Stereoselective Formation of C2-Symmetric ansa-Lanthanocenes by Reductive Coupling of Acenaphthylene with Activated Ytterbium or Samarium

Abstract

A fulvene‐type coupling results from the reduction of acenaphthylene by activated samarium or ytterbium in THF. This leads exclusively to the formation of the respective C2‐symmetric trans‐rac‐ansa‐lanthanocene complexes [(η5‐C12H8)2Ln(thf)2] [Eq. (1); Ln=Sm, Yb].

[(η5-C5Me5)Ru]+ fragments ligated to polyaromatic hydrocarbons: an experimental and computational approach to pathways for haptotropic migration

“…In particular, isomers 1A and 2A are found to be the global minima of 1 and 2, respectively, also in agreement with X-ray structures of related species. 3g,15j, 21,27,[35][36][37][38] On the other hand, isomers 3A and 3B are found to be nearly isoenergetic (Table 1), in agreement with the fact that both isomers were isolated in the solid state although only the major isomeric product 3A produced suitable X-ray quality single crystals. Contrary to what has been observed in the acenaphthylene series, 37,38 no structure of a fluoranthene complex η 5 -coordinated through its five-membered ring to a metal center has been reported to date.…”

“…3g,15j, 21,27,[35][36][37][38] On the other hand, isomers 3A and 3B are found to be nearly isoenergetic (Table 1), in agreement with the fact that both isomers were isolated in the solid state although only the major isomeric product 3A produced suitable X-ray quality single crystals. Contrary to what has been observed in the acenaphthylene series, 37,38 no structure of a fluoranthene complex η 5 -coordinated through its five-membered ring to a metal center has been reported to date. 39 Since the first extended Hückel investigation of Albright et al 10 on haptotropic rearrangements in transition-metal complexes of polycyclic polyenes, a substantial number of DFT calculations have been performed on various systems of this type.…”

Alkali‐Metal Aminotroponiminates: Selectivities and Equilibria in Reversible Radical Coupling of Delocalized π‐Electron Systems

“…In practice, some dimerizations of delocalized radical species indeed yield a large number of different isomers, which sometimes cannot be separated due to their similar physical and physicochemical properties . In contrast, there are also cases which proceed with remarkable selectivity despite the presence of a larger number of chemically inequivalent potentially reactive sites –. In some of these reports, possible reasons for the observed selectivities have not been discussed in detail .…”

“…In contrast, there are also cases which proceed with remarkable selectivity despite the presence of a larger number of chemically inequivalent potentially reactive sites –. In some of these reports, possible reasons for the observed selectivities have not been discussed in detail . In other standalone case studies, steric protection and reversibility of radical recombination have been discussed as possible driving forces for unexpectedly high selectivities .…”

Calcium-Mediated Fulvene Couplings. 2. Survey of 6-Aryl- and 6-Alkylfulvenes for Their rac Selectivity in the Synthesis of ansa-Calcocenes

“…In these cases inclusion of the exo CdC bond of the fulvene within an annulated ring is key to the stereoselectivity of the coupling. [30][31][32] Our ability to capture the dynamic conformational changes in the backbone of the chelating ligand framework of meso-5 on the NMR time scale is due to the barrier imposed on the rearrangement by the bulky tertbutyl substituents. In the absence of such bulky substituents, the rearrangements are too fast to be observed on the NMR time scale, [33][34][35] although Piemontesi, 34 Resconi, 35 and co-workers have been able to determine the equilibrium ratios and thus the energy differences between the λ and δ conformers of rac ethylene-bridged bis(indenyl)zirconocene dichloride complexes by analyzing the coupling between the hydrogens on the bridge.…”