Hydride complexes iridium

H, Hydride, iridium complex, 26 117, 119, 120. 123-125. 202 iron complex. 26 244 iron-tungsten complex. 26 336-340... 

By a suitable choice of conditions (metal hydrides or metal/ammonia) ketones at the 1-, 2-, 4-, 6-, 7-, 11-, 12- and 20-positions in 5a-H steroids can be reduced to give each of the possible epimeric alcohols in reasonable yield. Hov/ever, the 3- and 17-ketones are normally reduced to give predominantly their -(equatorial) alcohols. Use of an iridium complex as catalyst leads to a high yield of 3a-alcohol, but the 17a-ol still remains elusive by direct reduction. 

Iridium(III) hydride forms complexes with DIOP, BDPP (2,4-bis(diphenyl-phosphino)pentane), NORPHOS, and BINAP ligands to produce amines in 11 -80% ee.679 Similar modest results are obtained in the reduction of N-arylketimines with an iridium(HI) complex with (2S,3 S) -C HIRA PHOS as the chiral ligand.680 The indium complexes with chiral phosphinodihydrooxazoles catalyze the enantioselective hydrogenation of imines in supercritical carbon dioxide with up to 80% ee, but generally lower ee values are observed in... 

Structural studies on the nature of the organometallic intermediates following chelation-assisted CH additions of pincer iridium complexes have been carried out. The product was found to have an unexpected /ram-disposition of the hydride with respect to the metallated aromatic group. This is not the expected direct outcome of a chelation-assisted reaction since coordination of oxygen to iridium prior to C-H activation would be expected to afford the m-isorner (Equation (97)). 

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 reaction may proceed as follows (see Scheme 10.4). An acrylate 51 coordinates to the iridium-hydride complex generated in situ, and then inserts into the Ir-H bond to form a o-lr complex 55 the coordination and insertion of another acrylate to 55 leads to an iridium complex, 56. A (5-hydride elimina-hon of the iridium-hydride from the intermediate 56, followed by isomerization of the double bond to a more stable internal aUcene, results in a head-to-tail dimer. 

Abstraction of one of the metal-bound hydrides from complex 5a provides the cationic iridium(lll) complex 28, which is an efficient precatalyst for alkyl halide reduction in the presence of EtsSiH (Equation 12.11) [31]. 

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. 

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. 

This product was characterized by its NMR spectrum and also by reaction with HC1 followed by BF3/methanol to yield methylcyanoacetate ester. The reaction occurs readily, and in the absence of detectable amounts of the oxidative addition product of acetonitrile with the iridium complex, [Hlr-(depe)2CH2CN]+. In contrast, neither Rh(depe)2Cl nor Rh(dmpe)2Cl (dmpe = Me2PCH2CH2PMe2) react with C02 in acetonitrile, though Rh(dmpe)2Cl does react with C02 in nitromethane to form the analogous nitro-acetate hydride complex, (57). 

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