Experimental and Computational Investigations of Tautomerism and Fluxionality in PCP‐ and PNP‐Bridged Heavy Chalcogenides
Bibliographic record
Abstract
Abstract The reaction of H2C(PCl2)2 with four equivalents of iPrMgCl produces H2C(PiPr2)2, which was treated with tellurium in boiling toluene, or selenium in toluene at room temperature, to give the monochalcogenides EPiPr2CH2PiPr2 (E = Te, 4a; E = Se, 4b) in high yields. X‐ray structural determinations show that 4a and 4b exist as the CH2 tautomers in the solid state with E–P–C–P dihedral angles of 56.1(2)° and 56.7(1)°, respectively. DFT calculations were carried out for the isolectronic series EPR2CH2PR2 and EPR2NHPR2 (E = Se, Te; R = Me, iPr, tBu, Ph) and for their non‐chalcogenated precursors in order to elucidate the factors that determine the preference for PH tautomers in some PNP‐bridged systems. Compounds 4a and 4b were also characterized by multinuclear (1H, 13C, 31P, 77Se, 125Te) NMR spectroscopy. In solution, 4a exhibits fluxional behavior, which has been investigated by variable‐temperature and variable‐concentration multinuclear NMR spectroscopy. The observed behavior is consistent with an intermolecular tellurium transfer with an activation energy of 21.9 ± 3.2 kJ mol–1; consideration of selenium exchange in 4b indicates a much higher energetic barrier. DFT calculations provide insights into the pathway for the chalcogen exchange process in 4a (ΔE = 20.4 kJ mol–1). The outcome of reactions of 4a with selenium and nBuLi reflects the lability of the P‐Te functionality.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".