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 methylchloro[bis(o,o'-diisopropylphenyl-imino)acenaphthene]palladium

The synthesis and characterization of the rigid bidentate nitrogen ligands bis-(phenylimino)camphane (Ph-BIC) and a series of bis(arylimino)acenaphthenes (Ar-BIAN) is described. These ligands were synthesized by the reaction of camphorquinone or acenaphthenequinone with the corresponding (substituted) aniline in the presence of ZnCl2 or NiBr2, followed by removal of the metal salt in a subsequent step. NDDO calculations on p Tol-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)acenaphthene plane, leading to the formation of syn and anti isomers for the ortho-substituted derivatives o-MeC6H4-BIAN and o-i PrC6H4-BIAN. In solution one isomer is observed for these ligands, but upon coordination to a Pd(Me)Cl fragment both syn and anti forms are present, as two isomers are formed. Furthermore, the attempted synthesis of bis(isopropylimino)cyclohexane is described, but it was found that a tautomeric imine-enamine compound is formed which coordinates to palladium(II) in a monodentate fashion, which could not be converted to a chelating ligand. The structures of p Tol-BIAN and Pd(Me)Cl(o,o′-i Pr2C6H3-BIAN) in the solid state were determined by X-ray diffraction. p Tol-BIAN is monoclinic, space group C2, a = 20.021(2), b = 8.7703(10), c = 5.5664(10) A, β = 103.37(1)°, Z = 2, final R = 0.040 for 963 reflections with I > 2.5σ(I). Pd(Me)Cl(o,o′-i Pr2C6H3-BIAN) is orthorhombic, space group Pbca, a = 11.440(2), b = 21.250(3), c = 27.087(2) A, Z = 8, final R = 0.043 for 2433 reflections with I > 2.0σ(I >).