Ferrocenyl-based diphosphines

Nnmerons other protocols have been developed to prepare magnesium enolates by asymmetric 1,4-addition of Grignard reagents to electron-deficient alkenes. Recently, an enantioselective metal-catalyzed version of this key reaction has been studied with enones and a, S-unsaturated thioesters Using chiral ferrocenyl-based diphosphines leads to... 

Asymmetric hydroformylation of styrene has been studied with a range of bidentate phosphines, van Leeuwen reported phosphorus-chiral ferrocenyl-based diphosphines, the hydride complexes of which showed varying ee-ea ratios depending on ligand basicity, as determined by HP-IR and HP-NMR. This contrasted to the clear ea preference shown by complexes of the achiral l,l -bis(diphenylphosphino)ferrocene (dppf) ligand. Claver and van Leeuwen " " " investigated BDPP [(2A,4A)-bis(diphenylphosphino)pentane] and CHIRAPHOS [(2R,3R)-bis (diphenylphosphino)butane] for the same transformation. High pressure spectroscopic data for the catalytic species... 

Table 4.5 Ferrocenyl-based diphosphine boranes 41 prepared from 9.

The most common chiral auxiliaries are diphosphines (biphep, binap and analogues, DuPhos, ferrocenyl-based ligands, etc.) and cinchona and tartaric acid-derived compounds. It is clear that the optimal chiral auxiliary is determined not only by the chiral backbone (type or family) but also by the substituents of the coordinating groups. Therefore, modular ligands with substituents that can easily be varied and tuned to the needs of a specific transformation have an inherent advantage (principle of modularity). 

The search for a commercially viable process took many years [126], Several approaches with Rh or Ir complexes using commercially available diphosphine ligands were not successful. A critical breakthrough was achieved when Ir complexes with a new class of ferrocenyl-based ligands (now called Solvias Josiphos) were used. Extremely active and productive catalysts were obtained, especially in the presence of acid and iodide ions. Different Josiphos ligands were tested and a selection of the best results obtained is shown in Table 37.5. 

Rh(I)-complexes prepared from ferrocenyl-aryl-based diphosphine ligands have been successfully applied for enantioselective hydrogenation of the a-isopro-pylcinnamic acid derivative 115 to the corresponding... 

Sturm T, Weissensteiner W, Spindler F (2003) A novel class of ferrocenyl-aryl-based diphosphine ligands for Rh- and Ru-catalysed enantioselective hydrogenation. Adv Synth Catal 345 160-164... 

A number of C2 symmetric diphosphine ligands with a ferrocenyl backbone (see Figure 15.5) have been described and tested with sometimes very good results. Interesting examples are f-binaphane (11),14 ferrotane (12),15 the sugar-based phospholane 13,16 the ferrocenyl bisphosphonite 14,17 and the P-chiral phosphine 15.18... 

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