Catalysis in a porous molecular capsule: activation by regulated access to sixty metal centers spanning a truncated icosahedron.
Catalysis in a porous molecular capsule: activation by regulated access to sixty metal centers spanning a truncated icosahedron.
复制标题
DOI：
10.1021/ja304513t
复制
发表时间：
2012-07
影响因子：
15
通讯作者：
Sivil Kopilevich;A. Gil;M. Garcia-Ratés;J. Bonet-Ávalos;C. Bo;A. Müller;I. Weinstock
中科院分区：
文献类型：
--
作者：
Sivil Kopilevich;A. Gil;M. Garcia-Ratés;J. Bonet-Ávalos;C. Bo;A. Müller;I. Weinstock
连接多孔金属氧化物胶囊的12个带负电荷的五边形“配体”{（Mo（VI））Mo（VI）5 O21（H2O）6}（6-）的30个阳离子{Mo（V）2 O 4（乙酸盐）}（+）单元[{Mo（VI）6 O21（H2O）6}12{Mo（V）2 O 4（乙酸盐）}30]（42-）为有机“客体”的催化转化提供活性位点。这是证明使用一个良好的行为模型反应，完全可逆的裂解和形成甲基叔丁基醚（MTBE）在温和的条件下，在水中。五个独立的证据表明，反应的MTBE客人发生在ca。6 × 10（3）（3）球形胶囊的内部。{Mo（V）_2O_4（乙酸根）}（+）连接体的Mo原子--横跨约100个原子。3-nm截短的二十面体--在空间上可接近底物，并且控制去除它们内部结合的乙酸根配体产生具有不稳定水配体的催化活性{Mo（V）2 O 4（H2O）2}（2+）单元，以及刘易斯-和布朗斯特-酸性质。这些单元的活性通过动力学数据证明，该动力学数据揭示了MTBE裂解速率对无乙酸根的{Mo（V）2 O 4（H2O）2}（2+）连接体的数量的一级依赖性。DFT计算指出了一个涉及两个Mo（V）中心的途径，以及异丁烯在正向和反向反应中的中间性。一个合理的催化循环-满足微观可逆性-支持活化参数的MTBE裂解，氘和氧-18标记的研究，并通过故意添加异丁烯和水溶性异丁烯类似物的反应。更一般地说，孔限制封装，配体调节访问多个结构完整的金属中心，并在这种新型的纳米反应器内修改微环境的选项，建议通过这种和相关的氧化钕基胶囊的有机基板的许多额外的转换。
The 30 cationic {Mo(V)2O4(acetate)}(+) units linking 12 negatively charged pentagonal "ligands," {(Mo(VI))Mo(VI)5O21(H2O)6}(6-) of the porous metal-oxide capsule, [{Mo(VI)6O21(H2O)6}12{Mo(V)2O4(acetate)}30](42-) provide active sites for catalytic transformations of organic "guests". This is demonstrated using a well-behaved model reaction, the fully reversible cleavage and formation of methyl tert-butyl ether (MTBE) under mild conditions in water. Five independent lines of evidence demonstrate that reactions of the MTBE guests occur in the ca. 6 × 10(3) Å(3) interior of the spherical capsule. The Mo atoms of the {Mo(V)2O4(acetate)}(+) linkers--spanning an ca. 3-nm truncated icosahedron--are sterically accessible to substrate, and controlled removal of their internally bound acetate ligands generates catalytically active {Mo(V)2O4(H2O)2}(2+) units with labile water ligands, and Lewis- and Brønsted-acid properties. The activity of these units is demonstrating by kinetic data that reveal a first-order dependence of MTBE cleavage rates on the number of acetate-free {Mo(V)2O4(H2O)2}(2+) linkers. DFT calculations point to a pathway involving both Mo(V) centers, and the intermediacy of isobutene in both forward and reverse reactions. A plausible catalytic cycle--satisfying microscopic reversibility--is supported by activation parameters for MTBE cleavage, deuterium and oxygen-18 labeling studies, and by reactions of deliberately added isobutene and of a water-soluble isobutene analog. More generally, pore-restricted encapsulation, ligand-regulated access to multiple structurally integral metal-centers, and options for modifying the microenvironment within this new type of nanoreactor, suggest numerous additional transformations of organic substrates by this and related molybdenum-oxide based capsules.