Carbonyl complexes of iridium

Vaska, L. and DiLuzio, J.W. (1961) Carbonyl and hydrido-carbonyl complexes of iridium by reaction with alcohols-hydrido complexes by reaction with acid. J. Am. Chem. Soc., 83, 2784. 

The carbonyl complexes of iridium have perhaps not been as extensively studied as those of some other metals (see Carbonyl Complexes of the Transition Metals Carbonylation Processes by Homogeneous Catalysis, and Organic Synthesis using Transition Metal Carbonyl Complexes). Nevertheless some interesting findings in this area both in terms of stmeture and reactivity have been reported. 

The arena of mononuclear carbonyl complexes of iridium is dominated by Vaska s compound, [IrCl(CO)(PPh3)2] (29), and its variants. The most conunon variation found in the literature comes from replacement of the chloride ligand with other monoanionic hgands such as halides and pseudohalides. Infrared spectroscopy has been used (by examining... 

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 reactivities of several hydrido(carboxylato) complexes of iridium have been studied [58]. Complexes 88 reacted with carbon monoxide to afford carbonyl complexes, [IrCl(H)(OCOR)(CO)(PPh3)2] (98), in which the carboxylato ligands changed to monodentate ligands and exist as a mixture of isomers (Eq. 6.31). 

It has been suggested (162) that there exists only negligible 7r-backbonding in [AuCl(CO>], and a number of displacement reactions have been described (162, 163). Vibrational and NMR spectroscopic studies have been made of this complex (164), and the results have been compared with those for carbonyl complexes of palladium, platinum, rhodium, and iridium. 

If ethylene is present during the carbonylation of methanol catalyzed by IrCl4, once again with Mel as promoter, methyl propionate is formed.416 The reaction depends on the presence of iridium hydride species in solution, and a rhodium analogue of the reaction exists. The full details of the mechanism are not known but the basic steps are shown in Scheme 34. The intermediates are all believed to be complexes of iridium(IIl). 

These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

The chemistry of the metal carbonyl hydrides and metal carbonylates remained the principal research topic for Hieber until the 1960s. He mentioned in his account [25], that it was a particular pleasure for him that in his laboratory the first hydrido carbonyl complexes of the manganese group, HMn(CO)5 and HRe(CO)5, were prepared by careful addition of concentrated phosphoric acid to solid samples of the sodium salts of the [M(CO)5] anions, giving the highly volatile hydrido derivatives in nearly quantitative yield [45, 46]. In contrast to HCo(CO)4 and its rhodium and iridium analogues, the pentacarbonyl hydrido compounds of manganese and rhenium are thermally remarkably stable, and in... 

Several mononuclear carbonyl complexes may be synthesized with iridium(I), but most intriguing of those are the binary carbonyls. [Ir(CO)4] (46) may be synthesized by the reduction of Ir4(CO)i2 (45) with sodium under an atmosphere of carbon monoxide. More vigorous reduction of (45) with sodium can also yield the very reactive trianion, [Ir(CO)3] (47) (equation 13). These anions may then be used for the synthesis of other mono and polynuclear (see Polynuclear Complexes) carbonyl compounds of iridium. 

Chloro- and other halo- containing carbonyl compounds of iridium may also be synthesized under mild conditions. Unlike [Rh(CO)2Cl]2, [Ir(CO)2Cl] is not obtainable by the direct reaction of an iridium chloride solution with CO. Instead, [Ir(CO)2Cl2]n (48) is obtained in low yields by reaction between IrCl3-H20 and carbon monoxide. The predominant mononuclear compound obtained upon carbonylation of iridium chloride salts is the tricarbonyl [Ir(CO)3Cl] (49), which appears in the sohd state to be a polymeric array consisting of stacking square-planar Ir(CO)3Cl units with short fr-Ir bonds. Even though [Ir(CO)3Cl] is polymeric, it is sublimable and is stiU a convenient source of iridium(I) containing carbon monoxide. (49) will react with a number of nucleophiles to form mononuclear iridium carbonyl complexes. 

