Iridium-catalyzed hydrogenation asymmetric

One of the emerging applications of 4,5-dihydroimidazole-based compounds is as chiral auxiliaries in metal complexes used for asymmetric synthesis for example, 457 in ruthenium-catalyzed DielsAlder reactions <2001 J(P 1)1500, 2006JOM(691)3445> 458 in diethylzinc addition to aldehydes <2003SL102> 459 in asymmetric intramolecular Heck reactions <20030L595> and 460 in ruthenium-catalyzed epoxidation <2005OL3393> and iridium-catalyzed hydrogenation of imines <2004TA3365>. 

Kallstrom, K. Hedberg, C. Brandt, P. Bayer, A. Andersson, P. G. Rationally designed ligands for asymmetric iridium-catalyzed hydrogenation of olefins. /. Am. Chem. Soc. 2004,126,14308-14309. 

In spite of the overwhelming number of publications dedicated to the development of chiral bisphosphines [7], the development of the corresponding NHCP analogs has attracted much less attention. Partially, this is due to the fact that only one highly selective system has been developed to this point [27]. The majority of the newly developed ligands have been tested in asymmetric rhodium- and iridium-catalyzed hydrogenations (Figure 10.2) [27a, 28]. 

Figure 10.2 Chiral NHCP metal complexes used in asymmetric rhodium- and iridium-catalyzed hydrogenations (the highest selectivity exhibited for a certain type of substrate...

In situ-generated iridium complexes containing bulky 3,3 -substituted H8-phosphoroamidites 20 as ligands catalyzed the asymmetric hydrogenation of... 

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands 33... 

Virtually every iridium catalyst of the formula [Ir(L )(COD)] [X] for asymmetric olefin hydrogenation that has appeared after the initial counterion effect studies was based on BArp as the preferred anion [14]. The anion effect is broadly applicable in iridium-catalyzed reductions as experiments with a direct analog of the Crabtree catalyst of the formula [Ir(pyridine)(Cy3P)(COD)]BArp indicates (Fig. 2). 

Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands 55 Table 4 Asymmetric hydrogenation of a-substltuted a,(3-unsaturated amides with ligand 24... 

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