Can weak interactions modify the binding properties of a strong nitrogen donor? Unusual N-coordination of a phosphoranylidene-substituted pyrazolone unit towards palladium(ii) centres: an experimental and theoretical study

Abstract

Selective N(2)-binding of 3-methyl-1-phenyl-4-(triphenylphosphoranylidene)-2-pyrazolin-5-one (L) has been found in two palladium(II) complexes, [PdCl₂L₂] (2) and [Pd(o-C₆H₄CH₂NMe₂)ClL] (3). X-Ray diffraction studies show that the pyrazole rings lie almost perpendicular to the coordination plane. In both complexes the metal atom is located out of the plane defined by the pyrazole ring(s) (dihedral angle between the plane and the Pd–N vector ∼30°). To investigate the origin of this distortion, a theoretical study was carried out on a simplified model of complex 2, where a single pyrazolone ligand was replaced by NH₃. From this study it could be inferred that the out-of-plane distortion mainly involves weak, electrostatic interactions between a chlorine atom and an ortho-aromatic H atom of the N(1)-linked phenyl group, as well as between the other chlorine atom and an ortho-aromatic H atom of the PPh₃ group.