Iridium trichloride

Synthesis. The principal starting material for synthesis of iridium compounds is iridium trichloride hydrate [14996-61-3], IrCl3-a H2 0. Another useful material for laboratory-scale reactions is [Ir20l2(cod)2] [12112-67-3]. 

The dichlororuthenium arene dimers are conveniently prepared by refluxing ethanolic ruthenium trichloride in the appropriate cyclohexadiene [19]. The di-chloro(pentamethylcyclopentadienyl) rhodium dimer is prepared by refluxing Dewar benzene and rhodium trichloride, whilst the dichloro(pentamethylcyclo-pentadienyl)iridium dimer is prepared by reaction of the cyclopentadiene with iridium trichloride [20]. Alternatively, the complexes can be purchased from most precious-metal suppliers. It should be noted that these ruthenium, rhodium and iridium arenes are all fine, dusty, solids and are potential respiratory sensitizers. Hence, the materials should be handled with great care, especially when weighing or charging operations are being carried out. Appropriate protective clothing and air extraction facilities should be used at all times. 

An interesting method to produce water-soluble iridium nanoparticles was proposed by Chaudret and coworkers [13]. Here, aqueous soluble iridium nanoparticles were synthesized by the chemical reduction of iridium trichloride with sodium borohydride in an aqueous solution of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (Scheme 15.2). The precursor reduction was assisted by sonication, while the gradual conversion of Ir(lll) ions to lr(0) nanoparticles was followed using UV spectroscopy. The use of a molar surfactant Ir ratio of 10 proved sufficient to obtain stable aqueous soluble iridium nanoparticles however, if the molar surfactant Ir ratio used was <10 then agglomeration was observed in solution after several days. TEM analysis of the iridium nanoparticles revealed a monodispersed size distribution and a mean diameter of 1.9 0.7nm (Figure 15.2). 

Chloro - pentammino - iridium Chloride, [Ir(NH3)sCl]Cl2, is formed by the action of ammonia on iridium trichloride, iridium tetrachloride, or the ehloro-double salts. It may also be prepared from chloro-pentammino-iridium sulphate by treating it with barium chloride. Prepared by the first method it separates in wine-coloured crystals, whilst by the second method it is yellow. The red colour of the first product is due to a small quantity of iridium trichloride, which separates with the chloro-ehloride and may be removed by heating the hot aqueous solution with hydrogen sulphide. It crystallises in 1 Jorgensen, J. prakt. Ghem., 1888, 34, 394 Palmaer, Ber., 1891, 24, 2090. 

Chloro - pentammino - iridium Chloro - iridite, [Ir(NH3)5Cl]3 (IrCl6)2, is formed when the chloro-chloride is mixed with iridium trichloride. It separates as a flocculent yellow powder, and on recrystallising separates as a yellow crystalline powder. It is slowly attacked by sulphuric acid at 110° C.., and is decomposed on heating, yielding iridium, ammonium chloride, and hydrochloric acid. 

The cMor-iridiie, [Ir(NH 3)4C12] 3[IrCl 6], is precipitated from a solution of the dichloro-eliloride by iridium trichloride or potassium hexa-chloridite. It is slightly yellow in colour, sparingly soluble in water, and crystallises from hot water in fine needle-shaped crystals. 

Treatment of iridium trichloride with Bu2P(CH2)5PBu2 gives a mixture of binuclear five-coordinate iridium(III) hydrides, [Ir2H2Cl4- Bu P(CH2)5PBu 2] with 16-atom rings and a red, volatile,... 

Tricyclohexylphosphine was obtained from Strem Chemicals. Ruthenium, rhodium, and iridium trichlorides were obtained as trihydrates from Johnson, Matthey Limited. Iridium tetrachloride was obtained from Platinum Chemicals. The precursor complexes [RhCl(COD)]2 (57), [RhCl(COT)2]2 (58), [RhCl(C2H4)2]2 (59), [IrCl(COD)]2 (14), and [HIrCl2-(COD)]2 (31) were made according to the literature procedures. 

We thank NATO for a grant which allowed us to initiate this work and the Natural Sciences and Engineering Research Council of Canada for subsequent financial support. Johnson, Matthey, Ltd. generously loaned us the ruthenium, rhodium, and iridium trichlorides. 

Bernhard and coworkers [58] have addressed the discovery of ionic iridium(III) and ruthenium(II) complexes by combinatorial luminophore synthesis and screening (Scheme 5.9). Starting from iridium trichloride, cyclometalation with (hetero)arylpyridyl ligands 45 (Fig. 5.17) gives rise to the formation of binuclear iridium complexes 46. Upon complexation with bidentate N,N- or P,P-ligands 47 (Fig. 5.17), the cationic complex 48 is formed, which upon anion metathesis with hexafluorophosphate is transformed into the target complex 49. In this sequence, the step from 46 to 48 was performed in a traditional and a parallel manner, the latter leading to a library of 100 iridium and 10 ruthenium complexes. 

Although cobalt chloride can unite with other chlorides to form double salts, no well-defined series of such salts exists. Rhodium and iridium trichlorides yield hexachlor-rhodites and hexaclilor-iridites respectively, of general formulas M3RhCl8 and M3IrCl8. These are isomorphous, and are analogous in constitution to the hexachlor-osmites, M3OsCle. 

