Synthesis and structural characterization of 5-coordinate cobalt(II), copper(II) and 4-coordinate zinc(II) complexes containing N′-cyclopentyl substituted N,N-bispyrazolylmethylamine

Novel [LnMCl2] complexes (Ln = LA, LB; M = Co, Cu, Zn) containing the N,N-chelating ligands N,N-bis((1H-pyrazol-1-yl)methyl)cyclopentanamine (LA) and N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)cyclopentanamine (LB) have been synthesized and characterized. The X-ray crystal structures of the Co(II) and Cu(II) complexes revealed that the ligands are coordinated in an N,N,N-tridentate manner, resulting in distorted trigonal bipyramidal geometries through the coordinative interaction of the nitrogen atom of the cyclopentylamine moiety and the metal centers. [LAZnCl2] showed a distorted tetrahedral geometry involving a non-coordinative interaction of the Namine atom and the Zn(II) center, resulting in the formation of an eight membered chelate ring. [LACoCl2] exhibited the highest catalytic activity (7.67 × 104 g PMMA/mol Co h) for the polymerization of MMA in the presence of MMAO at 60 °C and yielded PMMA with a high molecular weight (Mw) (11.2 × 105 g/mol) and narrower polydispersity index (PDI) 1.01 compared to its Cu(II) and Zn(II) analogs. Syndiotactic enriched PMMA was obtained with Tg in the range 120–132 °C. The introduction of bulky methyl substituents played an influential role on controlling the catalytic activities while the syndiotacticities remained unaffected.

Novel Co(II), Cu(II) and Zn(II) complexes ligated to N′-cyclopentyl substituted N,N-bispyrazolylmethylamine have been synthesized and characterized. These complexes polymerize methyl methacrylate in the presence of MMAO to yield syndiotactic poly(methylmethacrylate) at 60 °C. The Co(II) complexes exhibited higher catalytic activity compared to the Cu(II) and Zn(II) analogs. The catalytic activities were affected by the steric encumbrance around the metal center.Figure optionsDownload as PowerPoint slide