The photocatalytic mechanism reported in a recent Communication to produce the radical anion of pyrenes postulates a highly endergonic electron transfer process. An analysis of the thermodynamics is ...reported together with the proposal of an alternative thermodynamically feasible mechanism.
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Here we report the application of dual nickel/photoredox catalysis to the allylation of aliphatic, aromatic and heteroaromatic aldehydes by using commercially available reagents. The process utilizes ...the combination of a Ni(
ii
) complex, Ru(bpy)
3
2+
as a photoredox catalyst, and allylacetate under blue LED irradiation, and allows the synthesis of a large variety of homoallylic alcohols.
Here we report the application of dual nickel/photoredox catalysis to the allylation of aliphatic, aromatic and heteroaromatic aldehydes by using commercially available reagents.
Metallosalen are privileged complexes that have found important applications in catalysis. In addition, their luminescent properties have also been studied and used for sensing and biological ...applications. Salen metal complexes can be efficient photosensitizers, but they can also participate to electron transfer processes. Indeed, we have found that commercially available Al(Salen)Cl is an efficient photoredox catalyst for the synergistic stereoselective reaction of alkyl aldehydes with different bromo ketones and malonates to give the corresponding enantioenriched α‐alkylated derivatives. The reaction was performed in the presence of a MacMillan catalyst. Al(Salen)Cl is able to replace ruthenium complexes, showing that also aluminum complexes can be used in promoting photoredox catalytic reactions.
A benchmark photoredox alkylation of aldehydes is effectively promoted by using 5 mol‐% of the commercially available Al(Salen)Cl, in the presence of a MacMillan organocatalyst (14 mol‐%) under irradiation with a CFL light bulb.
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The preparation of homoallylic alcohols by addition of organometallic allyl compounds to carbonyls is an important strategy in organic chemistry. Allylating organometallic cobalt species can be ...generated employing stoichiometric quantities of Zn acting as reductant. To avoid the employment of stoichiometric amount of Zn, we have developed an allylation reaction of aromatic and aliphatic aldehydes promoted by photoredox catalysis in the presence of a cobalt complex, and we present herein a full account of our research. In the presence of the abundant CoBr2 (10 mol %), 4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl (dtbbpy, 10 mol %), allyl acetate (3 equiv.), Ir(dtbbpy)(ppy)2PF6 (ppy=2‐phenylpyridine, 2 mol %), and N,N‐diisopropylethylamine (4 equiv.), an allylation of aldehydes is taking place, in moderate to good yields. Substrates scope, limitations, and photophysical investigations of this new process are reported.
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A shape‐persistent molecule, featuring four bipyridinium units, has been synthesized that upon reduction undergoes intermolecular pimerization because of the rigid architecture of the molecule. The ...pimerization process has been investigated by a variety of techniques, such as absorption measurements, EPR spectroscopy, as well as gamma and pulse radiolysis, and compared with the behavior of a model compound. Computational studies have also been performed to support the experimental data. The most interesting feature of the tetramer is that pimerization occurs only above a threshold concentration of monoreduced species, on the contrary to the model compound. Furthermore, there is an increase of the apparent pimerization constant by increasing the concentration of reduced bipyridinium units. These results have been interpreted by the fact that pimerization is favored in the tetrahedrally shaped molecule because of a cooperative mechanism. Each multiply reduced molecule can indeed undergo multiple intermolecular interactions that enhance the stabilization of the system, also leading to hierarchical supramolecular growth. The resulting supramolecular system formed by such intermolecular pimerization should exhibit a diamond‐like structure, as suggested by a simplified modeling approach. The intermolecular nature of the pimerization process occurring in the tetramer has been demonstrated by measuring the corresponding bimolecular rate constant by pulsed radiolysis experiments.
Stay in shape: A shape‐persistent molecule made of four tetrahedrally arranged bipyridinium units undergoes intermolecular pimerization upon reduction, leading to hierarchical supramolecular growth (see figure).
