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 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".