Electrophilic lithium carbazolide as an efficient trap for organolithium species: complexes containing monomeric <i>n</i> -BuLi, <i>t</i> -BuLi and Me ₃ SiCH ₂ Li units

The lithiation reactions of superbulky 3,6-di-<i>tert</i>-butyl-1,8-bis-(2,4,6-triisopropylphenyl)-9<i>H</i>-carbazole (1) with a two-fold molar excess of <i>n</i>-BuLi, <i>t</i>-BuLi, or Me₃SiCH₂Li in heptane afford the binuclear lithium complexes [Carb^2,4,6-iPrLi(μ²-<i>n</i>-Bu)Li] (2), [Carb^2,4,6-iPrLi(μ²-Me₃SiCH₂)Li] (3), and [Carb^2,4,6-iPrLi(μ²-<i>t</i>-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 <i>t</i>Bu-substituted 4 prone to dissociation.