Rhodium-phosphine catalysts chiral

Some general reviews on hydrogenation using transition metal complexes that have appeared within the last five years are listed (4-7), as well as general reviews on asymmetric hydrogenation (8-10) and some dealing specifically with chiral rhodium-phosphine catalysts (11-13). The topic of catalysis by supported transition metal complexes has also been well reviewed (6, 14-29), and reviews on molecular metal cluster systems, that include aspects of catalytic hydrogenations, have appeared (30-34). 

Rhodium-phosphine complexes are usually active and effective in the asymmetric hydrosilylation of olefins, ketones, and aldehydes, allowing for the virtual synthesis of optically active alkoxysilanes and organic compounds of high purity. Chiral rhodium-phosphine catalysts predominate in the hydrosilylation of pro-chiral ketones. This subject has been comprehensively reviewed by several authors who have made major contributions to this field [52-54]. A mechanism for the hydrosilylation of carbonyl groups involving the introduction of asymmetry is shown in Scheme 3 [55]. 

The review of Morrison et al. (10) traces the development of the use of rhodium-chiral phosphine catalysts to about the end of 1974. This field was initiated by the suggested incorporation (216) of chiral phosphines, instead of triphenylphosphine, into the so-called Wilkinson catalyst, RhCl(PPh3)3 (Section II,A), or into closely related systems. Horner s group (217, 218) used such catalysts, formed in situ in benzene... 

Besides the major thrust using chiral phosphine catalysts, other chiral ligands have been used with rhodium and other metals for asymmetric hydrogenation. 

After the discovery of the high ee provided by rhodium/diphosphite and rhodium/phosphine-phosphite complexes, with total conversion in aldehydes and high regioselectivities, rhodium systems became the catalysts of choice for asymmetric hydroformylation. Important breakthroughs in this area have been the use of rhodium systems with chiral diphosphites derived from... 

Other hydrogenation methods are less chemoselective. Use of Raney nickel provides hydroxylamines in low yield °. Hydrogenation of 1-acetonaphthone oxime over rhodium-chiral phosphine catalysts was found to proceed under harsh conditions and provided low... 

Figure 7 A rhodium complex of chiral phosphine-phosphite ligand (H,S)-BINAPHOS used as a catalyst for asymmetric hydroformylation.

An efficient asymmetric hydrogenation of a-acetamidocin-namic acids has been achieved using a rhodium-chiral phosphine catalyst. This paper describes the preparation of the catalyst and the hydrogenation procedure as well as studies on structure vs. activity. 

It has been reported that the chiral NMR shift reagent Eu(DPPM), represented by structure 19, catalyzes the Mukaiyama-type aldol condensation of a ketene silyl acetal with enantiose-lectivity of up to 48% ee (Scheme 8B1.13) [29-32]. The chiral alkoxyaluminum complex 20 [33] and the rhodium-phosphine complex 21 [34] under hydrogen atmosphere are also used in the asymmetric aldol reaction of ketene silyl acetals (Scheme 8BI. 14), although the catalyst TON is quite low for the former complex. 

Fig. 7.2. The chiral (phosphine)rhodium(I) catalyst used for asymmetric catalytic hydrogenation of an amino acid precursor.

Discrete Chiral Rhodium Phosphine Complexes as Catalysts for Asymmetric Hydrosilation of Ketones... 

II. Homogeneous Rhodium-Chiral Phosphine Catalyst Systems. 85... 

Homogeneous Hydroformylation of Olefins in the Presence of Chiral Rhodium(I)-Phosphine Catalysts... 

Homogeneous rhodium(I)-chiral tertiary phosphine catalysts have been used to hydrogenate ketones directly and to hydrosilylate ketones and imines thus accomplishing, after hydrolysis, indirect hydrogenation. 

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