Hydroxides iridium catalysts

In the past, this field has been dominated by ruthenium, rhodium and iridium catalysts with extraordinary activities and furthermore superior enantioselectivities however, some investigations were carried out with iron catalysts. Early efforts were reported on the successful use of hydridocarbonyliron complexes HFcm(CO) as reducing reagent for a, P-unsaturated carbonyl compounds, dienes and C=N double bonds, albeit complexes were used in stoichiometric amounts [7]. The first catalytic approach was presented by Marko et al. on the reduction of acetone in the presence of Fe3(CO)12 or Fe(CO)5 [8]. In this reaction, the hydrogen is delivered by water under more drastic reaction conditions (100 bar, 100 °C). Addition of NEt3 as co-catalyst was necessary to obtain reasonable yields. The authors assumed a reaction of Fe(CO)5 with hydroxide ions to yield H Fe(CO)4 with liberation of carbon dioxide since basic conditions are present and exclude the formation of molecular hydrogen via the water gas shift reaction. H Fe(CO)4 is believed to be the active catalyst, which transfers the hydride to the acceptor. The catalyst presented displayed activity in the reduction of several ketones and aldehydes (Scheme 4.1) [9]. 

II. 5).204,205 Unsupported iridium catalysts have been prepared by reducing an iridium oxide of Adams type at 165°C under a stream of hydrogen206 or by reducing iridium hydroxide, prepared by addition of lithium hydroxide to an aqueous solution of irid-ium(III) chloride, at 80-90°C and 8 MPa H2.204 Unsupported and supported iridium catalysts may also be prepared by reduction of iridium(IV) chloride with sodium boro-hydride.207 It is noted that the catalytic activity of deactivated iridium can be almost completely regenerated by treatment with concentrated nitric acid.205... 

Hydrogenation catalysts Dichlorotris(triphenylphosphine)ruthenium. Iridium. Iridium tetrachloride-Triethyl phosphite. Iridium-BaSO, or CaC04. Lithium aluminum hydride. Nickel catalyst, Raney. Palladium hydroxide. Platinum catalysts. Potassium hydride. Trihydridobis(triphenyIphosphine)iridium (III). 

The substrate (0.5 ml) was hydrogenated over 5 mg of iridium black in 7 ml t-BuOH at 80°C and 4.9 MPa H2. The same catalyst, prepared from the iridium hydroxide precipitated at pH 7, was used throughout the experiments. 

HYDROGENATION, CATALYSTS (1,5-Cyclooctadiene)bis(methyldiphenyl-phosphine)iridium(I) hexafluorophos-phate. Di- i-chlorodichlorobis(penta-methylcyclopentadienyOrhodium. Dichlorotris(triphenyljJhosphine)-ruthenium(II). Palladium catalysts. Palladium hydroxide. Rhodium. 

Iridium(IV), d, salts of halides, hydroxide, sulfide, se-lenide, and telluride have been reported. The commercial product H2[IrCl6] 6H2O is water soluble and acts as a catalyst. Ir02 is prepared from the hexahydroxo complex. Iridium(IV) does not form many complexes, but the six-coordinate halides (excluding the iodo species), and some amine and pyridine complexes are known. Compounds with phosphorus, arsenic, and sulfur donor atoms are not stable these ligands reduce iridium(IV) to the iridium(in) state. 

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