SYNTHESIS AND CHARACTERIZATION OF RIGID BIDENTATE NITROGEN LIGANDS AND SOME EXAMPLES OF COORDINATION TO DIVALENT PALLADIUM - X-RAY CRYSTAL-STRUCTURES OF BIS(P-TOLYLIMINO)ACENAPHTHENE AND DIISOPROPYLPHENYL-IMINO)ACENAPHTHENE]PALLADIUM(II)

The synthesis and characterization of the rigid bidentate nitrogen lig ands bis-(phenylimino)camphane (Ph-BIC) and a series of bis(arylimino) acenaphthenes (Ar-BIAN) is described. These ligands were synthesized b y the reaction of camphorquinone or acenaphthenequinone with the corre sponding (substituted) aniline in the presence of ZnCl2 or NiBr2, foll owed by removal of the metal salt in a subsequent step. NDDO calculati ons on pTol-BIAN showed that the electronic properties of this ligand are comparable to the open-chain analogue Ph-DAB (DAB = 1,4-diaza-1,3- butadiene). The aromatic group on the imine N atom of Ar-BIAN ligands is orientated out of the bis(imino)acehaphthene plane, leading to the formation of syn and anti isomers for the ortho-substituted derivative s o-MeC6H4-BIAN and o-iPrC6H4-BIAN. In solution one isomer is observed for these ligands, but upon coordination to a Pd(Me)CI fragment both syn and anti forms are present, as two isomers are formed. Furthermore , the attempted synthesis of bis(isopropylimino)cyclohexane is describ ed, but it was found that a tautomeric imine-enamine compound is forme d which coordinates to palladium(II) in a monodentate fashion, which c ould not be converted to a chelating ligand. The structures of pTol-BI AN and Pd(Me)CI(o,o'-iPr2C6H3-BIAN) in the solid state were determined by X-ray diffraction. Tol-BIAN is monoclinic, space group C2, a = 20. 021(2), b = 8.7703(10), c = 5.5664(10) angstrom, beta = 103.37(1), Z = 2, final R = 0.040 for 963 reflections with I > 2.5sigma(I). Pd(Me)Cl (o,o'-iPr2C6H3-BIAN) is orthorhombic, space group Pbca, a = 11.440(2), b = 21.250(3), c = 27.087(2) angstrom, Z = 8, final R = 0.043 for 243 3 reflections with I > 2.0sigma(I).