Elementary Steps in Olefin Metathesis: Nickelacyclobutanes via Cycloaddition to Nickel Carbenes
Bibliographic record
Abstract
High Resolution Image Download MS PowerPoint Slide Olefin metathesis and cyclopropanation, major reactions in the synthetic toolbox, are predominantly catalyzed by platinum-group metals. First-row transition metal alternatives are desirable from the perspective of supply-chain sustainability. Although cyclopropanation by nickel catalysts is well established, limited evidence exists for the chemical feasibility of the cycloaddition step essential for inner-sphere cyclopropanation or olefin metathesis. We describe Ni(PP)(=CPh 2 ) complexes that provide this missing evidence. These complexes react with styrene and phenyl vinyl sulfone (PVS) to form β-H elimination products that imply nickelacyclobutane (NiCB) intermediates. For the PVS system, the NiCB could be observed directly by NMR analysis and X-ray crystallography. This is the sole example to date of an obervable NiCB generated via cycloaddition, beyond the fluorinated examples. Computations pinpoint a decreased energy barrier to cycloreversion, relative to reductive elimination or β-H elimination, as the core requirement to achieve metathesis. This work thus demonstrates that nickel complexes can engage in cycloaddition, the missing elementary step essential for olefin metathesis, and establishes the design parameters essential to close the catalytic cycle.
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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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".