Synthesis and X-ray crystal structures of palladium(II) and platinum(II) complexes of the PCP-type chiral tridentate ligand (1R,1′R)-1,3-bis[1-(diphenylphosphino)ethyl]benzene.: Use in the asymmetric aldol reaction of methyl isocyanoacetate and aldehydes

Enantiomerically pure (1R, 1'R)-1,3-bis[1-(diphenylphosphino)ethyl]benzene (4) has been obtained for the first time. The key step involves in situ tosylation of chiral (1S, 1'S)-dimethyl-1,3-benzenedimethanol (6) followed by nucleophilic attack with LiPPh2(BH3) to give [(1R,1'R)-1,3-bis[1-(diphenylphosphino)ethyl]benzene]-bisborane (7). The bisborane-protected phosphine can be easily handled and purified before deprotecting with HBF4. OMe2 to give the title compound. [(1R, 1'R)-2,6-bis[1-(diphenylphosphino)ethyl]phenyl]chloropalladium(II) (9) and the platinum(II) analogue (8) were synthesized through reaction of the chiral PCP-type ligand with PdCl2(PhCN)(2) and [Pt-2(mu-Cl)(2)(eta(3)-CH2C(CH3)CH2)(2)], respectively, and their X-ray crystal structures were determined. Removal of chloride with AgOTf provided an active catalyst species for the asymmetric aldol reaction of methyl isocyanoacetate and aldehydes.