PREPARATION, B-11 NMR AND VIBRATIONAL-SPE CTRA OF MULTIALKYLATED HEXABORATES AND CRYSTAL-STRUCTURES OF CIS-[P(C6H5)(4)][B6H5(CH3)52)] AND TRANS-[P(C6H5)(4)][B6H5(CH3)(2)] AND MER-[P(C6H5)(4)][B6H4(CH3)(3)]

By treatment of protonated monoalkyl-closo-hexaborates [B(6)H(6)R](-), R = CH3, C2H5, n-C3H7, i-C3H7 in aqueous alkaline solution with [As(C 6H5)(4)]Cl the yellow orange deprotonated tetraphenylarsonium salts ar e precipitated, which react with methyl iodide or ethyl iodide to give dialkylated and protonated B-6-compounds. The cis/trans isomers forme d in a 1:1 ratio have been separated by ion exchange chromatography on diethylaminoethyl cellulose. Repeated deprotonation and reaction with methyl iodide affords mer-[B6H4(CH3)(3)](-). The crystal structures o f cis-[P(C6H5)(4)][B6H5(CH3)(2)] (I), trans-[P(C6H5)(4)][B6H5(CH3)(2)] (II) and mer-[P(C6H5)(4)] [B6H4(CH3)(3)](III) have been determined by single crystal X-ray diffraction analyses; I and II are monoclinic, s pace group P2/n, I with a = 11.8690(5), b = 7.2575(7), c = 15.8689(3)A ngstrom, beta = 111.454(17)degrees; II with a = 13.2853(7), b = 7.4608 (8), c = 13.3549(11), beta = 93.5(11); III is tetragonal, space group P4/n with a = 13.363(2), c = 7.5051(13). The three methyl substituents are statistically distributed over four equatorial positions of the B -6 cage. The B-11 NMR spectra of the di- and trialkylated compounds ex hibit shifts of ipso-B atoms to lower, of antipodal-B atoms to higher field compared with [B6H7](-). The IR and Raman spectra of the di- and trimethyl derivatives are similar to those of monomethylhexaborate.