An official website of the United States government
Recently, dual catalytic strategies towards the decarboxylative elimination of carboxylic acids have gained attention. Our lab previously reported a photoredox/cobaloxime dual catalytic method that allows the synthesis of enamides and enecarbamates directly from N ‐acyl amino acids that avoids the use of any stoichiometric reagents. Further development, detailed herein, has improved upon this transformation’s utility and further experimentation has provided new insights into the reaction mechanism. These new developments and insights are anticipated to aid in the expansion of photoredox/cobalt dual catalytic systems.
more »
« less
Direct Aroylation of Olefins through a Cobalt/Photoredox‐catalyzed Decarboxylative and Dehydrogenative Coupling with α−Oxo Acids
A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects decarboxylation of α−ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the co-balt catalyst abstracts an H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, suggesting a change in product-determining step in the catalytic mechanism.
more »
« less
- PAR ID:
- 10380641
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Reductive catalysis with earth-abundant metals is currently of increasing importance and shows potential in replacing precious metal catalysis. In this work, we revealed catalytic hydroboration and hydrosilylation of ketones and aldehydes achieved by a structurally defined manganese( ii ) coordination polymer (CP) as a precatalyst under mild conditions. The manganese-catalysed methodology can be applied to a range of functionalized aldehydes and ketones with turnover numbers (TON) of up to 990. Preliminary results on the regioselective catalytic hydrofunctionalization of styrenes by the Mn-CP catalyst are also presented.more » « less
-
Abstract Cobalt phthalocyanine (CoPc) is a promising molecular catalyst for aqueous electroreduction of CO2, but its catalytic activity is limited by aggregation at high loadings. Codeposition of CoPc onto electrode surfaces with the coordinating polymer poly(4‐vinylpyridine) (P4VP) mitigates aggregation in addition to providing other catalytic enhancements. Transmission and diffuse reflectance UV–vis measurements demonstrate that a combination of axial coordination and π‐stacking effects from pyridyl moieties in P4VP serve to disperse cobalt phthalocyanine in deposition solutions and help prevent reaggregation in deposited films. Polymers lacking axial coordination, such as Nafion, are significantly less effective at cobalt phthalocyanine dispersion in both the deposition solution and in the deposited films. SEM images corroborate these findings through particle counts and morphological analysis. Electrochemical measurements show that CoPc codeposited with P4VPonto carbon electrode surfaces reduces CO2with higher activity and selectivity compared to the catalyst codeposited with Nafion.more » « less
-
The Photoredox Paradox: Electron and Hole Upconversion as the Hidden Secrets of Photoredox CatalysisAlthough photoredox catalysis is complex from a mechanistic point of view, it is also often surprisingly efficient. In fact, the quantum efficiency of a puzzlingly large portion of photoredox reactions exceeds 100% (i.e., the measured quantum yields (QYs) are >1). Hence, these photoredox reactions can be more than perfect with respect to photon utilization. In several documented cases, a single absorbed photon can lead to the formation of >100 molecules of the product, behavior known to originate from chain processes. In this Perspective, we explore the underlying reasons for this efficiency, identify the nature of common catalytic chains, and highlight the differences between HAT and SET chains. Our goal is to show why chains are especially important in photoredox catalysis and where the thermodynamic driving force that sustains the SET catalytic cycles comes from. We demonstrate how the interplay of polar and radical processes can activate hidden catalytic pathways mediated by electron and hole transfer (i.e., electron and hole catalysis). Furthermore, we illustrate how the phenomenon of redox upconversion serves as a thermodynamic precondition for electron and hole catalysis. After discussing representative mechanistic puzzles, we analyze the most common bond forming steps, where redox upconversion frequently occurs (and is sometimes unavoidable). In particular, we highlight the importance of 2-center-3-electron bonds as a recurring motif that allows a rational chemical approach to the design of redox upconversion processes.more » « less
-
Exciting progress has been made in the area of solar fuel generation by CO 2 reduction. New photocatalytic materials containing well-defined surface catalytic sites have emerged in recent years, including heterogenized molecular catalysts and single atom catalysts. This Feature Article summarizes our recent research in this area, together with brief discussions of relevant literature. In our effort to obtain heterogenized molecular catalysts, a diimine-tricarbonyl Re( i ) complex and a tetraaza macrocyclic Co( iii ) compound were covalently attached to different surfaces, and the effects of ligand derivatization and surface characteristics on their structures and photocatalytic activities were investigated. Single atom catalysts combine the advantages of homogeneous and heterogeneous catalysis. A single-site cobalt catalyst was prepared on graphitic carbon nitride, which demonstrated excellent activity in selective CO 2 reduction under visible-light irradiation. Doping carbon nitride with carbon was found to have profound effects on the structure and activity of the single-site cobalt catalyst. Our research achievements are presented to emphasize how spectroscopic techniques, including infrared, UV-visible, electron paramagnetic resonance, and X-ray absorption spectroscopies, could be combined with catalyst synthesis and computation modeling to understand the structures and properties of well-defined surface catalytic sites at the molecular level. This article also highlights challenges and opportunities in the broad context of solar CO 2 reduction.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/chem.202202781
