Altered torquoselectivity of fluorine in the iron-tricarbonyl-mediated thermal ring opening of 3-fluorocyclobutene: a density-functional exploration

2016 ◽  
Vol 22 (11) ◽  
Author(s):  
Chandresakaran Prathipa ◽  
Lakshminarayanan Akilandeswari
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Iron Tricarbonyl

A Density Functional Theory Study on the Ring-Opening Polymerization of D-Lactide Catalyzed by a Bifunctional-Thiourea Catalyst

2009 ◽  
Vol 62 (2) ◽  
pp. 157 ◽  
Author(s):  
Rong-Xiu Zhu ◽  
Ruo-Xi Wang ◽  
Dong-Ju Zhang ◽  
Cheng-Bu Liu
Keyword(s):  
Density Functional Theory ◽  
Ring Opening ◽  
Density Functional ◽  
Population Analysis ◽  
Density Functional Theory Calculations ◽  
Ring Opening Polymerization ◽  
Acyl Transfer ◽  
Frontier Molecular Orbital ◽  
Functional Theory ◽  
Elimination Pathway

The thiourea-catalyzed methanolysis of d-lactide, a model system for the initiation and propagation of the organocatalyzed ring-opening polymerization (ROP) of lactide, has been studied by performing density functional theory calculations. Both the catalyzed and uncatalyzed reactions are explored along two possible pathways: one involves the stepwise addition–elimination pathway and the other is related to the concerted pathway. It is found that the reaction without the presence of the catalyst is difficult because the barrier involved is as high as 176 kJ mol–1. With the aid of a thiourea catalyst, the barrier is reduced to 88 kJ mol–1 with a preference for the stepwise addition–elimination mechanism over the concerted one. The role of the catalyst has been rationalized by analyzing the frontier molecular orbital interactions between the catalyst and substrates and by performing natural population analysis. Finally, another mechanism involving acyl transfer is discussed for the thiourea-catalyzed ROP.

Density Functional Study of the Insertion and Ring-Opening Mechanism of MCP over Cp2LaH and Cp2LuH Catalysts

2003 ◽  
Vol 125 (52) ◽  
pp. 16210-16212 ◽  
Author(s):  
Yi Luo ◽  
Parasuraman Selvam ◽  
Akira Endou ◽  
Momoji Kubo ◽  
Akira Miyamoto
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Functional Study ◽  
Density Functional Study

Predicting the origin of selectivity in NHC-catalyzed ring opening of formylcyclopropane: a theoretical investigation

2021 ◽  
Author(s):  
Yang Wang ◽  
Yan Qiao ◽  
Yu Lan ◽  
Donghui Wei
Keyword(s):  
Density Functional Theory ◽  
Theoretical Investigation ◽  
Ring Opening ◽  
Density Functional ◽  
Functional Theory

Using density functional theory, we investigated the origin of selectivity in the N-heterocyclic carbene (NHC)-catalyzed transformation of formylcyclopropane with an alkylidene oxindole.

scholarly journals DFT Visualization and Experimental Evidence of BHT-Mg-Catalyzed Copolymerization of Lactides, Lactones and Ethylene Phosphates

Polymers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1641 ◽  
Author(s):  
Ilya Nifant’ev ◽  
Andrey Shlyakhtin ◽  
Maxim Kosarev ◽  
Dmitry Gavrilov ◽  
Stanislav Karchevsky ◽  
...  
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Point Of View ◽  
Basis Set ◽  
Random Copolymers ◽  
Key Factors ◽  
Functional Theory ◽  
Cyclic Esters ◽  
Dft Modeling ◽  
Derivatives Of

Catalytic ring-opening polymerization (ROP) of cyclic esters (lactides, lactones) and cyclic ethylene phosphates is an effective way to process materials with regulated hydrophilicity and controlled biodegradability. Random copolymers of cyclic monomers of different chemical nature are highly attractive due to their high variability of characteristics. Aryloxy-alkoxy complexes of non-toxic metals such as derivatives of 2,6-di-tert-butyl-4-methylphenoxy magnesium (BHT-Mg) complexes are effective coordination catalysts for homopolymerization of all types of traditional ROP monomers. In the present paper, we report the results of density functional theory (DFT) modeling of BHT-Mg-catalyzed copolymerization for lactone/lactide, lactone/ethylene phosphate and lactide/ethylene phosphate mixtures. ε-Caprolactone (ε-CL), l-lactide (l-LA) and methyl ethylene phosphate (MeOEP) were used as examples of monomers in DFT simulations by the Gaussian-09 program package with the B3PW91/DGTZVP basis set. Both binuclear and mononuclear reaction mechanistic concepts have been applied for the calculations of the reaction profiles. The results of calculations predict the possibility of the formation of random copolymers based on l-LA/MeOEP, and substantial hindrance of copolymerization for ε-CL/l-LA and ε-CL/MeOEP pairs. From the mechanistic point of view, the formation of highly stable five-membered chelate by the products of l-LA ring-opening and high donor properties of phosphates are the key factors that rule the reactions. The results of DFT modeling have been confirmed by copolymerization experiments.

scholarly journals Dinitrosyl rhenium complexes for ring-opening metathesis polymerization (ROMP)

