A Molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction

Marx, Frans Thomas Ignatius; Jordaan, Johannes H.; Lachmann, G.; Vosloo, Hermanus C.M.

doi:10.1002/jcc.23641

Cited by 11 publications

(7 citation statements)

References 78 publications

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“…The G parameter obtained by the Solid-G program helps one to understand the character of the chiral environment of the N , N ′-dioxide–Mg(II) complex and gain insight into the enantioselectivity of the reaction . The steric hindrance of the individual chiral ligand could be described as a percentage of the metal coordination sphere shielded by the ligand, G (L).…”

Section: Resultssupporting

confidence: 71%

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Wang

Yang

et al. 2016

J. Org. Chem.

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The mechanism and origin of the stereoselectivity of the asymmetric carbonyl-ene reaction between N-methyl-protected isatin and 2-methyloxypropene catalyzed by the N,N'-dioxide-Mg(OTf)2 complex were investigated by DFT and ONIOM methods. The background reaction occurred via a two-stage, one-step mechanism with a high activation barrier of 30.4 kcal mol(-1) at the B3LYP-D3(BJ)/6-311G**(SMD, CH2Cl2)//B3LYP/6-31G*(SMD, CH2Cl2) level at 303 K. Good linear correlations between the global nucleophilicity index (N) and the activation energy barrier (ΔG(⧧)) were found. The chiral N,N'-Mg(II) complex catalyst could enhance the electrophilicity of the isatin substrate by forming hexacoordinate Mg(II) reactive species. The substituent at the ortho positions of aniline combined with the aliphatic ring of the backbone in the chiral N,N'-dioxide ligand played an important role in the construction of a favorable "pocket-like" chiral environment (chiral pocket) around the Mg(II) center, directing the preferential orientation of the incoming substrate. An unfavorable steric arrangement in the re-face attack pathway translated into a more destabilizing activation strain of the ene substrate, enhancing enantiodifferentiation of two competing pathways for the desired R product. This work also suggested a new phosphine ligand (N-L1) for the formation of the Mg(II) complex catalyst for the asymmetric carbonyl-ene reaction. The chiral environment and Lewis acidity of the Mg(II) complex could be fine-tuned by introduction of P-donor units into the ligand for highly efficient asymmetric catalysis.

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Section: Resultssupporting

confidence: 71%

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Wang

Yang

et al. 2016

J. Org. Chem.

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“…When the re face of the cyclic enol silyl ether (R2) approached the si face of the alkynone (R1), the steric repulsion between the tert -butyldimethylsilyl (TBS) and adjacent o - i Pr of aniline distorted the Zn(II) complex significantly, with an increased Zn–O 6 distance of 2.285 Å. This structural deformation could also be verified by te small G parameter , ( G (L2)) of 64.6% (that is, a percentage of the metal coordination sphere shielded by the ligand) in L2- re -TS1, in comparison to L2-COM (65.3%). Accordingly, the active barrier (Δ G ⧧ ) via transition state L2- re -TS1 was 2.7 kcal mol –1 higher than that via L2- si -TS1 (9.6 vs. 6.9 kcal mol –1 ).…”

Section: Resultsmentioning

confidence: 99%

Theoretical Study on Asymmetric [2 + 2] Cycloaddition of an Alkynone with a Cyclic Enol Silyl Ether Catalyzed by a Chiral N,N′-Dioxide-Zn(II) Complex

