Zinc (II), palladium (II) and cadmium (II) complexes containing 4‐methoxy‐<i>N</i>‐(pyridin‐2‐ylmethylene) aniline derivatives: Synthesis, characterization and methyl methacrylate polymerization

Abstract

A series of Zn (II), Pd (II) and Cd (II) complexes, [(L) n MX 2 ] m (L = L‐a–L‐c; M = Zn, Pd; X = Cl; M = Cd; X = Br; n , m = 1 or 2), containing 4‐methoxy‐ N ‐(pyridin‐2‐ylmethylene) aniline ( L‐a ), 4‐methoxy‐ N ‐(pyridin‐2‐ylmethyl) aniline ( L‐b ) and 4‐methoxy‐ N ‐methyl‐ N ‐(pyridin‐2‐ylmethyl) aniline ( L‐c ) have been synthesized and characterized. The X‐ray crystal structures of Pd (II) complexes [L 1 PdCl 2 ] (L = L‐b and L‐c) revealed distorted square planar geometries obtained via coordinative interaction of the nitrogen atoms of pyridine and amine moieties and two chloro ligands. The geometry around Zn (II) center in [(L‐a)ZnCl 2 ] and [(L‐c)ZnCl 2 ] can be best described as distorted tetrahedral, whereas [(L‐b) 2 ZnCl 2 ] and [(L‐b) 2 CdBr 2 ] achieved 6‐coordinated octahedral geometries around Zn and Cd centers through 2‐equivalent ligands, respectively. In addition, a dimeric [(L‐c)Cd( μ ‐ Br)Br] 2 complex exhibited typical 5‐coordinated trigonal bipyramidal geometry around Cd center. The polymerization of methyl methacrylate in the presence of modified methylaluminoxane was evaluated by all the synthesized complexes at 60°C. Among these complexes, [(L‐b)PdCl 2 ] showed the highest catalytic activity [3.80 × 10 4 g poly (methyl methacrylate) (PMMA)/mol Pd hr −1 ], yielding high molecular weight (9.12 × 10 5 g mol −1 ) PMMA. Syndio‐enriched PMMA (characterized using 1 H‐NMR spectroscopy) of about 0.68 was obtained with T g in the range 120–128°C. Unlike imine and amine moieties, the introduction of N ‐methyl moiety has an adverse effect on the catalytic activity, but the syndiotacticity remained unaffected.