Cobalt(II) complexes containing N′-substituted N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine ligands: The formation of four-coordinate or five-coordinate complexes as a function of the N′-substitution group in N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine
作者:Sunghye Choi、Saira Nayab、Jongho Jeon、Sang Hyun Park、Hyosun Lee
DOI:10.1016/j.ica.2015.09.008
日期:2015.11
N,N-bis((1H-pyrazol-1-yl)methyl)(cyclohexyl)methanamine (L-A), N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-diethylbenzenamine (L-B), N,N-bis((1H-pyrazol-1-yl)methyl)-4-bromobenzenamine (L-C), N,N-bis((1H-pyrazol-1-yl)methyl)cyclohexanamine (L-D), N,N-bis((1H-pyrazol-1-yl)methyl)(furan-2-yl)methanamine (L-E), N,N-bis((1H-pyrazol-1-yl)methyl)-2-methoxyethanamine (L-F), and N,N-bis((1H-pyrazol-1-yl) methyl)-3-(methylthio)propan-1-amine (L-G) with [CoCl2.6H(2)O] in ethanol yield a novel series of Co(II) chloride complexes; i.e. [LnCoCl2] (L-n = L-A-L-G), respectively. The molecular structures of [LnCoCl2] (L-n = L-A-L-C) and [LnCoCl2] (L-n = L-D-L-G) exist as monomeric four-coordinated and five-coordinated complexes, respectively. [LnCoCl2] (L-n = L-A-L-C) showed a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of the N'-substitution amine moiety and the Co(II) centre, resulting in the formation of an eight-membered chelate ring. The geometry at each Co(II) centre in [LnCoCl2] (L-n = L-D-L-G) were best described as a distorted trigonal bipyramid involving coordination of the nitrogen atom of the N'-substitution amine group and the Co(II) centre. Specifically, a distorted trigonal bipyramid was achieved in [LDCoCl2] through a coordinative interaction of the nitrogen atom of the cyclohexylamine unit and the Co(II) atom with an sigma plane of symmetry based on the bond length of Co-N-cyclcohexylamine [2.466(4) angstrom]. Moreover, [LDCoCl2] showed the highest activity for methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane (MMAO) at 60 degrees C and yielded poly(methylmethacrylate) (PMMA) with a high molecular weight (M-w) and narrower polydispersity index (PDI) compared to the other Co(II) complexes. However, all Co(II) complexes produced syndiotactic (PMMA), characterised using H-1 NMR spectroscopy, with ca. 0.70. (C) 2015 Elsevier B.V. All rights reserved.