Comparative Theoretical Study on Homopolymerization of α-Olefins by Bis(cyclopentadienyl) Zirconocene and Hafnocene: Elemental Propagation and Termination Reactions between Monomers and Metals

Abstract

A comparative quantum chemical study has been performed to shed light on the fundamental differences between hafnocenes and zirconocenes concerning reactions between the metals and R-olefin monomers, namely, ethene, propene, 1-butene, and 1-hexene. Analogous species along the R-olefin polymerization pathways were studied for bis(cyclopentadienyl) zirconocene and hafnocene, taking into account the structural variations of the first two monomer insertion steps and of the competitive chain-termination reactions. The results were analyzed as a function of both the metal and the monomer, the metal showing more distinct differences. The most notable difference in the reactions of the zirconocene and hafnocene can be seen in β-hydrogen transfer to metal, activation energies for which are significantly higher for the hafnocene.

Ultra‐Rigid Metallocenes for Highly Iso‐ and Regiospecific Polymerization of Propene: The Search for the Perfect Polypropylene Helix

“…The difference between the zirconocene 10 a and the hafnocene 10 b is the amount of regioerrors (Table 2, entries 1–3 and 5–7). For [Cp 2 MCl 2 ] (M=Zr, Hf) theoretical investigations show the same trend as the energy difference between the transition states of a 1,2 and a 2,1‐insertion is higher for the hafnocene compared to the corresponding zirconocene species 23…”

“…For [Cp 2 MCl 2 ] (M= Zr, Hf) theoretical investigations show the same trend as the energy difference between the transition states of a 1,2 and a 2,1-insertion is higher for the hafnocene compared to the corresponding zirconocene species. [23] Additionally, there is a clear dependency of propene concentration on the amount of stereodefects (entries 7 and 8). The formation of a stereoerror is known to proceed either through the choice of the "wrong" enantioface of the monomer or due to a chain end epimerization process (CEP).…”

NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d 0 group 4 metal complexes

“…Although many computational studies have been carried out on these complexes and their role in oligo-and polymerization reactions (67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83), the electronic structures and relative energies of relevant reactants, intermediates, and transition states are computed with the same method used for optimizing the geometries for NMR calculations for consistency. ZrEt + is more deshielded in both the β-H and α-H agostic structures, but this effect is much more pronounced in the latter (Fig.…”

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

“…Previously, Pakkanen et al demonstrated different possibilities of 1,2 and 2,1 propylene attack to Cp 2 MCH 3 + (M = Zr, Hf ) based on the regiostructures as well as stereostructures. 59 As a result, four products are formed in each combination of the two successive insertion steps which are 1,2 and 1,2, 1,2 and 2,1, 2,1 and 1,2, and 2,1 and 2,1 insertions (Scheme 2). There are other different possibilities in propylene attack, the propylene CH 3 group being up or down.…”