Homogeneous Single-Component Betaine Ziegler−Natta Catalysts Derived from (Butadiene)zirconocene Precursors

Abstract

(Butadiene)zirconocene adds B(C(6)F(5))(3) at a terminal diene carbon atom to yield the zirconocene-(mu-hydrocarbyl)-borate betaine Cp(2)Zr[C(4)H(6)-B(C(6)F(5))(3)] (4). The dipolar complex 4 contains a distorted pi-allyl moiety and features an additional stabilizing Zr-F-C(arene) coordination. Under kinetic control, an isomeric betaine system is formed, characterized by an internal Zr(+).CH(2)[B](-) ion-pair interaction, that rearranges to 4 upon heating. A great variety of ansa-metallocene(butadiene) complexes and related systems cleanly form analogous metallocene-(mu-conjugated diene)-borate betaines upon treatment with B(C(6)F(5))(3) and related Lewis acids. Most of these systems represent very active homogeneous single-component Ziegler-Natta catalysts for alpha-olefin polymerization and copolymerization. In addition, these betaine catalysts are ideally suited for carrying out mechanistic studies in active Ziegler-Natta catalyst systems. They allow for an experimental observation of the first alkene insertion step at the active single-component catalyst. This feature has been used for studying the mechanism of transfer of the stereochemical information from the bent metallocene backbone and for an experimental characterization of the energy profile of the alkene addition/alkene insertion reaction sequence in active homogeneous Ziegler-Natta systems. The neutral dipolar single-component catalysts (e.g., 4) produce a polyolefin-modified R'-(CHR-CH(2))-C(4)H(6)-B(C(6)F(5))(3)(-) counterion at the end of the initiation period upon entering into the repetitive active catalytic cycle.

Revisiting the Stereochemistry of Propylene Isotactic Polymerization Reaction Mechanism on C2 Symmetric [SiH2(Ind)2ZrCH3]+ and [SiH2(Ind)2ZrCH3]+[CH3B(C6F5)3]−

“…Erker experimentally investigated the stereochemistry for first propylene insertion in [rac-Me 2 Si-(Ind) 2 ]Zr(®-C 4 H 6 )B(C 6 F 5 ) 3 and observed that α agostic metal CH interaction could be a reason for the isoselective nature of propylene attack. 32 The αCH agostic interaction might decrease the activation energy for insertion and give more space for propylene attack. 33 However, analytical tools such as NMR and X-ray techniques have provided considerable proof for the formation of βCH agostic structures in the resting states.…”

Synthesis and Reactivity of Oxametallacyclic Niobium Compounds by Using α,β‐Unsaturated Carbonyl Ligands

“…This formulation was confirmed by comparison with the related tantalum compound [TaCp*Cl 3 {CH 2 CH 2 C(O)OMe}], for which the X-ray molecular structure has been reported. [29] The same reaction with compounds 2a, 2b, and 3a and related reactions employing HCl as the Brönsted acid led to decomposition of the starting materials, whereas none of these compounds reacted with the related Lewis acids [Me 3 O][BF 4 ] and (Me 3 Si)OTf. [30] Reaction with the Lewis Acids E(C 6 F 5 ) 3 …”

“…[4,8,31] We have investigated the reactivity of complexes 2a-b and 3a-b with the Lewis acids E(C 6 F 5 ) 3 (E = B, Al) with the aim of abstracting the alkyl ligand to generate a cationic enolate compound, considering that early transition-metal derivatives of this type have been used as precursors for the catalytic polymerization of acrylates. [12][13][14][15][16] Although the nucleophilicity of the oxygen atom bonded to the niobium atom could compete with that of the carbon atom, we have previously observed that alkoxido complexes of the type [Cp*TaMe 3 (OR)] reacted with these Lewis acids E(C 6 F 5 ) 3 at the Ta-C bond.…”

“…Hence, complexes with this type of ligand are better represented with contributions from two main canonical forms, σ 2 ,π-metallacyclic or π 2 -butadiene ( Figure 1). [1][2][3][4][5] 2b and 3b to give the three-membered metallacyclic (or η 2 -enone) compounds [NbCp R Cl 2 {η 2 -CH 2 =CHC(OMe){O· E(C 6 F 5 ) 3 }}] [Cp R = C 5 H 4 SiMe 2 Cl, E = B (5), Al (6); Cp R = C 5 H 4 SiMe 3 , E = B (7), Al (8)], which decomposed to the corresponding adducts MA·E(C 6 F 5 ) 3 . The same reaction with the 2a and 3a derivatives only allowed the observation of the corresponding adducts MMA·E(C 6 F 5 ) 3 Replacement of at least one of the terminal CR 2 moieties by an isolobal fragment such as NR, O, S, etc.…”

Transition metal-based polymer chemistry: a critical micro-review

“…It would certainly exceed by far the scope of this article if one attempted to give a comprehensive review on group IV-based polyole n chemistry. Fortunately, some excellent reviews on this topic, including carbocationic alkene polymerization [28], have been published quite recently and will serve as a reference for comprehensive reading [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Nevertheless, a few aspects of this chemistry that certainly deserve to be discussed will be mentioned.…”