Phosphineborane chemistry. — An anionic tripod ligand featuring three ylide functions and the structure of the corresponding electroneutral double‐ylide

In a search for a tripod ligand featuring three ylidic functions based on a phosphineborane skeleton, hydrotris(trimethylphosphonio)borate dibromide [HB{P(CH₃)₃}₃]²⁺ Br 2− was treated with potassium hydride in tetrahydrofuran to give the corresponding triple‐ylide salt potassium hydrotris[methylido(dimethyl)phosphonio]borate, K⁺[HB{P(CH₃)₂CH₂}₃]⁻. In an attempt to prepare a barium salt of this tripod ligand, the electroneutral doubleylide HB[P(CH₃)₃][P(CH₃)₂CH₂]₂ was isolated from the reaction mixture obtained from equivalent amounts of the potassium salt and barium chloride in tetrahydrofuran with ultrasound activation. Solvent and protic impurities are the probable sources for the protonation. NMR data are presented for the double‐ylide and its anionic precursor, and the crystal and molecular structure of the double‐ylide has been determined by single‐crystal X‐ray diffraction. The unit cell of the crystals contains two independent molecules of very similar configuration. Assignments of the P(CH₃)₃ and P(CH₃)₂CH₂ units are based on bond distance and bond angle criteria.