Synthesis and X-ray crystal structure of derivatives from the N,N-bis(1H-pyrazolyl-1-methyl)aniline(dichloro)Zn(II) complex: Substituent effects on the phenyl ring versus the pyrazole ring

The reaction of anhydrous ZnCl2 with ancillary ligands, including N,N-bis(1H-pyrazolyl-1-methyl)aniline (L1), N,N-bis(1H-pyrazolyl-1-methyl)-p-methoxyaniline (L2), N,N-bis(1H-pyrazolyl-1-methyl)-p-fluoroaniline (L3) and N,N-bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline (L4), in ethanol yields Zn(II) chloride complexes, i.e., L1ZnCl2, L2ZnCl2, L3ZnCl2 and L4ZnCl2. X-ray crystallographic analysis revealed that the Zn atoms of all of the synthesized complexes have a distorted tetrahedral geometry involving a nitrogen atom from each of two pyrazole groups and two chloro ligands. However, the nitrogen atom of the aniline group is not coordinated to the Zn center, resulting in the formation of an eight-membered chelate ring. The catalytic activity of the Zn(II) complexes in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) results in a higher molecular weight and a narrow polydispersity index (PDI) range.

Graphical abstractComplexes [LnZnCl2], for example L1 is N,N-bis(1H-pyrazolyl-1-methyl)aniline, were synthesized and characterized by X-ray crystallography. Their catalytic activity for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) was proven to be moderate.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Derivatives of N,N-bis(1H-pyrazolyl-1-methyl)aniline(dichloro)Zn(II) as a catalyst. ► Activated with MMAO, [LnZnCl2] proved to be efficient for MMA polymerization. ► The polymerization outcomes are affected by the substituents on the pyrazole ring in [LnZnCl2].