Catalysis of Cross-Coupling and Homocoupling Reactions of Aryl Halides Utilizing Ni(0), Ni(I), and Ni(II) Precursors; Ni(0) Compounds as the Probable Catalytic Species but Ni(I) Compounds as Intermediates and Products
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Bibliographic record
Abstract
Both Ni(0) and Ni(I) compounds are believed to exhibit cross-coupling catalytic properties under various conditions, and the compounds Ni(PPh 3 ) 4 and NiCl(PPh 3 ) 3 are compared as catalysts for representative Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions. The Ni(0) compound exhibits catalytic activities, for cross-coupling of chloro and bromoanisole with phenylboronic acid and of bromobenzene with styrene, yielding results which are comparable with those of many palladium-based catalysts, but our findings with NiCl(PPh 3 ) 3 are at this point unclear. It seems to convert to catalytically active Ni(0) species under Suzuki–Miyaura reaction conditions and is ineffective for Heck–Mizoroki cross-coupling. The paramagnetic Ni(I) compounds NiX(PPh 3 ) 3 (X = Cl, Br, I) are characterized for the first time by 1 H NMR spectroscopy and are found to exhibit broad meta and para resonances at δ 9–11 and 3–4, respectively, and very broad ortho resonances at δ 4−6; these resonances are very useful for detecting Ni(I) species in solution. The chemical shifts of NiCl(PPh 3 ) 3 vary with the concentration of free PPh 3, with which it exchanges, and are also temperature-dependent, consistent with Curie law behavior. The compound trans -NiPhCl(PPh 3 ) 2, the product of oxidative addition of chlorobenzene to Ni(PPh 3 ) 4 and a putative intermediate in cross-coupling reactions of chlorobenzene, is found during the course of this investigation to exhibit entirely unanticipated thermal lability in solution in the absence of free PPh 3 . It readily decomposes to biphenyl and NiCl(PPh 3 ) 2 in a reaction relevant to the long-known but little-understood nickel-catalyzed conversion of aryl halides to biaryls. Ni(I) and biphenyl formation is initiated by PPh 3 dissociation from trans -NiPhCl(PPh 3 ) 2 and formation of a dinuclear intermediate, a process which is now better defined using DFT methodologies.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.002 | 0.004 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it