Laser‐Induced Wurtz‐Type Syntheses with a Metal‐Free Photoredox Catalytic Source of Hydrated Electrons

Abstract

Upon irradiation with ns laser pulsesa t3 55 nm, 2aminoanthracene in SDS micelles readily produces hydrated electrons. These "super-reductants" rapidly attack substrates such as chloro-organics and convert them into carbon-centred radicals through dissociative electron transfer.F or ac atalytic cycle, the aminoanthracene needs to be restored from its photoionizationb y-product,t he radical cation, by as acrificial donor.T he ascorbate monoanion can only achieve this across the micelle-water interface, but the monoanion of ascorbyl palmitate resultsi nafully micelle-contained regenerative electron source.T he shielding by the micelle in the latter case not only increases the life of the catalystb ut also strongly suppresses the interception of the carbon-centred radicals by the hydrogen-donating ascorbate moiety;a nd in conjunction with the high local concentrations effected by the pulsed laser,t ermination by radicald imerizationt hus dominates. We have obtained ac omplete and consistent picture through monitoring the individual steps and the assembled systemb yf lash photolysis on fast ands low timescales, from microseconds to minutes;a nd in preparative studies on av ariety of substrates, we have achieved up to quantitative dimerizationw ith at urnover on the order of 1mmol per hour.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.

Multi‐Photon Excitation in Photoredox Catalysis: Concepts, Applications, Methods

“…Natural lifetimes ( τ 0 ) of circa 1 μs for T 1 or longer are advantageous; the higher‐excited T n states typically have lifetimes in the picosecond regime and can only react when very high concentrations of possible reaction partners are present . Micellar environments can help suppress undesirable side reactions and improve PC stability, as discussed in further detail in the next section.…”

Reactivity control of a photocatalytic system by changing the light intensity

“…A related e aq c À induced dimerization procedure in aqueous solution has been published very recently. 18 In that system, the e aq c À formation step requires a pulsed UV laser and a sophisticated micellar system to enable the formation of dimers. However, owing to the micellar shielding of potential hydrogen atom donors, even the efficient dimerization of very reactive radicals is possible with that approach.…”

“…An attractive alternative, but yet underexplored strategy to gain control over photochemical reactivity is provided by regulating the light intensity while keeping all other parameters constant. The approach of intensity dependent one-(low intensity) and two-photon (high intensity) chemistry is rather well-established under laser ash photolysis conditions, 14,[17][18][19][20][21][22] which however necessitates expensive pulsed lasers that are inaccessible for most synthetic laboratories. Catalytic cycles comprising the consecutive absorption of two photons with an excited state as intermediate (i.e., without converting the excited state into a long-lived radical anion) 23,24 were realized under continuous wave (cw) excitation conditions only very recently.…”

Minisci C-H Alkylation of Heteroarenes Enabled by Dual Photoredox/bromide Catalysis in Micellar Solutions

“…Recent reports show that they may also play a vital role in photocatalysis. 30,[45][46][47][48] From the viewpoint of the designed Minisci reaction, structured aqueous solution could provide the necessary pre-association of the starting materials and the photocatalyst, improve the kinetics of the reaction and thus eliminate the harsh reaction conditions or stoichiometric additives, including radical promoters and acids.…”