Nordic Consortium for CO2 Conversion

Nordic Consortium for CO2 Conversion

Research Article: AU

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Title:
Ex-Situ Generation of Bis(trifluoromethyl)disulfide and Applications to Trifluoromethylthiolation Reactions

Abstract:
Herein, a convenient and operationally simple protocol for the ex-situ generation of bis(trifluoromethyl)disulfide from the readily available and commercial Langlois reagent is reported. The one-step synthesis of the toxic and volatile CF3SSCF3 is performed in a two-chamber reactor with simple PPh3 and N-bromosuccinimide as the activator, allowing for the safe handling and tandem utilization in direct trifluoromethylthiolation reactions. The versatility of the ex-situ generated CF3SSCF3 is demonstrated in known electrophilic, nucleophilic, and a radical trifluoromethylthiolation reactions. Furthermore, the application of the CF3SSCF3 in a copper-catalyzed cross-coupling with boronic acids is disclosed, showing good to excellent yields of trifluoromethyl-substituted aryl products, including pharmaceutically relevant molecules.

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Research Article: AU

graphical abstract

Title:
Low Pressure Carbonylation of Benzyl Carbonates and Carbamates for Applications in 13C Isotope Labeling and Catalytic CO2 Reduction

Abstract:
Herein, we report a methodology to access isotopically labeled esters and amides from carbonates and carbamates employing an oxygen deletion strategy. This methodology utilizes a decarboxylative carbonylation approach for isotope labeling with near stoichiometric, ex situ generated 12C, or 13C carbon monoxide. This reaction is characterized by its broad scope, functional group tolerance, and high yields, which is showcased with the synthesis of structurally complex molecules. A complementary method that operates by the catalytic in situ generation of CO via the reduction of CO2 liberated during decarboxylation has also been developed as a proof-of-concept approach that CO2-derived compounds can be converted to CO-containing frameworks. Mechanistic studies provide insight into the catalytic steps which highlight the impact of ligand choice to overcome challenges associated with low-pressure carbonylation methodologies, along with rational for the development of future methodologies.

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Research Article: UiT

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Title:
Comparative study of CO2 insertion into pincer supported palladium alkyl and aryl complexes

Abstract:
The insertion of CO2 into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO2 utilization. Here, we synthesize pincer-supported palladium complexes of the type (tBuPBP)Pd(alkyl) (tBuPBP = B(NCH2PtBu2)2C6H4; alkyl = CH2CH3, CH2CH2CH3, CH2C6H5, and CH2-4-OMe-C6H4) and (tBuPBP)Pd(C6H5) and compare the rates of CO2 insertion into the palladium alkyl bonds to form metal carboxylate complexes. Although, the rate constant for CO2 insertion into (tBuPBP)Pd(CH2CH3) is more than double the rate constant we previously measured for insertion into the palladium methyl complex (tBuPBP)Pd(CH3), insertion into (tBuPBP)Pd(CH2CH2CH3) occurs approximately one order of magnitude slower than (tBuPBP)Pd(CH3). CO2 insertion into the benzyl complexes (tBuPBP)Pd(CH2C6H5) and (tBuPBP)Pd(CH2-4-OMe-C6H4) is significantly slower than any of the n-alkyl complexes, and CO2 does not insert into the palladium phenyl bond of (tBuPBP)Pd(C6H5). While (tBuPBP)Pd(CH2CH3) and (tBuPBP)Pd(CH2CH2CH3) are resistant to β-hydride elimination, we were unable to synthesize complexes with n-butyl, iso-propyl, and tert-butyl ligands due to β-hydride elimination and an unusual reductive coupling, which involves the formation of new C–B bonds. This reductive process also occurred for (tBuPBP)Pd(CH2C6H5) at elevated temperature and a related process involving the formation of a new H–B bond prevented the isolation of (tBuPBP)PdH. DFT calculations provide insight into the relative rates of CO2 insertion and indicate that steric factors are critical. Overall, this work is one of the first comparative studies of the rates of CO2 insertion into different metal alkyl bonds and provides fundamental information that may be important for the development of new catalysts for CO2 utilization.

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Research Article: AU

graphical abstract

Title:
Nickel-Catalyzed Carbonylative Coupling of Alkylzinc Reagents and α-Bromo-α,α-difluoroacetamides

Abstract:
We report a nickel-catalyzed carbonylative cross-coupling of alkyl zinc reagents with α,α-difluorobromoacetamides to obtain α,α,-difluoro-β-ketoamides in moderate to good yields. The reaction is catalyzed by a bench-stable nickel(II) pincer complex, in contrast to other reports involving palladium catalysts. The carbonylative reaction is performed in a two-chamber system (COware) in which carbon monoxide (CO) is generated ex situ from the solid precursor SilaCOgen, and then consumed in the adjacent chamber. The reaction operates at low temperatures using near-stoichiometric amounts of CO. Isotopically labeled products can be effortlessly accessed, as demonstrated by using 13C-labeled SilaCOgen.

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Research Article: HU

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Title:
Dual Nickel Photocatalysis for O-Aryl Carbamate Synthesis from Carbon Dioxide

Abstract:
We report the use of dual nickel photocatalysis in the synthesis of O-aryl carbamates from aryl iodides or bromides, amines, and carbon dioxide. The reaction proceeded in visible light, at ambient carbon dioxide pressure, and without stoichiometric activating reagents. Mechanistic analysis is consistent with a Ni(I–III) cycle, where the active species is generated by the photocatalyst. The rate-limiting steps were the photocatalyst-mediated reduction of Ni(II) to Ni(I) and subsequent oxidative addition of the aryl halide. The physical properties of the photocatalyst were critical for promoting formation of O-aryl carbamates over various byproducts. Nine new phthalonitrile photocatalysts were synthesized, which exhibited properties that were vital to achieve high selectivity and activity.

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