Iridium XYLIPHOS

A good example of conventional gaseous hydrogenation methodology is the very efficient imine reduction shown in Figure 1.21 using iridium XYLIPHOS catalyst. 

Iridium nanoparticles, preparation, 12, 82 Iridium(III) O-ligated complexes, preparation, 7, 315 Iridium polyhydrides, preparation and characteristics, 7, 405 Iridium pyrrolyl derivatives, reactivity, 7, 282 Iridium tetrahydrides, characteristics, 7, 407-408 Iridium trihydrides, preparation, 7, 405 Iridium vinylidenes, synthesis and characteristics, 7, 352 Iridium xyliphos complexes, properties, 7, 442 Iridoids, via Pauson-Khand reaction, 11, 360 Iron(arene) (cyclopentadienyl) cations, preparation and reactivity, 6, 166... 

Another impressive example of a P-containing catalyst is provided by the Novartis process for the manufacture of the herbicide metalchlor. This employs an iridium complex of xyliphos, and achieves a product purity of 80% ee (12.378) [13,58]. 

Scheme 12 Iridium (iodo) and (hydrido) (iodo) complexes containing the xyliphos ligand.

Studies of imine binding to iridium employed a slightly simpler 2,6-dimethylphenyl-substituted imine rather than the 2-methyl-6-ethylphenyl-substituted imine of the commercial process. Treatment of [Ir(cod)(xyliphos)]BF4 with the imine under H2 resulted in displacement of 1,5-cyclooetadiene, oxidative addition of H2, and binding of the imine in a chelate manner. The Ir(lll) dihydride adduct, [Ir(xyliphos)(MeOCH2-C(Me)=N(2,6-Me2C6H3)H2]BF4, was shown by NMR spectroscopy to exist as a mixture of foru stereoisomers, each having m-hydride ligands, with the methyl ether function always trans to hydride and the imine N trans to P. The two major isomers, shown in Scheme 13, are formed in almost equal amounts. 

Nowadays enantioselective synthesis of the herbicide (5)-metolachlor (Dual Magnum) is, to our knowledge, one of the most successful commercial applications of asymmetric C=N bond hydrogenation. Developed by Blaser and Spindler as a key step in the technical synthesis of (5)-metolachlor, the enantioselective hydrogenation of an imine intermediate 193 proceeds in the presence of an iridium ferrocenyl-diphosphine catalyst bearing a Solvias Josiphos-type chiral ligand (/ )-Xyliphos to give... 

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