Lithium Aluminate Complexes and Alumoles from 1,4-Dilithio-1,3-Butadienes and AlEt2Cl

A series of lithium aluminate complexes and alumoles were synthesized from 1,4-dilithio-1,3-butadienes 1 and AlEt2Cl. Their structures were characterized using single-crystal X-ray structural analysis and NMR spectroscopy. The structure of the lithium aluminate complex 2-TMEDA showed that the Al atom adopted a tetracoordinated mode bonded with two butadienyl C-sp2, atoms and two ethyl C-sp3 atoms. The lithium cation was located above the alumole ring. The structure of 3a revealed a dimeric 1-ethylalumole in the solid state. Diffusion ordered spectroscopy NMR spectra showed that 3a was also a dimer in C6D6 solvent. However, in tetrahydrofuran (THF) solution, the dimeric 3a dissociated into the 1-ethylalumole THF adduct. The lithium aluminate complex 2 transformed into 3a-THF when treated with 1.0 equiv of AlEt2Cl. Preliminary reaction chemistry and synthetic applications of the lithium aluminate complex were also investigated.