Meng

Zuo

et al. 2019

Organometallics

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The reaction mechanism and enantioselectivity of the asymmetric [2 + 2] cycloaddition between an alkynone (R1) and a cyclic enol silyl ether (R2) were studied theoretically by the DFT method at the B3LYP-D3(BJ)/6-311G**(CH2Cl2,SMD)//B3LYP-D3(BJ)/def2-SVP(CH2Cl2,SMD) theoretical level. The noncatalytic reaction occurred via a stepwise mechanism. The first C–C bond was constructed by coupling two pseudo radical centers generated at the most nucleophilic C2 atom in the cyclic enol silyl ether and the most electrophilic terminal Cβ atom in the alkynone, which was responsible for the regioselectivity of the reaction. The counterion NTf2 – could stabilize the Zn(II) complex by coordinating to the center metal, forming a high-reactivity hexacoordinate Zn(II)-complex intermediate. The bulky CF3 group in the NTf2 – ion adjusted the blocking effect of o-iPr in aniline of the ligand toward the reactive site (that is, the Cβ atom in the alkynone) and induced the si face of the cyclic enol silyl ether to approach the alkynone from its less hindered re face, achieving a high enanotioselectivity of products. The Pauli repulsion between the Zn(II)-associated moiety and cyclic enol silyl ether fragment was the main contributor to the stereodifference of the two competing pathways in chiral N,N′-dioxide-Zn(II)-catalyzed [2 + 2] cycloaddition. The unfavorable steric repulsion between the o-iPr group of aniline in the ligand and tert-butyldimethylsilyl (TBS) in the cyclic enol silyl ether along the re face path translated into a more destabilizing ΔE Pauli value, leading to the predominant cycloaddition product (P-RR) observed in experiments. Variation of the linkage and chiral backbone could affect the repulsion among the o-iPr in the ligand, the counterion NTf2 –, and substrates, leading to different stereochemical outcomes. These results are in good agreement with experimental observations.

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“…The physical absorption energies between SO 2 and [TMG][LAC]/[BMIM][BF 4 ]/[BMIM][PF 6 ] are important factors to evaluate the removal of SO 2 by [TMG][LAC], [BMIM][BF 4 ], and [BMIM][PF 6 ]. DMol 3 uses numerical functions that are much richer than traditional Gaussian functions, therefore, the basis set superposition error is comparatively small . The interaction energies between SO 2 and [TMG][LAC]/[BMIM][BF 4 ]/[BMIM][PF 6 ] were calculated by using the following equation:

true Δ E = - [E_{c o m p l e x} - (E_{I L s} + E_{S O_{2}})]

…”

Section: Resultsmentioning

confidence: 99%

Computational Study on the Absorption Mechanisms of SO₂ by Ionic Liquids

Gates

2018

ChemistrySelect

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A density functional theory study was conducted to explore the absorption mechanisms of SO2 by ionic liquids (ILs), including task specific ILs 1,1,3,3‐tetramethylguanidinium lactate ([TMG][LAC]), and normal ILs 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([BMIM][PF6]). The strength of chemical absorption by [TMG][LAC] is stronger than physical absorption, and the physical absorption energy follows the order of [TMG][LAC] > [BMIM][BF4] > [BMIM][PF6]. Other than O⋅⋅⋅H hydrogen bonding, S⋅⋅⋅O interactions are important for [TMG][LAC] physical absorption of SO2, and S⋅⋅⋅F interactions are critical for SO2 absorption by [BMIM][BF4] or [BMIM][PF6]. Both anions and cations of ILs contribute to the physical absorption of SO2. [TMG]+ plays an important role in the chemical reaction between SO2 and [TMG][LAC]. The proton transfer reaction barrier between 1,1,3,3‐tetramethylguanidine and lactic acid is 1.176 kcal/mol.

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A Molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction

Cited by 11 publications

References 78 publications

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Theoretical Study on Asymmetric [2 + 2] Cycloaddition of an Alkynone with a Cyclic Enol Silyl Ether Catalyzed by a Chiral N,N′-Dioxide-Zn(II) Complex

Computational Study on the Absorption Mechanisms of SO₂ by Ionic Liquids

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A Molecular modeling study of the changes of some steric properties of the precatalysts during the olefin metathesis reaction

Cited by 11 publications

References 78 publications

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)2 Complex

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)2 Complex

Theoretical Study on Asymmetric [2 + 2] Cycloaddition of an Alkynone with a Cyclic Enol Silyl Ether Catalyzed by a Chiral N,N′-Dioxide-Zn(II) Complex

Computational Study on the Absorption Mechanisms of SO2 by Ionic Liquids

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Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Mechanistic Study of the Asymmetric Carbonyl-Ene Reaction between Alkyl Enol Ethers and Isatin Catalyzed by the N,N′-Dioxide–Mg(OTf)₂ Complex

Computational Study on the Absorption Mechanisms of SO₂ by Ionic Liquids