Iridium carbonyl clusters

Iridium carbonyl clusters of several nuclearities (2, 4 and 6) have been prepared by a controlled carbonylation of [lr(CO)2(acac)] complex adsorbed in the cages of a NaY zeolite. Then, decarbonylation of the clusters gave rise to lr2, lr4 and Ir frames. Studies of the dependence of the catalytic activity on the size of the iridium frames in NaY zeolites show that there is no simple explanation for the variation in catalytic performance in ethene hydrogenation with cluster size [208]. 

Nucleation of lr(l) Carbonyl Species to Various Iridium Carbonyl Clusters on a Si02 Surface... 

Scheme 16.13 Pathways for the generation of iridium carbonyl clusters on the surface of Si02.

Fluorinated ionic liquids, characteristics, 1, 854 Fluorinated molecules, coordination, 1, 727 Fluorinated thiols, in nanoparticle preparation, 12, 80 Fluorination, and iridium carbonyl cluster complexes, 7, 299... 

Zhao, A., and Gates, B. C., Probing metal oxide surface reactivity with adsorbate organometallic chemistry Formation of iridium carbonyl clusters on P-AI2O3, Langmuir 13,4024 (1997). 

Polynuclear Iridium Carbonyl Clusters (See Metal Carbonyl Clusters)... 

From the other directions, there have been a number of studies of the cluster species that are formed when mononuclear iridium precursors are deposited onto inorganic supports and then subjected to carbon monoxide pressures. Gates and coworkers have shown that Ir(CO)2(acac) will form higher nuclearity iridium carbonyl clusters, the exact nature of which depends on the substrate and the carbonylation conditions. For zeolite NaY, they have observed that Ir(CO)2(acac) will yield both It4(CO)i2 (45) and fr6(CO)i6... 

Figure 8. Polyhedral hybrid representation of Osmium and Iridium carbonyl clusters.

Adams RD, Captain B, Smith JL Jr, Hall MB, Beddie CL, Webster CE (2004) Superloading of tin ligands into rhodium and iridium carbonyl cluster complexes. Inorg Chem 43 7576... 

The decarbonylations of iridium carbonyl clusters in NaY zeolite are reversible [12]. Infrared spectra show that [Ir6(CO)i6] in the supercages was decarbonylated by treatment in hydrogen at 300°C [12]. When CO was adsorbed at -196°C on the decarbonylated clusters formed from [Ir6(CO)i6] (or from [Ir4(CO)i2]) and the temperature raised with the sample under CO, mononuclear iridium carbonyls formed at about -30°C. These were converted at about 50°C into [Ir4(CO)i2] and at about 125°C into [Ir6(CO)i6] [12]. In contrast, the decarbonylations of the iridium cluster carbonyl anions [HIr4(CO)ii] and [Ir6(CO)i5]2 supported on MgO were found to be irreversible [13]. 

Zeolite-supported iridium clusters formed by decarbonylation of supported iridium carbonyl clusters characterization by EXAFS spectroscopy"... 

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. ... 

The nitrido carbonyl cluster anion [Co-yNlCO) 5 is found to have a carbonyl stereochemistry quite different from that of its rhodium analog . The 2-D nutation Co-59 NMR of solid CO4[Pg.151]

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. 

The chemistry of anionic Iridium carbonyl clusters in NaX zeolite parallels that in basic solutions and on the basic MgO surface (Fig. 4-9). In basic solutions, the reductive carbonylation of [Ir4(CO)i2] with KOH in methanol under CO initially gives [HIr4(CO) ]-, [61, 67] then [Ir8(CO)22] , [62, 67] and finally [Ir6(CO),5]. ... 

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 summary, the interactions of the carbonyl ligands of rhodium and iridium carbonyl clusters with the Lewis add sites in zeolites are indicated by shifts in the stretching frequendes of the CO ligands, and the pattern parallels that observed for metal carbonyl clusters in solutions containing Lewis adds and on surfaces of metal oxides containing Lewis add sites. 

The used NaY zeolite catalyst containing iridium carbonyl clusters was yellow when removed from the flow reactor after three days of continuous operation at 250 °C and 20 bar, consistent with the presence of the [Ir((CO)i6] isomer with face bridging ligands. [5] The catalyst used under the same conditions but supported in the NaX zeolite was reddish brown after a day of operation, consistent with the presence of [Ir6(CO)is]. [4, 60]... 

The confinement affects what can be formed in the cages. For example, when iridium carbonyl clusters are synthesized either on the surface of MgO or in solution, [HIr4(CO)n] is formed first, followed by [Ir8(CO)22p (which is a dimer of the tetrairidium cluster), and finally [Ir (CO)isp. In contrast, within the super-cages of NaX zeolite, [HIt4(CO),i] and then [Ir6(CO)is] are formed, but [Irg(CO)22] is not observed, presumably because it is too large to fit in the cage and therefore cannot exist there. 

The use of the cobalt triad carbonyls as catalysts continues to provide many papers for this report. Publications cover the silylformylation of 1-Hexyne catalyzed by diodium-cobalt carbonyl clusters the formation of hydroxycarbene cobalt carbonyl derivatives, the use of rhodium cluster carbonyls in the water-gas shift reaction Rh4(CO) 2> and Co3Rh(CO)] 2 catalysts for the hydrosilation of isoprene, cyclohexanone and cyclohexenone catalytic reduction of NO by CO and the carbonylation of unsaturated compounds The chemistry of iridium carbonyl cluster complexes has been extended by making use of capping reactions with HgCl2and Au(PPh3)Q... 

The dimeric complexes [M2(CO)io] (M = Mn or Re) continue to be actively studied. The presence of 17-electron free radicals, [M(CO)s], as intermediates in the thermal substitution reactions, and the chemistry of these and other 17-electron complexes are the questions being addressed. Substitution reactions of cobalt and iridium carbonyl clusters, with an attempt to define and separate electronic and steric effects, has also been an especially active area. This chemistry is discussed in Section 10.1.4. 

Of the larger clusters, the 1,2,3-triphenylphosphirene derivatives of the iridium carbonyl clusters [HIr4(CO)9L( u-PPh2)] (L = CO, PPhs) resulting from substitution, insertion and hydrometallation processes are discussed by Hitchcock et... 

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-... 

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