2006 ◽  
Vol 78 (10) ◽  
pp. 1877-1887 ◽  
Author(s):  
Christian Manfred Frech ◽  
Olivier Blacque ◽  
Heinz Berke
Keyword(s):  
Phosphine Oxide ◽  
Ring Opening ◽  
Density Functional ◽  
Ring Opening Metathesis Polymerization ◽  
Olefinic Bond ◽  
Metathesis Polymerization ◽  
Molecular Weights ◽  
Cyclic Olefins ◽  
Phosphine Complexes ◽  
Unique Reaction

The treatment of benzene solutions of the cations [Re(NO)2(PR3)2][BArF4] (R = Cy and R = iPr; [BArF4] = tetrakis{3,5-bis(trifluoromethyl)phenyl}borate) with phenyldiazomethane afforded the moderately stable cationic rhenium(I) benzylidene dinitrosyl bis(trialkyl) phosphine complexes as [BArF4]- salts in good yields. The cationic rhenium dinitrosyl bisphosphine complexes catalyze the ring-opening metathesis polymerization (ROMP) of highly strained nonfunctionalized cyclic olefins to give polymers with relatively high polydispersity indices, high molecular weights, and Z configurations of the double bonds in the polymer chain backbones of over 80 %. The benzylidene derivatives are almost inactive in ROMP catalysis with norbornene and in olefin metathesis. NMR experiments gave first hints for the initial formation of carbene complexes when [Re(NO)2(PR3)2][BArF4] was treated with norbornene. The carbene formation is initiated by an unique reaction sequence where the cleavage of the strained olefinic bond starts with phosphine migration forming a cyclic ylid carbene complex. The [2+2] addition of a norbornene molecule to the Re=C bond leads to the rhenacyclobutane complex, which is expected to be converted into an iminate complex by attack of the ylid function onto one of the NNO atoms followed by Wittig-type phosphine oxide elimination. The formation of phosphine oxide was confirmed by NMR spectroscopy. This species is thought to drive the ROMP metathesis with alternating rhenacyclobutane formations and cycloreversions. The proposed mechanism is supported by density functional theory (DFT) calculations.

scholarly journals DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2078 ◽  
Author(s):  
Ilya Nifant’ev ◽  
Pavel Ivchenko
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Comparative Modeling ◽  
Ring Opening Polymerization ◽  
Proton Exchange ◽  
Dft Methods ◽  
Experimental Proof ◽  
Cyclic Esters ◽  
Dft Modeling

Organocatalysis is highly efficient in the ring-opening polymerization (ROP) of cyclic esters. A variety of initiators broaden the areas of organocatalysis in polymerization of different monomers, such as lactones, cyclic carbonates, lactides or gycolides, ethylene phosphates and phosphonates, and others. The mechanisms of organocatalytic ROP are at least as diverse as the mechanisms of coordination ROP; the study of these mechanisms is critical in ensuring the polymer compositions and architectures. The use of density functional theory (DFT) methods for comparative modeling and visualization of organocatalytic ROP pathways, in line with experimental proof of the structures of the reaction intermediates, make it possible to establish these mechanisms. In the present review, which continues and complements our recent manuscript that focused on DFT modeling of coordination ROP, we summarized the results of DFT modeling of organocatalytic ROP of cyclic esters and some related organocatalytic processes, such as polyester transesterification.

Facile formation of azines from reactions of singlet methylene and dimethylcarbene with precursor diazirines: theoretical explorations

1999 ◽  
Vol 77 (5-6) ◽  
pp. 540-549 ◽  
Author(s):  
Gennady V Shustov ◽  
Michael TH Liu ◽  
K N Houk
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Activation Barrier ◽  
Thermal Reaction ◽  
Orbital Theory ◽  
Functional Theory ◽  
Activation Barriers ◽  
Singlet Methylene

The reactions of the singlet methylene (1a) and dimethylcarbene (1b), with their diazirine precursors, diazirine (2a), and dimethyldiazirine (2b), have been studied theoretically using ab initio and density functional theory. The reaction has no activation barriers for the parent system (1a + 2a) and proceeds via a reactive complex and a transition state with a small negative enthalpy of activation Δ Hnot =298 = -1.1 kcal mol-1, ΔSnot =298 = -34.4 cal mol-1 K-1, ΔG°298 = 9.2 kcal mol-1) for the dimethyl derivatives (1b + 2b). The formation of N-methylene diazirinium ylides (3a,b) is exothermic by 64-80 kcal mol-1. The isomer, 1,3-diazabicyclo[1.1.0]butane (4a), is more stable (5-12 kcal mol-1) than isomer 3a, but can neither be formed by direct thermal reaction of 1a with 2a nor undergo the direct rearrangement into formaldazine (5a). The rearrangement of ylides 3a,b into azines 5a,b proceeds by conrotatory C3-N1 ring opening. The predicted activation barrier of ca. 15 kcal mol-1 for the ring opening in ylide 3b is in excellent agreement with experimental data. The formation of pyridinium ylides from carbenes and pyridine is also studied.Key words: diazirinium ylide, ab initio MO (molecular orbital) theory, density functional theory, pyridinium ylide, CIS (singles configuration interaction) transition energies.

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