New Structural Motifs of Lithium N-Heterocyclic Carbene Complexes with Bis(3-tert-butylimidazol-2-ylidene)dialkylborate Ligands

Employment of bidentate, anionic bis(3-tert-butylimidazol-2-ylidene)dialkylborate N-heterocyclic ligands [BIM^tBuBR₂]⁻ (R = Ph or Me) led to the isolation of two unprecedented lithium carbene complexes: monomeric chelating [(BIM^tBuBPh₂)Li(OEt₂)] (4a) and nonchelating, dimeric μ₂-κC²:κC^2′-[(BIM^tBuBMe₂)₂Li₂] (4b). Both have been characterized by spectroscopic methods and by single-crystal X-ray diffraction.