Atomistic Simulation of Hf-Pyridyl Amido-Catalyzed Chain Transfer Alkene Polymerization Reaction and Its Machine Learning for Extraction of Essential Descriptors: Effect of Microscopic Steric Hindrance on the Monomer Insertion Process.

The microscopic effects of each substituent of the Hf catalyst and the growing polymer on the monomer insertion process were investigated for Hf-pyridyl amido-catalyzed coordinative chain transfer polymerization using the Red Moon method. Since the Hf catalyst has two reaction sites, cis- and trans-sites, we separately applied the appropriate analysis methods to each one, revealing that the naphthalene ring influenced monomer insertion at the cis-one, while the i-Pr group and the hexyl group of the adjacent 1-octene unit did the trans-one. It was interesting to find that the hexyl group of the 1-octene-inserted catalyst (oHfCat) pushes the naphthalene ring toward the cis-site and narrows the space at the cis-site, thus indirectly creating a steric hindrance to cis-insertions. Further, the relative position of the Hf catalyst and the growing polymer was found to be strongly influenced by the patterns of insertion reactions, i.e., cis- or trans-insertions. In particular, it was clarified that, after trans-insertions, the growing polymer on the Hf atom covers the cis-site, making cis-insertion less likely to occur. These studies reveal the microscopic effects of the catalyst substituents and the growing polymer on the catalyst during the polymerization reaction process; these microscopic analyses using the RM method should provide atomistic insights that are not easy to obtain experimentally for advanced catalyst design and polymerization control.

Atomistic Chemical Elucidation of the Higher-Rate Reaction Mechanism in Hf-Pyridyl Amido-Catalyzed Copolymerization of Ethene and 1-Octene: Application of Red Moon Simulation with Polymer Propagation Diagrams.

The Hf-pyridyl amido complex ((pyridylamido)Hf(IV)) is a cationic catalyst activated by ion-pairing with auxiliary catalyst B(C6F5)4 to show high activity for α-olefin polymerization. Previously, it was experimentally observed that the consumption rate of 1-octene in the 1-octene/ethene copolymerization is 3-fold compared to the 1-octene homopolymerization in coordinative chain transfer polymerization using the catalyst HfCat+-B(C6F5)4- ion pair (IP) and the chain transfer agent (CTA) ZnEt2. In the present study, we have performed atomistic chemical simulations of the IP-catalyzed homopolymerization of 1-octene and copolymerization of 1-octene and ethene on the basis of the Red Moon (RM) methodology. Using the analysis by polymer propagation diagrams (PPDs), in the 1-octene homopolymerization and the 1-octene/ethene copolymerization with the 1-octene-inserted catalyst (oHfCat), it is theoretically shown that the propagation reactions intermittently pause due to the steric hindrance of two hexyl groups of the oHfCat and the 1-octene inserted adjacent to the Hf atom. On the other hand, in the polymerizations with the ethene-inserted catalyst (eHfCat), it is reasonably recognized that the propagation reactions occur smoothly at a constant rate, and the polymerization continuously proceeds due to the relatively smaller steric hindrance. In conclusion, it was shown, for the first time, that the RM method can be used to reveal the microscopic effects of monomers and substituents in the polymerization reaction processes. Therefore, our current work using PPDs demonstrates the promising potential of the RM methodology in studying catalytic olefin polymerizations and complex chemical reaction systems in general.

(Pyridylamido)Hf(IV)-Catalyzed 1-Octene Polymerization Reaction Interwoven with the Structural Dynamics of the Ion-Pair-Active Species: Bridging from Microscopic Simulation to Chemical Kinetics with the Red Moon Method.

We performed the atomistic simulation of 1-octene polymerization reaction catalyzed by the ionic pair (IP) consisting of the cationic active species of (pyridylamido)Hf(IV) catalyst, HfCatPn+, and different counteranions (CAs), B(C6F5)4- and MeB(C6F5)3-, at different monomer concentrations. Using a hybrid Monte Carlo/molecular dynamics method, that is, the Red Moon (RM) method, the reaction progress measured by the "RM cycle" was transformed into effective real time using the time transformation theory. Then, the degree of polymerization was found to be consistent with that in the chemical kinetics, a macroscopic theory, and experimental ones. Remarkably, the current simulation has revealed the different dynamical features in the polymerization behavior originating from the CA. Namely, the HfCatPn+-B(C6F5)4- IP mainly forms an outer-sphere IP (OSIP) throughout the polymerization. The HfCatPn+-MeB(C6F5)3- IP, on the other hand, forms an inner-sphere IP (ISIP) in the initial stage of polymerization, and the ratio of ISIP steeply drops after the first monomer insertion because the IP interaction is reduced by the steric hindrance between the inserted monomers and the CA. In conclusion, we have shown that the microscopic IP dynamics interwoven with the polymerization reaction can be computationally observed in the real-time domain by using the RM method. Therefore, our current work demonstrates the promising potential of the RM method in studying catalytic olefin polymerization and complex chemical reaction systems.

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.

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.

Palladium-Catalyzed Intramolecular C-H Arylation versus 1,5-Palladium Migration: A Theoretical Investigation.

Theoretical investigations were carried out to elucidate the origin of chemoselectivity in the palladium-catalyzed reactions of 2-(dimethylphenylsilyl)phenyl triflates with or without an amino group at the 3-position. The selective formation of a 5,10-dihydrophenazasiline rather than a dibenzosilole from the substrate with an amino group at the 3-position could be successfully explained by proposing a new 1,5-palladium migration pathway that involves a neutral diorganopalladium(II) intermediate along with the subsequent formation of a low-energy amine-coordinated palladacycle intermediate prior to the C-N bond-forming process.

Synthesis of Quinoidal Fused Oligosiloles by Rhodium-Catalyzed Stitching Reaction and Theoretical Investigation of Their Properties.

New quinoidal fused oligosiloles containing an even number of silole units have been synthesized by a rhodium-catalyzed stitching reaction. Employing [RhCl(tfb)]2 as the catalyst significantly improved the stitching efficiency, and up to six siloles could be fused in quinoidal form. A systematic comparison of the physical properties of Si1-Si6' confirmed the unique trend in their LUMO levels, which become higher with longer π conjugation. To understand the origin of this unusual trend, theoretical calculations were also carried out using various model compounds, and the results indicated that the terminal indenylidene (cyclopentadienylidene) moieties in Si1-Si6 (Si1a-Si6a) are primarily responsible for this phenomenon through their frontier orbital correlations with the HOMO of the central polyene unit, which becomes higher in energy with longer π conjugation.

Rhodium-Catalyzed Synthesis and Optical Properties of Silicon-Bridged Arylpyridines.

A convergent and regioselective synthesis of silicon-bridged 4-arylpyridines has been developed through a rhodium-catalyzed [2+2+2] cycloaddition of silicon-containing diynes with nitriles. The absorption and emission properties of these compounds have been examined and could be tuned by varying the substituent on the benzene ring, as well as through the protonation or alkylation of the nitrogen atom on the pyridine ring. A catalytic asymmetric synthesis of silicon-centered axially chiral spirocyclic derivatives has also been achieved with high enantioselectivity by using a newly modified MeO-MOP (MeO-MOP=2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl) derivative as the chiral ligand. These spirocyclic compounds were found to be CPL-active (CPL=circularly polarized luminescence), representing the first CPL-active compounds based on the chirality at silicon.