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 R 2 NB[P(SiMe 3 ) 2 ] 2 intermediates prepared in situ from combinations of R 2 NB(Cl)P(SiMe 3 ) 2 and LiP(SiMe 3 ) 2 , and c) organylphosphane elimination from aminobis(organylphosphino)boranes R 2 N‐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 B 2 P 2 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 (Δ E = 5 kcal/mol) for the dimerization of the boraphosphene H 2 NBPMe to the diphosphadiboretane (H 2 NBPMe) 2 .