Synthesis and molecular structure of optically active oxazolidine complexes of platinum(II) and palladium(II)

Two series of optically active complexes of the type trans-PtCl2(C2H4)(oxazolidine) (3) and trans-PdCl2(PPh3)(oxazolidine) (4) oxazolidine=NHCH(p-ClC6H4)OCH2CHR (R=a Me; b Et; c Bui; d Bz; e Ph) have been prepared and characterized. The synthesis involves metal promoted cyclization of the optically active Schiff's bases p-ClC6H4CHNCH(R)CH2OH and proceeds for both metal centers in high chemical and optical yield (diastereomeric excesses of 78–96%). Attack of the oxygen at the imine carbon results in preferential formation of complexed five-membered rings which have the cis-geometry with respect to the C-2 and C-5 substituents. The solid-state structures for 3b and 4c have been determined by X-ray diffraction. Both structures reveal expected coordination spheres with the MCl2 (C2H4 or PPh3) fragment occupying a pseudo trans position with respect to the oxazolidine C-2 C-5 substituents. This observation, combined with solution 2-D NOESY measurements, is used to rationalize the observed diastereomeric excesses. Crystallographic data for the complexes are as follows: 3b, orthorhombic, space group P212121a=7.003(1), b=16.573(1), c=29.088(4) Å, V=3376.1(7) Å3, Z=8; 4c orthorhombic space group P212121a=11.921(2) b=12.241(1) c=21.107(2) Å, V=3080(1) Å3, Z=4. The structures have been refined to R factors of 0.04 and 0.05, respectively.