Iridium tetrachloride

A mixture of the ketone (4.62 g), iridium tetrachloride (1.23 g), trimethyl phosphite (15 ml), propan-2-oI (200 ml) and water (50 ml) is heated under reflux for 21 hr. Much of the solvent is then distilled off ca. 215 ml) and the organic products remaining are isolated by extraction with ether. If reduction is essentially complete, the product at this stage may be sufficiently pure for most preparative purposes. Pure components can be obtained by chromatography over alumina, a representative experiment (on the above scale) gives unchanged ketone (0.13 g), cw-alcohol (4.36 g) and tmns-2 co o (0.16 g) (eluted in this order by pentane, and then by pentane containing ether). 

To a solution of 1.0 g (0.003 mole) of iridium tetrachloride in 0.5 ml of concentrated hydrochloric acid is added 15 ml of trimethylphosphite. This solution is added to a solution of 7.7 g (0.05 mole) of 4-/-butylcyclohexanone in 160 ml of isopropanol in a 500-ml flask equipped with a reflux condenser. The solution is refluxed for 48 hours, then cooled, and the isopropanol is removed on a rotary evaporator. The residue is diluted with 65 ml of water and extracted four times with 40-ml portions of ether. The extracts are dried with anhydrous magnesium sulfate, filtered, and the ether is removed on the rotary evaporator. The white solid residue is recrystallized from 60 % aqueous ethanol affording cis alcohol of greater than 99% purity, mp 82-83.5°. 

Iridium tetrachloride Chemicals Procurement Laboratories, College Point, N.Y Goldsmith Chemical and Metal Corporation, Evanston, 111. 

Iridium tetrachloride, in modified Meerwein-Ponndorf reduction, 50, 13... 

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. 

Iodoprogesterone, 448 Introduction of double bonds, 265 Iridium complex, 91, 101 Iridium tetrachloride, 101... 

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. 

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... 

Several of these aquo salts have been isolated.16 Iridium Tetrachloride, IrCl4, has been prepared in a variety of ways, notably ... 

Iridium tetrachloride may also be obtained by direct union of the elements,1 the chlorine being introduced under high pressure. Thus at 60° C., in the presence of liquid chlorine, under a pressure of about 20 atmospheres, iridium was gradually converted into the tetrachloride in five days whilst a year was required at 15° C. under a pressure of 8 atmospheres. 

Iridium tetrachloride has been obtained crystallised in the form of tetrahedra,2 but in this form it contains water, which is expelled, together with hydrogen chloride, on heating. At higher temperatures metallic iridium alone is left as residue. 

Iridium tetrachloride is readily reduced to the trichloride. Its aqueous solution, on dilution, yields hypoehlorous acid and the trichloride. On boiling, a precipitate of oxychloride is obtained. Addition of excess of alkali precipitates part of the iridium as dioxide, the remainder staying in solution as sesquioxide, being precipitated only upon neutralisation of the alkali. Addition of alcohol to the alkaline solution precipitates metallic iridium, aldehydes and alkali formates being simultaneously produced. Reducing agents, such as stannous chloride, sulphur dioxide, nitric oxide, hydrogen sulphide, ferrous sulphate, etc, convert the tetrachloride into trichloride. 

Iridium tetrachloride unites with chlorides of the alkali metals to form chloriridates, of which the most important are ... 

Sodium Chloriridate, Na2IrCl6.6H20, is conveniently prepared in a similar manner to the potassium salt. It also results when solutions of iridium tetrachloride and sodium chloride are mixed and concentrated. The salt crystallises in triclinic prisms 3 isomorphous with the corresponding platinum salt, Na2PtCl6.6H20. 

Ammonium Chloriridate, (NH4)2IrCI8, is readily produced by decomposing the sodium salt with ammonium chloride in aqueous solution.1 It crystallises in regular octahedra, reddish black in colour, and but slightly soluble in cold water, although appreciably soluble in hot. It does not dissolve in solutions of ammonium or potassium chloride. When evaporated with aqua regia, the ammonia is expelled, iridium tetrachloride remaining. Heated to 440° C. in a current of chlorine the tetrachloride is first formed and decomposes into the anhydrous trichloride. 

Rubidium Chloriridate, Bb2IrCl6, is obtained by mixing a solution of iridium tetrachloride with excess of rubidium chloride, whereby a deep red, crystalline precipitate is obtained. The salt dissolves slightly in hot water to yield an orange-red solution. ... 

Hydrated Iridium Dioxide, Ir02.2H20, results (1) when excess of caustic alkali is added to a solution of chloriridate or of iridium tetrachloride. Any sesquioxide simultaneously produced passes into solution, but is converted into the dioxide by boiling in air, by addition of hydrogen peroxide, or by passing a current of oxgen through the solution. 

