Odd Electron Transition Metal Hydride and Amine Complexes and their Associated Proton/Electron/Hydrogen Atom Reactivity
Bibliographic record
Abstract
This thesis is focused on furthering our understanding of the thermodynamics associated with metal hydrides and coordinated amines, namely the acidity, electrochemistry, and M-H and MN-H bond strengths. This understanding will improve catalyst development and should make industrial processes more sustainable and environmentally benign. In chapter 2, literature-reported electrochemistry of metal-hydride complexes is combined with estimated acidities of the oxidized species, in order to examine trends in electrochemical reversibility, acidity, and metal-hydride bond strength. It was found that oxidations to acidic metal hydrides tend to be irreversible due to proton loss. On the other hand, regions of electrochemical reversibility are usually associated with more reducing, less acidic complexes. In addition, the ligand acidity constant (LAC) method of estimating the pKa of metal hydrides and dihydrogen complexes is applied to paramagnetic metals. It was found that the LAC method generally works well for paramagnetic complexes, even though it was empirically derived from pKa of diamagnetic hydrides. Using the work from chapter 2 as a guide, a series of paramagnetic manganese(II) hydride com- plexes were synthesized, as discussed in chapter 3. This series is of the type trans-[MnH(L)(dmpe)2]+ were L is PMe3, C2H4, or CO. All of these complexes were studied by frozen solution EPR spec- troscopy. However, at room temperature, the trans ligand was found to determine the radical stability, and in cases of instability, the decomposition products. trans- PMe3 provides steric bulk and basicity, which stabilizes the radical. The trans-C2H4 complex decomposed by loss of ethylene and ethane, which ultimately yielded the homoleptic tris-dmpe complex and other unidentified side- products. The trans-CO complex provided little steric bulk and was more acidic, such that this complex cleanly lost 1/2 H2 in MeCN to give the MnI product [Mn(CO)(MeCN)(dmpe)2]+. In chapter 4, the focus is on coordinated amines, specifically a secondary amine in a tri-dentate phosphorous-nitrogen-nitrogen (PNN) ligand, which is coordinated to iron and rhodium. This case study used cyclic voltammetry and NMR to measure the acidity, electrochemistry, and MN-H bond dissociation free energies for the complexes.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| 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; both teacher heads agree on what is shown here.
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".