HYDRIDOGALLIUM BIS(TETRAHYDROBORATE), HGA(BH4)(2) - SYNTHESIS AND PROPERTIES

The 'mixed' gallium-boron hydride HGa(BH4)(2) has been synthesized by the reaction between lithium tetrahydroborate and gallium(III) chlorid e or dichlorogallane, [HGaCl2](2), in the absence of a solvent at 238- 263 K. The compound, which decomposes to elemental gallium, dihydrogen and B2H6 at ambient temperatures, has been characterized by chemical analysis, by vapour-density measurements, and by its vibrational, mass , and H-1 and B-11 NMR spectra. The physical and spectroscopic propert ies of the compound imply that the monomeric molecule HGa(BH4)(2) (wit h a single terminal Ga-H bond and two bidentate BH4 groups) is subject to loose aggregation in the condensed phases. Thus, the NMR spectra o f toluene-d(8) solutions at temperatures in the range 190-270 K sugges t that the monomer and an oligomer [HGa(BH4)(2)](n) (where n = 2 in al l probability) co-exist in equilibrium. Chemical properties of the gal lane to be investigated include (i) the reactions with bases as varied as CO, NMe(3) and NH3, which bring about homolytic or heterolytic cle avage of the Ga(mu-H)(2)BH2 fragments; and (ii) the exchange or protol ysis reactions induced by Me(3)Ga or HCl and MeOH, respectively. No ev idence was found for the formation of gallium tris (tetrahydroborate), Ga(BH4)(3), even at low temperatures.