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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
Tuning Cyclopentadiene Isomerization by Substituent Effects
1Cracow University of Technology, Faculty of Chemical Engineering and Technology, 24 Warszawska St., Cracow, PL-31-155, Poland. agnieszka.lapczuk@pk.edu.pl.
Journal of Molecular Modeling
|August 5, 2026
Summary
This study explores substituent effects on cyclopentadiene rearrangements, revealing distinct R-shift pathways and a consistent proton migration mechanism. These insights advance understanding of sigmatropic rearrangements and proton transfer processes.
Area of Science:
- Organic Chemistry
- Computational Chemistry
- Reaction Mechanisms
Background:
- Substituted cyclopentadienes are key models for studying sigmatropic rearrangements and proton transfer.
- Understanding substituent effects is crucial for predicting reaction pathways and kinetics.
Purpose of the Study:
- To systematically investigate R- and proton-shifts in various substituted cyclopentadienes.
- To elucidate the influence of different substituents on reaction mechanisms and transition states.
Main Methods:
- Density functional theory (DFT) calculations using Gaussian 16 at the ωB97X-D/6-311+G(d,p) level.
- Inclusion of solvent effects (toluene, acetone, nitromethane) via the PCM model.
- Transition state identification (QST2) and mechanism verification (IRC, ELF, QTAIM, BET analyses).
Main Results:
- R-shifts proceed via single-step pathways, with substituent-dependent interactions between the migrating group and the ring.
- Bulky/electron-withdrawing groups (tBu, SiMe3, NO2) induce polarized transition states.
- Proton migration follows a conserved non-classical mechanism involving a transient trisynaptic basin.
- Activation barriers are moderate to high, with SiMe3Cp showing the lowest values; all reactions are exergonic.
Conclusions:
- Substituents significantly modulate R-shift transition state characteristics and electronic reorganization in proton shifts.
- The fundamental mechanisms of R- and proton-shifts in these systems are robust.
- All investigated processes are formally classified as [1,5]-sigmatropic rearrangements.
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