To a solution of 4.0 g. (0.012 mole) of iridium tetrachloride (Note 1) in 4.5 ml. of concentrated hydrochloric acid is added ISO ml. of water followed by 50 ml. of trimethyl phosphite (Note 2). This solution is added to a solution of 30.8 g. (0.20 mole) of 4-t-butylcyclohexanone (Note 3) in 635 ml. of 2-propanol contained in a 2-1. flask equipped with a reflux condenser. The solution is heated at reflux for 48 hours (Note 4). At the end of this time the 2-propanol is removed on a rotary evaporator at reduced pressure, and the remaining solution is diluted with 250 ml. of water and extracted with four 150-ml. portions of el her. The ether solution is washed with two 100-ml. portions of wafer which are combined with the aqueous residue (Note 5). Tin ether extract is dried over magnesium sulfate or potassium carbonate and then concentrated on a rotary evaporator at reduced pressure to obtain cis-4-t-butylcyclohexano] as a w hite solid (2ft—31 g. 93-99%). Analysis of the crude product by glpc demonstrates it to contain 95.8-96.2 % eis-alcohol and 12 3 8 % of the trans isomer with essentially no ketone remaining (Note 6). Itecrystallization from 40% aqueous ethanol an nrds greater than 99% pure ri.s-alcohol, m.p. 82-83.5° after Hiihlimulion2 (Nole 7). 

The iridium catalyst used in this preparation may be regenerated by reducing the volume of the aqueous residue to about 200 ml. at diminished pressure. This solution is then used instead of the iridium tetrachloride and water called for in the procedure. 

The present6 procedure employs a readily available starting material and produces essentially pure cis isomer in good yield with little purification necessary. In view of the fact that the catalyst may be reused several times with little loss in stereoselectivity, the expense of the iridium tetrachloride is not a serious impediment. 

Iridium tetrachloride, treated with excess of alkali hydroxides, gives n green solution with a small black precipitate uf the double chloride. Ou heating the solution first becomes rod, then deep a /.urc blue, due to the precipitation of Ir(OH),. This test, distinguishes iridium from platinum. 

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). 

Iridium tetrachloride, IrCl4 [1, 519, before Iron], Mol. wt. 334.03, brownish black hygroscopic mass. Supplier Platinum Chemicals, Box 565, Asbury Park, N.J. 07712. 

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... 

Hydrogenation catalysts Dichlorotris(triphenylphosphine)ruthenium. Iridium. Iridium tetrachloride-Triethyl phosphite. Iridium-BaSO, or CaC04. Lithium aluminum hydride. Nickel catalyst, Raney. Palladium hydroxide. Platinum catalysts. Potassium hydride. Trihydridobis(triphenyIphosphine)iridium (III). 

Reducing agents Aluminum hydride. Bis-3-methyl-2-butylborane. n-Butyllithium-Pyridine. Calcium borohydride. Chloroiridic acid. Chromous acetate. Chromous chloride. Chromous sulfate. Copper chromite. Diborane. Diborane-Boron trifluoride. Diborane-Sodium borohydride. Diethyl phosphonate. Diimide. Diisobutylaluminum hydride. Dimethyl sulfide. Hexamethylphosphorous triamide. Iridium tetrachloride. Lead. Lithium alkyla-mines. Lithium aluminum hydride. Lithium aluminum hydride-Aluminum chloride. Lithium-Ammonia. Lithium diisobutylmethylaluminum hydride. Lithium-Diphenyl. Lithium ethylenediamine. Lithium-Hexamethylphosphoric triamide. Lithium hydride. Lithium triethoxyaluminum hydride. Lithium tri-/-butoxyaluminum hydride. Nickel-aluminum alloy. Pyridine-n-Butyllithium. Sodium amalgam. Sodium-Ammonia. Sodium borohydride. Sodium borohydride-BFs, see DDQ. Sodium dihydrobis-(2-methoxyethoxy) aluminate. Sodium hydrosulflte. Sodium telluride. Stannous chloride. Tin-HBr. Tri-n-butyltin hydride. Trimethyl phosphite, see Dinitrogen tetroxide. 

Iridium tetrachloride, 2,228-229. Additional supplier Alfa Inorganics. 

Reduction of cyclohexanones. Henbest and Mitchell2 have described in detail their method for reduction of substituted cyclohexanones predominantly to axial alcohols using a soluble iridium-phosphite catalyst prepared in situ from iridium tetrachloride and phosphorous acid (or an easily hydrolyzed ester of this acid). Often 96% or more of the axial alcohol is obtained in this way. 

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