Iridium water-soluble

An interesting method to produce water-soluble iridium nanoparticles was proposed by Chaudret and coworkers [13]. Here, aqueous soluble iridium nanoparticles were synthesized by the chemical reduction of iridium trichloride with sodium borohydride in an aqueous solution of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (Scheme 15.2). The precursor reduction was assisted by sonication, while the gradual conversion of Ir(lll) ions to lr(0) nanoparticles was followed using UV spectroscopy. The use of a molar surfactant Ir ratio of 10 proved sufficient to obtain stable aqueous soluble iridium nanoparticles however, if the molar surfactant Ir ratio used was <10 then agglomeration was observed in solution after several days. TEM analysis of the iridium nanoparticles revealed a monodispersed size distribution and a mean diameter of 1.9 0.7nm (Figure 15.2). 

When recovered from the mineral osmiridium, the mineral is fused with zinc to convert it into a zinc alloy. The alloy is then treated with hydrochloric acid to dissolve the zinc away leaving a finely divided material. This finely divided sohd then is fused with sodium peroxide and caustic soda to convert osmium and ruthenium into their water-soluble sodium salts, sodium osmate and sodium iridate, respectively. While osmium is fully converted to osmate salt, most ruthemium and a small part of iridium are converted to ruthenate and iridate, respectively. The fused mass is leached with water to separate metals from sohd residues. 

The mineral osmiridium may alternatively be chlorinated at elevated temperatures on a bed of sodium chloride. Osmium is converted to water-soluble sodium chloroosmate. Iridium and ruthenium also are converted into water-soluble sodium chloroiridate and chlororuthenate. The insoluble residues are filtered out. Osmium is recovered from this solution in several steps as mentioned above. 

With the knowledge that 14 can activate aldehydes in 1, the role of 1 in the reaction was explored further. Specifically, the relative rates of C—H bond activation and guest ejection, and the possibility of ion association with 1, were investigated. The hydrophobic nature of 14 could allow for ion association on the exterior of 1, which would be both cn t h al pi cal I y favorable due to the cation-it interaction, and entropically favorable due to the partial desolvation of 14. To explore these questions, 14 was irreversibly trapped in solution by a large phosphine, which coordinates to the iridium complex and thereby inhibits encapsulation. Two different trapping phosphines were used. The first, triphenylphosphine tris-sulfonate sodium salt (TPPTS), is a trianionic water-soluble phosphine and should not be able to approach the highly anionic 1, thereby only trapping the iridium complex that has diffused away from 1. The second phosphine, l,3,5-triaza-7-phosphaadamantane (PTA), is a water-soluble neutral phosphine that should be able to intercept an ion-associated iridium complex. 

D. ftwis-CHLOROCARBONYLBIS[(ME714-SULFONATOPHENYL) DIPHENYL-PHOSPHINE]IRIDIUM(I), SODIUM SALT (WATER-SOLUBLE ANALOG OF YASKA S COMPLEX)... 

The complex [mer-IrH2Cl(PMe3)3] was used as a catalyst for the hydrogenation of alkynes and alkenes in water, and water-soluble ethylenediamine (en) complexes of iridium, [Ir(COD)(en)]Cl, were found to be excellent catalysts for aqueous hydrogenations (94). It would be interesting to determine the loss of iridium during application of these complexes in biphasic catalysis. 

Iridium black is only slightly soluble in aqua regia. When fused with alkalies and alkaline nitrates or NuTT. the metal is converted to an aetd-soluhle form. The metal at red heal reacts to a small extent with O., S. and P. At elevated temperature, die metal is attacked by CL and F-When fused with NaCl and treated with Cli, the water-soluble sodium hexachloroiridaletIVi. NadrCI,.. is formed. 

As mentioned above in connection with the acetic acid synthesis, iridium complexes catalyze the water-gas shift reaction (equation 70). From IrCl3-3H20 and sulfonated derivatives of bipy and phen, water-soluble catalysts were obtained.444 Using dioxane as solvent, complexes of the type [Ir(cod)L2]+ (L= PMePh2, PPh3), [Ir(cod)L ]+ (L = diphos, phen, 4,7-Me2-phen, 4,7-Ph2-phen, 3,4,7,8-Me4-phen) and [Ir(cod)X] (X = 4,7-diphenylphenanthroline disulfonate) also catalyzed the reaction, with the anionic species being most active.470 The mechanism was thought... 

Iridium - The authors are not aware of any water-soluble iridium porphyrin. 

Iridium Black.204 Iridium(III) hydroxide is reduced in water at 90°C and 8 MPa H2 for 40 min, in the same way as in the preparation of osmium black. The iridium(III) hydroxide is prepared by adding an aqueous lithium hydroxide solution dropwise to an 1% aqueous solution of water-soluble iridium(III) chloride, IrCl3 3H20, at 90-95°C until the pH of the solution becomes 7.5-7.8 under stirring. By keeping the solution at the same temperature under stirring, the precipitate of iridium(III) hydroxide is separated out from its colloidal solution. The precipitate is collected, washed repeatedly with hot water, and then dried in vacuo. 

A relatively recent development in catalysis by iridium with an oxygen-donor environment comes in the form of catalysis by iridium with aquo ligands and in aqueous solvent. Water-soluble compounds of iridium, either by virtue of attachment of water-soluble ligands or by direct interaction of water with the metal, are receiving a great deal of attention because of their potential as catalysts in aqueous solution. 

The Oppenauer Oxidation. When a ketone in the presence of an aluminum alkoxide is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation. This is the reverse of the Meerwein-Ponndorf-Verley reaction (19-36) and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum ferf-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the preparation of ketones, it has also been used for aldehydes. An iridium catalyst has been developed for the Oppenauer oxidation, and also a water-soluble iridium catalyst An uncatalyzed reaction under supercritical conditions was reported. 

More recent work on the hydrogenation of thiophenic molecules catalyzed by water-soluble metal complexes is pursuing the use of polyphosphine ligands (cf. Section 3.2.2). These studies follow the success obtained with the tridentate phosphine MeC (CH2PPh2)3 (TRIPHOS), which forms rhodium and iridium catalysts for the hydrogenation, hydrogenolysis, and desulfurization of various thiophenic... 

The water-soluble iridium(III) complex, [IrCp (H20)3]2+ (Cp = p5-C5Me5) was found a suitable catalyst precursor for reduction of aldehydes and ketones by hydrogen transfer from aqueous formate [254], Under the conditions of Scheme 3.34 turnover frequencies in the range of 0.3-4.3 h-1 were determined. Of the several water-soluble substrates the cyclic cyclopropanecarboxaldehyde reacted faster than the straight-chain butyraldehyde, and aldehydes were in general more reactive than the only simple ketone studied (2-butanone). While glyoxylic acid was reduced fast, pyruvic acid did not react at all. 

In the case of metal particle preparation the choice of the metal precursor is of paramount importance. Obviously, water-soluble precursors are desired, generally transition metal salts, but even then different behaviours may be expected from different precursors. From Table 4 it can be observed that the solubility of chloroplatinic acid in a microemulsion is seven times higher than that of rhodium, iridium and palladium chlorides l... 

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