1 -Hexene asymmetric hydroformylation

Effects of GO and H2 partial pressures on the reaction rate and selectivity of asymmetric hydroformylation of 1-hexene and styrene are examined using (7 ,A)-BINAPHOS-Rh catalyst system. For both substrates, high GO partial pressure tends to retard the reaction the partial pressure of H2 hardly affects the reaction rate (Phz -5 MPa). In most cases, the regio- and enantioselectivities are independent of H2 and GO pressure. Deuterioformylation experiments clearly demonstrate the irreversibility of the olefin-insertion step at total pressures of 2-10MPa (D2/G0=I/I). This fact proves that the regio- and enantioselectivity of the present hydroformylation should be controlled by the olefin-insertion step. Herrmann reported the theoretical calculation of the olefin coordination step, explaining selectivity obtained with (i ,A)-BINAPHOS/Rh system for the hydroformylation of styrene. 

Fig. 9. Transition states determining regio- and stereoselectivity in asymmetric hydroformylation of (Z)-2-hexene using Rh/(—)-DIOP...

Significant, but usually only low asymmetric inductions are obtained with unsymmetrically substituted internal aliphatic olefins such as (Z)-2-pentene, (Z)-2-hexene and ( )-2-hexene (Table 2). Most of these results, although of only limited synthetic value, give insight into the mechanism and principles of asymmetric hydroformylation. 

In asymmetric reactions in which only one isomer is formed, enantioface discrimination corresponds to asymmetric induction. However, in reactions in which two isomers are formed if both isomers are chiral, as in the hydroformylation of (Z)-2-hexene, the optical purities of the two isomers are in general different and enantioface discrimination does not correspond quantitatively (and sometimes not even quali-... 

By comparison with the non-immobilized catalyst, similar reaction rates in the hydroformylation of 1-hexene were noted. By ultrafiltration on an asymmetric polyethersulfone membrane, the catalyst could be repeatedly recycled with 2-7% loss of rhodium. 

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