Coordination reactions of 2-pyridinecarboxaldehyde-phenylhydrazonatolithium with selected transition metal (Zn, Sn, Fe, Co, Ni and Zr) chlorides and its coupling reaction with dichloromethane

Abstract

The reactions of 2-pyridinecarboxaldehyde-phenylhydrazonatolithium C₅H₄N_py–CHN_i–N_aLi(Ph) (abbreviated as LiL) with a 1/2 equivalent of anhydrous metal (Zn, Sn, Fe and Co) chlorides or NiCl₂(DME) (DME = 1, 2-dimethoxyethane) produced the corresponding mononuclear metal(II) complexes (1–4 and 7), in which each ligand acts as a bidentate ligand and the coordination geometries around the metals are shown to be tetrahedral within the complexes 1, 3, 4 and 7, respectively, and a tetragonal pyramid in the complex 2. The reaction of LiL successively with sodium tert-butoxide and anhydrous ZrCl₄ afforded the unanticipated bizirconium complex 5, in which each monoanionic ligand behaves as a tridentate bridge. Whereas treatment of LiL with NiCl₂ and then CH₂Cl₂ led to an interesting methylene-bridged bis(2-pyridyl-phenylhydrazone) compound 6 in moderate yield; a comparative experiment showed that when the LiL reacted with CH₂Cl₂, the coupling compound 6 was also obtained but in very low yield. A plausible mechanism of compound 6 formation was also proposed and supported by the density functional theory (DFT) calculations. All the synthesized compounds 1–7 were characterized by single-crystal X-ray diffraction.