Ortho Derivatization of Phenols through C–H Nickelation: Synthesis, Characterization, and Reactivities of Ortho-Nickelated Phosphinite Complexes
Bibliographic record
Abstract
Reported here are the synthesis and characterization of ortho-nickelated complexes derived from phosphinite ligands and investigated as model compounds in the development of C–H functionalization strategies for arenol substrates. Reaction of i -Pr 2 POPh with 0.6 equiv of [( i -PrCN)NiBr 2 ] n and 0.8 equiv of NEt 3 in toluene (100 °C, 36 h) gave the yellow, monomeric cyclometalated complex trans -{κ 2 P, C -C 6 H 4 OP( i -Pr) 2 }Ni(i-Pr 2 POPh)Br ( 3a ) in 93% yield. The closely related yellow-orange dimeric species [{κ 2 P, C -C 6 H 4 OP( i -Pr) 2 }Ni(μ-Br)] 2 ( 4a ) was obtained in 70% yield when i -Pr 2 POPh was treated with 2 equiv each of the Ni precursor and NEt 3 . These complexes have been characterized fully and shown to interconvert in the presence of excess ligand ( 4a → 3a ) or excess Ni precursor ( 3a → 4a ). Treatment of 3a or 4a with benzyl bromide at 90 °C over extended periods led to benzylation of the Ni–aryl moiety in these complexes. Examination of the cyclometalation pathway for i -Pr 2 POPh has shown that the first species formed from its ambient-temperature reaction with [( i -PrCN)NiBr 2 ] n is trans -( i -Pr 2 POPh) 2 NiBr 2 ( 2a ). NMR studies showed that 2a undergoes a rapid ligand exchange at room temperature, which can be slowed down at −68 °C; this fluxional process shifts in the presence of NEt 3, implying the partial formation of an amine adduct. Heating toluene mixtures of 2a and NEt 3 at 90 °C for 38 h led to the formation of 3a via C–H nickelation. That phosphinite dissociation from 2a precedes the C–H nickelation step is implied by the observation that the formation of 3a is hindered in the presence of excess i -Pr 2 POPh. The impact of phenol ring substituents on the C–H nickelation rate was probed by preparing substituted derivatives of 2a, trans -(4-R-C 6 H 4 OP( i -Pr 2 )} 2 NiBr 2 (R = OMe ( 2b ), Me ( 2c ), COOMe ( 2d )), and measuring their relative rates of C–H nickelation. These studies showed that the formation of cyclonickelated products is favored in the order COOMe < Me < OMe, which is consistent with an electrophilic nickelation mechanism. Studying the C–H nickelation of 3-F-C 6 H 4 OP( i -Pr 2 ) allowed us to establish that metalation is favored at the para position with respect to F (85:15).
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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) | 0.001 | 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".