Iridium hydroxo

Belyaev, A.V., Venediktov, A.B., Fedotov, M.A., and Khranenko, S.P. (1985) Koord Khim., 11, 794 cited in Term, W.J. HI, (2007) CH activation and catalysis with iridium hydroxo and methoxy complexes and related chemistry. PhD thesis. University of Southern California, p. 108. 

Burford RJ, Piers WE, Ess DH, Parvez M. Reversible interconversion between monomeric iridium hydroxo and a dinuclear iridium (1-oxo complex. J Am Chem Soc. 2014 136 3256-3263. 

Merola reported the preparation of hydrido(carboxylato)iridium(lll) complexes, mer-[lrCl(0C(0)R)(H)(PMe3)3] (90) (R = Ph, Me), by oxidative addition of acetic acid or benzoic acid to [Ir(cod)(PMe3)3]Cl (67) [46]. The structure of 90 (R = Ph) in which the carboxylato ligand coordinates as an T -ligand, was confirmed by X-ray analysis. The reaction of 67 with salicylic acid yielded the product 91, which resulted from activation of the O-H bond of the carboxylato but not of the hydroxo group (Scheme 6-13). 

We also found that iridium hydrido(hydroxo) complexes like [ lrH(diphos-phine) 2( x-OH)2( x-Cl)]Cl (43) and the precursor diphosphine complexes 42 can also catalyze the hydration of nitriles. In the presence of catalyhc amounts of these complexes, heating acetonitrile and benzonitrile with excess water at 120°C gave the corresponding amides [47, 50]. 

The ion Rh(H20) + is well characterized in aqueous solution from H2 0 exchange studies. The hydroxy species is more labile. There is an absence of pressure dependency measurements, but an mechanism is favored. 2-22 The formation and cleavage of some hydroxo-bridged rhodium(lll) and iridium(lll) eomplexes have been studied. Kinetic studies of oxidation by Rh(lll) indieate that RhOH2+ is the sole oxidant. 22 Kinetic data for substitution in Rh(N)5H20 + are sparse. An mechanism is favored for water exchange... 

HYDROXO-BRIDGED COMPLEXES OF CHROMIUM(III), COBALT(III), RHODIUM(III), AND IRIDIUM(III)... 

Fig. 1. The di-, tri-, and tetranuclear structures observed in X-ray crystal structures of hydroxo-bridged oligomers of cobalt(III), rhodium(III), iridium(III), or chromium(III) structures 4b, 7b, and 7c have never been observed, but the last two have been mentioned as possible structures for two of the known isomers of Cj4(OH)66+...

There are several examples of well-characterized tri- and tetranu-clear hydroxo-bridged complexes of chromium(III) and cobalt(III). Penta- and hexanuclear aqua chromium(III) complexes have been prepared in solution, but their structure and properties are unknown. Oligomers of nuclearity higher than four have not been reported for cobalt(IIl), with the exception of some hetero-bridged heteronuclear species (193, 194). There appear to be no reports of rhodium(III) or iridium(III) complexes of nuclearity higher than two. 

The cleavage of polynuclear hydroxo-bridged rhodium(III) and iridium(III) complexes into the corresponding mononuclear fragments has been reported in only a few instances, but the well-established tendency of mononuclear complexes of these metal ions to undergo substitution reactions with retention of configuration indicates the possibility of analytical and synthetic applications such as described above for chromium (III). 

The activation parameters for the ethylenediamine complexes of rhodium(III) and iridium(III) are also in keeping with an essentially dissociative mechanism. The observation that AHt(k-t) is larger than AHt(k 2) for iridium(III) has been rationalized in terms of stabilization of the aquahydroxo species by intramolecular hydrogen bond formation. Similarly, the observation for the rhodium(III) system that AHl(k ) < AHt(k-2) for ammonia, whereas A// (, ) AHt(k 2) for ethylenediamine may, in part, by rationalized in terms of the observed differences in the degree of intramolecular hydrogen bond stabilization of the aqua hydroxo species in the two systems [ZCH(en) > J h(NH3) see Table XXI]. 

Structural, thermodynamic, and kinetic studies have shown that hydroxo-bridged polynuclear complexes of (diromium(III), cobalt(III), rhodium(III), and iridium(III) have many general features in common. Structurally, the four metal ions exhibit an almost identical pattern, and in particular the occurrence of many well-characterized oligomers... 

Hydroxo-Bridged Complexes of Chromium(III), Cobalt(III), Rhodium(III), and Iridium(III) Johan Springborg... 

The Iridium Carbonyl Iridium (III)zeolite could be obtained by conventional ion-exchange of sodium ions by Ir(NHj)cCl + complex in aqueous solution and subsequent activation in flowing oxygen at temperatures not exceeding 250 C. Then Ir(III)-hydroxo species were obtained (8). This latter may undergo subsequent carbonylation at low or atmospheric pressure in the temperature range 150-170°C. 

Ir(OH)3] precipitates as a result of the reaction between K3[IrCl6] and KOH under a C02 atmosphere. The product is usually colloidal, and ranges in colour from yellow-green to blue-black. Iridium(III) hydroxo species (including [Ir(OH)6]3 and [Ir(0H)5(H20)]2 are thought to be present in alkaline solutions of lr203.310... 

The hydroxide ion is a well-established bridging ligand, and hydroxo-bridged complexes of iridium(III) have been reviewed. Among the dinuclear iridium(I) complexes that have structures supported by 0H ligands is [Cp Ir(/u.-0H)3lrCp ]+, and closely related to this is (cod)Ir(/u.-OPh)2lr(cod). The presence of the three OH... 

Hydroxo-Bridged Complexes of ChromiumdIIl, Cobalt(II), Rhodium(IIl), and Iridium(lII)... 

Similarly, reference is made to another more recent review (41) of the author s contributions to the chemistry of rhodium, iridium, rhenium, osmium and ruthenium alkoxo, and hydroxo complexes, following a similar earlier publication (40) on the alkoxo derivatives of platinum metals. Reference may also be made to the first X-ray structural study (265, 266) of a siloxy derivative, [(cod)Rh(/i-OSiMe)3]2. 

Oxidative addition of water to iridium(I) has also been known [185], In this reaction, reaction of [Ir(PMe3)4]+[PF6] with water in THF gave a rare mononuclear hydroxo complex c/5-[Ir(H)(OH)(PMe3)4] [PF6] in high yield. A neutral iridium(I) complex IrCl(dmso)3 is recently reported to show high activity toward oxidative addition of water [186],... 

The only isolated metal-hydroxo complex that has been shown to react with olefins to form products from transfer of hydroxide is Cp Ir(PMe3)(Ph)(OH). However, this formal insertion process does not occur by a migratory insertion mechanism. Instead, the reaction with olefin is catalyzed by trace amounts of Cp Ir(PMe3)(Ph)(OTf) and appears to involve replacement of tiiflate with ethylene to generate the cationic [Cp Ir(PMe3)(Ph)(CjH )], which undergoes attack by the separate iridium hydroxido complex, as shown in Scheme 9.11. 

The search for earth abundant substitutes for ruthenium and iridium is a fundamental target towards WOC sustainability and hydrogen economy. Recently, an increasing interest grew towards cobalt-based electrode coatings and molecular cobalt complexes to promote water oxidation. Cobalt oxide and related aquo or hydroxo complexes have been known as water oxidation catalysts since the early SOs. ... 

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