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A series of modular ImPy–carbene–Au(I) complexes are synthesized and fully characterized both in the solid state and in solution. The presence of oligoaryl units (phenyl and thienyl rings) at the ...C5-position of the ImPy core (in close proximity to the gold center) imprints on the organometallic species fine-tunable and predictable catalytic properties. A marked accelerating effect was recorded in several Au(I)-catalyzed electrophilic activations of unsaturated hydrocarbons when a CF3-containing aromatic ring was accommodated at the ImPy core.
The herein reported visible‐light‐activated catalytic asymmetric 3+2 photocycloadditions between cyclopropanes and alkenes or alkynes provide access to chiral cyclopentanes and cyclopentenes, ...respectively, in 63–99 % yields and with excellent enantioselectivities of up to >99 % ee. The reactions are catalyzed by a single bis‐cyclometalated chiral‐at‐metal rhodium complex (2–8 mol %) which after coordination to the cyclopropane generates the visible‐light‐absorbing complex, lowers the reduction potential of the cyclopropane, and provides the asymmetric induction and overall stereocontrol. Enabled by a mild single‐electron‐transfer reduction of directly photoexcited catalyst/substrate complexes, the presented transformations expand the scope of catalytic asymmetric photocycloadditions to simple mono‐acceptor‐substituted cyclopropanes affording previously inaccessible chiral cyclopentane and cyclopentene derivatives.
Molecular complexity in a single step: Asymmetric 3+2 photocycloadditions between cyclopropanes and alkenes or alkynes catalyzed by a chiral‐at‐metal rhodium complex are reported. The reactions, enabled by a mild single‐electron reduction of visible‐light‐excited catalyst‐bound substrates, provide access to chiral cyclopentanes and cyclopentenes.
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Exploring the ancient chemistry of mercury Marchini, Marianna; Gandolfi, Massimo; Maini, Lucia ...
Proceedings of the National Academy of Sciences - PNAS,
06/2022, Volume:
119, Issue:
24
Journal Article
Peer reviewed
Open access
This paper explores the chemistry of mercury as described in ancient alchemical literature. Alchemy's focus on the knowledge and manipulation of natural substances is not so different from modern ...chemistry's purposes. The great divide between the two is marked by the way of conceptualizing and recording their practices. Our interdisciplinary research group, composed of chemists and historians of science, has set off to explore the cold and hot extraction of mercury from cinnabar. The ancient written records have been perused in order to devise laboratory experiments that could shed light on the material reality behind the alchemical narratives and interpret textual details in a unique perspective. In this way, it became possible to translate the technical lore of ancient alchemy into the modern language of chemistry. Thanks to the replication of alchemical practices, chemistry can regain its centuries-long history that has fallen into oblivion.
“Vitriol” is a term that appeared during the Middle-Ages to indicate a wide range of ingredients widely used both in medicinal and alchemical recipes. Green, blue, or white vitriols are easily ...associated with iron( ii ), copper( ii ), and zinc sulphate respectively thanks to the historical sources composed in the time period when the ancient and modern nomenclatures overlapped. However, other colours of vitriols are attested throughout history, such as yellow, red, or black. The identification of these compounds is significantly less straightforward, and often chalked up to Decknamen (code names) or unspecified impure ores. Moreover, from several sources it is apparent that some of these compounds are artificial, or at least the result of technical operations rather than mineral ores used as they are. By thermal manipulation of iron( ii ) sulphate, we managed to identify several compounds that fit with historical descriptions, which were later characterized through XRPD. Moreover, by using a Kofler bench and variable temperature XRPD, we were able to further investigate the transitions between these phases.
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Catalytic amounts (2.5 mol %) of Fe(bpy)3Br2 complex in the presence of visible light and the MacMillan catalyst 3 (20 mol %) are highly effective in promoting an enantioselective organocatalytic ...photoredox alkylation of aldehydes with various α-bromo carbonyl compounds. Reaction yields of isolated compounds and enantioselectivities are very good and comparable to the ones obtained by Ru(bpy)32+, organic dyes, or semiconductors, in the presence of the same organocatalysts. The use of first-row, abundant, and cheap metals in photocatalyzed reactions can open new perspectives in stereoselective organic synthesis.
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