The different types of acceptorless alcohol dehydrogenation (AAD) reactions are discussed, followed by the catalysts and mechanisms involved. Special emphasis is put on the common appearance in AAD ...of pincer ligands, of noninnocent ligands, and of outer sphere mechanisms. Early work emphasized precious metals, mainly Ru and Ir, but interest in nonprecious metal AAD catalysis is growing. Alcohol–amine combinations are discussed to the extent that net oxidation occurs by loss of H2. These reactions are of potential synthetic interest because they can lead to N heterocycles such as pyrroles and pyridines. AAD also has green chemistry credentials in that an oxidation occurs without the need for an oxidizing agent and hence without the waste formation that would result from its use.
Dihydrogen Complexation Crabtree, Robert H
Chemical reviews,
08/2016, Volume:
116, Issue:
15
Journal Article
Peer reviewed
Dihydrogen complexation with retention of the H–H bond, once an exotic concept, has by now appeared in a very wide range of contexts. Three structural types are currently recognized: Kubas ...dihydrogen, stretched dihydrogen, and compressed dihydrides. These can be difficult to distinguish, hence the development of a number of novel spectroscopic methods for doing so, mainly based on NMR spectroscopy. Three important reactivity patterns are identified: proton loss, oxidative addition, and dissociation, each of which often contributes to larger reaction schemes, as in homogeneous hydroformylation. Main group examples are beginning to appear, although here it is mainly by computational studies that the relevant structures can be identified. Enzymes such as the hydrogenases and nitrogenases are also proposed to involve these structures.
An overview of chemical reactions producing carbon-hydrogen bonds is presented. It is noted that overoxidation is a confounding factor in creating such bonds.
Dehydrogenation reactions in green chemistry and pharmacology are examined. These reactions create active molecules of the desired drug without inactive or toxic waste products.
The title topic is reviewed with selected examples taken from recent work, such as: the 'hydrogen borrowing' amine alkylation by alcohols; the dehydrogenative coupling of amine and alcohol to give ...amide; Ru complexes as solar cell photosensitizers; Ir organometallics as water oxidation catalyst precursors and as OLED emitters; as well as recent hydrogen storage strategies involving catalytic dehydrogenation of ammonia-borane and of organic heterocycles.
Nitrogen heterocycles have advantages as hydrogen storage materials, including easier H2 release, better biodegradability, and low vapor pressure. The challenges that face practical applications, for ...example to vehicular transport, are discussed. Beyond heterocycles, amine/amide and amine/nitrile strategies are also covered.
Molecular Catalysts for Water Oxidation Blakemore, James D; Crabtree, Robert H; Brudvig, Gary W
Chemical reviews,
12/2015, Volume:
115, Issue:
23
Journal Article
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