For the traditional reduction of ketones and aldehydes, NH₃BH₃ (AB) and N‐methyl amine borane (M _nAB) have been effective reducing agents. However, the reaction process is indefinite and different mechanisms have been proposed; also the solvent effect, which is closely related to the mechanism, has not been considered seriously. Here we employ density functional theory to carry out a comprehensive study on the mechanism. The calculated free energy of the concerted double hydrogen transfer process is lower than the hydroboration mechanism by 4.7 kcal/mol, which indicates that reduction of carbonyl by AB is likely due to be the concerted double hydrogen transfer in both aprotic (tetrahydrofuran) and protic (MeOH) solvents. For the reduction by M _nAB, the corresponding free energies of all reactions are higher than those of AB. Meanwhile, the reduction of benzaldehyde by M _nAB (n = 1, 2) also favors a concerted double hydrogen transfer rather than hydroboration.

中文翻译：

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溶剂对氨硼烷和N-甲胺硼烷化学计量还原羰基化合物的影响的理论见解

对于传统的酮和醛还原，NH ₃ BH ₃（AB）和N-甲胺硼烷（M _n AB）是有效的还原剂。然而，反应过程是不确定的，并且已经提出了不同的机理。与机理密切相关的溶剂效应尚未得到认真考虑。这里我们运用密度泛函理论对机理进行了全面的研究。一致的双氢转移过程的计算出的自由能比氢硼化机理低4.7 kcal / mol，这表明AB还原了羰基 这可能是由于在非质子传递溶剂（四氢呋喃）和质子传递溶剂（MeOH）中都发生了协同的双氢转移。为了通过减少中号_Ñ AB，所有反应的相应的自由能比的更高AB。同时，苯甲醛的由减速中号_Ñ AB（Ñ = 1，2）也有利于协同双氢转移而不是氢硼化。