Pre-catalyst resting states: a kinetic, thermodynamic and quantum mechanical analyses of [PdCl2(2-oxazoline)2] complexes
Bibliographic record
Abstract
The treatment of cold ( approximately 3 degrees C) methanolic solutions of Li(2)PdCl(4) with two equivalents of 2-phenyl-2-oxazoline (Phox) results in the isolation of [PdCl(2)(Phox)(2)] (3). This complex undergoes remarkably slow isomerisation (CHCl(3)-d) at room temperature to a corresponding thermodynamic form. In addition to a theoretical treatment (DFT), the isomerisation behaviour has been analysed both kinetically and thermodynamically. These investigations lead to the conclusion that the initially formed (i.e. kinetic) isomer of 3 is the cis-form which undergoes conversion to the corresponding thermodynamic trans-form via a dissociative (D) mechanism involving loss of a Phox ligand. The activation parameters DeltaS(double dagger) and DeltaH(double dagger) are found to be +304 (+/-3) J K(-1) mol(-1) and +176 (+/-1) kJ mol(-1), respectively and indicate a high barrier to Pd-N bond cleavage under these conditions. The thermodynamic parameters show the expected endothermic nature of this process (+140 +/- 17 kJ mol(-1)) and a slight positive overall entropy (DeltaS degrees = +17 +/- 2 J K(-1) mol(-1)); this latter parameter is presumably due to the formation of the lower dipole moment trans-product when compared to the cis-isomer. Calculated (DFT) values of DeltaG(double dagger) and DeltaH(double dagger) are in excellent agreement to those found experimentally. Further theoretical investigation suggests that two 14-electron three-coordinate T-shaped transition states (i.e., [PdCl(2)(Phox)](double dagger)) are involved; the form pre-disposed to yield the thermodynamic trans-product following re-attachment of the released oxazoline is found to be energetically favoured. The analogous alkyloxazoline system [PdCl(2)(Meox)(2)] (4: Meox = 2-methyl-2-oxazoline) has likewise been investigated. This material gives no indication of cis-trans isomerisation behaviour in solution (NMR) and is shown to exist (X-ray) in the trans-form in the solid-state (as do previously reported crystalline samples of 3). A DFT study of 4 reveals similar values of DeltaS(double dagger) and DeltaH(double dagger) if a D type mechanism were operating to rapidly convert cis- to trans-4. However, a significantly higher thermodynamic stability of the trans-isomer relative to the cis-form is revealed versus similar calculations of the Phox derivative 3. This suggests the possibility that (i) reactions of Meox with Li(2)PdCl(4) may lead directly to the trans-form of [PdCl(2)(Meox)(2)] or alternatively (ii) that alkyloxazoline complexes such as 4 may have a different, and presumably much more rapid, mechanism for isomerisation. The results are placed into the context that isomerisation behaviour, or lack thereof, could play a key preliminary role in later substrate modification. This is due to the fact that [PdX(2)(oxazoline)(2)] compounds are well-known (pre-)catalysts for C-C bond forming chemistry.
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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) | 0.000 | 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) | 0.005 | 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 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".