Phenol-Tethered N-Heterocyclic Benzimidazol-2-ylidene Carbene Interactions with the Early Lanthanides

The cyclization of salophan with triethyl orthoformate in the presence of HBr results in a bisphenol benzimidazolium carbene precursor 1,3-bis(2-hydroxybenzyl)-2H-benzimidazolium bromide (H3OBBIm). By reacting H3OBBIm in a one-pot synthesis with Ln(N(SiMe3)2)3 (Ln = La–Sm excl. Pm) and an excess of KN(SiMe3)2, the N-heterocyclic carbene (NHC) complexes, [Ln(OBBIm)2(N″)][K2THFx], can be prepared and isolated. These complexes were characterized by single-crystal X-ray diffraction, solution- and solid-state UV–vis–near-infrared spectroscopy, and 1H NMR. These complexes possess distorted pentagonal bipyramid geometries.