STEREOCHEMICAL INVESTIGATION OF BIS(BIDENTATE)-PALLADIUM(II) COMPLEXES - TRANSMISSION OF RING CHIRALITIES BETWEEN CHELATING AMINE LIGANDS VIA THEIR PROCHIRAL N-METHYL SUBSTITUENTS

Three diastereomeric palladium(II) complex cations containing the orth ometalated (S)-dimethyl(1-(alpha-naphthyl)ethyl)amine together with th e (R,R)-, (S,S)- and (R,S)- forms of N,N,N',N'-tetramethyl-2,3-butaned iamine have been prepared separately as their perchlorate salts. The ( S,R,R) isomer with [alpha D +167-degrees (c 1.0, CH2Cl2) crystallizes in the space group P2(1)2(1)2, with a = 7.872 (3) angstrom, b = 15.843 (5) angstrom, c = 20.273 (6) angstrom, Z = 4, and R = 0.0372. The squ are-planar geometry around palladium is slightly distorted. The (SSS) isomer with [alpha]D +87-degrees (c 1.0, CH2Cl2) crystallizes in the s pace group P2(1) with a = 7.978 (2) angstrom, b = 20.856 (2) angstrom, c = 15.218 (2) angstrom, beta = 90.06 (2)degrees, Z = 4, and R = 0.03 62. The coordination geometry around palladium is distorted seriously from square-planar due to severe ligand-ligand interactions. The (S,R, S) isomer with [alpha]D +158-degrees (c 1.0, CH2Cl2) crystallizes ster eoselectively as a sole conformer in the space group P2, with a = 11.6 61 (3) angstrom, b = 9.982 (2) angstrom, c = 13.227 (4) angstrom, beta = 105.29 (2)degrees, Z = 2, and R = 0.0319. In solution, the diamine ligands of these complexes are found to be labile under ambient condit ions, as evidenced by facile intermolecular ligand redistributions bet ween diastereomers. For the (S,R,S) isomer, a marked temperature depen dent asymmetric equilibration occurred between two possible internal d iastereomeric structures. Furthermore, it has been shown that although steric factors govern the relative thermodynamic stabilities in this series of complexes, these effects are frequently outweighed by lattic e effects in isolated solids, where a sterically unfavorable isomer ca n be isolated readily from a diastereomeric equilibrium mixture in the crystallization process.