Iridium carbonyl coordination

Iridium nanopartides also catalyze the hydrogenation of benzyhnethylketone, with high selectivity in reduction of the aromatic ring (92% selectivity in saturated ketone, 8% in saturated alcohol at 97% benzylmethylketone conversion). This preferential coordination of the aromatic ring can be attributed to steric effects that make carbonyl coordination difficult. Therefore, metallic iridium nanoparticles prepared in ILs may serve as active catalysts for the hydrogenation of carbonyl compounds in both solventless and biphasic conditions. 

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... 

This chapter will not deal with iridium complexes in which the coordination chemistry of the iridium-carbon bond is implicated inasmuch as Leigh and Richards have very recently (1982) provided an excellent detailed review on such compoimds organoiridium and iridium carbonyl complexes were also previously reviewed. Iridium complex chemistry has been reviewed (1980) along with rhodium," and in annual reviews. Additionally, iridium complexes have been treated in Comprehensive Inorganic Chemistry . ... 

Under the reaction conditions the starting complexes react with CO with displacement of coordinated diolefin to form iridium carbonyl compounds, which are the active catalytic species for the WGSR. The catalytic activity slightly increases when bidentate ligands are used and appears to be rather sensitive to temperature. 

The stereospecific polymerization of alkenes is catalyzed by coordination compounds such as Ziegler-Natta catalysts, which are heterogeneous TiCl —AI alkyl complexes. Cobalt carbonyl is a catalyst for the polymerization of monoepoxides several rhodium and iridium coordination compounds... 

Cases of the S-coordinated rhodium and iridium are quite scarce. To complete the picture, we next consider the possibilities of S-coordination using complicated derivatives of thiophene. 2,5-[Bis(2-diphenylphosphino)ethyl]thiophene is known to contain three potential donor sites, two phosphorus atoms and the sulfur heteroatom, the latter being a rather nucleophilic center (93IC5652). A more typical situation is coordination via the phosphorus sites. It is also observed in the product of the reaction of 2,5-bis[3-(diphenylphosphino)propyl]thiophene (L) with the species obtained after treatment of [(cod)Rh(acac)] with perchloric acid (95IC365). Carbonylation of [Rh(cod)L][C104]) thus prepared yields 237. Decarbonylation of 237 gives a mixture of 238 and the S-coordinated species 239. Complete decarbonylation gives 240, where the heterocycle is -coordinated. The cycle of carbonylation decarbonylation is reversible. 

The Ti coordination via the carbocycle prevails for indole and carbazole, although the species were also found in organomanganese and -iridium chemistry. Osmium carbonyls tend to produce the species with the bridging indole function. Some illustrations of the ti N) coordination exist. 

Two other publications on Ir (73 keV) Mossbauer spectroscopy of complex compounds of iridium have been reported by Williams et al. [291,292]. In their first article [291], they have shown that the additive model suggested by Bancroft [293] does not account satisfactorily for the partial isomer shift and partial quadrupole splitting in Ir(lll) complexes. Their second article [292] deals with four-coordinate formally lr(l) complexes. They observed, like other authors on similar low-valent iridium compounds [284], only small differences in the isomer shifts, which they attributed to the interaction between the metal-ligand bonds leading to compensation effects. Their interpretation is supported by changes in the NMR data of the phosphine ligands and in the frequency of the carbonyl stretching vibration. 

A wide range of carbon, nitrogen, and oxygen nucleophiles react with allylic esters in the presence of iridium catalysts to form branched allylic substitution products. The bulk of the recent literature on iridium-catalyzed allylic substitution has focused on catalysts derived from [Ir(COD)Cl]2 and phosphoramidite ligands. These complexes catalyze the formation of enantiomerically enriched allylic amines, allylic ethers, and (3-branched y-8 unsaturated carbonyl compounds. The latest generation and most commonly used of these catalysts (Scheme 1) consists of a cyclometalated iridium-phosphoramidite core chelated by 1,5-cyclooctadiene. A fifth coordination site is occupied in catalyst precursors by an additional -phosphoramidite or ethylene. The phosphoramidite that is used to generate the metalacyclic core typically contains one BlNOLate and one bis-arylethylamino group on phosphorus. 

Ir(OH)(cod)]2 catalyzed a formal [3+2] cycloaddition of 2-formylphenylboronic acid and 1,3-dienes (Scheme 11.41) [50]. The transmetaUation of boronic acid with iridium would yield aryliridium, where the carbonyl group coordinates to the metal. An electrophihc attack of the diene terminus to formyl carbon would then... 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

There are marked differences between the carbonyl cations of cobalt and its congeners, rhodium and iridium. For instance, the heavier elements form square-planar carbonyl cations as well as higher coordinate complexes. This is paralleled by the isocyanide cations thus cobalt forms [Co(CNR)5]+ cations (191), whereas rhodium and iridium form [M(CNR)4]+ cations (191, 192, 194). 

An important feature of the present reaction is the chemoselective addition of activated nitriles to the CN triple bonds of nitriles in the presence of carbonyl groups, because of the strong coordination ability of nitriles toward metals. The iridium-catalyzed addition of ethyl cyanoacetate to 4-acetylbenzonitrile (30) gives ethyl (Z)-3-(4-acetylphenyl)-3-amino-2-cyano-2-propenoate (31, 59%) chemoselec-tively, while the same reaction promoted by a conventional base such as AcONH4 and NaOH gives ethyl 2-cyano-3-(4-cyanophenyl)-2-butenoate (32) ( Z= 55 45) [20]. 

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