Rh diphosphine complexes

Enantioselectivities >90% were reported for a Ti-ebthi catalyst (Table 34.4 entry 4.1) and for some Rh-diphosphine complexes (entries 4.2-4.4). Interestingly, the highest ee-values were obtained using sulfonated diphosphines (bdppsuif) in an aqueous biphasic medium (entry 4.3). The degree of sulfonation strongly affected the enantioselectivity the Rh-mono-sulfonated bdpp gave 94% ee, compared to 65% ee with Rh-bdpp in MeOH, and almost racemic product with bis-or tris-sulfonated ligands. In addition, the activity of the mono-sulfonated cata-... 

Rh-diphosphine complex, [Rh(Chiraphos, 106)](C104)2, was used as a catalyst for the intramolecular hydrosilylations of homoallylic silane 107 and silyl allyl ether 108 in acetone at 25°C to give the corresponding 1,4-diol 109 (60% ee, R) in 84% yield and 1,3-diol 110 (with 56% ee, R) in 96% yield, respectively [64] (Scheme 2.7). The Rh-Chiraphos catalyzed reaction of l-(3-phenylpropen-2-yloxy)silacyclohexane (111a) gave diol 112 with 74% ee (R) in 61%... 

Mechanistic studies of the isomerization of a prochiral allylamine with a Rh-diphosphine complex gave some evidence for a nitrogen-triggered mechanism in which the allylamine chelates to the metal center. The suggested mechanism, which was elaborated on the basis of a chiral Rh-BINAP catalyst, is depicted in Scheme 4 [8]. 

Immobilised Rh Diphosphine Complexes as catalysts for Enantioselective Hydrogenations... 

Scheme 12.13 Rh-diphosphine complexes adsorbed onto a heteropolyacid (HPA) supported on silica or active carbon.

There are several studies in which Rh-diphosphine complexes are generated in situ using Rh(COD) as Rh precursor and adding diphosphines. Results are similar to those obtained by synthesizing the Rh-diphosphine complex prior to the reaction [20]. 

The preparation of the three MEA enamides proved to be rather difficult. Disappointingly, we did not succeed in hydrogenating any of the three isomers using seven different Rh-diphosphine complexes at normal pressure and temperatures up to 50 °C. 

Most rhodium catalysts for the enantioselective reduction of the C=N group are prepared in situ from a dimeric Rh-diene complex and a chiral diphosphine. Only few of the tested diphosphine ligands exhibit enantioselectivities >70% bdpp, cycphos, and phephos for imines and duphos for acylhydrazones. The activity of most Rh-diphosphine complexes for imine hydrogenation is low and therefore most of them are of limited practical use. Although some catalysts work already at ambient reaction conditions, most Rh-diphosphine complexes show low tof s even at elevated hydrogen pressures (>60 bar). 

This method relies on the size of the metal complex rather than on a specific adsorptive interaction. There are two different preparation strategies One, often called the ship-in-a-bottle approach, is based on building up catalysts in well defined cages of porous supports. Recently, enantioselective Mn epoxidation catalysts with different salen ligands have been assembled in zeolites. In zeoHte EMT [35] ees up to 88% and in zeolite Y [36] ees up to 58% were obtained with czs-P-methylstyrene. However, both entrapped catalysts were much less active than their homogeneous counterparts. Rh diphosphine complex were entrapped in the interlayers of Smectite [37]. The resulting catalyst was active for the enantioselective hydrogenation of N-acetamidoacrylic acid (ee 75%). 

Keywords Imine hydrogenation, Ir diphosphine complexes, Ir ferrocenyldiphosphine complexes, Rh diphosphine complexes. Technical process. Industrial application, MEA imine, Ir ferrocenyldiphosphine complexes, (S)-Metolachlor, Chiral switch... 

There have been many reports that described protein composites containing metal complexes [1-3, 5, 6], Three different approaches for the incorporation of synthetic metal complexes into protein cavities have been reported (i) modification of natural snbstrates, (ii) covalent anchoring, and (iii) non-covalent insertion. For example, Whiteside et al. constructed artificial metaUoenzymes by the conjugation of a Rh diphosphine complex with biotin, which strongly binds to avidin [8], Ward et al. have improved this method to increase the reaction activities [25]. They optimized the reaction conditions by screening the structures of metal complexes and protein environments. Finally, optimized composites catalyzed asymmetric hydrogenation with np to 97% ee (Fig. 2a) [2, 3, 26],... 

Unlike the Wilkinson catalyst that irreversibly yields a dihydride complex when treated with dihydrogen, the Rh-diphosphine complexes after hydrogenating off diene ligand from the catalytic precursor 1 give solvate complexes 2 (Scheme 1.1). ... 

Tsuruta, H. Imamoto, T. Yamaguchi, K. Gridnev, I. D. Evidence for the importance of conformational equilibria in Rh-diphosphine complexes for the enantioselection in Rh-catalyzed asymmetric hydrogenation. Tetrahedron Lett. 2005, 46,2879-2882. 

Rh(modified xan-thene)H(CO)L and [Rh(diphos-phineXHHCO) complexes Rh diphosphine complexes... 

Fig. 10.30 Enantioselective [4 + 2] cyclizations of dien-ynes promoted by Rh-diphosphine complexes [44, 45]...

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