Other Bisphosphine Ligands

The other Bisphosphine Ligands for Enantioselective Alkene Hydrogenation... 

Gratifyingly, full conversion was attained after 24 h when increasing the reaction temperature to 100 °C, and an 87 % yield could be secured upon column chromatography (entry 2). Changing to the tertiary amine base diisopropylethyl-amine (DIPEA) also led to full conversion but only resulted in a 66 % isolated yield (entry 3). Other bisphosphine ligands such as DPPP or ( )-BINAP proved inferior compared to DPPF (entries 4 and 5). In addition, DPPE, DPPPe (1,2-bis(diphenylphosphino)pentane) and D/PrPF resulted in incomplete reaction but stiU afforded the a-arylated olefin exclusively, demonstrating the generation of the intermediary cationic palladium(II) species to be rather flexible (results not... 

Just as Wilkinson s catalyst gave rise to the bisphosphine ligands, Crabtree s catalyst [304] spawned the family of phosphorus-nitrogen ligands for simple al-kenes. Subsequently, Pfaltz developed the Phox family, which provides high ee-values with nonfunctionalized alkenes [305-310]. Other analogues are also illustrated in Figure 23.5. 

This chapter describes atropisomeric biaryl bisphosphine ligands modified DIOP-type ligands P-chiral bisphosphane ligands other bisphosphane ligands and their applications in the enantioselective hydrogenation of olefins. 

Nickel catalyst complexed with unfunctionalized chelating bisphosphine ligands, (R,R) norphos (75) 151 ] and 76 [ 19,52], also induced a high selectivity in the reaction shown in Scheme 8F.5 (Table 8F. 1, entries 38-39). The results reported with other phosphine ligands 33, 77-80 [30,53-56] are summarized in the Table 8F.1 (entries 40-44). 

Still, the question remains why is the one diastereomer of the catalyst-substrate complex so much more reactive than the other In 1977, Knowles suggested, based on examination of the crystal structures of several metal complexes having chiral bisphosphine ligands, that the orientation of the P-phenyl groups could be the source of the enantioselectivity of these reactions [125]. The common feature Knowles observed (Figure 7.8) is that the two equatorial phenyls are oriented such that - with the bisphosphine in the horizontal plane and the metal in front - their... 

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