Synthesis, X-ray Structural Analysis, and Ethylene Polymerization Studies of Group IV Metal Heterobimetallic Aluminum-Pyrrolyl Complexes
Bibliographic record
Abstract
The synthesis, structural characterization, and ethylene polymerization performance of heterobimetallic aluminum-pyrrolyl complexes of group IV metals are described. The combination of MCl 4 (M = Ti, Zr, Hf), aluminum alkyls and pyrroles leads, depending on stoichiometry, to mono- and bis(aluminum-pyrrolyl) complexes that are remiscent of the corresponding mono- and bis- cyclopentadienyl systems. The bis(aluminum-pyrrolyl) complexes (η 5 -2,5-Me 2 C 4 H 2 NAlClMe 2 ) 2 TiMe 2 ( 1 ), zirconium (η 5 -2,5-Me 2 C 4 H 2 NAlClMe 2 ) 2 ZrClMe ( 2 ), (η 5 -2,5-Me 2 C 4 H 2 NAlCl 2 Et) 2 ZrCl 2 ( 3 ), and hafnium (η 5 -2,5-Me 2 C 4 H 2 NAlClMe 2 ) 2 HfClMe ( 4 ) were found to be inactive toward ethylene polymerization. By contrast, the electron-deficient mono(aluminum-pyrrolyl) piano stool complexes (η 5 -2,5-Me 2 C 4 H 2 NAlCl 2 Me)TiCl 2 Me ( 5 ), (η 5 -2,3-Me 2 C 8 H 4 NAlCl 2 Me)TiCl 2 Me ( 6 ), and (η 5 -3,4,5,6-C 12 H 12 NAlCl 2 Me)TiClMe 2 ( 7 ), obtained by treatment of TiCl 4 with equimolar amounts of trimethyl aluminum and the corresponding pyrrole ligands, were found to be moderately active for ethylene polymerization with MAO or [Ph 3 C] + [B(C 6 F 5 ) 4 ] −, in all cases producing UHMWPE. The NMR scale reaction of 5 with B(C 6 F 5 ) 3 showed the formation of a solvent-separated ion pair, formed by the abstraction by B(C 6 F 5 ) 3 of a methyl group from Al-CH 3 rather than from Ti-CH 3 . 1 H and 13 C NMR analysis of 6 and 7 revealed that several stable structural isomers exist in solution, with a slow interconversion on the NMR time scale. The dimeric zirconium complexes [(η 5,κ 1 -2,5-Me 2 C 4 H 2 NAlClMe 2 )ZrMeCl(μ-Cl)] 2 ( 8 ) and [(η 5,κ 1 -2,5-Me 2 C 4 H 2 NAlCl 2 Et)ZrCl 2 (μ-Cl)] 2 ( 9 ), prepared by the reaction of 2 equivalents of ZrCl 4, 1 equivalent of 2,5-dimethylpyrrole, and 1 equivalent of aluminum alkyl, showed structures containing a bridging chloride between aluminum and zirconium, thereby giving structural evidence for the lack of catalytic behavior of these complexes. A possible explanation for the moderate or absence of catalytic activity of the aluminum-pyrrolyl complexes was proposed based on DFT calculations.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.012 | 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".