Hydrides of gallium

The hydride of gallium is a hquid. When gallium trimethyl and hydrogen are subjected to an electric discharge, Ga2(Me)4H2 may be isolated from the products. It reacts quantitatively with triethylamine ... 

The hydrides of the later main-group elements present few problems of classification and are best discussed during the detailed treatment of the individual elements. Many of these hydrides are covalent, molecular species, though association via H bonding sometimes occurs, as already noted (p. 53). Catenation flourishes in Group 14 and the complexities of the boron hydrides merit special attention (p. 151). The hydrides of aluminium, gallium, zinc (and beryllium) tend to be more extensively associated via M-H-M bonds, but their characterization and detailed structural elucidation has proved extremely difficult. 

The chemistry has also been extended to related formamidinato metal hydrides of aluminum and gallium. In the case of aluminum, LiAlH4 and AlH3(NMe3) served as metal hydride precursors. Scheme 39 summarizes the synthetic routes. The complexes thus formed are thermally very stable. °... 

The simple, salt elimination reaction of Equation (8.1) has been employed for amides of all the group 13 metals. In addition, it is currently the only well-established route to M(I) metal amides where M = Ga or Tl. The alkane elimination route of eqn. (8.2) is generally employed only for M = Al or Ga. This synthetic approach is also used for the metal imides (RMNR )n where a primary amine H2NR is the reactant. The use of metal hydrides, of which Equation (8.3) is but one example, is limited mainly to aluminium and, to a lesser extent, gallium because of the decreased stability of the heavier metal hydrides. 

Lithium tetrahydridogallate, which was first prepared by Finholt, Bond, and Schlesinger,1 is a very useful starting material for the preparation of gallium hydride derivatives.2-3 The present synthesis is based on an adaptation of the original preparation.1-4 Since gallium-hydrogen bonds are susceptible to hydrolysis, it is necessary to perform the preparation in the absence of air. The procedure described is based on the use of Schlenk-type inert-atmosphere techniques. 

Lithium tetrahydridogallate(l —) is a moisture-sentitive solid similar in many respects to lithium tetrahydridoaluminate(l —). It reacts with protic solvents, but is soluble without reaction in a variety of ethers. The solid decomposes slowly at room temperature, but may be stored with decomposition at — 78° under an inert atmosphere or in vacuum. Ether solutions are stable for at least several days. A variety of gallium hydride derivatives may be prepared from Li[GaH4], including (CH3)3N GaH3.1,2,6 Infrared and Raman data have been reported for [GaH4]-.7... 

Research in the organometallic and hydride chemistry of gallium is hampered by the absence of a convenient, reliable preparation of gallium trichloride, which is the common starting material in most preparations. 

Earlier searches starting with elemental gallium having been to no avail, the first substantive claim to the synthesis of gallium hydride... 

Other complexes of gallium have been more exhaustively studied. Gallium hydride, GaH3, forms with trimethylamine a 1 1 solid complex which melts at 69°C. and decomposes slowly even at room temperature (23), X-ray diffraction studies of the 1 1 complex show the presence of H3GaN(CH3)3 units with two molecules per unit cell. A coordination number of 4 for gallium is indicated (21). 

A review of the chemistry of Group III complexes shows that many of the concepts of Werner s coordination chemistry may be applied to these elements. Furthermore, the differences observed in the complexing behavior between ammonia and trimethylamine refiect fundamental differences in the amines. Ammonia tends to give ionic compounds, whereas trimethylamine tends to give non-ionic products. Trends observed with the metal halides can be extrapolated into hydrides of boron, aluminum, and gallium. An extension of Werner s concepts provides a significant... 

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