Theoretical Elucidation of the Effect of Counteranions on the Olefin Polymerization Activity of (Pyridylamido)Hf(IV) Catalyst by QM and REMD Studies: MeB(C₆F₅)₃^– versus B(C₆F₅)₄^–

Abstract

1-Octene insertion reaction by the cationic active species of (pyridylamido)­Hf­(IV) catalyst (HfCat+) was investigated, focusing on the effect of the counteranions (CAs), MeB­(C6F5)3 – and B­(C6F5)4 – on catalyst activity. Quantum mechanical (QM) calculation showed a remarkable difference in TS structures that HfCat+–MeB­(C6F5)3 – complex forms an “inner-sphere” ion pair (ISIP), while HfCat+–B­(C6F5)4 – forms an “outer-sphere” ion pair (OSIP). However, the activation free energies of 1-octene insertion by both complexes are almost identical to each other. Meanwhile, replica exchange molecular dynamics (REMD) calculation revealed that the time duration of the HfCat+ capturing 1-octene monomers throughout the REMD trajectories of HfCat+–B­(C6F5)4 – complex was ∼2.5 times that of HfCat+–MeB­(C6F5)3 –. This is because B­(C6F5)4 – is more likely to dissociate from HfCat+ to form an OSIP than MeB­(C6F5)3 – and thus allows monomers to approach HfCat+ more easily. Using these microscopic data, we have numerically evaluated the 1-octene polymerization reaction rate constants and succeeded in qualitatively reproducing the experimentally observed tendency of the polymerization reaction with B­(C6F5)4 – faster than with MeB­(C6F5)3 –. Finally, it is theoretically elucidated that the monomer capture process before the monomer insertion process determines the overall polymerization reaction rates in this catalytic system.

Atomistic Simulation of the Polymerization Reaction by a (Pyridylamido)hafnium(IV) Catalyst: Counteranion Influence on the Reaction Rate and the Living Character of the Catalytic System

“…50 Thus, there are four possible coordination patterns of 1-octene insertion, i.e., trans-1,2, cis-1,2, trans-2,1 and cis-2,1. 57…”

“…Table 1 shows the polymerization reaction rate constant k 2 exp in each IP system that can be estimated from the experiment. 50,57 In Figure 3, the polymerization reaction in the HfCat Pn+ −B(C 6 F 5 ) 4…”

“…The numerical value of ΔE a R i for each 1-octene insertion process (R i ) was taken from the QM calculation in our previous research. 57 Under this calculation condition, ten RM simulations were performed for 3000 RM cycles, starting from the ten different initial structures, for each HfCat Pn+ − MeB(C 6 F 5 ) 3…”

Catalyst Activation and Chain Transfer Agents in Metallocene Catalysts for Ethylene Polymerization: A Computational Investigation

“…Kumawat et al [3] have also reported the 19.5 kcal/mol energy barrier for the ethylene monomer insertion into the HfÀ C 3 H 7 bond with B(C 6 F 5 ) 3 cocatalyst. Nagaoka and coworkers [55] have reported the 1-octene polymerization using HfCat + À MeB(C 6 F 5 ) 3/4 À catalyst system where the monomer insertion rate was found to ΔG � = 17.6 and 17.9 kcal/ mol for the MeB(C 6 F 5 ) 3 À and B(C 6 F 5 ) 4 À cocatalysts. Parveen et al [56] have studied a range of metallocene catalysts for ethylene polymerization.…”

Polymerization via Insertion of Ethylene into Al−C bond under Mild Conditions: Mechanistic Studies on the Promotion Exerted by a Catalytic Amount of Cationic Gadolinium Metallocene

“…Much effort has been put into exploring activation and propagation mechanisms in cationic catalyst. [25][26][27][28][29][30][31][32][33][34][35] As a result of these efforts, it is generally accepted that the polymerization process is initiated with an anion displacement step, where the first incoming monomer displaces the counter anion in the inner-sphere contact ion pair to form the outer-sphere ion pair of monomer-coordinating intermediate and the counter anion. In this study, we considered that the additional ethylene monomer or alkyl aluminum needs to interfere with the coordination of the counter anion to the Gd cation in order to keep the counter anion away from the Gd cation in toluene solvent.…”