challenging substrates such as electrondeficient olefins. The cooperation between the carbene radical and the metal is of crucial importance for catalysis and is actually similar to the way metallo-enzymes gain control over radicals in several enzymatic processes.…”

Section: Carbon-centered Radicals In Catalysismentioning

confidence: 99%

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

et al. 2015

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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.

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“…On the other hand, a trans selectivity was observed by running cyclopropanations in the presence of porphyrin complexes reported in Scheme 8, but unfortunately enantioselectivities were not satisfying. Since then, Zhang et al developed the synthetic procedure [75,76] shown in Scheme 9, by using bromoporphyrins as synthons, to reach a wide pool of chiral porphyrins with D 2 symmetry ( Figure 6). …”

Section: Cobalt-catalysed Reactionsmentioning

confidence: 99%

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes

2011

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Keywords: Cyclopropanation / Diazo compounds / Porphyrins / Cobalt / Rhodium / IridiumThe one-pot reaction of diazo compounds with olefins represents a useful strategy to synthesise cyclopropanes, which are important both as starting materials for the synthesis of organic compounds and because of their intrinsic pharmaceutical properties. Herein we describe the catalytic activity of group 9 metal porphyrin complexes to cyclopropanate ole-

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Bromoporphyrins as Versatile Synthons for Modular Construction of Chiral Porphyrins: Cobalt-Catalyzed Highly Enantioselective and Diastereoselective Cyclopropanation

Cited by 207 publications

References 17 publications

The nature of chemical innovation: new enzymes by evolution

The nature of chemical innovation: new enzymes by evolution

EPR Spectroscopy as a Tool in Homogeneous Catalysis Research

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes

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