Extremely Facile Transformations of Tris(3,5‐dimethylpyrazolyl)borate: a Bidentate Nitrogen Ligand and a C 2 ‐Chiral Cation

Two novel transformations are reported for the well‐known hydridotris(3,5‐dimethylpyrazolyl)borate (Tp* – ). The uncommon Lewis base abstractor aryldiazonium cation (ArN 2 + ; Ar = p ‐Br‐C 6 H 4 , p ‐MeO‐C 6 H 4 ) if used in equimolar amounts, removes a hydride from Tp* – in acetone to produce the formal acetone adduct of tris(3,5‐dimethylpyrazolyl)borane (pz* 3 B · C 3 H 6 O, compound 1 ). Frustrated Lewis pair (FLP) like behavior is thus found for a tris(pyrazolyl)borane. If 2 equiv. of ArN 2 + are used, 3,5‐dimethylpyrazolate is now being abstracted from 1 , and the resulting intermediate bifunctional borane adds another equivalent of acetone to form cation 2 + {[pz* 2 B · (C 3 H 6 O) 2 ] + , obtained as 2 ‐BF 4 }, a boronium cation that is the formal addition product of 2 equiv. of acetone to the bis(3,5‐dimethylpyrazolyl)borinium cation. Compounds 1 and 2 + are characterized by 1 H, 13 C, and 11 B NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. Compound 1 is potentially useful as a charge‐neutral bidentate chelate ligand with controlled sterics, and 2 + is a C 2 ‐chiral cation.