Tuning Reactivities of tert-Butyllithium by the Addition of Stoichiometric Amounts of Tetrahydrofuran

In alkyllithium chemistry the highest reactivity has historically been linked to the smallest degree of aggregation possible. Since tert-butyllithium is known to form a monomer in tetrahydrofuran solution, using just stoichiometric amounts of the lewis base to selectively form a dimeric species seemed irrational. In this study, we showed a considerable increase of the reactivity of t-BuLi when using stoichiometric amounts of THF in the non-polar solvent n-pentane in order to enable the deprotonation of simple methyl silanes and other low C-H-acidic substrates. In this context, we were able to obtain the corresponding aggregates of t-BuLi with the ligand THF in suspension and as crystalline solids and investigate them by single crystal X-ray structural analysis, in situ FTIR spectroscopy and quantum chemical calculations. Furthermore, we were able to explain the enhanced reactivity of t-BuLi with stoichiometric amounts of THF on the basis of structural features of the bridged dimer obtained under these conditions. With these findings, we present a new target in the aggregation of alkyllithium reagents: the selectively formed "frustrated" aggregates!

Towards Substrate-Reagent Interaction of Lochmann-Schlosser Bases in THF: Bridging THF Hides Potential Reaction Site of a Chiral Superbase

The metalation of N,N-dimethylaminomethylferrocene in THF by the superbasic mixture of ⁿ BuLi/KO^t Bu proceeds readily at low temperatures to afford a bimetallic Li₂ K₂ aggregate containing ferrocenyl anions and tert-butoxide. Starting from an enantiomerically enriched ortho-lithiated aminomethylferrocene, an enantiomerically pure superbase can be prepared. The molecular compound exhibits superbasic behavior deprotonating N,N-dimethylbenzylamine in the α-position and is also capable of deprotonating toluene. Quantum chemical calculations provide insight into the role of the bridging THF molecule to the possible substrate-reagent interaction. In addition, a benzylpotassium alkoxide adduct gives a closer look into the corresponding reaction site of the Lochmann-Schlosser base that is reported herein.

Crystal structure of N,N,N',N'-tetra-methyl-ethane-di-amine

N,N,N′,N′-tetra­methyl­ethanedi­amine, C₆H₁₆N₂, crystallizes in the monoclinic crystal system in the space group P2₁/c. For the investigation of the conformation, quantum chemical methods were used and for inter­molecular inter­actions, a Hirshfeld surface analysis was performed.

The title compound N,N,N′,N′-tetra­methyl­ethanedi­amine, C₆H₁₆N₂, is a bidentate amine ligand commonly used in organolithium chemistry for deaggregation. Crystals were grown at 243 K from n-pentane solution. The complete mol­ecule is generated by a crystallographic center of symmetry and the conformation of the di­amine is anti­periplanar. To investigate the inter­molecular inter­actions, a Hirshfeld surface analysis was performed. It showed that H⋯H (van der Waals) inter­actions dominate with a contact percentage of 92.3%.