Ni(ii) and Pd(ii) pyridinyloxazolidine-compounds: synthesis, X-ray characterisation and catalytic activities in the aza-Michael reaction

Abstract

The 3-phenyl-2-(pyridin-2-yl)oxazolidine ligand (ppo) was synthesised and its coordination behaviour regarding Ni(II) and Pd(II) centres was studied. The reaction with K₂PdCl₄ affords [Pd(N,N′-ppo)Cl₂] (1), in which ppo binds to palladiumvia the pyridyl nitrogen and the oxazolyl nitrogen atoms. On the contrary, reaction with NiCl₂·6H₂O produces [Ni(N,O-ppo)₂Cl₂] (2), in which two ppo ligands are coordinated via the pyridyl nitrogen and the oxygen atom of the oxazolidine ring. The X-ray diffraction analysis of the complexes confirms a square planar geometry for Pd(II) in 1 and an octahedral configuration around Ni(II) in 2, which, to the best of our knowledge, represents the first reported example of a structurally characterised nickel-oxazolidine compound. In addition, both complexes prove to be active catalysts under mild conditions in the aza-Michael reaction of (E)-4-phenylbut-3-en-2-one (benzalacetone) with aliphatic amines.