New P-chirogenic diphosphines and their use in catalytic asymmetric
reactions*
Tsuneo Imamoto
Department of Chemistry, Faculty of Science, Chiba
University, Inage-ku, Chiba 263-8522, Japan
Abstract: Enantiomerically pure (S,S) -1,2-bis[(o-alkylphenyl)
phenylphosphino]ethanes (o-alkylphenyl = o-methylphenyl, o-ethylphenyl,
o-isopropylphenyl, 5',6',7',8'-tetrahydro-naphthyl) , (S,S) -1,2-bis
(alkyl-methylphosphino) ethanes (alkyl = t-butyl, 1-adamantyl, 1-methylcyclo-hexyl,
1,1-diethylpropyl, cyclopentyl, cyclohexyl) (abbreviated as BisP*) ,
and (R,R) -1,1-bis (alkylmethylphosphino) methanes (alkyl = isopropyl,
t-butyl, cyclohexyl, phenyl) (abbreviated as MiniPHOS) were prepared
from phosphorus trichloride via short routes using phosphine-boranes
as intermediates. The crystal structures of cationic rhodium complexes,
[Rh ((S,S) -1,2-bis ((phenyl) (5',6',7',8'-tetrahydronaphthyl) phosphino)
ethane) (cod)]BF4, [Rh ((S,S) -t-Bu-BisP* (nbd))]BF4, and
[Rh ((R,R) -t-Bu-MiniPHOS) 2]PF6, clearly indicate
the ideal asymmetric environments. These ligands exhibited an excellent
to almost perfect level of enantioselectivity in asymmetric hydrogenations
of a-dehydroamino acid derivatives and other catalytic asymmetric reactions.
* Lecture presented at the XIXth International Conference
on Organometallic Chemistry (XIX ICOMC) , Shanghai, China, 23-28 July
2000. Other presentations are published in this issue, pp. 205-376.
** Corresponding author
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