Electrophilic lithium carbazolide as an efficient trap for organolithium species. Complexes containing monomeric n-BuLi, t-BuLi and Me 3 SiCH 2 Li units

Abstract

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 [Carb 2,4, 4, Li(μ 2 -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 alkyl group μ 2 -bridging two lithium centers, one of which is also η 6 -coordinated with the phenyl fragment of carbazolyl ligand. For complexes 2 and 3 the binuclear structures are retained in solution as evidenced by 1 H, 13 C, 7 Li and 1 H DOSY NMR spectroscopy. QTAIM and NCI data reveal a difference in strength of Li-C interactions between 2-4, which are weaker for 4, and rationalised the tBu-subctituted 4 prone to dissociation.