Investigating Transformations in Catalytic Pathways and Site Selectivity of Pd <sub>3</sub> Nanocluster-Catalyzed Cross-Coupling Reactions
Bibliographic record
Abstract
Atom-precise nanoclusters (NCs) of Pd have emerged as highly active and selective catalytic systems for cross-coupling and hydrogenation reactions. The unique Pd speciation in NCs has enabled unconventional site selectivity in cross-coupling reactions, which is challenging to obtain using mononuclear Pd complexes. However, the mechanism behind the distinct catalytic behavior of NCs in cross-coupling reactions and the influence of reaction conditions on these mechanisms are poorly understood. Herein, the catalytic behavior and speciation evolution of [Pd 3 (μ-Cl)(μ-PPh 2 ) 2 (PPh 3 ) 3 ] + (i.e., Pd 3 ) NCs have been studied in Suzuki–Miyaura cross-coupling reactions using in situ XAS analysis complemented by mass spectrometry. Our results indicate that the Pd 3 NCs can catalyze cross-coupling reactions via a homogeneous pathway and show very high site selectivity toward atypical C 4 -arylation in the cross-coupling reaction between 2,4-dibromopyridine and phenylboronic acid. After extended reaction times (>2 h), the transformation of Pd 3 NCs into nanoparticles generates additional heterogeneous catalytic centers in the reaction mixture, which significantly influences the overall outcome of the reaction by switching the site selectivity from C 4 -arylation to C 2 -arylation. This further favors a secondary arylation of the C 4 -arylated product to form a biarylated product. However, the addition of quaternary ammonium hydroxide to the reaction mixture and/or performing the reaction under mild conditions (∼25 °C) provided stability to Pd 3 NCs against aggregation, leading to very high C 4 -arylation selectivity (i.e., ∼70%) throughout the reaction. The quaternary ammonium salts were found to directly interact with the metallic core of the Pd 3 NCs, forming another homogeneous intermediate in the reaction mixture. Overall, the results from this work indicate that the use of Pd NCs as catalysts in cross-coupling reactions can provide unusual site selectivity; however, care needs to be taken to ensure their stability in long and large-scale catalytic processes.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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 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".