Aldehyde complexes, osmium

Pyrimidinethione complexes, osmium, 37 296 Pyriminethionate, as bridging ligands in platinum dimers, 40 202-205 Pyrochlores, 17 108 Pyrococcus furiosus, 38 344-383 aldehyde ferredoxin oxidoreductase, 38 374-381... 

One group of NADH oxidants, which does not fit the proposed reaction scheme in Fig. 2.4 are the metal complexes. Examples of this type include nickel hexacyanoferrate deposited on porous nickel electrodes [29], gold electrodes modified with cobalt hexacyanoferrate films [30] and adsorbed l,10-phenanthroline-5,6-dione complexes of ruthenium and osmium [31]. It is unclear how these systems work and no mechanism has been proposed to date. It may be worth noting that dihydronicotinamide groups have been shown to reduce aldehydes in a non-enzymatic reaction when the reaction is catalysed by zinc, a metal ion [15]. In a reaction between 1,10-phenanthroline-2-carboxaldehyde and N-propyl-l,4-dihydronicotinamide, no reaction was seen in the absence of zinc but when added to the system, the aldehyde was reduced and the nicotinamide was oxidised. This implies that either coordination to, or close proximity of, the metal ion activates... 

A detailed stu of over 45 catalysts, primarily from Group VIII metal salts and complexes, showed palladium(II) compounds to be the most effective in the dehydrogenation of a variety of aldehydes and ketones. Soluble palladium(II) salts and complexes such as dichloro(tTiphenylphosphine)palladium(II) and palladium(II) acetylacetonate have been shown to be optimal, with the salts of rhodium, osmium, iridium and platinum having reduced efficacy. Since the d ydrogenation reaction is accompanied by reduction of the palladium(II) catalyst to palladium(0), oxygen and a cooxidant are required to effect reoxidadon. Copper(II) salts are favored cooxidants, but quinones, and especially p-benzoquinone, are also effective (Scheme 24). - ... 

In 1985, Orchin and coworkers [1] raised the question, Is the hydroformylation reaction reversible . Indeed, several investigations give clear evidence that aldehydes can be degraded under hydroformylation conditions or at least by the effect of typical hydroformylation-active complexes based on rhodium, cobalt, palladium, ruthenium, iridium, or osmium [2, 3]. As the result of the decarbonylation, an alkane is formed (Scheme 8.1). In 2015, also a clean dehydroformylation protocol operating under smooth conditions was discovered, which afforded olefins [4]. 

Oxidation of aliphatic aldehydes by benzyltrimethylammonium chlorobromate to the corresponding carboxylic acid proceeds via the transfer of a hydride ion from the aldehyde hydrate to the oxidant. The oxidation of aUyl alcohol with potassium bromate in the presence of osmium(Vin) catalyst in aqueous acidic medium is first order in bromate, Os(Vni) and substrate, but inverse fractional order in H+ the stoichiometry of the reaction is 2 3 (oxidantsubstrate). The active species of oxidant and catalyst in the reaction were understood to be BrOs and H2OSO5, respectively, which form a complex. Autocatalysis by Br, one of the products, was observed, and attributed to complex formation between Br and osmium(VIII). First-order kinetics each in BrOs, Ru(VI), and substrate were observed for the ruthenium(VI)-catalyzed oxidation of cyclopentanol by alkaline KBrOs containing Hg(OAc)2. A zero-order dependence on HO concentration was observed and a suitable mechanism was postulated. The oxidation reaction of aniUne blue (AB+) with bromate at low pH exhibits interesting non-linear phenomena. The depletion of AB+ in the presence of excess of bromate and acid occurs at a distinctly slow rate, followed by a very rapid reaction. A 12-step reaction mechanism, consistent with the reaction dynamics, has been proposed. The novel cyclohexane-l,4-dione-bromate-acid system has been shown to exhibit a rapid oscillatory redox reaction superimposed on a slower... 

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