Crystalline magnesium chloride-electron donor complexes: new support materials for Ziegler-Natta catalysts

In this study, crystalline magnesium chloride-electron donor complexes were prepared by recrystallization of δ-MgCl₂ in the presence of chelating electron donors, including two diethers (1,2-dimethoxyethane; DME and 1,3-dimethoxypropane; DMP) and one diamine (N,N'-diethylethylenediamine; DEEDA). The syntheses and crystal structures of such magnesium chloride complexes with chelating ligands have been rarely reported, even though they can provide important information for the selection of electron donors for stereoselective MgCl₂-supported Ziegler-Natta catalysts. The synthesized complexes were characterized using single-crystal X-ray diffraction, and FTIR and CP/MAS ¹³C NMR spectroscopy methods. A polymeric complex [MgCl₂(DME)]_n and molecular complexes [Mg₂Cl₄(DMP)₂(H₂O)] and [MgCl₂(DEEDA)₂] were formed in recrystallizations. In all complexes, the bidentate electron donors are bound in chelate binding mode. The [MgCl₂(DME)]_n complex, the structure of which consists of a helical polymeric MgCl₂ backbone chain and one DME molecule coordinated to each Mg atom, can be considered as a structural model for layered MgCl₂. The crystal structure of the [Mg₂Cl₄(DMP)₂(H₂O)] complex is composed of a tetrahedral Mg atom with four Cl ligands and a distorted octahedral Mg atom with two DMP molecules, one water molecule, and one Cl ligand. The two types of Mg atoms are connected to each other with a bridging Cl ligand. In the [MgCl₂(DEEDA)₂] complex, magnesium is octahedrally coordinated by two chloride ligands trans to each other and two DEEDA molecules. The structures of the obtained magnesium chloride-electron donor complexes clearly show how diether and diamine electron donors can dictate the crystal structure of MgCl₂.