Iridium ionic

Kinetic mles of oxidation of MDASA and TPASA by periodate ions in the weak-acidic medium at the presence of mthenium (VI), iridium (IV), rhodium (III) and their mixtures are investigated by spectrophotometric method. The influence of high temperature treatment with mineral acids of catalysts, concentration of reactants, interfering ions, temperature and ionic strength of solutions on the rate of reactions was investigated. Optimal conditions of indicator reactions, rate constants and energy of activation for arylamine oxidation reactions at the presence of individual catalysts are determined. 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

S. J. Pool and K.H. Shaughnessy. Effects of ionic liquids on oxidative addition to square planar iridium and rhodium complexes. Abstracts of Papers, 231st ACS National Meeting, Atlanta, GA, USA, March 26-30,2006 (2006). 

The ionic iridium(III) carbene complex (47) is prepared from the reaction of IrHCl(03SCF3)-(CO)(PPh3)2] with [RC=NMe](03SCF3).61 Addition of Na(barf) (barf = B(3,5-C6H3 (CF3)2)4) to [Ircp (PMe3)(CH3)(0S02CF3)] in CH2C12 yields the structurally determined species... 

The ionic cycle is important under reaction conditions where iodide ion can exist, e.g., higher water levels (CH3OH + HI CH3I + H20) or with salt additives. However, while higher ionic iodide levels give an iridium species capable of very rapid reaction with methyl iodide, they also serve to inhibit the formation of an acyl species. The relatively slow conversion of [CH3Ir(CO)2I3] to an acyl species is almost certainly not... 

Recently, Dupont and coworkers described the use of room-temperature imi-dazolium ionic liquids for the formation and stabilization of transition-metal nanoparticles. The potential interest in the use of ionic liquids is to promote a bi-phasic organic-organic catalytic system for a recycling process. The mixture forms a two-phase system consisting of a lower phase which contains the nanocatalyst in the ionic liquid, and an upper phase which contains the organic products. Rhodium and iridium [105], platinum [73] or ruthenium [74] nanoparticles were prepared from various salts or organometallic precursors in dry 1-bu-tyl-3-methylimidazolium hexafluorophosphate (BMI PF6) ionic liquid under hydrogen pressure (4 bar) at 75 °C. Nanoparticles with a mean diameter of 2-3 nm... 

Catalysts other than homogeneous (molecular) compounds such as nanoparticles have been used in ionic liquids. For example, iridium nanoparticles prepared from the reduction of [IrCl(cod)2] (cod = cyclooctadiene) with H2 in [bmim][PF6] catalyses the hydrogenation of a number of alkenes under bipha-sic conditions [27], The catalytic activity of these nanoparticles is significantly more effective than many molecular transition metal catalysts operating under similar conditions. 

Iridium nanoparticles generated in l-n-butyl-3-methylimidazolium (BMI)-based ionic liquids were found to be excellent recyclable catalytic systems for the hydrogenation of a variety of substrates, including ketones such as simple ketones. The Ir nanoparticles were prepared by simple reduchon of [Ir(cod)Cl]2 dispersed in BMI-PFis at 75 °C under 4 atm of H2. Benzaldehyde, cyclopentanone, methyl butanone and derivatives were hydrogenated with almost complete conversion, with TOFs ranging from 17 to 96h under solventless conditions (substrate Ir ratio = 250, 75 °C, 4 atm FI2) [102]. 

Scheme 15.3 Preparation of soluble iridium nanoparticles from in situ reduction of the organometallic precursor [ir(COD)Cl]2 in imidazolium ionic liquids.

The typical in situ reduction of the precursor [lr(COD)Cl]2 by molecular hydrogen under the same reaction conditions have been also performed in 1-n-butyl-3-methylimidazolium trifluoromethanesulfonate (BMl-CFsSOs) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMl-BF [25]. The iridium nanoparticles prepared in BMTCF3SO3 and BM1-BF4 ILs, as previously observed with BM1-PF6, display irregular shapes with a monomodal size distribution (Figure 15.4). Mean diameters in the range of 2-3 nm were estimated with in situ TEM and small-angle X-ray scattering (SAXS) analyses of the lr(0) nanoparticles soluble in the ionic hquids, and by X-ray diffraction (XRD) of the isolated material. The mean diameters of iridium nanoparticles synthesized in the three ILs, as estimated by TEM, SAXS and XRD, are summarized in Table 15.1. 

Redox potential pH Ionic activities Inert redox electrodes (Pt, Au, glassy carbon, etc.) pH-glass electrode pH-ISFET iridium oxide pH-sensor Electrodes of the first land and M" /M(Hg) electrodes) univalent cation-sensitive glass electrode (alkali metal ions, NHJ) solid membrane ion-selective electrodes (F, halide ions, heavy metal ions) polymer membrane electrodes (F, CN", alkali metal ions, alkaline earth metal ions)... 

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