Mechanistic Models for LAH Reductions of Acetonitrile and Malononitrile. Aggregation Effects of Li+ and AlH3 on Imide鈥揈namide Equilibria

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• 作者：Rainer Glaser ; Laura Ulmer ; Stephanie Coyle
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：February 1, 2013
• 年：2013
• 卷：78
• 期：3
• 页码：1113-1126
• 全文大小：650K
• 年卷期：v.78,no.3(February 1, 2013)
• ISSN：1520-6904

文摘

The results are reported of an ab initio study of the addition of LiAlH₄ to acetonitrile and malononitrile at the MP2(full)/6-311+G* level considering the effects of electron correlation at higher levels up to QCISD(T)/6-311++G(2df,2pd) and including ether solvation. All imide (RCH₂CH鈺怤^{鈥?/sup>) and enamide (RCH鈥?/sup>CH鈺怤H 鈫?RCH鈺怌HN鈥?/sup>H) adducts feature strong interactions between the organic anion and both Li+ and AlH₃. The relative stabilities of the tautomeric LAH adducts are compared to the tautomer preference energies of the LiH adducts and of the hydride adducts of the nitriles. Alane affinities were determined for the lithium ion pairs formed by LiH addition to the nitriles. The results show that alane binding greatly affects the imide鈥揺namide equilibria and that alane complexation might even provide a thermodynamic preference for the imide intermediate. While lithium enamides of malononitrile are much more stable than lithium imides, alane binding dramatically reduces the enamide preference so that both tautomers are present at equilibrium. Implications are discussed regarding to the propensity for multiple hydride reductions and with regard to the mechanism of reductive nitrile dimerization. A detailed mechanism is proposed for the formation of 2-aminonicotinonitrile (2ANN) in the LAH reduction of malononitrile.}