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首页> 外文期刊>Chemistry: A European journal >New Mechanistic Insight into the Coupling Reactions of CO_2 and Epoxides in the Presence of Zinc Complexes
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New Mechanistic Insight into the Coupling Reactions of CO_2 and Epoxides in the Presence of Zinc Complexes

机译：锌络合物存在下CO_2与环氧化物偶联反应的新机理研究

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Coupling reactions of CO_2 and epoxide to produce cyclic carbonates were performed in the presence of a catalyst [L_2ZnX_2] (L = pyridine or substituted pyridimine; X = Cl, Br, I), and the effects of pyridine and halde ligands on the catalytic were investigated. The catalysts with electron-donating substituents on pyridine ligands exhibit higher activity than those with unsubstituted pyridine ligands. On the other hand, the catalysts with electron-with-drawing substituents at the 2-position of the pyridine ligands show no activity; this demonstrates the importance of the basicity of the pyridine ligands. The catalytic activity of [L_2ZnX_2] was found to decrease with increasing electronegativity of the halide ligands. A series of highly active zinc complexes bridged by pyridinium alkoxy ions of the general formula [{(mu-OCHRCH_2L)ZnBr_2}_n] (n = 2 for R = CH_3; n = 3 for R = H; L = pyridine or substituted pyridine) were synthesized and characterized by X-ray crystallography. The dinuclear zinc complexes obtained from propylene oxide adopt a square-planar geometry for the Zn_2O_2 core with two bridging pyridinium propoxy ion ligands. Trinuclear zinc complexes prepared from ethylene oxide adopt a boat geometry for the Zn_3O_3 core, in which three zinc and three oxygen atoms are arranged in an alternate fashion. These zinc complexes bridged by pyridinium alkoxy ions were also isolated from the coupling reactions of CO_2 and epoxides performed in the presence of [L_2ZnBr_2]. Rapid CO_2 insertion into the zinc-oxygen bond of the zinc complexes bridged by pyridinium alkoxy ions leads to the formation of zinc carbonate species; these which yield cyclic carbonates and zinc complexes bridged by pyridinium alkoxy ions upon interaction with epoxides. The mechanistic pathways for the formation of active species and cyclic carbonates are discussed on the basis of results from structural and spectroscopic analyses.
机译：在催化剂[L_2ZnX_2]（L =吡啶或取代的嘧啶; X = Cl，Br，I）的存在下，进行CO_2和环氧化物的偶联反应，生成环状碳酸酯，吡啶和卤代配体对催化剂的影响为调查。在吡啶配体上具有给电子取代基的催化剂比在未取代吡啶配体上具有更高的活性。另一方面，在吡啶配体的2-位具有吸电子取代基的催化剂没有活性。这证明了吡啶配体的碱性的重要性。发现[L_2ZnX_2]的催化活性随着卤化物配体的电负性的增加而降低。由通式[{（mu-OCHRCH_2L）ZnBr_2} _n]的吡啶鎓烷氧基离子桥连的一系列高活性锌配合物（对于R = CH_3，n = 2;对于R = H，n = 3; L =吡啶或取代的吡啶，n = 2合成并通过X射线晶体学表征。由环氧丙烷获得的双核锌配合物对具有两个桥接吡啶鎓丙氧基离子配体的Zn_2O_2核采用正方形平面的几何形状。由环氧乙烷制备的三核锌络合物对Zn_3O_3核采用舟形几何形状，其中三个锌原子和三个氧原子以交替方式排列。还从[L_2ZnBr_2]存在下进行的CO_2和环氧化物的偶联反应中分离了这些由吡啶鎓烷氧基离子桥接的锌配合物。快速CO_2插入由吡啶烷氧基离子桥接的锌络合物的锌-氧键中会导致形成碳酸锌物质。它们在与环氧化物相互作用时产生由吡啶鎓烷氧基离子桥接的环状碳酸酯和锌络合物。根据结构和光谱分析的结果，讨论了形成活性物质和环状碳酸酯的机理。

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