Mn(Ⅰ)催化亚胺和炔烃脱氢偶联反应的机理研究

Mechanism Study of Mn(Ⅰ) Complex-catalyzed Imines and Alkynes Dehydrogenation Coupling Reaction

近年来随着过渡金属催化剂的发展和广泛使用,C—H键的活化成为了有机合成中的一大热点,尤其是在构建有机化合物C—C键中应用广泛.作为一种储量较大的廉价催化剂,Mn催化的C—H活化表现出巨大的应用价值和研究潜力.我们采用密度泛函理论(DFT),对1,4-二氧六环溶液中Mn活化C—H/N—H键实现[4+2]脱氢环化的反应机理进行了系统的研究.我们发现该反应的催化循环包括溴负离子辅助的催化剂引发、炔烃的插入、双键迁移成环、β-H消除释放产物异喹啉以及催化脱氢循环的C—H键活化等步骤.旨在深入理解Mn(I)活化C—H键脱氢气的具体过程,为更多Mn催化的C—H活化反应提供理论依据.

With the development and widespread use of transition metal catalysts, C-H activation has become a hot topic in organic synthesis, especially in the construction of C-C bond of organic compounds. As an important and cheap catalyst, manganese complex has shown great potential for catalyzing C-H activation both in academic and industrial applications. In this paper, the mechanism of manganese-catalyzed dehydrogenative [4＋2] annulation by C-H/N-H activation was investigated systematically with the aid of density functional theory （DFT） calculations in 1,4-dioxane solvent. In detail, we use M06-L/[SDD：6-311＋G（d,p）（SMD）]//M06-L/[LANL2DZ：6-31G（d）] to examine the Gibbs free energy, structure and other properties of possible intermediates and transition states in this catalytic cycle. By comprehensive comparison and discussion, we obtained a favorable pathway consisting of five steps： （1） catalyst initiation occurred with the assistance of bromine anion rather than imide to form active catalyst; （2） alkyne inserted into the active catalyst to generate a seven-membered manganacycle after dissociation of a carbon monoxide; （3） double bond migration happened in this seven-membered manganacycle to form a product precursor; （4） the product precursor would dissociate by fl-H elimination and generated product isoquinoline and active Mn-H complex; （5） the active Mn-H complex was subsequently combined with an imine followed by dehydrogenative C-H activation to complete the whole catalytic cycle. In this context, the reason for the highly atom-economical C-H activation by direct dehydrogenation （eliminates the necessity for oxidants or additives） has been clarified by this mechanism. The present study was aimed at further understanding of Mn（I）-catalyzed dehydrogenative C-H activation, and provided more theoretical basis for future more Mn-catalyzed C-H activation.