Zirconium Phosphinimide Complexes:  Synthesis, Structure, and Deactivation Pathways in Ethylene Polymerization Catalysis

Abstract

Zirconium phosphinimide complexes of the form CpZr(NP-t-Bu 3 )Cl 2 (1) and Cp*Zr(NPR 3 )-Cl 2 (R ) i-Pr (2), t-Bu (3)) were readily prepared under ambient conditions via the reaction of [CpZrCl 3 ] n or Cp*ZrCl 3 with the appropriate trialkylphosphinimide lithium salt (R 3 PNLi). A series of derivatives were readily obtained via alkylation or arylation of the above dihalide precursors. These included CpZr(NP-t-Bu 3 )Me 2 (4), Cp*Zr(NPR 3 )Me 2 (R ) i-Pr (5), t-Bu (6)),. Reaction of 17 with the borane B(C 6 F 5 ) 3 yielded the zwitterionic and cationic complexes Cp*Zr(NP-t-Bu 3 )(CH 2 C(CH 3 )C(CH 3 )CH 2 B(C 6 F 5 ) 3 ) (18) and Cp*Zr(NP-t-Bu 3 )(THF)-(CH 2 C(CH 3 )C(CH 3 )CH 2 B(C 6 F 5 ) 3 ) (19). A number of the above compounds were screened for their potential as catalyst precursors in ethylene polymerization. In general, upon activation with methylaluminoxane, the resulting catalysts exhibit low activity. Efforts to understand the deactivation pathway for these zirconium catalysts involved investigating the interactions of catalyst precursors with activators. For example, reaction of 4 with the borane B(C 6 F 5 ) 3 leads to aryl group transfer and formation of catalytically inactive CpZr(NP-t-Bu 3 )(C 6 F 5 ) 2 (20). Interactions with MAO were modeled via reaction with AlMe 3 . The Zr clusters (Cp*Zr) 4 -(µ-Cl) 5 (Cl)(µ-CH) 2 ( 21) and (Cp*Zr) 5 (µ-Cl) 6 (µ-CH) 3 ( 22) were two of the products that were characterized from these reactions. The isolation of 21 and 22 infers that aryl for methyl exchange, ligand abstraction, and C-H bond activation may be catalyst deactivation pathways.

Inner-sphere two-electron reduction leads to cleavage and functionalization of coordinated dinitrogen

“…The Ta(1)-Ta(2) distance is 2.7007(6) Å similar to other Ta(IV)-Ta(IV) species (45); the PAN bond distance of 1.595(9) Å in this unit is typical of other groups 4 and 5 phosphinimide complexes (46,47). The zirconium nitride moiety is somewhat uncommon in the literature; however, comparison of Zr1-N2 at 2.040(9) Å shows it to be shorter that other bridging zirconium nitrides that range from 2.21 to 2.35 Å (48-50).…”

Aspects of coordination polymerization in heterogeneous and homogeneous catalysis. A computational survey

“…However, it should be noted that other factors might render zirconium systems less active than their titanium analogues. Some zirconium systems are known to be deactivated by abstraction of a C 6 F 5 group from the counterion by the precatalyst [57].…”

Non-Cp type homogeneous catalytic systems for olefin polymerization

“…Ligands such as boratabenzenes [23][24][25][26][27][28][29][30][31][32], phosphinimides [33][34][35][36][37][38][39], tropidynyl ligand [40] and hydrido(trispyrazolyl)borate ligand [41] that are considered as electronically and sterically analogous to Cp have been employed in synthesizing numerous olefin polymerization catalytic systems. Some examples 1-7 are illustrated in Fig.…”