Rhodium Silyl Hydrides in Oxidation State +5: Classical or Nonclassical?
Bibliographic record
Abstract
Four families of silyl hydride complexes of rhodium in the formal oxidation state +5 were investigated by means of DFT calculations, supplemented by the calculation of Mayer bond indices and Si−H coupling constants. In each case some degree of interligand Si−H interaction has been found. In the compounds CpRh(SiMe 3 ) 2 H 2 ( 1 ), CpRh(SiMe 3 ) 3 H ( 2 ), CpRh(SiMe 3 ) 2 (SiEt 3 )H ( 3 ), and [Cp(Me 3 P)Rh(SiMe 3 ) 2 H] + ( 4 ) the hydride(s) interact(s) with both silyl ligands. Relaxed potential energy scans indicate that the potential energy surface is extremely flat. It takes only 1 kcal·mol - 1 to compress the Si−H bond from 2.3 Å to 2.0 Å in 1, and 2 kcal·mol - 1 to compress the Si−H distance from 1.990 Å to 1.70 Å in complex 2 . ONIOM calculations of the compound CpRh(SiMe 3 ) 3 H and optimization of the lowest energy conformers of complex CpRh(SiMe 3 ) 2 (SiEt 3 )H show that their geometries are largely determined by steric effects. Increasing steric hindrance promotes Si−H interactions because they result in longer Rh−Si bond lengths, leading to the relief of steric strain. The same conclusion has been drawn from the comparison of complexes [Cp(PMe 3 )Rh(SiMe 3 ) 2 H] + and [Cp*(PMe 3 )Rh(SiMe 3 ) 2 H] +, the latter compound having stronger Si−H interactions. A very low barrier of 1.9 kcal·mol - 1 (on the scale) has been found for the hydride shift in complex 2, accounting for its fluxionality. In contrast, the complexes [Cp(PMe 3 )Rh(SiMe 3 ) 2 H] + ( 4 ) and [Cp(PMe 3 )Rh(SiMe 3 )H 2 ] + ( 8 ) are not fluxional because the hydride migration is accompanied by a highly unfavorable loss of one of the Si···H interactions. The calculated Si−H coupling constants are negative when the silyl and hydride ligands are cis (consistent with the presence of Si−H bonding) and positive for the trans pairs (no Si−H bonding). The magnitude of the calculated J (H−Si) is in very good accord with experimental data, when the latter are available.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.038 | 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".