Spinumkehr und Reaktivität

Abstract

Der Wechsel (zwischen zwei Spinzuständen) macht's! Ein Wechsel des Spinzustandes kann dann eine Reaktion erleichtern, wenn sich die Energiehyperflächen des Grund‐ und des angeregten Zustandes entlang der Reaktionskoordinate kreuzen (siehe schematische Darstellung). Dies wird hier anhand einer Reihe von Reaktionen aus der Organischen, Anorganischen und Metallorganischen Chemie demonstriert.

Two-State Reactivity as a New Concept in Organometallic Chemistry

“…In addition to these examples, TSR may affect other reactions of transitionmetal compounds and is also involved in reactions of some organic molecules. 25,26 (a) Atom Transfer: The V + + CS 2 System. A particularly intriguing situation with respect to TSR was found for the endothermic sulfur atom transfer from CS 2 to atomic V + (reaction 2).…”

“…These are elementary reactions in which the role of TSR has been established by experimental and theoretical data. In addition to these examples, TSR may affect other reactions of transition-metal compounds and is also involved in reactions of some organic molecules. , …”

Predictions of Geometries and Multiplicities of the Manganese−Oxo Intermediates in the Jacobsen Epoxidation

“…A low-spin (singlet or triplet) complex is favored with weak coordination or absence of a sixth ligand, while a higher spin (quintet or triplet) state occurs upon association of a stronger ligand. The rates of Mn−oxo reactions could be influenced by spin-state crossing effects as in other Mn−oxo 6 or Fe−oxo systems. , …”

“…The rates of Mn-oxo reactions could be influenced by spin-state crossing effects as in other Mn-oxo 6 or Fe-oxo systems. 16,17 This implies that different experimental results may occur with different ligands, since they will influence spin multiplicities, and potentially the relative rates of stereospecific concerted and stepwise nonconcerted processes. Experimentally, weak ligands, like pyridine N-oxide, increase the enantioselectivity.…”

ChemInform Abstract: Thermal N—H Bond Activation on Anionic and Cationic Platinum Clusters: Non‐Predetermined Reaction Pathways Indicate Transitions to a Bulk Surface Reactivity.

“…[72][73][74][75] Reaction pathways were calculated for both doublet and quartet spin multiplicities in order to discuss the effect of interspin crossing and possible contributions of a two-state reactivity scenario. [76][77][78][79][80][81][82][83][84][85][86][87][88] All calculations were performed with the Gaussian03 package. [89]…”