Divalent ansa-Zirconocenes: Stereoselective Synthesis and High Activity for Propylene Polymerization

The reduction of ZrCl4(PR3)2 with Li powder, in the presence of a stoichiometric amount of trans-1,4-diphenyl-1,3-butadiene, affords the Zr(II) diene complexes (1) in 90−93% yields. This reaction consists of a rate-limiting step for the formation of the chloride-bridged Zr(III) dimer (2) and a fast diene-driven disproportionation of 2 to 1 and ZrCl4(PR3)2 that re-enters the reduction cycle. The reaction of 1 with Li2{Me2Si(2-Me-4-Ph-Ind)2} in toluene produces quantitatively the desired racemic, divalent ansa-zirconocene (3) that is a highly active isospecific propylene polymerization catalyst upon activation with common activators.

以Li粉末还原ZrCl4(PR3)2，并在等摩尔量的trans-1,4-二苯基-1,3-丁二烯存在下，可制得Zr(II)二烯络合物（1），产率高达90%-93%。该反应过程包括形成氯化桥接的Zr(III)二聚体（2）的速率控制步骤，以及2快速进行二烯驱动的歧化反应生成1和ZrCl4(PR3)2，后者重新进入还原循环。络合物1与Li2{Me2Si(2-Me-4-Ph-Ind)2}在甲苯中的反应可定量地生成所需的具有对映异构性的二价环锆烯化合物（3），该化合物在常规活化剂的作用下，是一种高效的均相丙烯聚合催化剂。