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

Abstract

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.

Nonconventional Catalysts for Isotactic Propene Polymerization in Solution Developed by Using High‐Throughput‐Screening Technologies

“…The performance of the new catalysts in toluene at 90 °C and a partial pressure of propene of 6.9 bar (100 psi) is compared in Table 1 with the state‐of‐the‐art C 2 ‐symmetric metallocene, rac ‐[Me 2 Si(2‐Me‐4‐phenyl‐1‐indenyl) 2 Zr(η 4 ‐1,4‐(phenyl) 2 ‐1,3‐butadiene)] 23. Strikingly, under the conditions explored, the unoptimized pyridyl‐amide catalysts displayed productivities up to 20 % of that of the highly optimized metallocene.…”

Diene complexes of early transition metals: ideas and progresses at Osaka University

“…Only recently, such data for the ansazirconocene diene complexes 18 [39] and 28 [73] have been reported [34]. These unique features are listed in Table 1.…”

“…Our approach has been based on the coordination space of half-metallocene fragments of niobium and tantalum, in which various catalytic and stoichiometric transformations have been performed. Tatsumi prepared bis(1,4-dithia-1,3-butadiene) complex, Cp*Ta(SCH@CHS) 2 (39), that adopts supineprone orientation [99]. The unique C-S bond fission of 39 led to the chemistry of the sulfide complexes such as [Cp*Ta(S) 3 ] 2À (40) [100], and since then he has been extending this line of the chemistry.…”

Developments of Chiral Metallocenes as Polymerization Catalysts

“…A 1,4-diphenyl-1,3-butadiene complex is also effective for rac -selective synthesis of bulky ansa -metallocenes ( Scheme 4 ) [ 15 ]. The diphenylbutadiene complex, ZrCl 2 (PR 3 ) 2 (DPBD) (R = Et, Pr i ; DPBD = 1,4-diphenyl-1,3-butadiene), can be prepared by the reduction of ZrCl 4 (PR 3 ) 2 with Li metal in the presence of diphenylbutadiene in 90-93% yields.…”