ABSTRACT
Christopher J. Cobley, Ian C. Lennon, Raymond McCague, James A. Ramsden, and Antonio Zanotti-Gerosa Chirotech Technology Ltd., Cambridge, United Kingdom
ABSTRACT
We have examined the effectiveness of cyclooctadiene (COD) and norbornadiene (NBD) precatalysts of the type [Rh(DuPHOS)(diolefm)]BF4 in catalytic asymmetric hydrogenation of prochiral olefins under conditions suitable for industrial ap.- plication. The NBD precatalyst can give rise to the catalytically active species more rapidly than the corresponding COD complex, but as catalyst loadings were reduced to improve the process economics, the difference between the use of COD and NBD precatalysts became insignificant. For some substrates, identical reaction profiles were observed for either precatalyst, but an important determinant of reaction rate was the efficiency of hydrogen introduction to the mixture. In addition, the effectiveness of a catalyst loading of 50,000/1 for the hydrogenation of dimethyl itaconate with [Rh(DuPHOS)(COD)]BF4, demonstrates that this precatalyst can be put to highly economic use.
