The synthesis and nuclear magnetic resonance investigation of the structure and chemical dynamics of new anionic tetra-allyl complexes of lanthanide ions

Anionic Monosubstituted Cyclopentadienylsamarium Derivatives: Catalysts for a Stereospecific Isoprene Polymerization

“…As a ance with the original synthesis [23] . Ethereal solutions of MeLi were consequence, a very high stereoselectivity (89 to 95% of 1,4-purchased from Aldrich.…”

“…compound was formed in the CpЈ series: a redistribution leading to a mixture of CpЈ 3 Sm [9] and Sm(C 3 H 5 ) 4 Li(dioxIn contrast, the dissociation of an allylic ligand in the anionic compound 2 is easy and allows the coordination of ane) [23] was observed (Scheme 3). the diene.…”

Mixed Allyl–Borohydride Lanthanide Complexes: Synthesis of Ln(BH4)2(C3H5)(THF)3 (Ln = Nd, Sm), Characterization, and Reactivity toward Polymerization

“…The first organolanthanide complexes containing the allyl moiety, (C 5 H 5 ) 2 Ln­(C 3 H 5 ) (Ln = lanthanide), were reported by Tsutsui in 1975 . Later in the 1980s, the anionic tetrakis­(allyl) lanthanide complexes [Li­(1,4-dioxane) n ]­[Ln­(allyl) 4 ] were reported by Mazzei and Lugli . Significant work in the chemistry of allylic derivatives of the rare earths was then performed during the 1990s by the group of Taube, who especially reported the neutral homoleptic tris­(allyl) complexes, obtained via allyllithium abstraction from their tetrakis­(allyl) anionic congeners [Ln­(allyl) 3 · x (dioxane)] n (Ln = La, x = 1.5; Ln = Nd, x = 1) and unsolvated Ln­(allyl) 3 after vacuum treatment .…”

Fluxional η3-Allyl Derivatives of ansa-Scandocenes and an ansa-Yttrocene. Measurements of the Barriers for the η3 to η1 Process as an Indicator of Olefin Binding Energy to d0 Metallocenes

“…Although the barriers for η 3 -C 3 H 5 ⇄ η 1 -C 3 H 5 interconversions generally have not been established, there are some unusual and poorly understood qualitative differences among seemingly closely related allyl complexes . Some complexes are firmly η 3 -coordinated; e.g ., (η 5 -C 5 Me 5 ) 2 Ln(η 3 -C 3 H 5 ) (Ln = La, Nd, Sm) are nonfluxional on the 1 H NMR time scale at 25 °C in hydrocarbon solvents (the neodymium complex is static on the magnetization transfer time scale at +90 °C) 5b. On the other hand, (η 5 -C 5 Me 5 ) 2 Sm(η 3 -C 3 H 5 ) is fluxional at 25 °C in THF solution, and (η 5 -C 5 Me 5 ) 2 Sm(η 3 -C 3 H 4 -1-CH 3 ) is fluxional even at −80 °C. 5a,c (η 5 -C 5 Me 5 ) 2 Sc(η 3 -C 3 H 5 ) requires cooling below 0 °C to obtain the spectrum for the static structure, in hydrocarbon solvents 4a.…”

“…Some complexes are firmly η 3 -coordinated; e.g ., (η 5 -C 5 Me 5 ) 2 Ln(η 3 -C 3 H 5 ) (Ln = La, Nd, Sm) are nonfluxional on the 1 H NMR time scale at 25 °C in hydrocarbon solvents (the neodymium complex is static on the magnetization transfer time scale at +90 °C) 5b. On the other hand, (η 5 -C 5 Me 5 ) 2 Sm(η 3 -C 3 H 5 ) is fluxional at 25 °C in THF solution, and (η 5 -C 5 Me 5 ) 2 Sm(η 3 -C 3 H 4 -1-CH 3 ) is fluxional even at −80 °C. 5a,c (η 5 -C 5 Me 5 ) 2 Sc(η 3 -C 3 H 5 ) requires cooling below 0 °C to obtain the spectrum for the static structure, in hydrocarbon solvents 4a. Isoelectronic cationic group 4 metallocenium cations also display both static and fluxional NMR character; e.g ., [(η 5 -C 5 Me 5 ) 2 Ti(η 3 -C 3 H 5 )] + is reported to be static at −18 °C, but the zirconium analogue is fluxional at 25 °C in toluene- d 8 and nearly static at −78 °C in methylene chloride- d 2 . 4l,r In contrast, [(η 5 -C 5 Me 5 ) 2 Zr(η 3 -C 3 H 5 )(CO)] + is static at 25 °C in methylene chloride- d 2 4l.…”