Contributions to the chemistry of boron, 188. Synthesis and Structures of New 1,3,2,4‐Diphosphadiboretanes

Three methods have been devised to prepare new diphosphadiboretanes: a) Base‐induced hydrogen halide elimination from (amino)phosphinoboron halides precursors, b) tris(trimethylsilyl)‐phosphane elimination from R2NB[P(SiMe3)2]2 intermediates prepared in situ from combinations of R2NB(Cl)P(SiMe3)2 and LiP(SiMe3)2, and c) organylphosphane elimination from aminobis(organylphosphino)boranes R2N‐B(PHR′)2. The molecular structures of three new 1,3,2,4‐diphosphadiboretanes (3, 4a, 4c) were determined by X‐ray diffractometry. These are characterized by a planar four‐membered B2P2 ring with the phosphorus substituents in trans positions. Their BP bonds represent single bond distances. Experimental results are compared with MNDO III calculations which reveal a low barrier (ΔE = 5 kcal/mol) for the dimerization of the boraphosphene H2NBPMe to the diphosphadiboretane (H2NBPMe)2.