Remarkable Reactions and Intermediates in Titanocene(IV) Chemistry: Migratory Insertion Reactions of 2,2-Disubstituted-1-alkenes, Intramolecular 1,5-σ Bond Metathesis via ε-Agostic Interactions, and a Rare Example of a β-Agostic Alkyltitanocene Complex
Bibliographic record
Abstract
The compound Cp(2)TiMe(2) reacts with [Ph(3)C][B(C(6)F(5))(4)] in CD(2)Cl(2) at 205 K to give, inter alia, [Cp(2)TiMe(CD(2)Cl(2))][B(C(6)F(5))(4)]. This solvent-separated ion pair reacts in turn with 2,4-dimethyl-1-pentene (DMP) to give a series of cationic species, the first being the alkene complex [Cp(2)TiMe(DMP)](+), which undergoes ready migratory insertion to form the σ-alkyl complex [Cp(2)Ti(CH(2)CMe(2)CH(2)CHMe(2))](+). The latter, which does not contain a β-hydrogen atom, rearranges rapidly via an unprecedented 1,5-σ bond metathesis reaction involving two isomeric ε-agostic species to give the σ-alkyl species [Cp(2)Ti(CH(2)CHMeCH(2)CMe(3))](+); this does contain a β-hydrogen atom and, in concurrent processes, eliminates H(2) or 2,4,4-trimethyl-1-pentene (a major product) to form respectively the allylic complex [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CMe(3)}](+) (a major product) or the hydride complex [Cp(2)TiH](+). The latter reacts reversibly with free DMP to give the insertion product [Cp(2)Ti(CH(2)CHMeCH(2)CHMe(2))](+) (V, a major product), in which the italicized hydrogen atom engages in a β-agostic interaction with the metal atom. Compound V is a rare example of both a β-agostic derivative of a group 4 metallocene and a β-agostic compound of any metal in which the (1)H resonance of the agostic hydrogen can be identified in the (1)H NMR spectrum (δ -3.43). Interestingly, a NOESY experiment on V indicates slow mutual exchange between the agostic hydrogen atom, the hydrogen atoms on C(1), and those of Me(2). These observations are consistent with the intermediacy of the allylic dihydrogen species [Cp(2)Ti(H(2)){η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+), which loses H(2) to form [Cp(2)Ti{η(3)-(CH(2))(2)CCH(2)CHMe(2)}](+) (a minor product). Support for all steps of the proposed reaction scheme comes from product distributions, from labeling studies utilizing [Cp(2)Ti(CD(3))(CD(2)Cl(2))](+), and from extensive DFT calculations. The observed titanocene-based chemistry stands in stark contrast to that of the analogous zirconium system, in which the unusual but well-characterized cationic methyl alkene complex [Cp(2)ZrMe(DMP)](+) does not undergo migratory insertion and subsequent reactions.
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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 | 0.001 | 0.001 |
| 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 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".