Unusual Coordination Pattern of the Lithium Center in a Chiral α-Lithiated Silicon Compound

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!

Synthesis and reactivity of alkali metal aluminates bearing bis(organoamido)phosphane ligand

In this study, we report a group of alkali metal aluminates bearing bis(organoamido)phosphane ligand. The starting complex {[PhP(NtBu)2]AlMe2}Li·OEt2 (1) was prepared by stepwise deprotonation of the parent PhP(NHtBu)2 by nBuLi and AlMe3. Further derivatization of aluminate 1 was performed by the virtual substitution of lithium -{[PhP(NtBu)2]AlMe2}K (2), methyl substituents - {[PhP(NtBu)2]AlH2}Li·THF (3), modification of steric bulk and induction effects on the phosphorus atom - {[tBuP(N-2,6-iPr2C6H3)2]AlMe2}Li·(OEt2)2 (4), and phosphorus atom oxidation state {[Ph(Y)P(NtBu)2]AlMe2}Li (Y = O (5), S (6), Se (7), Te (8)). The structure causing non-covalent interactions in 1-4 were evaluated with the help of theoretical calculations and topological analysis ranging from π-electron system-metal to agostic interactions of various types. The further reactions of 1 with various nucleophiles were found to be a versatile tool for the preparation of iminophosphonamides via the formation of P-E bond (E = Si, Ge, Sn, Pb, P, and C) and followed by P(III) → P(V) tautomeric shift.

Synthesis and coordination behaviour of aluminate-based quinolyl ligands

The effects of moving the donor N-atom from the 2-position in lithium (2-pyridyl)- and (2-quinolyl)aluminates to the more remote position in (8-quinolyl)aluminates have been investigated by solid-state structural and DFT computational studies of the new complexes [{EtAl(2-qy)₃}Li(μ-X)Li(THF)₃] (X = Cl/Br 62 : 38) [(1)Li(μ-X)Li(THF)₃], [{(EtAl(2-qy)₃)Li}₂(μ-Br)]^-Li(THF)₄⁺ [{1Li}₂(μ-Br)]^-Li(THF)₄⁺, [{EtAl(2-Me-8-qy)₃}Li] [(2)Li], [{Me₂Al(2-Me-8-qy)₂}Li(THF)] [(3a)Li(THF)], [{Me₂Al(6-Me-2-py)₂}Li(THF)₂] [(4)Li(THF)₂] and [{{EtAl(2-Me-8-qy)₂}₂O}(Li₂THF)] (5). Increasing the remoteness of the donor N-atom from the bridgehead results in large differences in the coordination of the Li⁺ cations by the (8-quinolyl)aluminate anions compared to 2-quinolyl or 2-pyridyl counterparts. The results are of potential interest in understanding how the coordination sites of ligands of this type can be tuned for the coordination requirements of specific metal centres.

Primary Amine Functionalization of Alkoxysilanes: Synthesis, Selectivity, and Mechanistic Insights

We report a highly selective substitution of silicon-bound methoxy groups by primary lithium amides. This unusual reactivity is possible because of the formation of particularly stable lithium methoxide, which compensates for the decreased Si-N bond enthalpy compared to Si-O bonds. In contrast to substitution reactions on halosilanes, highly selective monosubstitutions under mild conditions are possible, even in the presence of further reactive methoxy groups. A combination of experiments and density functional theory calculations was carried out in order to get an extensive understanding of the reaction. The calculations reveal a possible reaction mechanism with considerably low activation barriers and the entry of the nucleophile to be the rate-determining step. The low activation energies allow for the substitutions to be carried out at low temperatures, therefore preventing side reactions from occurring. The presented investigations expand the view of fundamental transformation processes on silicon and give access to a wide variety of functionalized silicon-based building blocks for various fields of chemistry.

The crystal structure of adamantylmethoxydiphenylsilane, C23H28OSi

C23H28OSi, monoclinic, P21/c (no. 14), a = 14.2882(11) Å, b = 17.8169(10) Å, c = 7.6201(6) Å, β = 103.780(8)°, V = 1884.0(2) Å3, Z = 4, R gt (F) = 0.0538, wR ref (F 2) = 0.1241, T = 173(2) K.