<i>ansa</i>-Zirconocenes with Aluminum or Gallium in Bridging Positions
Bibliographic record
Abstract
Bis(cyclopentadienyl)aluminum and -gallium species of the type (Pytsi)ECp 2 [E = Al ( 2a ), Ga ( 2b ); Pytsi = C(SiMe 3 ) 2 SiMe 2 (2-C 5 H 4 N)] have been prepared from NaCp and respective dichlorides (Pytsi)ECl 2 in isolated yields of 65% ( 2a ) and 83% ( 2b ). In addition to applying standard methods of characterization (NMR spectroscopy, CHN analysis, and MS), the molecular structures of both compounds were solved by single-crystal X-ray crystallography. Reactions between 2a or 2b with Zr(NMe 2 ) 4 in benzene, followed by addition of an excess of ClSiMe 3, gave the first ansa -zirconocene dichlorides with aluminum ( 4a ) or gallium ( 4b ) in bridging position. The gallium compound 4b was isolated in a yield of 40% and characterized by NMR spectroscopy, CHN analysis, and mass spectrometry. The aluminum species 4a could not be obtained in an analytically pure form; it was characterized by NMR spectroscopy, and its molecular structure was determined by single-crystal X-ray analysis. The angle between the two planes of the Cp ligands in 4a was found to be 57.17(11)°, which is larger than in Cp 2 ZrCl 2 (α = 53.5°) and smaller than in silicon-bridged ansa -zirconocene dichlorides (e.g., Me 2 Si(C 5 H 4 ) 2 ZrCl 2: α = 60.1°). Crystallization attempts of 4a from DCCl 3 solutions gave crystals of the new species (Pytsi)AlCl[(C 5 H 4 )ZrCp] ( 7 ), which was characterized by NMR spectroscopy and single-crystal X-ray analysis. In comparison to the Pytsi-containing species 2a and 2b, the less sterically protected compound [2-(Me 2 NCH 2 )C 6 H 4 ]AlCp 2 ( 6 ), which was prepared from NaCp and [2-(Me 2 NCH 2 )C 6 H 4 ]AlCl 2 in yields of 94% and characterized by standard methods (NMR, CHN, and MS), reacted with Zr(NMe 2 ) 4 to give the known Cp 2 Zr(NMe 2 ) 2 . The targeted ansa -species was not formed, as judged by 1 H NMR spectroscopy. The gallium-bridged compound 4b and Cp 2 ZrCl 2, respectively, had been tested for polymerizations of ethylene utilizing MAO as an activator (300 equiv of MAO; 5 or 10 μmol of precatalyst; 15 or 70 psi), resulting in activities of 637 to 1080 for 4b and of 640 to 2601 kg PE (mol Zr) −1 h −1 atm −1 for Cp 2 ZrCl 2 .
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".