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首页> 外文期刊>Chemistry: A European journal >Carbonyl Activation by Borane Lewis Acid Complexation: Transition States of H_2 Splitting at the Activated Carbonyl Carbon Atom in a Lewis Basic Solvent and the Proton-Transfer Dynamics of the Boroalkoxide Intermediate
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Carbonyl Activation by Borane Lewis Acid Complexation: Transition States of H_2 Splitting at the Activated Carbonyl Carbon Atom in a Lewis Basic Solvent and the Proton-Transfer Dynamics of the Boroalkoxide Intermediate

机译：硼烷路易斯酸络合的羰基活化：在Lewis碱性溶剂中活性羰基碳原子的H_2分裂的过渡状态和硼甲烷烃中间体的质子转移动力学

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摘要

By using transition-state (TS) calculations, we examined how Lewis acid (LA) complexation activates carbonyl compounds in the context of hydrogenation of carbonyl compounds by H_2 in Lewis basic (ethereal) solvents containing borane LAs of the type (C_6F_5)3B. According to our calculations, LA complexation does not activate a ketone sufficiently enough for the direct addition of H_2 to the O=C unsaturated bond; but, calculations indicate a possibly facile heterolytic cleavage of H_2 at the activated and thus sufficiently Lewis acidic carbonyl carbon atom with the assistance of the Lewis basic solvent (i.e., 1,4-dioxane or THF). For the solvent-assisted H_2 splitting at the carbonyl carbon atom of (C_6F_5)3B adducts with different ketones, a number of TSs are computed and the obtained results are related to insights from experiment. By using the Born-Oppenheimer molecular dynamics with the DFT for electronic structure calculations, the evolution of the (C_6F_5)3B-alkoxide ionic intermediate and the proton transfer to the alkoxide oxygen atom were investigated. The results indicate a plausible hydrogenation mechanism with a LA, that is, (C_6F_5)3B, as a catalyst, namely, 1) the step of H_2 cleavage that involves a Lewis basic solvent molecule plus the carbonyl carbon atom of thermodynamically stable and experimentally identifiable (C_6F_5)3B-ketone adducts in which (C_6F_5)3B is the "Lewis acid promoter", 2) the transfer of the solvent-bound proton to the oxygen atom of the (C_6F_5)3B-alkoxide intermediate giving the (C_6F_5)3B-alcohol adduct, and 3) the SN_2-style displacement of the alcohol by a ketone or a Lewis basic solvent molecule.
机译：通过使用过渡态（TS）计算，我们研究了路易斯酸（LA）络合在含有硼烷La的Lewis碱性（醚）溶剂的羰基化合物的氢化的背景下激活羰基化合物的含有硼烷La的溶剂化合物。根据我们的计算，La络合不会足够地激活酮足以使H_2直接加入O = C不饱和键;但是，计算表明在Lewis碱性溶剂（即1,4-二恶烷或THF）的辅助下，在活化的酸性羰基碳原子中的H_2可能存在容易的H_2。对于用不同酮（C_6F_5）3B加合物的羰基碳原子的溶剂辅助H_2分裂，计算了许多TSS，得到的结果与实验的见解有关。通过使用与DFT进行电子结构计算的DFT的出生对抗海默分子动力学，研究了（C_6F_5）3B-醇盐离子中间体和质子转移到醇盐氧原子的进化。结果表明，具有LA的合理的氢化机理，即（C_6F_5）3B，作为催化剂，即，1）H_2切割的步骤，其涉及Lewis碱性溶剂分子加上热力学稳定和实验稳定的羰基碳原子（C_6F_5）3B-酮加合物，其中（C_6F_5）3B是“路易斯酸启动子”，2）将溶剂结合的质子转移到（C_6F_5）3B-醇盐中间体的氧原子中给予（C_6F_5）3B ---醇加合物，和3）通过酮或甲糖基碱性溶剂分子的醇的SN_2式置换。

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