BODIPYs are renowned fluorescent dyes with strong and tunable absorption in the visible region, high thermal and photo-stability and exceptional fluorescence quantum yields. Transition metal ...complexes are the most commonly used triplet photosensitisers, but, recently, the use of organic dyes has emerged as a viable and more sustainable alternative. By proper design, BODIPY dyes have been turned from highly fluorescent labels into efficient triplet photosensitizers with strong absorption in the visible region (from green to orange). In this perspective, we report three design strategies: (i) halogenation of the dye skeleton, (ii) donor-acceptor dyads and (iii) BODIPY dimers. We compare pros and cons of these approaches in terms of optical and electrochemical properties and synthetic viability. The potential applications of these systems span from energy conversion to medicine and key examples are presented.
BODIPYs offer a versatile platform to build organic triplet photosensitisers for PDT, TTA upconversion and photocatalysis. Tuning their properties provides the opportunity of replacing heavy-metal complexes and can lead to improved sustainability.
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Schiff base ligands are considered "privileged ligands" because they are easily prepared by the condensation between aldehydes and imines. Stereogenic centres or other elements of chirality (planes, ...axes) can be introduced in the synthetic design. Schiff base ligands are able to coordinate many different metals, and to stabilize them in various oxidation states, enabling the use of Schiff base metal complexes for a large variety of useful catalytic transformations. Practical guidelines for the preparation and use of different Schiff base metal complexes in the field of catalytic transformations are discussed in this tutorial review.
Walking on water: Which alcohols react with nucleophiles on the surface of water? The correlations introduced by Mayr et al., in which electrophiles are characterized by the parameter E, gives ...practical indications about the reactivity of alcohols with nucleophiles in pure water. Stable carbocations generated from the alcohols and characterized by E<−2.5 readily react with nucleophiles in pure water at 80 °C, without added Brønsted or Lewis acids.
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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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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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Salen ligands are a class of Schiff bases simply obtained through condensation of two molecules of a hydroxyl-substituted aryl aldehyde with an achiral or chiral diamine. The prototype salen, or
,
...'-bis(salicylidene)ethylenediamine has a long history, as it was first reported in 1889, and immediately, some of its metal complexes were also described. Now, the salen ligands are a class of N,N,O,O tetradentate Schiff bases capable of coordinating many metal ions. The geometry and the stereogenic group inserted in the diamine backbone or aryl aldehyde backbone have been utilized in the past to efficiently transmit chiral information in a variety of different reactions. In this review we will summarize the important and recent achievements obtained in stereocontrolled reactions in which Al(salen) metal complexes are employed. Several other reviews devoted to the general applications and synthesis of chromium and other metal salens have already been published.
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9.
Direct Nucleophilic SN1-Type Reactions of Alcohols Emer, Enrico; Sinisi, Riccardo; Capdevila, Montse Guiteras ...
European Journal of Organic Chemistry,
February 2011, Volume:
2011, Issue:
4
Book Review, Journal Article
Peer reviewed
In 2005, the ACS Green Chemistry Institute (GCI) and the global pharmaceutical corporations developed the ACS GCI Pharmaceutical Roundtable to encourage the development of green chemistry and green ...engineering in the pharmaceutical industry. The Roundtable has established a list of key research areas including the direct nucleophilic reactions of alcohols. The substitution of activated alcohols is a frequently used approach for the preparation of active pharmaceutical ingredients. Alcohols are transformed into the reactive halides or sulfonate esters, thereby allowing their reaction with nucleophiles. Although the direct nucleophilic substitution of an alcohol should be an attractive process, as one of the byproducts from the reaction yields water, hydroxide is a poor leaving group that hinders the reaction. Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through an SN1 reaction with catalytic amounts of Brønsted or Lewis acids. In this review, the approaches leading to a greener process are examined in detail, and the advances achieved to date in this important transformation are presented.
In the cool of the pool! A catalytic amount of Brønsted and Lewis acids can be used in the direct nucleophilic SN1‐type reactions of alcohols with various nucleophiles. Water is the byproduct of this useful reaction.
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The new frontier in asymmetric catalysis is the selective formation of quaternary stereocenters. The enantioselective addition of nucleophiles to ketones is a particular challenge. Readily prepared ...Zn(salen) complexes promote the straightforward synthesis of tertiary alcohols from commercially available starting materials (see scheme), thus allowing the preparation of functionalizable chiral building blocks in a catalytic enantioselective procedure that shows broad scope.
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