Catalyst preparation and hydroformylation

The chiral diphosphites 4-9 have been used in the rhodium catalyzed asymmetric hydroformylation of styrene. The catalysts are prepared in situ by adding the diphosphite L to [Rh(acac)(CO)2] (acac = acetylacetonate) as a catalyst precursor. Under typical hydroformylation conditions the active catalyst precursor [RhH(diphosphite)(CO)2] is formed (See 5.2.3). Two important features have been found for the preparation of efficient catalyst using these diphosphites (1) An excess of diphosphite is used to exclude the 

Diphosphite T °C Turnover frequency Conversion % % 2-phenyl-propanal % ee (Absolute Confiauration) 

All reactions were carried out with 13.3 mmol of styrene.CO/H2 = 10 bar. Styrene catalyst molar ratio is 421, P Rh molar ratio is 2.5. In mol styrene (mol Rh )h determined after 2 h 

The catal5dic systems formed with the diphosphites based on (2R,4R)-pentane-2,4-diol in which the bisphenol moiety is substituted with methoxy groups at the para position, 5c and 6, give the highest activity. The catalyst based on (2S,5S)-hexane-2,5-diols show lower catal5dic activity than those based on (2R,4R)-pentane-2,4-diol (Table 1). 

The highest regioselectivity was obtained with trimethylsilyl and ter-butyl substituents at the ortho position. The reaction rates decreases as the steric bulk of the ortho substituents C(CH3)3 Si(CH3)3 Si(t-Bu)(CH3)2 Si(CH2CH3)3 increases. The bulky groups Si(t-Bu)(CH3)2 and Si(CH 20113)3 

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