《化學學報》發表本組綜述文章“堿在過渡金屬催化的有機化學反應中的作用”

 堿在過渡金屬催化的有機化學反應中的作用

歐陽昆冰  席振峰*

化學學報 DOI: 10.6023/A12110984

 堿，包括無機堿和有機堿，在過渡金屬催化的有機反應中發揮着重要作用。本文概括地介紹和讨論相關文獻中堿的作用機制。堿的作用與許多因素有關，包括：堿性、溶解度、電離度、溶劑、聚集度、金屬離子大小、金屬離子Lewis酸性、金屬離子的“軟硬”度、陰離子的大小、陰離子的配位作用等。堿可用于攫取質子、中和反應體系中的酸、活化催化劑、促進催化劑再生等；堿中金屬陽離子的作用主要集中在其對堿在有機溶劑中溶解度的影響和與底物或溶劑間相互作用力的強弱上；堿中陰離子的作用主要表現在離子與金屬的配位方式和穩定性上；有機堿和無機堿的主要區别體現在溶解度和空間位阻的不同上。另外，商品堿中極少量的過渡金屬雜質也有可能對反應産生影響。

Roles of Bases in Transition-Metal Catalyzed Organic Reactions

Kunbing Ouyang, Zhenfeng Xi*

Acta Chim. Sinica 2013, DOI: 10.6023/A12110984

Bases, either organic bases or inorganic ones, are very often added in transition-metal catalyzed organic reactions to promote the catalytic reaction efficiency and increase the yields of products. As a common practice for most published papers, a reaction condition screening table is given, listing a number of bases and the respective yield of products. However, no discussion or a little in some cases is provided on why one base works well to give a high yield formation of the product, but other bases afford no or low yields of the product. Furthermore, in many cases a certain base works well for one reaction but may not work for another. Indeed, for a complicated reaction mixture containing several different components, it is very difficult to analyze and understand the roles of certain bases. Yet there are sporadic discussions and rationalization on the roles of bases in the literature. The role of bases has been reported to be straightforward in some cases, for examples, to abstract protons or to neutralize acids in the reaction system, but very complicated in many other cases. The roles of bases may be affected by several factors, including basicity, solubility, ionization ability, solvent, aggregation state, the size of the metal cations, Lewis acidity of the metal cations, the HSAB theory, the size of the counter anions; the coordination ability of the counter anions, etc. In addition to abstract protons or to neutralize acids in the reaction system, a base may activate the catalysts and facilitate the regeneration of reactive catalytic species. The roles of the metal cation in a base may mainly influence the solubility of the base in organic solvents, or interact with substrates or solvents. The roles of the counter anion in a base may mainly contribute to the coordination with a metal center and subsequent stabilize the complex. The major differences between inorganic bases and organic bases include their solubility and bulkiness. Metal contaminants in bases may also have innegligible effect on the reactions, since in many cases a large excess amount of bases are added. This review is written based on the limited knowledge, focusing on commonly used inorganic bases such as LiOt-Bu, NaOt-Bu, KOt-Bu, LiOAc, NaOAc, KOAc, LiOH, NaOH, KOH, Li2CO3, Na2CO3, K2CO3, Cs2CO3, KF, CsF and organic bases such as DBU and Et3N.