LAUSR

Abstract An efficient procedure for the direct per- B -fluorination of the potassium salt of the mono-ammonioborane anion B 12 H 11 (NH 3 ) − in anhydrous CH 3 CN with 20:80 F 2 :N 2 is reported. It differs significantly from the previously reported procedure in that anhydrous CH 3 CN (a-CH 3 CN) replaced anhydrous HF (a-HF) as the solvent and the yield of recrystallized K(B 12 F 11 (NH 3 )) increased from 40% to 70%. It also differs from the published procedure for the direct per- B -fluorination of K 2 (B 12 H 12 ) to form K 2 (B 12 F 12 ) in CH 3 CN containing 2% H 2 O (wet CH 3 CN) in that (i) a-CH 3 CN was used instead of wet CH 3 CN and (ii) addition of excess KF at the start of the reaction to sequester the HF byproduct was deleterious in the case of K(B 12 H 11 (NH 3 )) fluorination, not advantageous as in the case of K 2 (B 12 H 12 ) fluorination. The addition of excess KF resulted in decomposition of B 12 H 11− n F n (NH 3 ) − intermediates as the average value of n approached 11, and even small amounts of K(B 12 F 11 (NH 3 )) free of incompletely fluorinated K(B 12 HF 10 (NH 3 )) could not be isolated. In contrast to the direct fluorination of K 2 (B 12 H 12 ) in wet CH 3 CN, which is inhibited by the buildup of HF, the fluorinations of both K(B 12 H 11 (NH 3 )) and K 2 (B 12 H 12 ) in a-CH 3 CN were not inhibited by HF. A competition experiment in which approximatetly equimolar amounts of K(B 12 H 11 (NH 3 )) and K 2 (B 12 H 12 ) were fluorinated together in a-CH 3 CN showed that B–H vertex fluorination was ca . 50% faster for B 12 H 12 2− than for B 12 H 11 (NH 3 ) − . The single-crystal X-ray structures of Na(H 2 O) 4 (B 12 F 11 (NH 3 )) and Na(H 3 O)(H 2 O) 3 (B 12 F 12 ) were determined. They both contain trans -Na(H 2 O) 2 F 4 moieties, with ranges of Na–O and Na–F distances of 2.331(1)–2.339(1) and 2.264(1)–2.456(1) A, respectively, in contrast to the cis -Na(H 2 O) 4 F 2 moieties in the published structure of Na 2 (H 2 O) 4 (B 12 F 12 ), with ranges of Na–O and Na–F distances of 2.368(9)–2.473(9) and 2.313(8)–2.381(7) A, respectively. The O atoms of the nearly-square array of four hydrogen-bonded H 2 O molecules in Na(H 2 O) 4 (B 12 F 11 (NH 3 )) or the H 3 O + ion and three H 2 O molecules in Na(H 3 O)(H 2 O) 3 (B 12 F 12 ) are co-planar to within 0.016 A and have O⋯O distances of 2.74–2.83 A and O⋯O⋯O angles of 80–100°.