Utilization of Pyridylamido-based Ligand System for Synthesis of Hafnium and Tungsten Complexes

Abstract

Complexes having early transition metal like Ti, Zr, and Hf are widely used in olefin polymerization as catalysts. These complexes have been actively researched since the invention of Ziegler-natta catalysts. And in 2007, Dow and symyx co-researched asymmetric structure based hafnium catalysts which have high activity and high isoselectivity in α-olefin polymerization. The structural features of this hafnium catalyst are pyridine nitrogen, amido nitrogen, aryl bond carbon and two methyl groups coordinating hafnium metal center. Because of this sterically surrounded system and asymmetric structure, hafnium complex has restricted size of active site and insertion direction of monomers. Although this pyridyl-amido complex has good catalytic activity in olefin polymerization, it has short catalytic lifetimes (< 50 minutes). For overcoming these short catalytic lifetimes, we tried to modifying ligand system. In our research, we synthesized ligand scaffold through organic synthesis and then proceeded metalation for hafnium complex. After synthesizing, we analyze the structure by NMR spectroscopy. And we confirmed whether the synthesized complex has catalytic activity in olefin polymerization through the copolymerization test of the synthesized complex. And then, we synthesized a metal complex by reacting with another metal (W) using the synthesized ligand and tried to confirm the reactivity through electrochemistry of the synthesized tungsten complex.