Ethylene Polymerization Using β-Diketimine Complexes of Zirconium
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Bibliographic record
Abstract
Ethylene polymerizations were conducted using β-diketimine complexes of Zr [LZrX 3 ( 1 ) and L 2 ZrX 2 ( 2 ) with L = MeC(NAr)CHC(NAr)Me and X = Cl, R (R = Me, Bn)] as well as Cp(L)ZrX 2 ( 3 ) in the presence of MAO. Complexes 1 possess low polymerization activities (ca. 10 5 g PE/(mol Zr h)) and provide PEs with a trimodal, molecular weight distribution. Both 2 and 3 behave as single-site catalysts under these conditions, with the activity of the latter being considerably higher than the former (ca. 10 6 −10 7 vs 10 5 g PE/(mol Zr h)). Induction periods of 10−20 min at 70 °C were observed in polymerizations involving 3 (Ar = Ph, X = Cl, Me) when activated by MAO. The use of [Ph 3 C][B(C 6 F 5 ) 4 ] and 3b (Ar = Ph, X = Me) in the presence of small amounts of MAO (ca. 100:1 Al:Zr) led to rapid monomer uptake and an increase in catalytic activity by about a factor of 4. Lower activities were observed in the presence of Me 3 Al or i Bu 3 Al. Little or no polymerization activity was observed when excess 3b was used as a scrubbing agent (in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ]), and rapid loss of activity was observed when excess 3b was added to a catalyst system already producing PE. Complex 3b reacts with [Ph 3 C][B(C 6 F 5 ) 4 ] in chlorobenzene- d 5 solution at 25 °C to provide [Cp(L)ZrMe][B(C 6 F 5 ) 4 ] ( 4 ). Complex 4 is transformed on heating in chlorobenzene to a dicationic (μ-Cl) 2 complex [(Cp(L)ZrCl) 2 ][B(C 6 F 5 ) 4 ] 2 ( 5 ), which was characterized by X-ray crystallography. Complex 4 forms dinuclear complexes with 3b or Me 3 Al in solution at room temperature. These complexes, [Cp(L)Zr(μ-Me) 2 AlMe 2 ][B(C 6 F 5 ) 4 ] ( 6 ) or [(Cp(L)ZrMe) 2 (μ-Me)][B(C 6 F 5 ) 4 ] ( 7 ), are fluxional in solution; at lower temperature, the solution NMR spectra are consistent with the structures shown. Complex 3b is a potent inhibitor of ethylene polymerization by 4, forming 7, which is resistant to dissociation. The presence of AlMe 3 (or MAO) appears to reversibly displace 3b from 7, allowing the reaction of 3b with [Ph 3 C][B(C 6 F 5 ) 4 ] to proceed to completion.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.302 | 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 it