Understanding the Reactivity of Strained Sandwich Compounds with Aluminum or Gallium in Bridging Positions: Experiments and DFT Calculations
Bibliographic record
Abstract
The aluminum and gallium dichlorides (Mamx)ECl(2)1a (E = Al; 82%) and 1b (E = Ga; 79%) (Mamx = 2,4-di-tert-butyl-6-[(dimethylamino)methyl]phenyl) reacted with dilithioferrocene or dilithioruthenocene to give [1]ferrocenophanes (2a, 2b) and [1]ruthenocenophanes (3a, 3b), respectively. The galla[1]ruthenocenophane 3b could be isolated from the reaction mixture through precipitation into hexane (50%), while 2a, 2b, and 3a underwent ring-opening polymerization under the reaction conditions of their formation reactions to give metallopolymers (M(w) (DLS) between 8.07 and 106 kDa). Monomer 3b was polymerized using Karstedt's catalyst resulting in an M(w) of 28.6(±6.3) kDa. In order to get an indication of the structure of polymers, bis(ferrocenyl) compounds (Mamx)EFc(2) (E = Al (4a), 51%; E = Ga (4b), 49%) were prepared and characterized by single crystal X-ray analysis. DFT calculations shed some light on the unexpected high reactivity of these new strained sandwich species. Optimized geometries of known aluminum and gallium-bridged [1]ferrocenophanes (Al(Pytsi) (6a), Ga(Pytsi) (6b); Pytsi = [dimethyl(2-pyridyl)silyl]bis(trimethylsilyl)methyl) and [1]ruthenocenophanes (Al(Me(2)Ntsi) (7a), Ga(Me(2)Ntsi) (7b); Me(2)Ntsi = [(dimethylamino)dimethylsilyl]bis(trimethylsilyl)methyl) matched very well with experimental molecular structures. Geometries of species 2a, 2b, 3a, and 3b were optimized (BP86/TZ2P) and the structural influence of the tBu group of the Mamx ligand in ortho position was evaluated by optimizing molecular structures of the four unknown species where the ortho-tBu group was replaced by an H atom (2a(H), 2b(H), 3a(H), and 3b(H)). The most pronounced structural effect was seen as a change of the orientation of the bridging moiety with respect to the sandwich unit. As the tBu group was removed, the aromatic ligand moved toward the freed-up space. The energetics (ΔE, ΔH(298K), and ΔG(298K)) accompanied by the structural changes were evaluated by a hydrogenolysis reaction of strained species resulting in Cp(2)M (M = Fe, Ru) and respective aluminum and gallium dihydrides. This nonisodesmic reaction showed that [1]metallocenophanes equipped with the ortho-tBu group were on average 5.5 kcal/mol higher strained (ΔH(298K)) than species where the tBu group was lacking. The investigation of the isodesmic reaction between strained species and Cp(2)M yielding bis(metallocenyl) compounds revealed that the ortho-tBu group sterically interacts with one of the metallocenyl units. The bis(metallocenyl) compounds are model compounds for the respective metallopolymers and one can conclude that even though the ortho-tBu group imposes additional strain on the starting metallocenophanes, this effect cancels out in ROPs because the ortho-tBu group imposes a similar strain on the resulting polymers. The uncovered steric repulsion between the ortho-tBu group and the sandwich moieties probably causes the ortho-tBu to act as an unusually sensitive NMR probe of the tacticity of the polymers.
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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) | 0.000 | 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".