Synthesis and Reactivities of New NCN-Type Pincer Complexes of Nickel
Bibliographic record
Abstract
This report describes the preparation, characterization, and reactivities of a new family of Ni(II) complexes based on the pincer-type ligands R-NCN pz (κ N,κ C,κ N ′ -1,3-bis(pyrazole),5-R-C 6 H 2; R = H, OMe). Ullman coupling of pyrazole with 1,3-diiodobenzene or 1,3-dibromo-5-methoxybenzene gave the compounds R-NC(H)N pz, which were refluxed in xylene with ( i -PrCN)NiBr 2 and NEt 3 to give the complexes (NCN pz )NiBr ( 1 ) and (MeO-NCN pz )NiBr ( 2 ) via C–H nickelation. The aryloxide derivative (NCN pz )Ni(OAr) ( 3; Ar = 2,6- t -Bu 2 -4-Me-OC 6 H 2 ) was prepared by treating the bromo precursor 1 with NaOAr, whereas the analogous reaction with NaOEt gave instead the protonated or ethoxy-functionalized ligand NC(H)N pz (major) and NC(OEt)N pz (minor). The new complexes 1 – 3 were fully characterized, including solid-state structures. Attempted oxidation of these complexes failed to give the target trivalent derivatives, leading instead to intractable, deeply colored Ni-containing solids, various ligand-derived side products, or an unusual I 2 adduct. For example, treatment of 1 or 2 with N -bromosuccinimide gave sparingly soluble dark solids that appear to be paramagnetic, whereas 3 reacted with Br 2 to give short-lived dark intermediates that decomposed over seconds to give ArOH. Reaction of the bromo complexes with aqueous H 2 O 2 (30%) gave the functionalized ligands Br-NC(OH)N pz and NC(OH)N pz (from 1 ) or MeO-NC(OH)N pz (from 2 ), whereas 1 reacted with I 2 to generate (NCN pz )NiBr·I 2, an iodine adduct displaying weak Br–I interactions. Heating 1 in EtOH in air generated NC(OEt)N pz . This ligand derivatization could be extended to other alcohols (MeOH, i -PrOH, CF 3 CH 2 OH) and amines (morpholine, cyclohexylamine, aniline). Possible mechanistic scenarios for the observed oxidative, Ni-promoted C ipso –X bond formation reactions are discussed in the context of relevant literature precedents.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 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) | 0.018 | 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".