Synthesis, Structural Elucidation, and Catalytic Properties in Olefin Epoxidation of the Polymeric Hybrid Material [Mo₃O₉(2-[3(5)-Pyrazolyl]pyridine)]_<i>n</i>

The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]­pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)]n (2) as a microcrystalline powder in yields of 72–79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)2(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]­pyridinium), containing a very rare example of the tetrahedral MoCl42– anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO­(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic–inorganic one-dimensional (1D) polymer, ∞1[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)­catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.将配合物[MoO₂Cl₂(pzpy)]（1）（其中pzpy为2-[3(5)-吡唑基]吡啶（2-[3(5)-pyrazolyl]pyridine））分别在敞口回流体系中反应16小时、微波合成体系内120℃反应2小时，或于聚四氟乙烯内衬不锈钢消解罐中100℃反应19小时，均可得到钼氧化物/吡唑基吡啶聚合物杂化材料[Mo₃O₉(pzpy)]ₙ（2），产物以微晶粉末形式分离，产率为72%~79%。化合物2也可通过MoO₃、pzpy与H₂O在160℃下进行水热反应3天制得。从反应溶液中分离得到的副产物包括盐类化合物(pzpyH)₂(MoCl₄)（3）（其中pzpyH为2-[3(5)-吡唑基]吡啶鎓（2-[3(5)-pyrazolyl]pyridinium）），该盐包含极为罕见的四面体MoCl₄²–阴离子，以及四核配合物[Mo₄O₁₂(pzpy)₄]（4）。将化合物2与过量叔丁基过氧化氢（tert-butylhydroperoxide，TBHP）反应，可分离得到二过氧氧合配合物[MoO(O₂)₂(pzpy)]（5）。本文报道了化合物3与5的单晶X射线晶体结构。基于密度泛函理论（density functional theory，DFT）计算，对化合物1、4和5的傅里叶变换（FT）红外光谱与FT拉曼光谱进行了峰位归属。化合物2的结构通过同步辐射粉末X射线衍射数据结合其他物理化学表征信息得以确定。作为有机-无机杂化一维（1D）聚合物，∞¹[Mo₃O₉(pzpy)]由两种截然不同的结构单元构筑而成：一类是与MoO₃晶体结构相似的双梯型无机核，另一类是由共角畸变{MoO₄N₂}八面体连接形成的一维链。将化合物2作为顺式环辛烯与TBHP环氧化反应的（预）催化剂时，表现出中等催化活性与高选择性。在该反应条件下，化合物2溶解性较差，并会逐步转化为5，而5至少部分贡献了该催化反应的活性。