Characterization of a Kinetically Stable, Highly Ordered, Octameric Form of Lithiumtert-Butoxide and Its Implications Regarding Aggregate Formation

Abstract

The controlled reaction of molecular oxygen with hydrocarbon solutions of tBuLi results in the unexpected formation of the octameric species [(tBuOLi)8], 18. Single-crystal X-ray diffraction studies indicate that the connectivity within 18 corresponds with the fusion of two face-opened tetrameric cubanes. Cryoscopic studies establish the stability of the octamer in benzene solution, but heating results in aggregate rearrangement to the commonly found prismatic hexameric form, 16. Theoretical calculations confirm that the hexameric form is the thermodynamically favored aggregate.

Synthesis and Structural Characterization of Lithium and Iron Complexes Containing a Chelating Phenolate Phosphane Ligand

“…The 1 H NMR spectra of these solutions are indicative of the presence of C 1 -symmetric molecules, due possibly to the formation of higher aggregates. [26][27][28] In agreement with this hypothesis, these precipitates re-dissolve in solution upon addition of an excess of diethyl ether. Similar phenomena were also found for {[L tBu ]Li 2 (DME)} 2 .…”

Alkali Metal Complexes of Silyl‐Substituted ansa‐(Tris)allyl Ligands: Metal‐, Co‐Ligand‐ and Substituent‐Dependent Stereochemistry

“…In the unusual, kinetically stable octamer [LiOtBu] 8 , the same dimers are believed to associate in the first instance to form face-opened tetramers, which themselves combine to form the octamer. [39] As with the 1 H NMR spectra of compounds 4 and 6 2 , that of compound 7 is also rather complicated in the allylic region. A series of broad overlapping multiplets at δ( 1 H) = 6.41-5.25 ppm coupled with three broadened doublets of doublets at 1.66-1.44 ppm point towards extensive conformational flexibility in benzene at 294.9 K. The sharp, intense singlet for the tert-butoxide protons at δ( 1 H) = 1.15 ppm overlaps with the allylic signals in this region, hindering their accurate integration.…”

Computational Perspectives on Organolithiums

“…Ruiz-López and coworkers [99] have performed a free energy MD study on dimers of lithium methoxide but even here only B3LYP and MP2 was used. Similarly, in 2004, standard B3LYP was employed in the study on aggregates of lithium tert-butoxide by the group of Henderson [100]. Here, however, nonsolvated gas-phase calculated energies were used in an attempt to rationalize the thermodynamically most stable hexameric aggregate.…”