氮氧偶极作催化剂的酮硅腈化理论研究.docVIP

 氮氧偶极作催化剂的酮硅腈化理论研究# 苏志珊，李唯一，胡常伟** （四川大学化学学院绿色化学与技术教育部重点实验室，成都 610064） 5 10 15 20 25 30 35 40 摘要：在 B3P86/6-31G*水平下对四种氮氧偶极作用下的酮硅腈化反应进行了研究，计算结 果表明，无氮氧偶极催化剂存在时，反应协同进行，通过一四元环状过渡态实现硅腈对 C=O 双键的加成应，能垒高达 33.3 kcal/mol。在催化条件下，氮氧偶极上 O 原子与 H3SiCN 中 Si 原子的配位作用，削弱了 Si-C 键，同时增强了-CN 的亲核性，从而使 C=O 双键上加成步骤 的能垒明显降低，使反应更容易进行。在催化剂 1，3，4 作用下，反应沿路径 a，即羰基上 的 O 从竖直位进攻 Si 的方式进行从能量上更为有利。脂肪类氮氧偶极 2 中的酚羟基与 H3SiCN 中 N 原子形成的氢键进一步活化了 Si-C 键，促进了 Si-C 键的断裂，使加成步骤能 垒显著降低。氮氧偶极上 O 原子的电荷、N-O 键的键长和强度及催化剂的空间结构等因素 可能是影响其反应活性的重要原因。 关键词：理论研究；酮；硅腈化；氮氧偶极 中图分类号：0643 Theoretical investigation on the mechanism of cyanosilylation reaction of ketone catalyzed by N-oxides SU Zhishan, LI Weiyi, HU Changwei (Key Laboratory of Green Chemistry Technology Ministry of Education, College of Chemistry, Sichuan University, Chengdu 610064) Abstract: The mechanisms of cyanosilylation reactions of ketone catalyzed by four N-oxides have been investigated at the B3P86/6-31G* level. In the absence of N-oxide catalysts, the reaction proceeds concertedly via a four-membered-ring transition state, with the high energy barrier of 33.3 kcal/mol. Calculations indicate that the strong electron donor (N-O) of N-oxides could play important role in enhancing the reactivity and nucleophilicity of H3SiCN by coordinating O atom to Si atom of H3SiCN, facilitating the production of the target cyanohydrinsilylethers. In the presence of N-oxides 1,3 and 4, the reactions take place preferably along the energetically favorable pathway a, where acetone attacks the pentacoordinate silicon compound perpendicularly to form four-membered rings transition states. The coordination of O atom of N-oxide 2 to Si atom, combining with the hydrogen bond between the hydroxyl group of phenol and N atom of –CN group, make the Si-C bond weakened remarkably, and the energy barrier for the addition step decreased. Some structural parameters and electronic properties of N-oxides, such as the charge accumulated on O atom, N-O bond length and intensity, and the geome