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

作者：Kim Dongil; Kim Sunghoon; Woo Hyun Yul; Lee Ha Jin; Lee Hyosun

来源：Applied Organometallic Chemistry, 2014, 28(6): 445-453.

DOI：10.1002/aoc.3148

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

The reaction of CdBr(2)4H(2)O with ancillary ligands, N,N-bis(1H-pyrazolyl-1-methyl)aniline (L-1), N,N-bis(1H-pyrazolyl-1-methyl)-p-methylaniline (L-2), N,N-bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline (L-3), N,N-bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline (L-4) and N,N-bis(1H-pyrazolyl-1-methyl)-2,6-dimethylaniline (L-5) 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 sigma plane of symmetry, based on the bond length of Cd?N-aniline (2.759(7) angstrom). [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 degrees C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [LnCdBr2](2) (L-n=L-1, L-2, L-3) or monomeric tetrahedral [L5CdBr2].

• 出版日期2014-6