Bis(4-benzhydryl-benzoxazol-2-yl)methane - from a Bulky NacNac Alternative to a Trianion in Alkali Metal Complexes.

A novel sterically demanding bis(4-benzhydryl-benzoxazol-2-yl)methane ligand 6 ( BoxCH ) was gained in a straightforward six-step synthesis. Starting from this ligand monomeric [M( BoxCH)] (M=Na (7), K (8 )) and dimeric [{M( BoxCH)} ] (M=K (8 ), Rb (9), Cs (10)) alkali metal complexes were synthesised by deprotonation. Abstraction of the potassium ion of 8 by reaction with 18-crown-6 resulted in the solvent separated ion pair [{(THF) K@(18-crown-6)}{bis(4-benzhydryl-benzoxazol-2-yl)methanide}] (11), including the energetically favoured monoanionic (E,E)-( BoxCH) ligand. Further reaction of BoxCH with three equivalents KH and two equivalents 18-crown-6 yielded polymeric [{(THF) K@(18-crown-6)}{K@(18-crown-6)K( BoxCH)}] (n→∞) (12) containing a trianionic ligand. The neutral ligand and herein reported alkali complexes were characterised by single X-ray analyses identifying the latter as a promising precursor for low-valent main group complexes.