Synthesis, characterization, and MMA polymerization activity of tetrahedral Co (II) complex bearing N, N-bis(1-pyrazolyl)methyl ligand based on aniline moiety

A new series of air-stable Co(II) complexes, [bpmaL1]CoCl2 (1a), [bpmaL2]CoCl2 (2a), [bpmaL3]CoCl2 (3a), and [bpmaL4]CoCl2 (4a), where, for example, [bpmaL1 = N,N-bis{(1-pyrazolyl)methyl}aniline], has been synthesized. X-ray crystallography of 2a indicated that it has a dipper-type structure in which the aniline moiety plays the role of the handle with a tetrahedral cobalt located at the edge with an eight-membered chelate ring formation. However, there is no indication that the metal is coordinated to the nitrogen of the aniline group. Moreover, complexes showed the highest catalytic activity in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) with an activity of 1.14 × 106 g PMMA/mol-Co·h at 60 °C and syndiotacticity of PMMA, characterized by 13 C NMR spectroscopy, which value was ca. 0.57.

Graphical AbstractA new series of air-stable Co(II) complexes, [bpmaL1]CoCl2 (1a), [bpmaL2]CoCl2 (2a), [bpmaL3]CoCl2 (3a), and [bpmaL4]CoCl2 (4a) have been synthesized and specifically, complex 2a was structurally characterized by X-ray crystallography. Complexes were evaluated as a catalyst for the polymerization of methyl methacrylate (MMA), the activity of MMA polymerization increased sharply with increasing temperature, the conversion reached up to 70% at 60 °C with narrow PDI (Mw/Mn) ca. 2. In addition, syndiotacticity of PMMA characterized by 13 C NMR spectroscopy, in which the value was ca. 0.57.Figure optionsDownload as PowerPoint slide