Iridium synthesis

B. R. Sutherland, M. Cowie, Hydroxy- and hydrido-bridged binuclear complexes of iridium synthesis, characterization, and attempts to model binuclear water-gas shift catalysts. Structure of [Ir2(CO)2(.mu.-H.Cl)(Ph2PCH2PPh2)2], Organometalhcs 4 (1985) 1637-1648. 

Synthesis. The principal starting material for synthesis of iridium compounds is iridium trichloride hydrate [14996-61-3], IrCl3-a H2 0. Another useful material for laboratory-scale reactions is [Ir20l2(cod)2] [12112-67-3]. 

With the exception of acetic, acryUc, and benzoic all other acids in Table 1 are primarily produced using oxo chemistry (see Oxo process). Propionic acid is made by the Hquid-phase oxidation of propionaldehyde, which in turn is made by appHcation of the oxo synthesis to ethylene. Propionic acid can also be made by oxidation of propane or by hydrocarboxylation of ethylene with CO and presence of a rhodium (2) or iridium (3) catalyst. 

The main use of rhodium is with platinum in catalysts for oxidation of automobile exhaust emissions. In the chemical industry, it is used in catalysts for the manufacture of ethanoic acid, in hydroformylation of alkenes and the synthesis of nitric acid from ammonia. Many applications of iridium rely on... 

Na,IrCl6 is a convenient starting material in the synthesis of iridium compounds. 

The best characterized complexes [146] are prepared as shown in Figure 2.83. In synthesis (a) the first step involves demethylation of both ligands only one phosphine chelates, demonstrating the stability of square planar d8 iridium(I) on oxidation, the CO is displaced (as C02) and both ligands chelate. 

In synthesis (b), the initial product is a 5-coordinate (sp) iridium(III) hydride complex, which is rapidly oxidized in solution to the planar iridium(II) complex. Both of the compounds are paramagnetic with one unpaired electron, as expected for square planar d7 complexes. 

The iridium(III) complexes are broadly similar to the rhodium(III) ammines a selection of synthesis is shown in Figure 2.84. 

Figure 2.100 Synthesis of some iridium nitrosyl complexes.

Scheme 22 Synthesis of iridium polysulfido complexes by the reaction of IrCl3-nH20 with polysulfide dianions...

Scheme 27 Synthesis of rhodium, iridium, and copper polysulfido clusters from the corresponding, u-hydrogensulfido complexes...

Deming T.J., Facile synthesis of block copol3fpeptides of defined architecture. Nature, 390, 386, 1997. Seidel S.W. and Deming T.J., Use of chiral mthenium and iridium amido-sulfonamidate complexes for controlled, enantioselective polypeptide synthesis. Macromolecules, 36, 969, 2003. 

Mossbauer spectroscopy is a specialist characterization tool in catalysis. Nevertheless, it has yielded essential information on a number of important catalysts, such as the iron catalyst for ammonia and Fischer-Tropsch synthesis, as well as the CoMoS hydrotreating catalyst. Mossbauer spectroscopy provides the oxidation state, the internal magnetic field, and the lattice symmetry of a limited number of elements such as iron, cobalt, tin, iridium, ruthenium, antimony, platinum and gold, and can be applied in situ. 

The mass balance of the processes (Figure 5.4) shows that the catalytic procedure (Scheme 5.2a) is much more resource efficient than the stoichiometric conversion (Scheme 5.2b). As expected, integrating the synthesis of the iridium catalyst results in an increase of the overall waste production (compare (a) II and (a) III, Figure 5.4). 

The iridium catalyst is very expensive (98.1 Euro for 0.25 g), therefore, the overall price of synthesis by means of the iridium catalyst (Figure 5.5a) is much higher than for the classical reaction (Figure 5.5b). 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

The formation of C-C bonds is of key importance in organic synthesis. An important catalytic methodology for generating C-C bonds is provided by carbonylation. In the bulk chemicals arena this is used for the production of acetic acid by methanol carbonylation (Eqn. (9)) in the presence of rhodium- or, more recently, iridium-based catalysts (Maitlis et al, 1998). 

An even more impressive example of catalytic efficiency has recently been disclosed by Novartis (Bader and Bla.ser, 1997). The key step in a proce.ss for the synthesis of the optically active herbicide, (S)-metolachlor involves asymmetric hydrogenation of a prochiral imine catalysed by an iridium-ferrocenyldipho-sphine complex (see Fig. 2.36). 

In 1998, Ruiz et al. reported the synthesis of new chiral dithioether ligands based on a pyrrolidine backbone from (+ )-L-tartaric acid. Their corresponding cationic iridium complexes were further evaluated as catalysts for the asymmetric hydrogenation of prochiral dehydroamino acid derivatives and itaconic acid, providing enantioselectivities of up to 68% ee, as shown in Scheme 8.18. 

---