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 |
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| Authors: | Dongil Kim Sunghoon Kim Hyun Yul Woo Ha‐Jin Lee Hyosun Lee |
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| Institution: | 1. Department of Chemistry and Green‐Nano Materials Research Center, Kyungpook National University, Daegu City, Republic of Korea;2. Jeonju Center, Korea Basic Science Institute (KBSI), Jeonju, Republic of Korea |
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| 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 , L3CdBr2]2 , L4CdBr2] and L5CdBr2] . The X‐ray crystal structures of L1CdBr2]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 L5CdBr2] . The geometry at each Cd(II) centre for L1CdBr2]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). L5CdBr2] 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 LnCdBr2]2 (Ln = L1 , L2 , L3 ) or monomeric tetrahedral L5CdBr2] . Copyright © 2014 John Wiley & Sons, Ltd. |
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| Keywords: | bispyrazolyl dimeric Cd(II) complex methyl methacrylate polymerization syndiotacticity |
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