On the Nature of the Agostic Bond between Metal Centers and β-Hydrogen Atoms in Alkyl Complexes. An Analysis Based on the Extended Transition State Method and the Natural Orbitals for Chemical Valence Scheme (ETS-NOCV)
Bibliographic record
Abstract
We have in the present account analyzed the bonding in β-agostic alkyl complexes between the carbon chain (R) and the transition metal center. The analysis is based on a recently proposed energy decomposition scheme (ETS-NOCV). We have considered R = Et, n-Pr, i-Pr, n-Bu, attached to the cationic Ni(II)- and Pd(II)-bis-diimine Brookhart complexes ( 1 ), the cationic Ti(IV)- or Zr(IV)-metallocenes ( 2 ), and the neutral Pd(II) Drent ( 3 ) complexes. We find for a given metal that the total M−R dissociation energy −Δ E total follows the order n-Bu > n-Pr > Et ≫ i-Pr. For the same R-group (n-Pr), −Δ E total for second-row metals is larger than for first-row, as 4d forms better overlaps with the alkyl orbitals than 3d. The major stabilizing contribution to −Δ E total is the σ-bond between the α-carbon and the metal. It is augmented by smaller contributions from the C β −M σ-interaction as well as the hyperconjugation of charge into the σ CC * and σ CH * alkyl orbitals. We finally have the β-agostic contribution from the interaction between a hydrogen atom on the β-carbon and the metal center. The strength of this bond is rather constant for the cationic species 1 and 2 . It can be considered as originating from a (largely) Coulombic interaction between the metal center and the electron pair in the C β −H bond, where the density of the pair has been polarized by the positive metal charge. The neutral Drent system ( 3 ) exhibits a weaker β-agostic interaction, as the net charge on the metal center is less positive.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.003 | 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 source (direct Gemma or distilled Codex), 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".