Some Transition Metal Complexes Bearing Artemisinin Derivatives and (N-N-O) Tridentate Chromium (III) Complexes Ligated by 2-benzoImidazo-yl-6-acetylpyridines for Catalytic Behaviour towards Ethylene

Abstract

Abstract: Interventions of metal complexes in the area of metallopharmeceutical and polymer sciences play a great economic importance to human challenges. Complexation behavior of some artemisinin derivatives with late transition metals and chromium-benzoimidazoylpyridine analogues have been investigated. The Fe(III), Zn(II) and Cd(II) complexes of artesunate and artemether and that of chromium-benzimidazoyl pyridine were synthesized with molar ratio of metal to ligand between 1:1 and 1:2. Structural elucidation using X-ray analysis and other characterization of the complexes (AAS, IR, UV, E.A, NMR) were carried out to explore the coordination affinity of them viz-a viz bonding, geometries and elemental composition. The IR absorption revealed that artesunate acts as monodentate specie through carbonyl group on coordination. However, its bidentate mode was also observed with carboxylic group acting as C=O and C-O bonding when deprotonation happened. Artemether (L2) was synthesized using artesunate and its structure was confirmed by single crystal X-ray crystallography as well as its Zn(II) complex exhibiting a square planar geometry. A series of 2-benzoimidazoylpyridine derivates (L3-L6) and their chromium complexes were synthesized and characterized. In the presence of methylaluminoxane (MAO), all chromium complexes show good activity for ethylene oligomerization and polymerization whereas with diethylaluminium chloride (Et2AlCl2) the complexes show moderate activity. The distribution of oligomers obtained follows Schulz- Flory rules with high selectivity for α-olefins. The combined productivity (meaning both activities of ethylene oligomerization and polymerization) are improved with increasing ethylene pressure. The results show that the reaction conditions greatly affect the properties of the polymer such as molecular weight distribution and melting point(Tm) with extremely broad molecular weight distributions. With elevating reaction temperature from 0 to 60 oC, the melting point (Tm) of resultant polyethylene decreased rapidly from 134 oC to 70 oC.