X-ray crystal structures and MMA polymerization of cadmium(II) complexes with bidentate pyrazole ligands: The formation of monomers or dimers as a function of a methyl substituent on the pyrazole and aniline rings

Dongil Kim, Sunghoon Kim, Hyun Yul Woo, Ha Jin Lee, Hyosun Lee

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

The reaction of CdBr2·4H2O with ancillary ligands, N,N-bis(1H-pyrazolyl-1-methyl)aniline (L1), N,N-bis(1H-pyrazolyl-1-methyl)-p-methylaniline (L2), N,N-bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline (L3), N,N-bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline (L4) and N,N-bis(1H-pyrazolyl-1-methyl)-2,6-dimethylaniline (L5) in ethanol yields novel Cd(II) bromide complexes, [L1CdBr2] 2, [L2CdBr2]2, [L 3CdBr2]2, [L4CdBr2] and [L5CdBr2]. The X-ray crystal structures of [L 1CdBr2]2, [L2CdBr2] 2 and [L3CdBr2]2 reveal a bromo-bridged dimeric species with crystallographic inversion symmetry. Conversely, [L4CdBr2] and [L5CdBr2] exist as monomeric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the ligand and cadmium centre for [L4CdBr2], and crowding around the cadmium metal by methyl substituents on the aniline residue in the ligand for [L 5CdBr2]. The geometry at each Cd(II) centre for [L 1CdBr2]2, [L2CdBr2] 2 and [L3CdBr2]2 is best described as a distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L4CdBr2] by coordinative interaction of the nitrogen atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd-Naniline (2.759(7) Å). [L 5CdBr2] exists with a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of aniline and the Cd centre, resulting in the formation of an eight-membered chelate ring. The catalytic activity of monomeric, five-coordinated [L4CdBr2] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [L nCdBr2]2 (Ln=L1, L 2, L3) or monomeric tetrahedral [L5CdBr 2].

Original languageEnglish
Pages (from-to)445-453
Number of pages9
JournalApplied Organometallic Chemistry
Volume28
Issue number6
DOIs
StatePublished - Jun 2014

Keywords

  • bispyrazolyl
  • dimeric Cd(II) complex
  • methyl methacrylate polymerization
  • syndiotacticity

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