NaBHT Generated In Situ from BHT and NaOtBu: Crystallographic Characterization and Applications in Buchwald-Hartwig Amination

NaBHT is a valuable medium-strength base useful for many applications, particularly for Buchwald-Hartwig coupling. The structures of solvent-free NaBHT and its solvates with Et2O, THF, tBuOH, and a THF/tBuOH mixture were established using single-crystal X-ray diffraction. While [NaBHT center dot Et2O](2) adopts a dimeric structure and crystallizes in a monoclinic cell, [NaBHT center dot THF](3), [NaBHT center dot tBuOH](3), and [NaBHT center dot(THF center dot tBuOH)](3) prefer a trimeric structure and crystallize in cubic cells. Solvent-free [NaBHT](n) is different from solvated NaBHT and from other known sodium phenolates. It is an inorganic polymer that crystallizes in an orthorhombic cell, with a NaO core spreading in the [1 0 0] direction. Agostic interactions of the tBu group hydrogens with Na, which were confirmed for all structures, may help explain the reductive properties of NaBHT. Further, interactions of BHT with tBuONa in solution and in the solid state were examined, reveraling that NaBHT does not need to be prepared from pyrophoric NaH or metallic Na every time. Instead, it can be generated efficiently in or ex situ using NaOtBu in solution or with only a stoichiometric amount of solvent to assist in bringing the reactants together. Application of this methodology was demonstrated with the efficient, solvent-free, and Pd-catalyzed C-N coupling with Pd(NHC) catalysts.

Automated summary

NaBHT is a valuable medium-strength base for various applications, especially in Buchwald-Hartwig coupling reactions. The structures of solvent-free NaBHT and its various solvates were determined using single-crystal X-ray diffraction. It was found that NaBHT has a unique inorganic polymer structure in its solvent-free form, different from other sodium phenolates, which may contribute to its reductive properties.