Synthesis and characterization of organometallic catalysts

Abstract

A new synthetic strategy of developing novel isospecific unbridged metallocene polypropylene catalytic system that can be in-situ generated during the MAO-assisted activation step was demonstrated by using amine-functionalized zirconocene $[1-(p-Me_2NC_6H_4)-3,4-Me_2C_5H_2]_2ZrCl_2$ that has racemic $C_2$ -symmetric nature in the solid state. This precatalyst shows high isospecificity in propylene polymerization under MAO activation but gives complete atactic polypropylene under $[Ph_3C][B(C_6F_5)_4]$ activation. This phenomenon is originated from the inhibition of the rigand rotation during propagation via the Lewis acid-base interaction between basic amine in catalyst and acidic sites in [Me-MAO]-. In order to establish the scope of the current synthetic strategy and obtain further information of this system, $-NEt_2$, -OMe, and -SMe substituted unbridged bis-zirconocenes were also synthesized and their catalytic behaviors in propylene polymerization were obtained. The isoselectivity of these complexes are in order of Lewis basicity, $-NMe_2$ > -OMe > -SMe. The well-defined, novel dinuclear group 4 metal complexes $[4,4``-(C_6H_4)_2(C_5Me_4)_2][CpZrX_2]_2$ (X = Cl, Me), $[4,4``-(C_6H_4)_2(C_5Me_4)_2][TiCl_3]_2$, and $[4,4``-(C_6H_4)_2(C_5Me_4)_2][Ti(O-2,6-iPr_2Ph)Cl_2]_2$ were synthesized and their ethylene and styrene polymerization behaviors were investigated. These complexes exhibit an increase of molecular weight as well as comparable or even higher catalytic activity than their mononuclear analogues, $(C_5Me_4Ph)CpZrX_2$ (X = Cl, Me), $(C_5Me_4biPh)CpZrCl_2$, $(C_5Me_4Ph)TiCl_3$, and $(C_5Me_4Ph)Ti(O-2,6-iPr_2Ph)Cl_2$. To endow the existing biphenylene group with flexibility that can provide better solubility as well as additional metal-metal interactions and at the same time to keep each metal center being highly active by minimizing a steric hindrance between two active centers, dinuclear zirconocenes containing bis(cyclopentadienyl) ligands derived f...