Stoichiometric Reactivity Relevant to the Mor-DalPhos/Pd-Catalyzed Cross-Coupling of Ammonia and 1-Bromo-2-(phenylethynyl)benzene
Bibliographic record
Abstract
While Mor-DalPhos/Pd precatalyst mixtures have in general proven to be highly effective for the monoarylation of ammonia employing a range of (hetero)aryl (pseudo)halide cross-coupling partners, we have observed previously that 1-bromo-2-(phenylethynyl)benzene (Ar*Br) is a challenging substrate for this catalyst system. We report herein on our efforts to examine some possible modes of catalyst inhibition by this substrate. Treatment of [CpPd(allyl)] with Mor-DalPhos in the presence of Ar*Br afforded [(κ 2 - P, N -Mor-DalPhos)Pd(Br)(Ar*)] ( 1; 85%), which was transformed into [(κ 3 - P, N,O -Mor-DalPhos)Pd(Ar*)] + OTf – ( 3; 83%) upon treatment with AgOTf. The characterization of 3 establishes the ability of the Mor-DalPhos ligand to adopt a κ 3 -P,N,O structure, which may influence the course of some Pd-catalyzed amination processes. While treatment of 1 with AgOTf in the presence of ammonia, or alternatively treatment of 3 with ammonia, resulted in the clean formation of [(κ 2 - P, N -Mor-DalPhos)Pd(NH 3 )(Ar*)] + OTf – ( 2 ), our efforts to isolate this compound were thwarted by the facile loss of ammonia from 2 to give 3 . Neither NMR spectroscopic nor X-ray crystallographic data obtained for 1 and 3 support the existence of significant Pd···alkyne interactions in these complexes. Treatment of the Pd(0) species [L 2 Pd(diphenylacetylene)] (L 2 = Mor-DalPhos, 4; L 2 = CyPF t Bu-JosiPhos, 5 ) with Ar*Br resulted in divergent behavior: while multiple phosphorus-containing products were observed in the case of 4, under analogous conditions 5 was transformed cleanly into [(κ 2 - P, P -JosiPhos)Pd(Br)(Ar*)] ( 6 ). The identification of 6 was facilitated via independent synthesis from Ar*Br, JosiPhos, and [CpPd(allyl)] (90%). These observations suggest that the inferior performance of Mor-DalPhos relative to JosiPhos in the arylation of ammonia using Ar*Br may be attributable in part to the inefficiency with which putative [(Mor-DalPhos)Pd(alkyne)] species re-enter the catalytic cycle via C–Br oxidative addition.
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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 | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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 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".