Synthesis, Characterization, and Electrochemical Studies of PPh<sub>3–<i>n</i></sub>(dipp)<sub><i>n</i></sub> (dipp = 2,6-Diisopropylphenyl): Steric and Electronic Effects on the Chemical and Electrochemical Oxidation of a Homologous Series of Triarylphosphines and the Reactivities of the Corresponding Phosphoniumyl Radical Cations
Bibliographic record
Abstract
Activation barriers to the electrochemical oxidation for the series PPh3-n(dipp)n (dipp = 2,6-diisopropylphenyl) in CH2Cl2/Bu4NPF6 were measured using large amplitude FT ac voltammetry. Increasing substitution across this series, which offers the widest range of steric requirements across any analogous series of triarylphosphines reported to date, increases the energetic barrier to electron transfer; values of 18, 24, and 25 kJ mol(-1) were found for compounds with n = 1, 2, and 3, respectively. These values are significantly greater than those calculated for outer sphere activation barriers, with deviations between observed and calculated values increasing with the number of dipp ligands. This suggests that the steric congestion afforded by these bulky substituents imposes significant reorganizational energy on the electron transfer processes. This is the first investigation of the effect of sterics on the kinetics of heterogeneous electron transfer across a structurally homologous series. Increased alkyl substitution across the series also increases the chemical reversibility of the oxidations and decreases the oxidation peak potentials. As the compounds for which n = 1 and 2 are novel, the synthetic strategies employed in their preparation are described, along with their full spectroscopic, physical, and crystallographic characterization. Optimal synthesis when n = 1 is via a Grignard reagent, whereas when n = 2 an aryl copper reagent must be employed, as use of a Grignard results in reductive coupling. Chemical oxidation studies were performed to augment the electrochemical work; the O, S, and Se oxidation products for the parent triarylphosphines for which n = 1 and 2 were isolated and characterized.
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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 | 0.001 | 0.004 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.006 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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 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".