Phosphane – Tetrahalodiborane(4) Adducts: Formation of closo ‐3,4,5,6‐Tetrabromo‐1,2‐diphosphahexaborane(4)

Tetrabromodiborane(4), B 2 Br 4 , forms a 1:2 adduct 1 with PBr 3 , which reacts at 350°C to closo ‐1,2‐P 2 B 4 Br 4 ( 4a ) in 25% yield. Compound 4a neither rearranges to the 1,6‐isomer nor decomposes to an appreciable extent upon heating to 650°C. B 2 C 14 reacts with equimolar amounts of either tris(trimethylsilyl)‐phosphane or 1,2‐bis(dichlorophosphanyl)ethane to give B 2 Cl 4 · P(SiMe 3 ) 3 ( 2 ) and B 2 Cl 4 · Cl 2 PCH 2 CH 2 PCl 2 ( 3 ), respectively. Compound 2 represents the first phosphane – diborane(4) monoadduct with two boron atoms in different coordination environment.