DIOP (2,3-''O''-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane) is an organophosphorus compound
that is used as a chiral ligand
in asymmetric catalysis
. It is a white solid that is soluble in organic solvents.
DIOP is prepared from the acetonide
of ''d,l''-tartaric acid
, which is reduced prior to attachment of the PPh2
The DIOP ligand binds to metals via conformationally flexible seven-membered C4
M chelate ring
DIOP is a historically important in the development of ligands for use in asymmetric catalysis, an atom-economical method for the preparation of chiral compounds. Described in 1971, it was the first example of a C2-symmetric diphosphine.] Its complexes have been applied to the reduction of prochiral olefins, ketones, and imines. Knowles et al. independently reported the related C2-symmetric diphosphine DIPAMP.
Since the discovery of DIOP, many analogues of DIOP have been introduced. These DIOP derivatives include MOD-DIOP, Cy-DIOP, DIPAMP, and DBP-DIOP. Out of many derivatives, DBP-DIOP exhibits good regio- and enantioselectivity in the hydroformylation of butenes and styrene. DIOP was the first chiral ligand used in the platinum-tin-catalyzed hydroformylation. The reactivity, chemo – and the enantioselectivity of DIOP is influenced by CO and H2 pressure and polarity of the solvents. The best results in asymmetric hydroformylation are achieved in solvents with medium polarity: benzene and toluene.