Iridium chloride complexes

The reversible complexing of carbon dioxide by bis[bis(l,2-diphe-nylphosphino)ethane]iridium(I) chloride, [Ir(dpe)2]Cl, in acetonitrile [Eq. (36)] (48) appears not to involve carboxylation of a cyanomethylir-idium(III) complex or its formation by decarboxylation of the cyanoacetate... 

Pincer complexes catalyze a variety of other organic reactions [49-51]. Hence, this work is currently being extended to other metals, and other more readily accessible PCP systems. For example, as shown in Scheme 3, lO-Rfs can be converted to the iridium hydride chloride complex 15-Rfs. Closely related dihydride complexes catalyze dehydrogenations of alkanes at high temperatures [52], However, no efforts to develop recoverable catalysts have been reported to date. 

The complexes of the composition [ Ir( t-X)(diene) 2], where X = halogen, OH, OMe (e.g. [IrCl(CO)(cod)]) appeared to be very effective catalysts for the hydrosilylation of allyl chloride by trialkoxy- and alkylalkoxy-silanes [22]. Other iridium complexes have been subsequently reported as catalysts for the synthesis of silane... 

The isomerization of the (Z)-isomer into the ( )-isomer promoted by the iridium complex explains the lack of stereospecificity of the transformation. O-Alkylated oximes and ketoximes do not react and this fact suggests that the presence of both hydrogen and a hydroxyl group is required for the success of the transformation. The authors proposed that the initial displacement of a chloride ion of the iridium complex by the oxime allows the iridium to remove both the oxygen and the hydride from the initial oxime. Swapping places of both substituents produces the amide. 

No complex was obtained on treatment of iridium (III) chloride with ethylene (67, 97, 138) or cyclo-octa-1,5-diene (45), but the ethylene complex [IrCl2(C2H4)] was reported to be formed by the action of ethanol on iridium chloride (67,138). No further examination of this complex has been reported. 

The main methods of reducing ketones to alcohols are (a) use of complex metal hydrides (b) use of alkali metals in alcohols or liquid ammonia or amines 221 (c) catalytic hydrogenation 14,217 (d) Meerwein-Ponndorf reduction.169,249 The reduction of organic compounds by complex metal hydrides, first reported in 1947,174 is a widely used technique. This chapter reviews first the main metal hydride reagents, their reactivities towards various functional groups and the conditions under which they are used to reduce ketones. The reduction of ketones by hydrides is then discussed under the headings of mechanism and stereochemistry, reduction of unsaturated ketones, and stereochemistry and selectivity of reduction of steroidal ketones. Finally reductions with the mixed hydride reagent of lithium aluminum hydride and aluminum chloride, with diborane and with iridium complexes, are briefly described. 

Iridium Complexes. The air-stable, rose-colored monohydride HIrCl2(PCy3)2, Complex 3, may be prepared directly from a commercially available chloride, or by adding HC1 to a toluene solution containing the cyclooctene dimer [IrCl(COT)2]2 and PCy3. The six-coordinate, yellow Complex 4 containing oxygen-bonded dma, v(CO) 1628 cm-1 (28), also is isolated readily. 

Methyl(chloride) pincer iridium complex, protonation, 7, 313 jV-Mcthylcobalammc, in metal biomethylation, 12, 609 Methyl coenzyme M reductase, characteristics and reactions, 1, 890... 

Ruthenium(VI)-catalysed oxidation of propane-1,2-diol, cyclohexane-1,2-diol, and propanetriol by alkaline HCF(III) exhibits a zero-order dependence on HCF(III) and first-order dependence on Ru(VI) and the rate increased with a decrease in alkali concentration. The reaction showed a Michaelis-Menten type of behaviour with respect to the reductant. A tentative mechanism has been proposed.63 In the ruthenium(in)-catalysed oxidation of sulfanilic acid by HCF(III) in alkaline medium, the proposed ruthenium(III) active species is [Ru(H20)50H]2+.64 Iridium(III) chloride-catalysed oxidation of diethylene glycol by alkaline HCF(III) is proposed to proceed through complex formation.65... 

Beck and coworkers211 have reviewed transition metal complexes of the fulminate ion, CNO, which bonds to the metal via the carbon atom. Fulminate complexes are, in general, similar to those with CN ligands. An extensive series of stable, non-explosive fulminates has been examined, including [Ir(CNO)6](AsPh4)3. [Ir(CNO)6]3- was prepared from hydrated iridium(III) chloride and Hg(CNO)2, and characterized by IR spectroscopy.21"1... 

The elimination of sulfur dioxide from arenesulfonyl chlorides is catalyzed by Vaska s complex,502 while this same iridium complex apparently catalyzes the aromatization of various 1,4-dihydro derivatives of aromatic hydrocarbons.500... 

In 1988, Tilley and coworkers first succeeded in the synthesis of a ruthenium-silene complex by the reaction of Cp Ru(PR3)Cl with a Grignard reagent, and the structure was confirmed by X-ray crystallography (Eq. 9) [10]. They later synthesized an iridium complex in a similar manner (Eq. 10) [11]. Berry synthesized a tungsten-silene complex by treatment of a tungsten-chloride complex with Mg (Eq. 11) [12]. Although reactions of transition metal-silene complexes with Mel, HX, and MeOH have been reported, little is known about their reactivities [11,12]. 

The bridging chloride ligands in these [Ir(olefin)2Cl]2 compounds are susceptible to metathesis reactions, yielding new dimeric compounds of the form [Ir(olefin)2B]2 where B represents a new bridging ligand. AUcoxides, thiolates, and carboxylates have all been employed successfully in the replacement of chloride. The complexes with B = Br, I have also been prepared, both by metathesis reactions and by direct reaction of cyclooctene or cyclooctadiene with IrBrs or Iris The olefin complexes also provide excellent starting materials for the syntheses of arene and cyclopentadienyl iridium complexes, a subject that will be discussed in the next section. 

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