SYNTHESIS OF AN OPTICALLY-ACTIVE PLATINUM(II) COMPLEX CONTAINING A NEW TERDENTATE P-C-P LIGAND AND ITS CATALYTIC ACTIVITY IN THE ASYMMETRIC ALDOL REACTION OF METHYL ISOCYANOACETATE - X-RAY CRYSTAL-STRUCTURE OF [2,6-BIS[1'S,2'S)-1'-(DIPHENYLPHOSPHINO)-2',3'-O-ISOPROPYLIDENE-2',3'-DIHYDROXYPROPYL[PHENYL](ETA'-NITRATO)PLATINUM(II)

The compound (E,E)-1,3-bis(3'-hydroxyprop-1'-enyl)benzene, obtained by reduction of (E,E)-1,3-bis[2'-(methoxycarbonyl)ethenyl]benzene with diisobutylaluminum hydride, was selectively transformed into 1,3-bis[(1'S,2'S)-1',2'-epoxy-3'-hydroxypropyl]benzene by a Sharpless oxidation. After protection of the hydroxyl groups as their TBDMS ethers, the epoxide rings were selectively opened by reacting them with LiPPh2 and the resulting diphosphine, after reaction with elemental sulfur,gavel,3-bis[(1'S,2'S)-1'-(diphenylthiophosphinyl)-2',3'-dihydroxypropyl]benzene. After conversion to the corresponding bis(dioxolane), the latter compound was desulfurized using P(n-BU)3. The overall yield of the ligand precursor, 1,3-bis[(1'S,2'S)-1'-(diphenylphosphino)-2',3'-O-isopropylidene-2',3'-dihydroxypropyl]benzene, based on the commercial isophthalaldehyde starting material used, was ca. 30%. The complex [2,6-bis[(1'S,2'S)-1'-(diphenylphos-phino)-2',3'-O-isopropylidene-2',3'-dihydroxypropyl]phenyl]chloroplatinum(II) (18) was obtained by reacting the above ligand precursor with [Pt2(mu-Cl)2(eta3-CH2C(CH3)CH2)2]. The X-ray crystal structure of [2,6-bis[(1'S,2'S)-1'-(diphenylphosphino)-2',3'-O-isopropylidene-2',3'-dihydroxy-propyl]phenyl[(eta1-nitrato)platinum(II) (19) obtained from 18, by reacting it with AgNO3, was determined. Its structural features are closely related to those of the corresponding compound in which the dioxolane unit has been replaced by a methyl group. Crystals of 19.toluene are orthorhombic, space group P2(1)2(1)2(1), Z = 4, a = 10.160(1) angstrom, b = 15.721(2) angstrom, and c = 28.799(2) angstrom. The corresponding triflato complex, obtained by reacting the chloro compound 18 with silver triflate, was used as catalyst precursor (1-2 mol %) in the aldol reaction of aldehydes with methyl isocyanoacetate in the presence of a cocatalytic amount of NEti-Pr2. Enantioselectivities up to 65 % were obtained for the major diastereoisomeric trans-oxazoline product, whereas the overall catalytic activity was comparable to that of known systems.