Size Selectivity of a Copper Metal-Organic Framework and Origin of Catalytic Activity in Epoxide Alcoholysis
Size Selectivity of a Copper Metal-Organic Framework and Origin of Catalytic Activity in Epoxide Alcoholysis
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DOI：
10.1002/chem.200901510
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发表时间：
2009-01-01
影响因子：
4.3
通讯作者：
Baiker, Alfons
中科院分区：
文献类型：
--
作者：
Jiang, Dongmei;Urakawa, Atsushi;Baiker, Alfons
{(Cu(bpy)(H₂O)₂(BF₄)₂(bpy)}（Cu - MOF；MOF = 金属 - 有机框架；bpy = 4,4'-联吡啶）具有三维互穿结构，且框架中铜配位位点饱和，在环氧化物与甲醇的开环反应中表现出出乎意料的高活性，尽管使用更庞大的醇时反应速率显著下降。这种（明显的）尺寸选择性以及晶体基质相同环境中的单个Cu²⁺位点类似于沸石。通过衰减全反射红外（ATR - IR）、拉曼、电子顺磁共振（EPR）和紫外/可见光谱对活性位点的真实性质进行了研究。Cu - MOF具有对甲醇响应的高度动态结构特性，其框架尺寸通过重构成四个bpy单元与Cu的对称配位从三维变为二维。这种相互作用伴随着Cu - MOF作为多铜簇的部分溶解，其中Cu²⁺离子与bpy配体相连。尽管分子催化和表面催化都对醇解的高速率有贡献，但可溶性低聚物种（Cuₘbpyₙ）的活性要高得多。最后，向反应混合物中加入乙醚促使溶解的和固体的Cu - MOF重构成原始框架结构，从而使Cu - MOF作为一种表观非均相催化剂具有优异的可回收性。相反，在与更大的醇（如异丙醇和叔丁醇）接触时，原始的Cu - MOF结构得以保持，因此在环氧化物开环反应中活性较差。
{(Cu(bpy)(H2O)(2)(BF4)(2)(bpy)} (Cu-MOF; MOF=metal-organic framework; bpy=4,4'-bipyridine), with a 3D-interpenetrated structure and saturated Cu coordination sites in the framework, possesses unexpectedly high activity in the ring-opening reaction of epoxides with MeOH, although the reaction rate drops remarkably with more bulky alcohols. This (apparent) size selection and the single Cu2+ sites in an identical environment of the crystalline matrix resemble zeolites. The real nature of active sites was investigated by attenuated total reflection infrared (ATR-IR), Raman, EPR, and UV/Vis spectroscopies. Cu-MOF has highly dynamic Structural properties that respond to MeOH, its framework dimensions change front 3D to 2D by restructuring to a symmetric coordination of four bpy units to Cu. This interaction is accompanied by the partial dissolution of Cu-MOF as multi-Cu clusters, in which Cu2+ ions are connected with bpy ligands. Although both molecular and Surface catalysis contribute to the high rate of alcoholysis, the soluble oligomeric species (Cu(m)bpy(n)) are far more active. Finally, addition of diethyl ether to the reaction mixture induces the reconstruction of dissolved and solid Cu-MOF to the original framework structure. thereby allowing excellent recyclability of Cu-MOF as all apparent heterogeneous catalyst. In contrast, the original Cu-MOF structure is maintained Upon contact with larger alcohols, Such as iPrOH and tBuOH, thus leading to poor activity in epoxide ring opening.