Some New Reactions of Complex Metal Hydrides of Aluminum

Abstract

The literature contains only two references to a complex between an alkali metal hydride and a zinc compound. Wittig and Hornberger2 reported that a complex ZndCeHj^'LiH could be isolated as an etherate from the reaction between diphenylzinc and lithium hydride. Frey and co-workers8 mentioned a complex between sodium hydride and diethylzinc; however, no attempts to characterize the complex were made.Preparation of Sodium Hydride Complexes of Diethylzinc and Zinc Chloride.--We have found that sodium hydride will form an adduct with both diethylzinc and zinc chloride in glycol ethers. With monoglyme or diglyme as solvent, one mole of sodium hydride dissolved rapidly per two moles of diethylzinc to give a soluble product, but no additional sodium hydride would dissolve. Attempts to isolate the compound resulted in decomposition. The reaction would not take place in aliphatic or aromatic hydrocarbons, nor in diethyl ether or tetrahy dr of uran. Anal.Gas composition on hydrolysis of NaH• 2Zn(C2H6)2: H2, 20; C2H", 80. Found: H2, 19.7; C2H6, 79.3.The corresponding adduct of sodium hydride and zinc chloride was prepared in solution by stirring 20 g. (0.15 mole) of zinc chloride and 4.0 g. (0.17 mole) of sodium hydride in glycol ethers. The solid reactants dissolved very slowly, requiring 2-24 hr. While the reaction was proceeding, in the presence of solid sodium hydride, two competing reactions apparently occurred, for precipitation of zinc metal and sodium chloride and some gas evolution were observed. These side reactions were more rapid in reactions run at elevated temperatures. The product solution after filtration contained active hydrogen as well as sodium, zinc, and chlorine, and apparently was stable at room temperature. After several weeks of storage, hydrolysis gave rapid gas evolution, indicating retention of hydride content.Attempts to isolate the solute by removing solvent under vacuum resulted in decomposition.Anal. Caled, ratios for NaH-2ZnCl2 in solution:Na/Zn/Cl/H = 1/2/4/1. Found: Na/Zn/Cl/H = 1.0/2.0/5.6/0.8. Ethylation of the Sodium Hydride Complexes.-A solution of NaH-2Zn(C2H6)2 in diglyme readily added (1) Presented in part before the Inorganic Division, 142nd National ACS Meeting, Atlantic City, N.

The First Structurally Characterized Diorganoaluminate

“…In 3 the rates of attack by MeI at AlϪH and LiϪH bonds appear to be similar so that a complex mixture of products is formed. The fact that the aluminum iodide rather than the hydride is isolated in reaction (2) indicates that under the conditions that we employed LiH is an ineffective reagent for reduction of AltBu 2 I. 2 , which formed a lattice of dimeric ion pairs having Li···HϪAl bridges like those in 3.…”

“…The reaction of 3 with iodomethane gave a complex mixture but reaction of the compound [{Li(THF) 2 [29] These results can be attributed to effects of steric hindrance to attack at bonds in the eight-membered Li 2 Al 2 H 4 rings. In 2 the two tBu groups attached to aluminum are not large enough to prevent coordination of the iodine of MeI and consequent reaction at AlϪH bonds.…”

“…Treatment of Li [AlH 4 ] with LiC(SiMe 3 ) 3 (THF) 2 or LiC-(SiMe 2 Ph) 3 (THF) gave the alkylaluminates 1b and 1a, in each of which one of the four hydride ligands has been replaced by a bulky organic group. Treatment of Li [AlH 4 ] with the smaller LitBu led to the replacement of two hydride ligands and the formation of a dialkylaluminate 2.…”

“…Diorganoaluminates are much less well characterized than the corresponding dialkoxo-and diaryloxoaluminates, which contain the ions [Al(OR) 2 …”

“…[1] The NaAlEt 4 NaAlH 4 phase diagram shows that sodium diethylaluminate is a thermodynamically stable species, [2] and both this and sodium dimethylaluminate are commercially available reducing agents. [3] Several routes to dialkylaluminates have been reported but evidence for individual species has been confined to elemental analysis (R ϭ Me, [4Ϫ6] Et, [2,4,5,7,8] nPr, [4] iBu [4,5,9] ), IR spectroscopy [6,8,10] and 27 Al NMR spectroscopy. [11] Dialkylaluminates are sometimes obtained from reaction mixtures that might be expected to yield monoalkylaluminates.…”