Paramagnetic Organometallic ComplexesUpdate based on the original article by Daniel B. Leznoff and Garry Mund,<i>Encyclopedia of Inorganic Chemistry</i>Second Edition © 2005, John Wiley & Sons, Ltd
Notice bibliographique
Résumé
Abstract The synthesis, characterization, and reactivity of paramagnetic (or open‐shell) organometallic species are described. Many stable complexes featuring transition metals, lanthanides, and actinides have been reported. These systems, which are exceptions to the 18‐electron rule (or 16‐electron rule), are increasingly being used in the catalytic realm, and also have different reactivity patterns compared to their diamagnetic counterparts due to the presence of unpaired electrons. The formation and subsequent stability of paramagnetic organometallic complexes in violation of the 18‐electron rule can be explained via molecular orbital (MO) theory in terms of (i) the use of π‐donor ligands (as opposed to the ubiquitous π‐acceptor ligands usually found in organometallic chemistry); (ii) kinetic stabilization with sterically demanding ligands; and (iii) partially filled MOs being non‐bonding or slightly antibonding/bonding. Although metallocene‐based complexes are probably the most well studied of all paramagnetic organometallic complexes, homoleptic σ‐alkyl and σ‐aryl complexes (particularly with bulky groups such as CH2SiMe3andmeta‐terphenyl respectively) and other non‐Cp systems have also been explored. Such non‐Cp ancillary ligands include amido‐, alkoxo‐, and thiolato‐ligands, β‐diketiminate ligands, tris(pyrazolylborate) andN‐heterocyclic carbene ligands. f‐Electron organometallic systems also utilize a similar range of ligands, but because of their larger size, they can accommodate more sterically congested coordination spheres; for example, Cp*3M complexes can be prepared, and they show unusual reactivity pathways. Open‐shell organometallic molecules are known to span a range of electron counts from 8 to 20. Nineteen‐electron organometallic complexes are of particular interest with respect to the location of the extra electron residing primarily on the metal or on the ligand (in this case, the complex is referred to as an 18 + δ system). Redox‐active ligands in general are now recognized to play a significant role in organometallic chemistry and catalysis and are discussed briefly. The discussion of short‐lived paramagnetic organometallic systems revolves around 17‐ and 19‐electron radicals, and their use in catalytic processes and as “super reducing agents.” Many reactivity pathways for such organometallic radicals (or “metalloradicals”) have been identified. Characterization tools for paramagnetic organometallic complexes, such as nuclear magnetic resonance (NMR) and electron spin resonance spectroscopy, density functional theory calculations, and magnetic measurements are presented. Variable‐temperature NMR studies and2H NMR can be of significant use in interpreting paramagnetic NMR spectra. Solid‐state NMR spectroscopy of paramagnetic organometallic systems is still in its infancy. The applications of paramagnetic organometallic complexes span many areas including catalysis (e.g., olefin polymerization), synthetic organic chemistry, and the development of molecule‐based magnetic materials.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,005 | 0,001 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».