Hydrogen activating iridium

The catalytic lifetime was studied by reusing the aqueous phase for three successive hydrogenation runs of toluene, anisole and cresol. Similar turnover activities were observed during the successive runs. These results show the good stability of the catalytically active iridium suspension as previously described with rhodium nanoparticles. 

Scheme 39.6 Enantiomeric hydrogenation of imine 22 in an IL/ scC02 biphasic system using an in-situ-activated iridium catalyst.

Scheme 1 A highly active iridium catalyst for transfer hydrogenation...

Carbon-hydrogen activation on rhodium and iridium is well documented. The complexes Cp Rh(PMe)3(H)2 Cp Ir(PMe3)H2, and Cp Ir(CO)2 provide the best examples of C-H activation. 

Two 16-electron intermediates dominate the carbon-hydrogen activation research on iridium centers. The complex Cp Ir(CO), studied by Graham and coworkers, and the complex Cp Ir(PMe3), studied by Bergman and coworkers, activate saturated carbon-hydrogen bonds. The 16-electron carbonyl complex was generated by photolysis of Cp Ir(CO)2. ... 

A few other iridium complexes activate carbon-hydrogen bonds Cp Ir2Cl2(/i-H)2 in the presence of PPha and benzene-60% aqueous KOH-[PhCH2NEta] Cl produces a product involving carbon-phosphorus and carbon-hydrogen activation . 

Certain neutral complexes of bivalent ruthenium (1) and osmium (1,2), and tervalent and univalent iridium (3,4) have been discovered to activate molecular hydrogen in solution at normal conditions. These reactions are of considerable interest because they permit comparison of hydrogen-activating characteristics of metal complexes with different coordination numbers and formal oxidation states, two properties which are believed to represent important factors in determining catalytic activation of hydrogen. 

Iridium is another transition metal of group 9 in the periodic table. Therefore it attracts special attention in particular in comparison with the corresponding rhodium catalysts [1, 2]. In general, in all investigations a lowered activity of Ir catalysts was stated. Already in early attempts the high hydrogenation activity of Ir catalysts was complained about [3]. 

Keywords Alcohols Amides Amines Carbon dioxide Catalysis Dehydrogenative coupling Esters Hydrogen Imines Iridium Metal-ligand cooperation O-H activation Pincer complexes PNN PNP Ruthenium... 

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