Ligand pyrphos

A PYRPHOS ligand was found to be effective for the hydrogenation of a / -aryl- or alkyl-substituted monoamido itaconate [107]. A MeO-BIPHEP-Ru catalyst was successfully applied for the enantioselective hydrogenation of an intermediate for the drug candoxatril in a mixed solvent (THF/H20) (Scheme 26.12) [108]. 

Fig. 19 Dendronized Pyrphos ligands bearing backfolded polyfaryl ether) dendrons...

Mahnstom and Andersson reported a pyrphos ligand [27] 12 and a PPM ligand [28] (PPM 4-phenylphosphino-2-(diphenylphosphinomethyl)pyrrolidine) bound to... 

In 2001, Engel and Gade [57] prepared a series of chiral phosphine-functionalized poly(propyleneimine) (PPI) dendrimers (29) by the reaction of carboxyl-linked C2-chiral pyrphos ligand (pyrphos, 3,4-bis(diphenylphosphino) pyrrolidine) with commercially available zero- to fourth-generation PPI. The subsequent metallation of multisite phosphines with [Rh(COD)2]-BF4 (COD, 1,5-cyclooctadiene) was in situ generated and carried out in the asymmetric hydrogenation of Z-methyl-a-acetamido cinnamate and dimethyl itaconate (Figure 4.28, Equation 1). In contrast... 

Rhodium-catalyzed enantioselective hydrogenation of acctamido -cinnamic in water was also achieved using pyrphos bound to poly-acrylic acid as ligand.337 Roucoux described some Rh° nanoparticles which function as reusable hydrogenation catalyst for arene derivatives in a biphasic water-liquid system.338... 

Several chiral ligands, such as PYRPHOS [78b], have been shown to be very efficient ligands for the hydrogenation of a-dehydroamino acid derivatives in terms of both high enantioselectivity and reactivity. 

Rh complexes with ChiraPhos, PyrPhos, or ferrocenyl phosphines lacking amino alkyl side chains (such as BPPFA) are much less active toward tetrasubstituted olefins. Table 6-1 shows that in asymmetric hydrogenations catalyzed by 5a-d, the coordinated Rh complex exerts high selectivity on various substrates. It is postulated that the terminal amino group in the ligand forms an ammonium carboxylate with the olefinic substrates and attracts the substrate to the coordination site of the catalyst to facilitate the hydrogenation. 

In a subsequent paper (87), the same authors investigated the palladium-catalyzed allylic aminations with pyrphos-functionlized PPI and PAMAM dendrimers as multidentate ligands. Zero to four generation PPI-(pyrphosPdCl2)x and PAMAM-(pyrphosPdCl2)x neutral dendrimers (97) showed a strong positive dendritic effect on the selectivity of the allylic amination of 1,3-diphenyl-1-acetoxypropene with morpholine (at 45°C in DMSO). 

Figure 4.6 Chiral dendrimer diphosphine ligands bearing Pyrphos at the focal point of the Frechet-type dendrimer.

Carboxylate groups were used in many cases to achieve water-solubilization of simple achiral phosphines. With the synthesis of the water-soluble polymer shown in Eq. (2) this methodology was extended into the field of chiral ligands [28a]. Acylation of the diphosphine (2S,4S)-4-diphenylphosphino-2-diphenylphosphinome-thylpyrrolidone (PPM) with poly(acrylic acid) (PPA) yields the hydrophilic macroligand PAA-PMM [28a,b] and PAA-pyrphos [28c]. 

A different type of C2-symmctric ligand is benzyl-pyrphos (Deguphos, 38) which has been used in hydrogenation of C C double bonds (Section D.2.5.1.2.1.1.). Benzyl-pyrphos 38 is obtained from tartaric acid by cyclization with benzylaminc, reduction of the amide functions, and normal conversion of the hydroxy groups to diphenylphosphine groups via the mesylate41. 

The ligands la, (2S,4S)-N-(tert.-butyloxycarbonyl)-4-(diphenylphosphino)-2-(diphenylphosphinomethyl)-pyrrolidine (BPPM) and (4S,5S)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-l,3-dioxolane (DIOP) were purchased from Fluka, 3-isocyanatopropyltriethoxysilane 4 from Petrarch Systems Inc.. Ligand 2a and (3R,4R)-l-benzyl-3,4-(bisdiphenylphosphine)pyrrolidine (PYRPHOS)... 

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