Cyclic and Bicyclic Poly(phosphane)borane Cations

✍ Scribed by Sigl, Mareus ;Sehier, Annette ;Schmidbaur, Hubert

• Book ID: 102790301
• Publisher: Wiley (John Wiley & Sons)
• Year: 1997
• Tongue: English
• Weight: 545 KB
• Volume: 130
• Category: Article
• ISSN: 0009-2940
• DOI: 10.1002/cber.19971301009

✦ Synopsis

Abstract

The reactions of (Me~2~S)BH~2~Br and (Me~2~S)BHBr~2~ with equimolar quantities of 1,2‐bis(diphenylphosphanyl)ethene (1) or ‐benzene (2) lead to cyclic, cationic bis(phosphane)boranes [4[(1)BH~2~]^+^ Br^−^; 6: [(2)BH~2~]^+^ Br; 7: [(2)BHBr]^+^ Br^−^]. The Br counterions can be exchanged in metathesis reactions (e.g. with AgBF~4~ to afford 4a). The tritertiary phosphane bis[2‐(diphenylphosphanyl)phenyl]phenyl‐phosphane (3), reacts with (Me~2~S)BHBr~2~ to give bicyclic dicationic tris(phosphane)borane 8, [(3)BH]^2+^ Br^−^, which can be converted into the bis(hexafluorophosphate) 8a using NH~4~PF~6~. All compounds have been characterized by analytical and NMR‐spectroscopic data. The crystal and molecular structures of 5 ‐ 7 have been determined by single‐crystal X‐ray diffraction. The five‐membered rings C~2~P~2~B have an envelope conformation and show no sign of electron delocalization. Attempts to deprotonate the BH functions in 5 – 8 have not been successful. Clearly, the two (5 – 7) or three phosphonium centers (8) adjacent to the boron atom are not sufficient to induce an “umpolung” of the BH group