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 [ L n MCl 2 ] complexes (L n = L A , L B ; M = Co, Cu, Zn) containing the N , N -chelating ligands N , N -bis((1H-pyrazol-1-yl)methyl)cyclopentanamine ( L A ) and N , N -bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)cyclopentanamine ( L B ) 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. [ L A ZnCl 2 ] showed a distorted tetrahedral geometry involving a non-coordinative interaction of the N amine atom and the Zn(II) center, resulting in the formation of an eight membered chelate ring. [ L A CoCl 2 ] exhibited the highest catalytic activity (7.67 × 10 4 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 ( M w ) (11.2 × 10 5 g/mol) and narrower polydispersity index (PDI) 1.01 compared to its Cu(II) and Zn(II) analogs. Syndiotactic enriched PMMA was obtained with T g 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. [ABSTRACT FROM AUTHOR]