Perhaps as a consequence of Johnson s failure, 20 years elapsed before Sessler and coworkers reported that certain p -type complexes could in fact be formed with heterosapphyrins.These latter workers were clearly inspired by their earlier successful syntheses of p -type rhodium(I) and iridium(I) carbonyl complexes of pentaazasapphyrins 5.21 and 5.23 vide supra). Thus, in a first experiment, they treated the monothiasapphyrin 5.71 with Rli2(CO)4Cl2 (Scheme 5.5.4). This afforded the structurally characterized [Rh(CO)2]2 monothiasapphyrin complex 5.100 (Figure 5.5.6). Subsequently, they prepared the bis-iridium complex 5.101 of the mono-selenasapphyrin 5.73. This complex was also characterized by X-ray diffraction analysis. The resulting structure then served to confirm the expected sitting-a-top binding mode (Figure 5.5.7). 

Carbonyl complexes of rhodium, ruthenium, osmium, iridium, and platinum, in the presence of H2O and a weak base (e.g., trimethylamine), act as catalysts for the conversion of propene to a mixture of butanol and methylpropanal with the exception of the platinum system, these catalysts are considerably more active than Fe(CO)s as reported by Reppe. Under the same conditions, but in the absence of olefin, the carbonyls act as catalysts for the conversion of CO and H2O to CO2 and H2. The metal carbonyls, together with Fe(CO)s, in the presence of H2O, CO, and a weak base such as McsN, serve as catalysts for the conversion of nitrobenzene, dinitrobenzene, and 2,4- and 2,6-di-nitrotoluene to the corresponding aminobenzene derivatives. 

Column structures have also been determined for carbonyl complexes of rhodium, iridium, and platinum. For platinum complexes of the formula [Pt3(CO)6] , the maximum value of n probably does not reach more than 20 (Figure 3.26) and therefore these carbonyls do not show anisotropy of conductivity. Various Ir(I) and Rh(I) complexes possessing column structures are known [IrX(CO)3] (X = C1, Br, I), [IrCl,o7(CO)2.93], [Ir(acac(CO)2], Ho.38lrCl2(CO)2(H20)2.9, Ko.58[IrCl2(CO)2], and... 

A problem is that the Pauson-Khand reaction uses two equivalents of cobalt. More efficient versions, many of them catalytic, using other metals have been developed. These include carbonyl complexes of titanium, molybdenum, tungsten (Scheme 7.15), rhodium and ruthenium (Scheme 7.16). Rhodium, iridium and iron (Scheme 7.17) have also been used with two alkynes to give cyclopentadienones, often as complexes 7.59. A version of the Pauson-Khand reaction employing a nickel catalyst and an isonitrile in place of CO has been developed. The product is an imine, which can be hydrolysed to a cyclopentenone. 

Monomethoxycarbonyl ruthenium complexes have been obtained by reaction of mthenium(O) clusters with methoxide anion in methanol [67]. Hydroxyl-carbonyl complexes of platinum were prepared by nucleophilic attack of OH on a carbonyl ligand [68] or by insertion of CO into a hydroxy platinum complex [69]. Hydroxycarbonyl-bpy complexes of ruthenium [21], iridium and rhodium [21] have been proposed as... 

P. Royo and F. Terreras, Reactions of bromo- and hydroxy-bis(pentafluorophenyl)thallium-(ill) with some carbonyl complexes of rhodium(i) and iridium(i). Chem. Abs., 1978, 89, 109916. 

Two distinct classes of promoters have been identified for the reaction simple iodide complexes of zinc, cadmium, mercury, indium and gallium, and carbonyl complexes of tungsten, rhenium, ruthenium and osmium. The promoters exhibit a unique synergy with iodide salts, such as hthium iodide, under low water conditions. Both main group and transition metal salts can influence the equilibria of the iodide species involved. A rate maximum exists under low water conditions and optimization of the process parameters gives acetic acid with a selectivity in excess of 99% based upon methanol. IR spectroscopic studies have shown that the salts abstract iodide from the ionic methyl iridium species and that in the resulting neutral species the migration is 800 times faster [127]. 

Organometallic Compounds. The predominant oxidation states of indium in organometalUcs are +1 and +3. Iridium forms mononuclear and polynuclear carbonyl complexes including [IrCl(P(C3H3)3)2(CO)2] [14871-41-1], [Ir2014(00)2] [12703-90-1], [Ir4(CO)22] [18827-81 -1], and the conducting, polymeric [IrCl(CO)3] [32594-40-4]. Isonitnle and carbene complexes are also known. 

Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

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