Cyclopentadienyl Chromium β-Diketiminate Complexes: Initiators, Ligand Steric Effects, and Deactivation Processes in the Controlled Radical Polymerization of Vinyl Acetate
Bibliographic record
Abstract
The new compounds CpCr(nacnac Ar,Ar′ ) with nacnac Ar,Ar′ = Ar−N --- C(Me) --- CHC(Me) --- N−Ar′ (Ar = Ar′ = C 6 H 2 Me 3 -2,4,6 or mes, 2; C 6 H 3 Et 2 -2,6 or dep, 3; Ar = C 6 H 3 Me 2 -2,6 or xyl and Ar′ = C 6 H 3 i Pr 2 -2,6 or dipp, 4 ) have been synthesized and used in polymerization experiments in addition to the previously known analogues with Ar = Ar′ = xyl, 1, or dipp, 5 . The compounds were used as moderators for the polymerization of vinyl acetate (VAc) initiated by V-70, according to an OMRP mechanism. The alkylchromium(III) thermal initiator CpCr(nacnac xyl,xyl )(CH 2 CMe 3 ) ( 8 ) was synthesized from CpCr(nacnac xyl,xyl )(OTs) ( 7 ) and Mg(CH 2 CMe 3 ) 2 (dioxane), while 7 was obtained from CpCr(nacnac xyl,xyl )Cl ( 6 ) and AgOTs. The polymerizations carried out with ( 1 − 5 )/V-70/VAc at elevated temperatures yielded rapid deactivation, suggestive of irreversible radical trapping. On the other hand, room-temperature polymerizations carried out with 6 /VAc proceeded, albeit slowly, to greater conversions. A labilizing effect of the Ar/Ar′ steric bulk is suggested by QM/MM calculations of Cr III −C BDE for models of the OMRP dormant species with 1, 5, and the parent system where Ar = Ar′ = Ph. Thermal deactivation of the nacnac xyl,xyl system has been evidenced, with formation of the acetate complex CpCr(nacnac xyl,xyl )(OAc), 9, as confirmed by an UV−vis study and by independent synthesis. This product is proposed to form by β-acetate transfer from the growing radical chain, triggered by a head−head monomer insertion. Compounds 2, 3, 6, 7, 8, and 9 have been structurally characterized by X-ray diffraction methods.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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; 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".