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, L ₂ZnCl₂, L₃ZnCl₂ and L ₄ZnCl₂. 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.