197634-56-3Relevant articles and documents
Cyclic and bicyclic poly(phosphane)borane cations
Sigl, Marcus,Schier, Annette,Schmidbaur, Hubert
, p. 1411 - 1416 (1997)
The reactions of (Me2S)BH2Br and (Me2S)BHBr2 with equimolar quantities of l,2-bis(diphenylphosphanyl)ethene (1) or -benzene (2) lead to cyclic, cationic bis(phosphane)boranes {4: [(1)BH2]+ [(1)BH2]; 5: [(l)BHBr]+ [(1)BH2]; 6: [(2)BH2]+ Br-; 7: [(2)BHBr]+ The (1)BH2]+ counterions can be exchanged in metathesis reactions (e.g. with AgBF4 to afford 4a). The tritertiary phosphane bis[2-(diphenylphosphanyl)phenyl]phenylphosphane (3), reacts with (Me2S)BHBr2 to give bicyclic dicationic tris(phosphane)borane 8, [(3)BH]2+-2 Br-, which can be converted into the bis(hexafluorophosphate) 8a using NH4PF6. 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 Xray diffraction.The five-membered rings C2P2B 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. WILEY-VCH Verlag GmbH,.