Perfluoroalkyl borates: congeners of perfluoroalkanes

This review describes the synthesis and properties of berates that carry CF 3 (or more generally, perfluoroalkyl R-f) groups bonded to baron. Some nove l amine-boranes R(CF3)(2)B . NHMe2 with R = CF3, C2F5, C4F9, C6F5, F2C=CF, CF3-FC=CF that are precursor molecules for the berates are reported; cleava ge of their BN bond by NEt3 x 3HF furnishes fluoroborates [R(CF3)(2)BF](-). Cyanomethylborates [R(CF3)(2)BCH2CN](-) with R = t-Bu, C6H5, F2C=F, CH2CN result from reaction of NCCH2(CF3)(2)B . NMe3 with RLi. The well-known amin oborate [(CF3)(3)BNX2](-) reacts with OCl- and OBr- to yield N,N-dihalogeno aminoborates [(CF3)(3)BNX2](-) (X = Cl and Br), which can be fluorinated to form the N,N-difluoroborate anion [(CF3)(3)BNF2](-). Condensation of [(CF3 )(3)BNH2](-) with ONRj yields diazenidoborates [(CF3)(3)BN=NRf](-). The flu oroborate [(CF3)(3)BF](=) is obtained by fluorination of [(CF3)(3)BNF2](-) or by pyrolysis of [(CF3)(3)BN=NRf](-), whereas [(CF3)(3)BX](-) (X = Cl and Br) are formed when dihalogenoaminoborates [(CF3)(3)BNX2](-) are pyrolyzed . Nitroborates [R-f(CF3)(2)BNO2](-) and [(C2F5)(3)BNO2](-) are accessible b y ozone oxidation of the corresponding dimethylamine-boranes. Anodic oxidat ion of [(CF3)(3)BNH2](=) furnishes [(CF3)(3)BNO2](-) and azodioxy-[(CF3)(3) BN(O)-N(O)B(CF3)(3)](2-) and azoxy-bis-tris(trifluoromethyl)borate [(CF3)(3 )BN=N(O)B (CF3)(3)](2=) dianions. The BN bonds of [(CF3)(3)BN(O)=N(O)B(CF3) (3)](2-), [(CF3)(3)BN=NCF3](-), and [(CF3)(3)BNO2](=) are hydrolyzed to yie ld the hydroxyborate [(CF3)(3)BOH](-). The NMR spectral and vibrational dat a of the novel berates are discussed and potential applications are suggest ed. (C) 2001 Elsevier Science B.V. All rights reserved.