NMR Studies of the Species Present in Cross-Coupling Catalysis Systems Involving Pd(η<sup>3</sup>-1-Ph-C<sub>3</sub>H<sub>4</sub>)(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) and [Pd(η<sup>3</sup>-1-Ph-C<sub>3</sub>H<sub>4</sub>)Cl]<sub>2</sub> Activated by PBu<sup>t</sup><sub>3</sub>, XPhos, and Mor-Dalphos: Nonexistence of Pd(XPhos)<sub><i>n</i></sub> and Pd(Mor-Dalphos)<sub><i>n</i></sub> (<i>n</i> = 1, 2) at Moderate Temperatures
Bibliographic record
Abstract
The compounds Pd(η 3 -1-Ph-C 3 H 4 )(η 5 -C 5 H 5 ) ( I ), Pd 2 (dba) 3 ( II ), Pd(OAc) 2 ( III ), and [Pd(η 3 -1-Ph-C 3 H 4 )Cl] 2 ( IV ) are frequently utilized as catalyst precursors for a variety of cross-coupling processes, including Suzuki–Miyaura, Heck–Mizoroki, Sonogashira, and Buchwald–Hartwig reactions. In the preceding paper in this issue, we assess and compare catalyst systems based on I – IV activated with PBu t 3, XPhos, and/or Mor-Dalphos for the prototypical Buchwald–Hartwig amination reactions of 4-bromo- and 4-chloroanisole with morpholine, noting several apparent incongruities which seem to indicate mechanistic dissimilarities for various reactant/precatalyst combinations. In this paper we investigate by NMR spectroscopy the solution chemistry of I and IV with PBu t 3, XPhos, and Mor-Dalphos, noting similarities and differences in the respective abilities of these precursor–ligand combinations to generate palladium(0) catalyst systems. We find inter alia that steric requirements prevent Xphos and Mor-Dalphos from forming 2:1 palladium(0) complexes and, surprisingly, that 1:1 palladium(0) complexes of Xphos and Mor-Dalphos are unstable with respect to dissociation to free ligand and palladium metal. In other words, these two ligands and, by implication, other sterically demanding phosphine ligands do not form palladium(0) compounds.
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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 | 0.011 | 0.009 |
| Meta-epidemiology (narrow) | 0.016 | 0.017 |
| Meta-epidemiology (broad) | 0.018 | 0.006 |
| Bibliometrics | 0.007 | 0.016 |
| Science and technology studies | 0.010 | 0.014 |
| Scholarly communication | 0.008 | 0.009 |
| Open science | 0.010 | 0.012 |
| Research integrity | 0.009 | 0.014 |
| Insufficient payload (model declined to judge) | 0.000 | 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; both teacher heads agree on what is shown here.
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".