Synthesis, Characterization, and Catalytic Activities for the Polymerization of Olefins Promoted by Zirconium(III) and Titanium(III) Allyl Complexes

Abstract

The reaction of early-transition-metal halides MCl 4 (M ) Zr, Ti) with 2 equiv of the lithium allyl compound ( t BuMe 2 SiCH) 2 CHLi‚TMEDA in toluene produced the corresponding reduced complexes [{( t BuMe 2 SiCH) 2 CH} 2 M(µ-Cl) 2 Li‚TMEDA] (M ) Zr (1), Ti (2)), that were isolated as air-sensitive dark brown (Zr) and brick red (Ti) crystals in 48% and 42% yield, respectively. In addition, each reaction is associated with the formation of the dimer of the allyl ligand (3). Complexes 1 and 2 and dimer 3 were fully characterized spectroscopically, including solid-state X-ray diffraction studies. Complex 1 represents the first solid-state characterization for a Zr(III)-allyl complex. Oxidation of complexes 1 and 2 allows the formation of the corresponding neutral complexes {( t BuMe 2 SiCH) 2 CH} 2 MCl 2 (M ) Zr (4), Ti 5)), which were isolated as air-sensitive light yellow (Zr) and orange (Ti) powders in 23% and 11% yields, respectively. The allylic moieties in complex 5 showed a dynamic interconverting coordination from η 3 to η 1 , causing an alternation between C 2 and C 2v symmetries of the complex. For the cationic complex 4 a similar dynamic interconverting coordination from η 3 to η 1 was observed. The catalytic activities of complexes 1 and 2 activated with MAO in the polymerization of propylene and ethylene were studied. The activity of complexes 1 and 2 was compared to the corresponding activities presented by complexes 4 and 5, respectively, indicating that during the polymerization process, Zr(III) and Ti(III) are oxidized to the corresponding cationic Zr(IV) and Ti(IV) species. For propylene, an elastomeric polypropylene was obtained, whereas for ethylene high-density polyethylene was produced. When the η 3 coordination modes of the ligands are operative in the complex, a cationic racemic octahedral compound is formed, which is responsible for the polymerization of the isotactic domains, whereas when the η 1 coordination modes of the ligands are effective, a cationic tetrahedral complex is obtained, accounting for the atactic domains. The formations of isotactic-atactic domains within a polymer chain give rise to elastomeric polypropylene.

EPR Identification of Zr(III) Complexes Formed upon Interaction of (2‐PhInd)2ZrCl2 and rac‐Me2Si(1‐Ind)2ZrCl2 with MAO and MMAO

“…This allows to reveal the partially resolved splitting (a Al ¼ 3.6 G, 27 Al, I ¼ 5/2) of the signal at g ¼ 1.956. This splitting arises from one aluminum nucleus.…”

Complexes with Sterically Bulky Allyl Ligands: Insights into Structure and Bonding

“…2 Li-(tmeda), along with the coupled dimer of the allyl ligand. [13] Some of the allyl anion serves as the reducing agent, which reduces the yield of the metal complex below 50 %. In the solid-state structures of both compounds, the allyl ligands are slightly slipped to one side of the metal, suggesting a distortion toward a σ,π-(η 3 ) bonding arrangement.…”

“…Multistep insertions are likely involved in the reaction between NiAЈ 2 and PMe 3 , which yields tetramethyltetraphosphane, (MeP) 4 . The product was identified with 1 H, 13 C, and 31 P NMR spectra and its formation studied with DFT methods. [17] Such studies suggest that the direct reaction NiAЈ 2 polymerization catalysts for ethylene (forming high density polyethylene) and propylene (forming an elastomeric polypropylene with the Ti complexes and a stereoregular polymer with the Zr species).…”

“…[17] Such studies suggest that the direct reaction NiAЈ 2 polymerization catalysts for ethylene (forming high density polyethylene) and propylene (forming an elastomeric polypropylene with the Ti complexes and a stereoregular polymer with the Zr species). [13] The cyclic {K(thf) 2 [45] Among the neutral lanthanide allyl complexes, the polymerization activity appears to vary with the radius of the lanthanide metals and with the number of coordinated allyls; i.e., with the access of MMA to the metal centers. The divalent complexes Sm[AЈ] 2 (thf) 2 and Eu[AЈ] 2 (thf) 2 , for example, which contain the larger metals samarium and europium (Sm 2+ ≈ Eu 2+ 1.17 Å for CN number 6), [85] have TOF values over ten times higher than Yb[AЈ] 2 (thf) 2 (Yb 2+ = 1.02 Å for CN number 6).…”

“…Fraenkel reported the synthesis of lithiated derivatives of [(SiMe 3 ) n C 3 H 5-n ] -anions in the early 1990s, [9][10][11] and allyl ligands with one to three trimethylsilyl substituents are known. [12] These and related variants such as dimethyl(tert-butyl)silylallyl [13] have remained the most extensively used ligand types in bulky allyl complex chemistry. The trimethylsilyl groups provide good solubility in hydrocarbon solvents, and substantially increase the size and steric demands of the ligands; e.g., at 216 Å 3 , the syn,syn- How much of an effect such increased bulk has on the properties of the association complexes varies not only with the degree of substitution, but also with the identity of the substituent.…”