An Acidity Scale for Phosphorus-Containing Compounds Including Metal Hydrides and Dihydrogen Complexes in THF: Toward the Unification of Acidity Scales
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Bibliographic record
Abstract
More than 70 equilibrium constants K between acids and bases, mainly phosphine derivatives, have been measured in tetrahydrofuran (THF) at 20 °C by 1 H and/or 31 P NMR. The acids were chosen or newly synthesized in order to cover the wide p K α THF range of 5−41 versus the anchor compound [HPCy 3 ]BPh 4 at 9.7. These p K α THF values are approximations to absolute, free ion p K a THF and are obtained by crudely correcting the observed K for 1:1 ion-pairing effects by use of the Fuoss equation. The acid/base compounds include 14 phosphonium/phosphine couples, 17 cationic hydride/neutral hydride couples, 9 neutral polyhydride/anionic hydride couples, 14 dihydrogen/hydride couples, and 4 other nitrogen- and phosphorus-based acids. The effects on p K α of the counterions BAr‘ 4 - and BF 4 - vs BPh 4 - and [K(2,2,2-crypt)] + versus [K(18-crown-6)] + are found to be minor after correcting for differences in inter-ion distances in the ion-pairs involved. Correlations with ν(M−H) noted here for the first time suggest that destabilization of M−H bonding in the conjugate base hydride is an important contributor to hydride acidity. It appears that Re−H bonding in the anions [ReH 6 (PR 3 ) 2 ] - is greatly weakened by small increases in the basicity of PR 3, resulting in a large increase in the p K α of the conjugate acid ReH 7 (PR 3 ) 2 . Correlations with other scales allow an estimate of the p K α THF values of more than 1000 inorganic and organic acids, 20 carbonyl hydride complexes, 46 cationic hydrides complexes, and dihydrogen gas. Therefore, many new acid−base reactions can be predicted and known reactions explained. THF, with its low dielectric constant, disfavors the ionization of neutral acids HA over HB +, and therefore separate lines are found for p K α THF (HA) and p K α THF (HB + ) when plotted against p K a DMSO or p K a MeCN . The crystal structure of [Re(H) 2 (PMe 3 ) 5 ]BPh 4 is reported.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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 it