Iridium carbonyls synthesis

Polymetallic iridium carbonyl complexes, preparation, 7, 291 Polymetallic nickel—alkenes, synthesis and reactivity, 8, 139 Polymetallocenes... 

Dodecacarbonyltetrairidium is the starting material for the synthesis of a large number of substitution products and of most anionic iridium carbonyl cluster compounds. Possible uses in catalysis of carbonyl and its substituted derivatives is also emerging. ... 

Figure 4-7. Ship-in-a-bottle synthesis of iridium carbonyl clusters. Schematic representation of the formation of [Ir4(CO)i2] and [Ir6(CO)i6] from [Ir(CO)2(acac)] in the cages of NaY zeolite. [3, 5] The precursor [Ir(CO)2(acac)j is small enough to diffuse into the zeolite supercages, where it reacts with CO to form the clusters, which are then trapped in the cages. For clarity, some of the CO ligands are not shown.

Kawi et al. [4, 60] reported on experiments comparing the iridium carbonyl chemistry in NaY zeolite with that in the more basic NaX zeolite (some of whose basicity should perhaps be attributed to the excess NaOH used in the preparation which was ultimately not washed out). The results showed that the supercages in the NaX zeolite were sufficiently basic to provide an effident medium for the synthesis of anionic iridium carbonyl clusters. When [Ir(CO)2(acac)] in NaX zeolite was treated with CO, it was transformed into [HIr4(CO)n] and then into [Irg(CO)t5]. The anionic carbonyl dusters trapped in the cages were characterized by infrared and EXAFS spectroscopies and could not be extracted from the zeolite by ion exchange with bis(triphenylphosphine)iminium chloride, [PPN][Q], in tetrahydrofuran solution. 

Figure 4-8. Synthesis of iridium carbonyl clusters in neutral solutions and on the nearly neutral surface of amorphous y-AljOs. The chemistry is very similar to that occurring in the cages of NaY zeolite (Fig. 4-7). [3, 5] Whereas the clusters can be readily extracted from the surface of y-AljOj, under the same conditions they cannot be extracted from the zeolite because they are too large to fit through the cage windows and are thus trapped in the supercages.

In the last decade, iridium carbonyl complexes have found many applications in homogeneous and heterogeneous catalysis, as well as in photoluminescent and optoelectronic devices. These aspects will be described in the corresponding sections. Here are summarized the main developments in the synthesis, characterization, and some, although brief, descriptions of use of the most remarkable iridium mono-, di-, polycarbonyl and cluster complexes. Specific reactivity of alkyl, aryl iridium carbonyl complexes are dealt with in the appropriate paragraph in this chapter. 

Iridium clusters were also prepared from polynuclear iridium carbonyl clusters prepared by a so-called ship-in-a-bottle synthesis. Lefebvre et al. [196] were the first to study the in situ synthesis of iridium carbonyls using IR and NMR spectroscopy. Monovalent dicarbonyls were formed by contacting an Ir(NH3)5CF -exchanged zeoHte calcined at 300 K with CO. Tetranuclear iridium carbonyls, Ir4(CO)i2, were formed by contacting the zeolite with a CO/H2O atmosphere, and Ir6(CO)i6 was synthesized merely by heating the Ir4(CO)i2-... 

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). 

A large number of reports have concerned transfer hydrogenation using isopropanol as donor, with imines, carbonyls-and occasionally alkenes-as substrate (Scheme 3.17). In some early studies conducted by Nolan and coworkers [36], NHC analogues of Crabtree catalysts, [Ir(cod)(py)(L)]PF,5 (L= Imes, Ipr, Icy) all proved to be active. The series of chelating iridium(III) carbene complexes shown in Scheme 3.5 (upper structure) proved to be accessible via a simple synthesis and catalytically active for hydrogen transfer from alcohols to ketones and imines. Unexpectedly, iridium was more active than the corresponding Rh complexes, but... 

The first, made by Ichikawa et al. [29], was the evidence that rhodium or iridium cluster carbonyls, when adsorbed on zinc oxide, titania, lanthanum oxides, zirconia or magnesia, could produce quite selectively ethanol by the Fischer-Tropsch synthesis. This was a timely discovery (metallic catalytic particles produced by traditional methods could not reproduce such selectivity) since it came at a period of geopolitical tension after the Kippur war in 1973, which caused the price of crude oil to increase enormously. Therefore, that period was characterized by intense research into selective Fischer-Tropsch catalysis. 

Our study on the synthesis, structure and catalytic properties of rhodium and iridium dimeric and monomeric siloxide complexes has indicated that these complexes can be very useful as catalysts and precursors of catalysts of various reactions involving olefins, in particular hydrosilylation [9], silylative couphng [10], silyl carbonylation [11] and hydroformylation [12]. Especially, rhodium siloxide complexes appeared to be much more effective than the respective chloro complexes in the hydrosilylation of various olefins such as 1-hexene [9a], (poly)vinylsiloxanes [9b] and allyl alkyl ethers [9c]. 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

Rearrangements of clusters, i.e. changes of cluster shape and increase and decrease of the number of cluster metal atoms, have already been mentioned with pyrolysis reactions and heterometallic cluster synthesis in chapter 2.4. Furthermore, cluster rearrangements can occur under conditions which are similar to those used to form simple clusters, e.g. simple redox reactions interconvert four to fifteen atom rhodium clusters (12,14, 280). Hard-base-induced disproportionation reactions lead to many atom clusters of rhenium (17), ruthenium and osmium (233), iron (108), rhodium (22, 88, 277), and iridium (28). And the interaction of metal carbonyl anions and clusters produces bigger clusters of iron (102, 367), ruthenium, and osmium (249). 

Deprotonation with aluminum alkys, 9, 272 mononuclear carbonyl iridium complexes, 7, 302 for palladium cyclopentadienyl complexes, 8, 390 in Ru and Os half-sandwich preparations, 6, 569 in silver carbene synthesis, 2, 206 Desulfurization... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

A material suitable for studies of the fundamental reactions of dinuclear complexes has been sought as a companion to Vaska s complex [Ir(CO)(PA3)2X]. This newly described carbonyl compound allows synthesis of several series of polynuclear compounds of iridium in formal oxidation states 4-1, +11, +III and plays the role of a typical dinuclear species. 

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