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
Abstract A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α‐ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H‐atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck‐like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product‐determining step in the catalytic mechanism.
more »
« less
- PAR ID:
- 10391943
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Chemistry – A European Journal
- Volume:
- 28
- Issue:
- 72
- ISSN:
- 0947-6539
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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
-
Abstract Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover a new electron‐primed photoredox catalyst capable of promoting the reductive cleavage of strong C(sp2)−N and C(sp2)−O bonds. We illustrate several examples of the synthetic utility of these deeply reducing but otherwise safe and mild catalytic conditions. Finally, we employ electrochemical current measurements to perform a reaction progress kinetic analysis. This technique reveals that the improved activity of this new system is a consequence of an enhanced catalyst stability profile.more » « less
-
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 In recent years, there has been a concerted drive to develop methods that are greener and more sustainable. Being an earth‐abundant transition metal, cobalt offers an attractive substitute for commonly employed precious metal catalysts, though reactions engaging cobalt are still less developed. Herein, we report a method to achieve the decarboxylative allylation of nitrophenyl alkanes, nitroalkanes, and ketones employing cobalt. The reaction allows for the formation of various substituted allylated products in moderate‐excellent yields with a broad scope. Additionally, the synthetic potential of the methodology is demonstrated by the transformation of products into versatile heterocyclic motifs. Mechanistic studies revealed an in situ activation of the Co(II)/dppBz precatalyst by the carboxylate salt to generate a Co(I)‐species, which is presumed to be the active catalyst.more » « less