Wohler and Streicher,13 however, have prepared the dichloride by ignition of iridium trichloride in chlorine at 770° C., and thus placed its existence beyond all doubt. It is a crystalline substance, brown in colour, and insoluble alike in acids and bases. Its limits of stability axe 763° to 773° C. in an atmosphere of chlorine. Above 773° C. it dissociates into the monochloride and free chlorine. 

Iridium Trichloride, IrCl3, is most conveniently prepared2 by heating the reduced metal—obtained by precipitation from an alkali chloriridate solution with magnesium—with sodium chloride in a current of chlorine at 600° to 620° C. The reaction is complete in a few minutes. The limits of stability of the salt under these conditions lie from below 100° C. up to 763° C. Above this latter temperature it dissociates in an atmosphere of chlorine into iridium dichloride and chlorine, and at still higher temperatures (773° C.) into the monochloride. 

Iridium trichloride is also obtained by heating ammonium chloriridate or iridium tetrachloride in a current of chlorine at 440° C. and cooling the product in an atmosphere of carbon dioxide.3... 

As obtained by the foregoing methods, iridium trichloride is a crystalline substance, olive-green in colour, of density 5-30. It is insoluble in water, alkalies, and acids even concentrated sulphuric acid and aqua regia having no action upon it. It is appreciably volatile at 470° C. 

An almost anhydrous salt is obtained by heating the yellow powder, produced by the action of sulphuric acid upon alkali chloriridites, in hydrogen chloride at temperatures up to 500° C. The colour remains essentially the same, and the composition of the product approaches very closely to that of iridium trichloride, with small quantities of hydrochloric acid and water, the formula being IrCl3.mHCl.nH2O, where m and n, however, are but small fractions of unity. 

Iridium trichloride readily unites with chlorides of the alkali metals, yielding chloriridites, of general formula M3IrCl6. 

Potassium Chloriridite, K3IrCl6.3HaO, results (1) when potassium carbonate and chloriridate are heated to redness (2) on heating potassium chloriridate in hydrogen chloride at 440° C. Some insoluble iridium trichloride is simultaneously produced (3) it is also formed by reducing a suspension of chloriridate in water with sulphur dioxide, hydrogen sulphide, or nitric oxide.6 The salt crystallises in olive... 

Potassium Iodiridite, K3IrI6, is obtained in the form of small, green crystals by the action of potassium iodide on iridium trichloride. Ammonium and Sodium Iodiridite have been prepared. 

Iridium Sesquiselenide, Ir2Se3, is obtained as a black precipitate by the action of hydrogen selenide upon a hot solution of iridium trichloride.5... 

Addition of reducing agents such as ferrous sulphate or stannous chloride to solutions of the alkali chlor-iridates reduces them to double salts of iridium trichloride, namely, 3MCl.IrCls or M3IrCl6, known generally as chlor-iridites. The solution is simultaneously decolorised, and the salts crystallise out on cooling. 

Iridium trichloride is also very inert and useless as a starting material (see Section 18-G-3). 

The nature of commercial black iridium trichloride hydrate is uncertain it is quite different from RhCl3(HaO)3,37 and can vary considerably depending on how it is made and dried. At ca. 120°C for short periods, lattice water is converted at least in part to coordinated water, as shown by ir spectra. The reactivity of the substance depends on the thermal treatment and overheating gives unreactive products. Removal of water by SOCl2 treatment also changes the reactivity. 

For the reduction of 4-t-butylcyclohexanone (Dow Chem. Co.) to the axial cis-alcohol (99% pure), Eliel and Doyle used iridium trichloride (Fisher) and noted that this catalyst could be reused many times with little loss in stereoselectivity. 

IR band separation and rates of glycol cleavage, 547 Iridium trichloride, 132 Iron, 519... 

Iridium trichloride (2.0 g, 5.7 mmol) is added to a mixture of 95 % ethanol (34 ml), water (17 ml), and 1,5-cyclooctadiene (6 ml). L nder nitrogen atmosphere the solution is stirred and refluxed for 24 h, during which lime the product separates as brick-red solid. After the mixture is cooled to room temperature, the solid is filtered and washed with ice-cold methanol. The orange-red solid is dried under vacuum. Yield 1.5 g (72 %). The compound is air-stable. Soluble in chloroform and benzene, sparingly soluble in acetone, and insoluble in ether. 

Iridium trichloride trihydrate (3.52 g, 10 mmol) and triphenylphosphine (13.1 g, 50 mmol) is added to 7V,A -dimethylformamide (150 ml). The mixture is stirred and refluxed for 12 h. The red-brown solution is filtered while hot, and immediately warm methanol (300 ml) is added to the filtered solution. After the mixture is cooled in an ice bath, the yellow crystals are filtered and washed with ice-cold methanol. The crystals are dried under vacuum. Yield 6.8-7.0 g (87-90 %). The crystals are air-stable, but take up oxygen in solution. Soluble in benzene and chloroform but insoluble in alcohols. 

Eventually, however, Eliel3 found that the original procedure did not work well because the commercially available iridium trichloride is not of reproducible solubility in HC1 if insoluble, it does not work. He then found that iridium tetrachloride can be substituted for the trichloride and that it works every time. For the new procedure, see Iridium tetrachloride (this volume). 

As noted (1, 132), an early procedure of Eliel and Doyle for the reduction of 4-t-butylcyclohexanone to cis-4-f-butylcyclohexanol used iridium trichloride supplied by Fisher. This reagent is no longer available and, in a newer procedure,1 iridium tetrachloride is used as catalyst in combination with trimethyl phosphite, which undergoes hydrolysis to phosphorous acid the actual reducing agent is probably... 

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