PUB - Publikationen an der Universität Bielefeld

Oxidation of the 1,3,2-diazaborole tBuN(a)CH=CHNb(tBu)BBr(N-a-B) (1h) with NO+PF6- afforded the diazaborolium salts [tBuN(a)=CH-CH=N-b(tBu)BF2(N-a-B)]X-+(-) (X = Br-, Br-3(-), PF6-) (3h) as the result of different oxidation processes. The same product was obtained when the 1,3,2-diazaborolidine tBuN(a)CH(2)CH(2)N(b)(tBu)BBr(N-a-B) (2h) was subjected to reaction with NO+PF6-. In contrast to this, oxidation of 1h and 2h with NO+BF4- cleanly furnished [tBuN(a)CH-CH=N-b(tBu)BFBr(N-a-B)]+BF4- (6h). Treatment of the 1,3,2-diazaboroles tBuN(a)CH=CHNb(tBu)BR(N-a-B) [R = H (1e), CN (1i), C CH (1j)] with NO+PF6- under comparable conditions led to the borolium salts [tBuN(a)=CH-CH=N-b(tBu)BRF(N-a-B)]+PF6- [R = H (3e), CN (3i), C CH (3j)]. All the borolium salts investigated in this study were reversibly reduced by cyclic voltammetry. The novel products were characterized by elemental analyses and NMR spectra (H-1, B-11, C-13, F-19 (31)p). The X-ray structure analysis of 3h reveals two independent planar cations in the asymmetric unit, accompanied by one bromide and one tribromide ion. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)