Nickel(II) and palladium(II) complexes with acylhydrazone ligands of α-diketones: the electronic and steric factors affecting the formation of the dimeric palladium(II) complexes

Palladium(II) acetate reacts with butane-2,3-dione bis(octanoylhydrazone) (H 2 oct) giving a dimeric [Pd 2 (oct) 2 ] complex as main product; as shown by X-ray crystal analysis, the ligands are bideprotonated and in each of them one carbonyl oxygen and the two imine nitrogens are bonded to one palladium ion, whereas one hydrazide nitrogen is bonded to the second palladium, giving rise to a N 3 O square planar coordination. The core of the complex is constituted by an unusual six-membered PdN 2 PdN 2 ring. The same arrangement is also found in [Pd 2 (ben) 2 ] (H 2 ben, butane-2,3-dione bis(benzoylhydrazone)) where the alkyl chains of the ligand H 2 oct are substituted by phenyl rings. On the contrary, the corresponding nickel(II) complexes are monomers and the coordination is N 2 O 2 square planar. Monomers are also the nickel(II) and palladium(II) complexes with butane-2,3-dione bis(thiobenzoylhydrazone) and phthalic dicarboxaldehyde bis(benzoylhydrazone).