Gallium complexes hydrides

Previously reported syntheses of the title compound have involved vacuumline techniques.1-2 We describe here a procedure in which commercially available Schlenk-type glassware is used.j The synthesis involves the reaction of the protic hydrogen of trimethylammonium chloride with a hydridic hydrogen of [GaH4], to liberate hydrogen and form the desired amine gallium complex. 

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. °... 

Hydrides, 23 607-631, 771 alkali metal, 23 608-610 alkaline-earth metal, 23 610-611 aluminohydrides, 23 621-624 complex, 23 613-621 covalent, 23 611-613 gallium, 22 355... 

A solution of Li[GaH4] in diethyl ether is prepared by the standard methods,J1 and is stored in a needle-valve O-ring flask. The concentration of Li[GaH4]-ether solution is determined by hydrolysis of a known volume of the solution followed by gallium determination by ethylenediamine-tetraace-tic acid, disodium salt using copper-PAN [l-(2-pyridylazo)-2-naphthol copper complex] as the indicator.4 It is assumed that all the gallium is present as the tetrahydrogallate. Only an approximate concentration need be determined since an excess of sodium hydride or potassium hydride is used. 

Both gallium hydride complexes are obtained as white, crystalline powders which remain white when stored at room temperature in the absence of air and moisture for periods in excess of one year. Their reaction with water is moderate when compared to the analogous aluminum hydride complexes. They undergo typical reactions for an [MH4] species, e.g.,... 

A mixed indium hydride halide complex, (l) InH2Cl (29) has been prepared from the 1 1 reaction of [InH2Cl(NMe3) ] with carbene (1) (R = Mes, R = H), as shown in Scheme iP The structure of (29) is monomeric with the geometry at the In center close to tetrahedral. The In-C distance (2.244(6) A) is similar to those observed in (28) (2.200(7) A) and (25) (2.253(5) A). A related mixed gallium hydride iodide complex (1) GaH2l (30) has been isolated from the reaction of (26) with GaT, with concomitant deposition of galhum metal. Complex (30) is isostructural with the related indium complex (29) and has a Ga-C bond distance of 2.022(4) A. 

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... 

---