Synthesis and structural characterisation of tetrahedral zinc(II) and trigonal bipyramidal cadmium(II) complexes containing N′-cyclohexyl substituted N,N-bispyrazolyl ligand

•Synthesis of Zn(II) and Cd(II) complexes with N′-cycloalkyl substituted N,N-bispyrazolyl ligands.•4-Coordinate Zn(II) and 5-coordinate Cd(II) complexes are assessed in MMA polymerisation.•Zn complexes are more active towards MMA polymerisation compared to Cd(II) complexes.

The bis(pyrazolyl)-based ligands L1 and L2, where L1 is N,N-bis((1H-pyrazol-1-yl)methyl)cyclohexanamine and L2 is N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)cyclohexanamine, reacted with [ZnCl2] and [CdBr2·4H2O], respectively, and resulted in mononuclear [LnMX2] (Ln = L1 and L2; M = Zn, X = Cl; M = Cd, X = Br) complexes in a facile yield and high purity. The synthesised complexes were characterised spectroscopically and X-ray crystallographically. The molecular structure of 4-coordinate [L1ZnCl2] was best described as a distorted tetrahedral, whereas 5-coordinate [L1CdBr2] and [L2CdBr2] exhibited distorted trigonal bipyramidal geometry involving the metal centres. [L1ZnCl2] showed the highest catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) with an activity of 4.40 × 104 g PMMA/molZn h at 60 °C and resulted in syndiotactic poly(methylmethacrylate) (PMMA).

Graphical abstractN′-cycloalkyl substituted N,N-bispyrazolyl based ligands and their Zn(II) and Cd(II) complexes have been synthesized and structurally characterised. The molecular structure of [L1ZnCl2] was best described as a distorted tetrahedral geometry whereas [L1CdBr2] and [L2CdBr2] structures were described as a distorted trigonal bipyramidal geometry involving the metal centre. [L1ZnCl2] showed the highest catalytic activity (4.40 × 104 g PMMA/molZn h) for MMA polymerisation in the presence of modified methylaluminoxane (MMAO) at 60 °C among other complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide