Synthesis and characterization of rigid bidentate nitrogen ligands and some examples of coordination to divalent palladium. X‐ray crystal structures of bis (<i>p</i>‐tolylimino) acenaphthene and methylchloro [bis(<i>o,o</i>′‐diisopropylphenyl‐imino) acenaphthene] palladium (II)

Abstract

Abstract 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 ZnCl 2 or NiBr 2 , 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 ‐MeC 6 H 4 ‐BIAN and o‐i PrC 6 H 4 ‐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 Pr 2 C 6 H 3 ‐BIAN) in the solid state were determined by X‐ray diffraction. p Tol‐BIAN is monoclinic, space group C 2 , a = 20.021(2), b = 8.7703(10), c = 5.5664(10) Å, β = 103.37(1)°, Z = 2, final R = 0.040 for 963 reflections with I &gt; 2.5σ( I ). Pd(Me)Cl( o,o ′‐ i Pr 2 C 6 H 3 ‐BIAN) is orthorhombic, space group Pbca , a = 11.440(2), b = 21.250(3), c = 27.087(2) Å, Z = 8, final R = 0.043 for 2433 reflections with I &gt; 2.0σ( I &gt;).