Fluoroborates by cleavage of trimethylamine-bis(trifluoromethyl)boranes with NEt3 x 3 HF. Structures of C6F5(CF3)(2)B center dot NMe3, K[C6H5CH2(CF3)(2)BF], and K[C6H5(CF3)(2)BF]

Trimethylamine -bis(trifluoromethyl)boranes R(CF3)(2)B NMe3 (R = cis/trans- CF3CF=CF (1/2), HC dropC (3), H2C=CH (4). C2H5 (5), C6H5CH2 (6), C6F5 (7), C6H5 (8)) react with NEt(3)x3HF depending on the nature of R at 155-200 deg reesC under replacement of the trimethylamine ligand to form the correspond ing fluoro-bis(trifluoromethyl)borates [R(CF3)(2)BF](-) (1a/2a-8a). The str uctures of 7, K[C6H5CH2(CF3)(2)BF] (K-6a), and K[C6H5(CF3)(2)BF] (K-8a) hav e been investigated by single-crystal X-ray diffraction. In 7 the CF3 group s make short repulsive contacts with NMe3 and C6F5 entities - the B-CF3 bon ds being unusually long. The B-F bond lengths of K-6a and K-8a (1.446(3) an d 1.452(2) Angstrom, respectively) are long for a fluoroborate.