Catalytic Linear Oligomerization of Ethylene to Higher α-Olefins: Insight into the Origin of the Selective Generation of 1-Hexene Promoted by a Cationic Cyclopentadienyl-Arene Titanium Active Catalyst
Bibliographic record
Abstract
A detailed theoretical investigation is presented of crucial elementary steps of the selective linear ethylene oligomerization to 1-hexene by the cationic [(η 5 -C 5 H 4 -(CMe 2 )-bridge)-C 6 H 5 )Ti IV (CH 3 ) 2 ] + precatalyst, employing a gradient-corrected DFT method. The essential aspects of the originally proposed mechanism have been confirmed and supplemented by novel insights into how the selective ethylene oligomerization operates. This includes the examination of the ability of titana(IV)cycle intermediates to grow and/or to decompose affording α-olefins as a function of their size, the prediction of the favorable route for precatalyst activation, and the exploration of the cycloalkane production as a possible side process. After the Ti IV −Me 2 precatalyst is smoothly converted into the active Ti II −(ethylene) 2 catalyst complex, the two ethylene moieties readily undergo oxidative coupling to afford first the titana(IV)cyclopentane species. Metallacycle growth through bimolecular ethylene uptake and subsequent insertion displays very similar structural and energetic characteristics for five- and seven-membered titana(IV)cycles. Decomposition of titana(IV)cycles to α-olefins preferably takes place via a concerted transition-metal-assisted β-H transfer for conformationally flexible metallacycles beginning with the titana(IV)cycloheptane, with very similar barriers having to be overcome. This decomposition path, however, is kinetically inaccessible for the rigid five-membered titana(IV)cyclopentane. Instead, the stepwise mechanism via a metastable Ti IV −alkenyl-hydride species is found to be operative in this case. A significantly raised activation barrier is connected with the stepwise path, which makes the growth of the titana(IV)cyclopentane to the seven-membered cycle the more favorable process than its decomposition to 1-butene. Cycloalkanes are less likely to be formed, due to a kinetically handicapped reductive CC elimination. On the basis of the detailed insights into the ability of titana(IV)cycles to undergo either growth or decomposition to α-olefins, the thermodynamic and kinetic aspects for the selectivity control of the linear ethylene oligomerization have been rationalized. The crucial role played by the hemilabile arene ligand for the selective oligomerization process has also been analyzed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".