Sodium trihydridozincate

Solid Na[Zn2(CH3)2H3] can be isolated in high yield by cooling the solution in a Dry Ice bath for several days, whereupon large, colorless, needle-like crystals form. These may be filtered off at — 78° using the apparatus shown in Fig. 3. After the crystals are washed with several 10-mL portions of cold, dry THF, they are held under vacuum at —22° (carbon tetrachloride slush bath)7 for several hours to remove excess THF. Under these conditions, the crystals lose solvent to form a white powder, which unlike the parent crystals does not melt upon warming to room temperature. Anal. Found Na/Zn/CH3/H, 1.01 1.98 1.98 3.01. In addition, 2.3 mol of THF was retained per mole of Na[Zn2(CH3)2H3] for this sample however, the exact value varies from one preparation to another. No iodide was detected in the product. 

When a sample of Na[Zn2(CH3)2H3] xTHF is exposed to high vacuum at room temperature, both dimethylzinc ( Caution. Spontaneously flammable in air.) and THF are slowly evolved. After 3 hr of pumping at room temperature, followed by about 1 hr of pumping at 80°, the evolution of volatiles, which are collected in a trap cooled with liquid nitrogen, should cease. If not, more pumping is required. Care must be exercised in adjusting 

Na[Zn2(CH3)2H3] -xTHF is sensitive to air, moisture, and heat and must be stored in a closed container at - 78°. At room temperature, the compound slowly decomposes, changing from a white powder to first yellow, then gray, aggregates. It loses dimethylzinc and THF readily at room temperature, eventually becoming sodium trihydridozincate(l -). 

The crude Na[Zn2(CH3)2H3] solution in THF may be used as a reducing agent.4 Like lithium tetrahydridoaluminate(l —), the zinc reagent reduces aliphatic ketones and esters to the corresponding alcohols and aliphatic nitriles to amines. However, of the two, the zinc compound is a somewhat milder reducing agent as shown by the reduction of benzonitrile to the corresponding imine under conditions in which lithium tetrahydrido-aluminate(l —) yields the amine. 

Sodium trihydridozincate( 1 —) is air- and moisture-sensitive, but can be stored at room temperature under vacuum or an inert atmosphere. Because of this stability Na[ZnH3] is a promising compound for the preparation of zinc hydride derivatives. The infrared spectrum and x-ray powder pattern of Na[ZnH3] are reported,4 and an alternate preparation has been mentioned.8 

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The reaction described here of methylzinc iodide with sodium hydride, to produce Na[Zn2(CH3)2H3], may be pictured as a combination of the two reaction types named above. Unlike many hydride preparations, the synthesis of sodium trihydridodimethyldizincate(l —) is easily performed using ordinary Schlenk-type bench-top techniques and commercially available starting materials.4 Sodium trihydridozincate( 1 —) is easily prepared by exposing Na[Zn2(CH3)2H3]-xTHF to high vacuum.4... 

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