Palladium(II) complexes containing N,N′-bidentate N-cycloalkyl 2-iminomethylpyridine and 2-iminomethylquinoline: Synthesis, characterisation and methyl methacrylate polymerisation

The reaction of [Pd(CH₃CN)₂Cl₂] with N-cyclopentyl-1-(pyridin-2-yl)methanimine (L₁), N-cyclohexyl-1- (pyridin-2-yl)methanimine (L₂), N-(piperidin-1-yl)-1-(pyridin-2-yl) methanimine (L₃) or N-cyclopentyl-1-(quinolin-2-yl)methanimine (L₄) in ethanol yields the bidentate (NN') PdCl₂ complexes [L₁PdCl₂], [L₂PdCl₂], [L ₃PdCl₂] and [L₄PdCl₂], respectively. The X-ray crystal structure of the Pd(II) complexes revealed that the Pd atom in [L_nPdCl₂] (L_n = L₁, L ₂, L₃, L₄) shows a distorted square planar geometry involving two nitrogen atoms and two chloro ligands. The complexes [L₁PdCl₂] and [L₄PdCl₂] (of which the ligands are N-cyclopentyl substituted) showed the highest catalytic activity for the polymerisation of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) with an activity of 1.45 × 10⁵ g PMMA/mol Pd h at 60 C and a PMMA syndiotacticity (characterized using ¹³C NMR spectroscopy) of ca. 0.70.