| 1. |
- Arkhypchuk, Anna I., et al.
(författare)
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Mechanistic Insights and Synthetic Explorations of the Photoredox-Catalyzed Activation of Halophosphines
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:45, s. 18391-18398
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Tidskriftsartikel (refereegranskat)abstract
- The light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent–child reaction to form diphosphines R2P–PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEA•+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations.
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| 2. |
- Gamache, Mira T., et al.
(författare)
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Elucidating Electron Transfer Kinetics and Optimizing System Performance for Escherichia coli-Based Semi-Artificial H-2 Production
- 2023
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 13:14, s. 9476-9486
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Tidskriftsartikel (refereegranskat)abstract
- Both photo- and biocatalysis are well-established andintensivelystudied. The combination of these two approaches is also an emergingresearch field, commonly referred to as semi-artificial photosynthesis.Semi-artificial photosynthesis aims at combining highly efficientsynthetic light harvesters with the self-healing and potent catalyticproperties of biocatalysis. In this study, a semi-artificial photocatalyticsystem featuring Escherichia coli bacteria,which heterologously express the [FeFe] hydrogenase enzyme HydA1 fromgreen algae, is employed as a hydrogen gas production catalyst. Toprobe the influence of photochemistry on overall system performance,the E. coli whole-cell catalyst iscombined with two different photosensitizers and redox mediators.The addition of a redox mediator greatly improves the rates and longevityof the photocatalytic system, as reflected in increases of both theturn-over number (0.777 vs 10.9 & mu;mol H-2 mL(-1) OD600 (-1)) and the turn-over frequency(175 vs 334 & mu;mol H-2 mL(-1) h(-1) OD600 (-1)). The redoxmediator is found to both protect from photobleaching and enable electrontransport to the hydrogenase from an extracellular photosensitizer.However, E. coli cells are stronglyaffected by the photocatalytic system, leading to a decrease in cellintegrity and cell viability, possibly due to toxic decompositionproducts formed during the photocatalytic process. We furthermoreemployed steady-state and transient absorption spectroscopy to investigatesolution potentials and the kinetics of electron transfer processesbetween the sacrificial electron donor, photosensitizer, redox mediator,and the [FeFe] hydrogenase as the final electron acceptor. These resultsallowed us to rationalize the different activities observed in photocatalyticassays and offer a better understanding of the factors that influencethe photocatalytic performance of E. coli-based whole-cell systems.
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| 3. |
- Patehebieke, Yerseen, et al.
(författare)
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β-Scission of Secondary Alcohols via Photosensitization : Synthetic Utilization and Mechanistic Insights
- 2024
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:1, s. 585-593
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Tidskriftsartikel (refereegranskat)abstract
- An efficient metal-free photocatalytic method for the alkylation of alkenes using accessible aliphatic alcohols as redox auxiliaries is presented. C-centered radicals can be generated under mild conditions and subsequently employed in a C(sp3)-C(sp3) bond-forming process, which overall provides a C1 tethering strategy of nucleophiles and electrophiles. The optimized conditions accommodate various electron-deficient alkenes and secondary/tertiary alcohols, with applications in late-stage functionalization of natural products and pharmaceutically relevant compounds. Mechanistic investigations revealed a complex mechanistic manifold, including non-PCET fragmentation and concerted/stepwise PCET. Even though the previously thought PCET type mechanism is compatible with our observations, the non-PCET mechanism most probably constitutes a main pathway.
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