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.