Chiral dendritic catalysts hydrogenation

Kollner et al. (29) prepared a Josiphos derivative containing an amine functionality that was reacted with benzene-1,3,5-tricarboxylic acid trichloride (11) and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (12). The second generation of these two types of dendrimers (13 and 14) were synthesized convergently through esterification of benzene-1,3,5-tricarboxylic acid trichloride and adamantane-1,3,5,7-tetracarboxylic acid with a phenol bearing the Josiphos derivative in the 1,3 positions. The rhodium complexes of the dendrimers were used as chiral dendritic catalysts in the asymmetric hydrogenation of dimethyl itaconate in methanol (1 mol% catalyst, 1 bar H2 partial pressure). The enantioselectivities were only... 

Chiral dendritic catalysts 194 derived from BINAP was prepared and used for the asymmetric hydrogenation of quinolines (Scheme 3.63) [126]. The corresponding cyclic amine products were obtained with high enantioselectivities up to 93% ee. The dendritic catalyst showed excellent catalytic activities (TOP up to 3450h" ) and productivities (TON up to 43 000). The dendritic catalyst was recovered by precipitation and filtration and reused at least six times, with similar enantioselectivity. 

The first reported example using macromolecule-supported catalysts in latent biphasic systems was work by Chan s group that employed a dendrimer-bound BINAP 127 that was used to form a chiral ruthenium hydrogenation catalyst [164]. The dendritic Ru-BINAP complex formed from the reaction of [RuCl2(benzene)2]2 and 127 was successfully used in four cycles in the hydrogenation of 2-phenylacrylic acid (Eq. 65) in a 1 1 (vol/vol) ethanol/hexane mixture. Addition of 2.5 vol% water to this mixture produced a biphasic mixture where >99% of the dendritic catalyst was in the hexane phase. Addition of a fresh ethanolic substrate solution to this hexane phase produced another miscible solution of catalyst and substrate. The second and subsequent cycles of hydrogenation carried out in this manner led to consistent conversions of substrate with synthetic yields of >91% with e.e. values of 90%. 

Pan et al. give an extensive review of immobilized asymmetric catalysts according to reaction classes and the land of support [9]. Saluzzo and Lemaire reviewed the use of polymer-supported BINAP for hydrogenation and hydrogen-transfer reduction with diamines or amino alcohols, respectively [10]. The immobilization and recycling of chiral catalysts was the topic of a recent book [11]. Dendritic catalysts... 

The asymmetric hydrogenation of 2,4-diaryl-l,5-benzodiazepines by Hj in CH2CI2 to chiral nitrogen-containing heterocycles with 85/15 dr and 96% ee is catalysed by Ir complexes of dendritic ligands with BArF as the counteranion. A positive dendritic effect on catalytic activity is observed, and the dendritic catalyst is usable three times but at the expense of relatively low catalytic activities. ... 

Brunner et al. attached chiral branches to non-chiral catalytically active sites. With the aim to influence the enantioselectivity of transition metal catalyzed reactions they synthesized several dendritically enlarged diphosphines such as 81 [101] (Fig. 29). In situ prepared catalysts from [Rh(cod)Cl]2and81 have been tested in the hydrogenation of (a)-N-acetamidocinnamic acid. After 20 hours at 20 bar H2-pressure (Rh/substrate ratio 1 50) the desired product was obtained with an enantiomer ratio of 51 49. 

Transfer hydrogenation of ketones using metal complexes with a chiral water-soluble [97,98] and a dendritic ligand [99] was investigated for use in recycling catalysts. The reaction with immobilized catalysts has also been reported [100]. 

In a related approach, Fan et al. synthesized a series of dendritic BINAP-Ru/chiral diamine ((R,R)-l,2-diphenylethylenediamine DPEN) catalysts for the asymmetric hydrogenation of various simple aryl ketones (Fig. 15) [42]. The resulting systems displayed high catalytic activity and enantioselectivity and allowed facile catalyst recycling. In the case of 1-acetonaphthone and... 

The same group also developed optically active dendronized polymeric BINAP ligands (see also Sect. 5) as a new type of macromolecular chiral catalyst for asymmetric hydrogenation. They could be synthesized by condensation of 5,5 -diamino-BINAP with dendritic dicarboxylic acid monomers (Scheme 5) [44],... 

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