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

Abstract

Atomistic simulation of the 1-octene polymerization reaction by a (pyridylamido)­Hf­(IV) catalyst was conducted on the basis of Red Moon (RM) methodology, focusing on the effect of the counteranions (CAs), MeB­(C6F5)3 –, and B­(C6F5)4 –, on the catalyst activity and chain termination reaction. We show that RM simulation reasonably reproduces the faster reaction rate with B­(C6F5)4 – than with MeB­(C6F5)3 –. Notably, the initiation of the polymerization reaction with MeB­(C6F5)3 – is comparatively slow due to the difficulty of the first insertion. Then, we investigated the free energy map of the ion pair (IP) structures consisting of each CA and the cationic (pyridylamido)­Hf­(IV) catalyst with the growing polymer chain (HfCatPn+), which determines the polymerization reaction rates, and found that HfCatPn+–MeB­(C6F5)3 – can keep forming “inner-sphere” IPs even after the polymer chain becomes sufficiently bulky, while HfCatPn+–B­(C6F5)4 – forms mostly “outer-sphere” IPs. Finally, we further tried to elucidate the origin of the broader molecular weight distribution (MWD) of the polymer experimentally produced with B­(C6F5)4 – than that with MeB­(C6F5)3 –. Then, through the trajectory analysis of the RM simulations, it was revealed that the chain termination reaction would be more sensitive to the IP structures than the monomer insertion reaction because the former involves a more constrained structure than the latter, which is likely to be a possible origin of the MWDs dependent on the CAs.

Verification for Temperature Dependence of Tacticity in Polystyrene Radical Polymerization with the Combination of Reaction Pathway Analysis and Red Moon Methodology

“…RM method regards chemical reactions as rare events which are treated by MC method in a long-time scale, while the molecular motions are treated via MD methods in a short-time scale. The RM method has been applied for a wide range of complex systems and has succeeded in predicting and explaining massive complex chemical reaction processes, such as catalytic polymerization − and solid–electrolyte interface layer formation. , Also in our previous research, we successfully predicted the temperature-dependent meso ratio curve of poly­(methyl methacrylate) (PMMA) produced by radical polymerization in bulk, which shows great coincidence with experimental results …”

Development of advanced electrolytes in Na-ion batteries: application of the Red Moon method for molecular structure design of the SEI layer

“…[59][60][61][62][63][64][65] In addition, the RM method has recently shown a high efficiency to treat the dynamic processes of catalytic polymerization reactions. 66,67 In fact, it can be applicable also to more complicated electrolyte systems such as polymer electrolytes or ionic liquids. On the other hand, it is also important to spell out some modeling limitations for this method, which must be understood carefully to overcome them in the future.…”

Metallocenes and Beyond for Propene Polymerization: Energy Decomposition of Density Functional Computations Unravels the Different Interplay of Stereoelectronic Effects

“…As a final step, we verified if the insights achieved by the ASM-NEDA protocol on the cationic active sites are still valid when the counterion (CI) is included in the calculations. We selected B­(C 6 F 5 ) 3 as a cocatalyst because it has been experimentally used in combination with 1a for controlled propene living polymerization and, additionally, the MeB­(C 6 F 5 ) 3 – anion obtained by methyl abstraction generates an inner-spere ion pair (ISIP) with the cationic active specie. ,, The PES governing the propene insertion in the presence of the CI is quite flat (see Computational Details in the Supporting Information); nevertheless, the low-lying TSs for “right” propene insertion at the PS (Figure A) and TBP (Figure B) sites as well as the TS for a stereoerror at the PS site (Figure S5) still show the main features characterizing the “naked” cationic active species (Figure A/B and Figure B). In analogy, the computed DFT energies for polymerization mechanism (see Δ E (Δ G ) Site values in Table ) and the stereoselectivity (see Δ E (Δ G ) Stereo(calc) values in Table ) calculated with and without CI are really close, making us confident that the insights achieved by our analysis on the naked active species may be transferred to the real systems in solution.…”

“…We selected B(C 6 F 5 ) 3 as a cocatalyst because it has been experimentally used in combination with 1a for controlled propene living polymerization 27 and, additionally, the MeB(C 6 F 5 ) 3 − anion obtained by methyl abstraction generates an inner-spere ion pair (ISIP) with the cationic active specie. 25,65,66 The PES governing the propene insertion in the presence of the CI is quite flat 66 (see Computational Details in the Supporting Information); never- theless, the low-lying TSs for "right" propene insertion at the PS (Figure 14A) and TBP (Figure 14B) sites as well as the TS for a stereoerror at the PS site (Figure S5) still show the main features characterizing the "naked" cationic active species (Figure 1A/B and Figure 9B). In analogy, the computed DFT energies for polymerization mechanism (see ΔE(ΔG) Site values in Table 1)…”