Activation of Cp<sub>2</sub>ZrX<sub>2</sub> (X = Me, Cl) by Methylaluminoxane As Studied by Electrospray Ionization Mass Spectrometry: Relationship to Polymerization Catalysis
Bibliographic record
Abstract
Activation of Cp 2 ZrCl 2 and Cp 2 ZrMe 2 by methylaluminoxane (MAO) in toluene is largely complete at Al:Zr ratios of 100:1 to 200:1 as revealed by electrospray ionization mass spectrometry (ESI MS). The anions present undergo chlorination in the case of Cp 2 ZrCl 2 . DFT calculations reveal that chlorination of MAO is favorable and involves dissociation of Me 3 Al, followed by association of Me 2 AlCl. Ethylene polymerizations were conducted using these catalyst precursors in toluene. The activity vs [Zr] data are essentially identical, while higher MW polyethylene is formed with a narrower MWD at lower Al:Zr ratios in the case of Cp 2 ZrMe 2 . The activity vs [Zr] data could be fit to a model which invokes bimolecular deactivation of growing chains. ESI MS reveals that a dinuclear Zr 2 cation with m / z 557 is formed on exposure of [Cp 2 Zr(μ-Me) 2 AlMe 2 ] + to ethylene, in addition to other cations that are dinuclear with respect to Zr. Labeling experiments using ethylene- d 4 indicate that these dinuclear cations are derived from ethylene, either through direct incorporation in the case of m / z 557, or indirectly through incorporation of deuterium following e.g. β-H elimination. These experiments shed light on the need for high Al:Zr ratios for ethylene polymerization using soluble metallocene catalysts. The active catalyst [Cp 2 ZrR][MAO(Me)] (R = H, Et or a higher homologue) suffers a second order deactivation, and thus activity improves upon dilution of the catalyst precursor at constant [Al].
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".