Synthesis and characterization of the anionic fluorocarboranes 6,7,8,9,10-CB9H5F5-, 6,7,8,9-CB9H5F4-10-OH-, and 6,7,8,9-CB9H5F4-10-NHCOCH3-

The reactions of salts of the 6,7,8,9-CB9H6F4- and CB9H10- anions with 1-ch loromethyl-4-fluoro-1,4-diazoniabicy-clo[2.2.2]octane bis(tetrafluoroborate ) (F-TEDA) in acetonitrile in the presence or absence of trifluoroacetic ac id were studied. The addition of trifluoroacetic acid to the reaction mixtu re significantly changed the concentration ratio of the two pentafluoro iso mers produced in the reactions, [6,7,8,9,10-CB9H5F5-]/[2,6,7,8,9-CB9H5F5-]. The ratio increased from 0.6 to > 23 when the solvent was changed from nea t acetonitrile to a 20% solution of trifluoroacetic acid in acetonitrile wh ile simultaneously raising the temperature from 25 degrees C to 60 degrees C. The synthesis and B-11 and F-19 NMR spectroscopic characterization of th e 6,7,8,9,10-CB9H5F5- anion are reported here for the first time. Chromatog raphic separation of the reaction mixtures led to the isolation of salts of two additional new anions, 6,7,8,9-CB9H5F4-10-NHCOCH3- and 6,7,8,9-CB9H5F4 -10-OH-. The structure of [PPh4][6,7,8,9-CB9H5F4-10-NHCOCH3] was determined by X-ray crystallography: monoclinic, space group P2(1)/n, a = 7.5169(3), b=23.2793(10), c = 16.6170(7) Angstrom, Z = 4, T = -113 degrees C, least-sq uares refinement on F-2, R-1 (I > 2 sigma(I)) = 0.0805, wR(2) (all data) = 0.1922. (C) 1999 Elsevier Science S.A. All rights reserved.