Electrophilic Lithium Carbazolide As an Efficient Trap for Organolithium Species: Complexes Containing Monomeric N-Buli, T-Buli and Me3SiCH2Li Units.

The lithiation reactions of superbulky 3,6-di-tert-butyl-1,8-bis-(2,4,6-triisopropylphenyl)-9H-carbazole (1) with a two-fold molar excess of n-BuLi, t-BuLi, or Me3SiCH2Li in heptane afford the binuclear lithium complexes [Carb2,4,6-iPrLi(μ2-n-Bu)Li] (2), [Carb2,4,6-iPrLi(μ2-Me3SiCH2)Li] (3), and [Carb2,4,6-iPrLi(μ2-t-Bu)Li] (4) in 80, 90, and 56% yields. The single-crystal X-ray diffraction studies revealed that 2-4 are binuclear ionic complexes comprising the alkyl group μ2-bridging two lithium centers, one of which is also η6-coordinated with the phenyl fragment of the carbazolyl ligand. For complexes 2 and 3, the binuclear structures are retained in solution as evidenced by 1H, 13C, 7Li, and 1H DOSY NMR spectroscopy. QTAIM and NCI data reveal a difference in the strength of Li-C interactions between 2-4, which are weaker for 4, and rationalised the tBu-substituted 4 prone to dissociation.