Synthesis, structural features, and methyl methacrylate polymerisation of binuclear zinc(II) complexes with tetradentate pyrazolyl ligands

The reaction of ZnCl₂ with ancillary ligands, including 1,4-bis-(N,N-di-(1H-pyrazolyl-1-methyl)amine)benzene (L₁) and 4,4′-bis-(N,N-di(1H-pyrazolyl-1-methyl)phenyl)methane (L₂), in ethanol yields Zn(II) chloride complexes, i.e., 1,4-bis-(N,N-di-(1H-pyrazolyl-1- methyl)amine)benzene(dichloro)Zn(II) [L₁Zn₂Cl₄] and 4,4′-bis-(N,N-di-(1H-pyrazolyl-1-methyl)phenyl)methane(dichloro) Zn(II) [L₂Zn₂Cl₄]. The X-ray crystal structures of Zn(II) complexes revealed that they are binuclear, and each zinc atom has a distorted tetrahedral geometry which involves a nitrogen atom from two pyrazole groups and two chloro ligands. The catalytic activity of [L₁Zn ₂Cl₄] and [L₂Zn₂Cl₄] for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) increased by twofold compared to the corresponding monomeric Zn(II) complex, N,N-bis(1H-pyrazolyl-1-methyl)aniline(dichloro)Zn(II) [LZnCl₂], at 60 C.