Phosphine-Phenoxide Nickel Catalysts for Ethylene/Acrylate Copolymerization: Olefin Coordination and Complex Isomerization Studies Relevant to the Mechanism of Catalysis
Bibliographic record
Abstract
The insertion copolymerization of ethylene and acrylate remains a challenge in polymer synthesis due to decreased activities upon incorporation of the polar monomer. Toward gaining mechanistic insight, two elusive four-membered chelated intermediates generated after acrylate insertion were prepared (1-CCO and 2-CCO), and their ligand coordination and substitution behavior were studied. Specifically, an ethylene-coordinated species was characterized by NMR spectroscopy upon exposing 2-CCO to ethylene at low temperatures, a rare observation for neutral late-transition metal polymerization catalysts. Thermodynamics of chelate-opening and monomer coordination from 2-CCO were determined at −90 °C (ΔG of 0.4 kcal/mol for ethylene and 1.9 kcal/mol for 1-hexene). The Gibbs energy barrier of ligand exchange from pyridine to ethylene, a prerequisite for ethylene insertion in catalysis, was determined to be 3.3 kcal/mol. Ligand-binding studies reveal that compared to NiMe and Ni(CH2SiMe3) complexes, acrylate inserted species 1L-CCO and 2L-CCO produce compressed thermodynamic binding scales for both electronically and sterically differentiating ligands, potentially related to their more electron-deficient nickel centers as suggested by computational studies. Triethylphosphine complexes 1P, 2P, and 2P–Me were observed as both cis and trans isomers in solution. 31P{1H} EXSY NMR studies of 2P reveal conversion between a cis and trans isomers that does not involve exchange with free PEt3, supporting the mechanism of intramolecular isomerization. 2-CCO, a neutral Ni(II) precatalyst that does not display an auxiliary ligand, serves as a highly active catalyst for copolymerization.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".