acetone to give scarlet tropenium iodide, m.p. 127°.8q10 On attempted sublimation (Go, 0.2 mm.) the iodoborate decomposed slowly; a mixture of tropeniuni iodide and triiodide collected on the V vI cold finger. Reaction of boron iodide with triphenylmethyl iodide in methylene chloride (conditions as above, then precipitation with cyclohexane) gave dark, viciously hygroscopic, light sensitive crystals for &mO VI1 V I I1 which satisfactory analyses could not be obtained. T h e formation of triphenylcarbonium iodoborate in the 2-methylanilinoniethylene' or the 2 -isopro- the methylene chloride solution is inferred from the poxymethylenej derivative of decalone. following: (1) Addition of cycloheptatriene to a Further studies are in progress on the reactions boron iodide-triphenylmethyl iodide solution in of the dicarbanions of formylacetone, formyldeca- methylene chloride gives an instantaneous precipilone and other /3-ketoaldehydes. tate of 57yGtropenium iodoborate of high purity and 95yo triphenylmethane is isolated from the ( 7 ) 4.J. Birch and 11. Robinson, J Chrirz. Soc., 601 (1944). reaction solution. This rapid hydride exchange DEPARTMEST OF CHEMISTRY the existence of an ionic triphenylTHOMAS M. HARRIS shows63isS,11 DUKEUXIVERSITY K. C. CHARLES K . HACSER carbonium salt; the iodoborate ion is the most DURHAM, probable anionic species." (2) B" n.m.r. spectralY RECEIVED MARCH26, 1962 of boron iodide-triphenylmethyl iodide solutions in methylene chloride show a single resonance a t 6 = CARBONIUM ION SALTS. IV. 112.2 (relative to (C2H6)20.BF3=O)compared to 'TETRAIODOBORATESl a value of 6 = + 5 . 5 for boron iodide. TriphenylSir : carbonium chloroborate (6 = -4.5) and bromoThe literature on complexes of boron iodide is borate (6 = +23.9) in methylene chloride show sparse. The single reference to iodoborate forina- similar shifts to higher field relative to the halides tion-a remarkably terse communication by \\:ad(BCl:(,6 = -45.6; RBr:{.6 = -4(1.1)14 as do alkali dington?-gives no details of preparation or metal haloborates in nitrobenzene. The theorecharacterization, and the ammonia adduct reported tical predictions of Landesman and \ f X a n i s ' 5 by Besson3has been shown4m5not to exist. JVe wish that tetrahedral iodoborate ion should show a to report that the method used for the preparation chemical shift greater than 6 = 100 (higher than of tropenium chloroborate6 and bromoborate' has any other known boron compound) are in agreeyielded tropenium iodoborate, and to present ment with the value observed for presumed evidence for the existence of triphenylcarbonium triphenylcarbonium iodoborate. iodoborate. (10) W. w n E . Iloering and I*. H. Knox, ibid., 79, 352 (1937). Boron iodide reacts rapidly and smoothly with (11) I ) . 1.. Pearson, Ph. 17. 'Thesis, University of Washington, 19.53; cycloheptatriene in dry methylene chloride (glove Di0), 280 mii for trouenium iun in this solvent. (9) W. r u n E . Iloering and L . H. Knox, i b z d , 76, 3'203 ( l Y X j , reiwrt A,,,,, 273 (&
