Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System
Bibliographic record
Abstract
The ethylene trimerization SNS ligand has been modified by replacing the methylene carbons flanking the nitrogen atom with dimethyl silyl groups. Three ligands, CySCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SCy ( a ), ( t -Bu)SCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 S( t -Bu) ( b ), and PhSCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SPh ( c ), have been prepared. Ligand a in either protonated or deprotonated forms was reacted with CrCl 3 (THF) 3 to afford the corresponding monomeric [CySCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SCy]CrCl 3 ( 1a ) or dimeric {[CySCH 2 Si(CH 3 ) 2 NSi(CH 3 ) 2 CH 2 SCy]CrCl(μ-Cl)} 2 ( 2a ). One-pot reaction of a in the presence of Et 2 AlCl with either Cr(III) or Cr(II) chlorides afforded in either case the divalent {[CySCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SCy]Cr{(μ-Cl)Al(CH 2 CH 3 ) 2 Cl} 2 ( 3a ). To deprotonate the N–H function of the Si-SNS ligand, n -BuLi was used for the purpose of preparing the divalent chromium analogue. The reaction afforded in the case of both a and b the two nearly isostructural divalent complexes {[CySCH 2 Si(CH 3 ) 2 NSi(CH 3 ) 2 CH 2 SCy]Cr(μ-Cl)} 2 ( 4a ) and {[( t -Bu)SCH 2 Si(CH 3 ) 2 NSi(CH 3 ) 2 CH 2 S( t -Bu)]Cr(μ-Cl)} 2 ( 4b ) in crystalline form. To further clarify the interaction of 4 with aluminate species, we have carried out in situ complexation in the presence of either AlCl 3 or AlMe 3 and using divalent instead of trivalent chromium salts. In the cases of ligands a and c and AlCl 3, two isostructural complexes, {[CySCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SCy]Cr{(μ-Cl)AlCl 3 } 2 ( 5a ) and {[PhSCH 2 Si(CH 3 ) 2 N(H)Si(CH 3 ) 2 CH 2 SPh]C{(μ-Cl)AlCl 3 } 2 ( 5c ), have been obtained. The reaction with AlMe 3 afforded {[CySCH 2 Si(CH 3 ) 2 N(Al(CH 3 ) 2 -μ-Cl)Si(CH 3 ) 2 CH 2 SCy]Cr{(μ-Cl)Al(CH 3 ) 3 } ( 6a ). Its structure was informative, showing a possible catalyst deactivation pathway. To better evaluate the role of the N–H function, we have also methylated ligand a at the N atom. The complexation to chromium was successful only in the presence of Me 2 AlCl and if a divalent chromium precursor was used. The reaction afforded the catalytically inactive divalent {[CySCH 2 Si(CH 3 ) 2 N(CH 3 )Si(CH 3 ) 2 CH 2 SCy]Cr(μ-Cl)} 2 {(Al(CH 3 ) 2 Cl) 2 )(μ-Cl)} 2 ( 7d ). Most of these species showed good catalytic activity upon activation but produced only statistical distributions of oligomers.
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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 | 0.000 |
| 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.050 | 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 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".