Theoretical Modeling of Ethylene Insertion by Nickel Iminophosphonamide and Amidinate Complexes
Bibliographic record
Abstract
Modeling of ethylene polymerization using density functional theory was undertaken for both generic and substituted nickel iminophosphonamide (PN 2 ) and amidinate (CN 2 ) complexes. The more highly substituted complexes were studied using quantum mechanics/molecular mechanics (QM/MM) techniques so as to probe the role of steric effects on insertion and chain-transfer processes. For the generic systems H 2 P(NSiH 3 ) 2 NiR(L) and HC(NSiH 3 ) 2 NiR(L) (R = alkyl; L = C 2 H 4 ), insertion had a higher barrier in the PN 2 versus CN 2 complex. The energy of ethylene binding was strongly affected by the nature of the R group. This was shown to be a function of agostic stabilization of the alkyl group in the absence of monomer. Insertion barriers are also strongly dependent on the nature of the alkyl group, particularly in the case of the sterically hindered Keim catalyst, which was modeled by (Me 3 Si) 2 NP(Me)(NSiMe 3 ) 2 NiR(L) and QM/MM techniques. Degenerate chain transfer was systematically studied in the case of the generic CN 2 complex HC(NSiH 3 ) 2 NiEt(C 2 H 4 ) and proceeds through five-coordinate intermediates with distorted trigonal-bipyramidal geometries. The highest-energy intermediate corresponds to a bis(ethylene)−NiH complex, where loss of ethylene would constitute (degenerate) chain transfer. Intermediates in the analogous PN 2 complexes lie higher in energy, and thus these complexes should provide higher molecular weight material, as observed experimentally. β-H elimination/chain walking was also investigated using both generic and substituted complexes. The ground states in these reactions are agostic alkyls, while the ethylene−NiH complex, in which ethylene is perpendicular to the square plane, is a weakly bound intermediate. These intermediates are related to those formed during chain transfer by binding of the monomer.
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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) | 0.000 | 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) | 0.012 | 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".