Abstract
During the last two decades, group-IV metals-based aminopyridinato complexes have attracted a tremendous research interest because of immense industrial needs for the catalyst which would be of higher activity and selectivity with lower toxicity and lower cost. Chemistry of titanium (Ti) and zirconium (Zr) complexes was more extensively explored as compared to hafnium (Hf) complexes. Direct synthesis, salt metathesis, amine elimination, alkane elimination, silyl chloride elimination, hydrogen chloride elimination and toluene elimination protocols have been used for the synthesis of group-IV metal complexes. Changes in ligand and complex design were made to optimize these catalysts for olefin polymerization. Most of these complexes have shown good catalytic activities when activated with dry methyl aluminoxane. Ligand transfer to aluminum was found in these complexes, particularly with less bulky ligands, and this ligand transfer problem was overcome by tridentate ligands but the activities of these complexes were not competitive to complexes with bidentate aminopyridinato ligands. Majority of these complexes produce high-molecular-weight polymers with broader molecular weight distributions, and Hf-complexes produce longer chain polymers than their comparative Ti and Zr aminopyridinato complexes. It could be deduced that group-IV metals inherit the potential for optimal polymerizing catalysts probably, because of their almost vacant d-orbitals, these act as hard acids which on combination with soft bases carry the opportunity to design and develop polymerization catalysts which could overcome the problems associated with existing systems.
Highlights
Polymer-based products have become critical necessities ranging from household appliances to aerospace jets [1]
A revolution was initiated by Zeigler and Natta by the discovery of group-IV metal catalysts due to their enormous industrial application which inspired intensive research and development of these catalysts for olefin polymerization [4] that led to the development of group-IV metallocene catalysts for olefins polymerization using Alalkyls as co-catalyst [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
In the light of industrial applications and scientific interest, we are providing the relevant updates on group-IV metals complexes with aminopyridine ligands including general mechanism, structural aspects and application in olefin polymerization catalysis as well as other closely related relevant developments
Summary
Polymer-based products have become critical necessities ranging from household appliances to aerospace jets [1]. In the light of industrial applications and scientific interest, we are providing the relevant updates on group-IV metals complexes with aminopyridine ligands including general mechanism, structural aspects and application in olefin polymerization catalysis as well as other closely related relevant developments. We expect that it will serve the relevant scientific community for further enhancements. Some researchers have used commercial form for polymerization reactions, but the disadvantage of using this MAO as in case of aminopyridinato-Ti-complexes is its AlMe3 content which reacts with the active catalysts, and these are converted into the Ap-aluminum complexes which do not have the capability to polymerize olefins [44].
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