Kinetically Controlled Porosity in a Robust Organic Cage Material
Kinetically Controlled Porosity in a Robust Organic Cage Material
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DOI：
10.1002/anie.201209922
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发表时间：
2013-01-01
影响因子：
16.6
通讯作者：
Doonan, Christian J.
中科院分区：
文献类型：
--
作者：
Avellaneda, Antonio;Valente, Peter;Doonan, Christian J.
微孔材料因其在气体储存、分离过程和催化中的核心作用而受到人们的广泛关注。[1-4]最近，由离散、形状持久的有机笼组成的微孔分子固体受到越来越多的关注[1]，因为它们具有独特的性能，使其有别于传统的扩展网络材料，如沸石、[2]金属有机框架、[3]和共价有机材料。 框架。[4]例如，分子固体易于溶液加工，[5]通过混合匹配合成可以轻松获得多组分材料，[6]并且凭借其非共价分子间堆积，可以表现出先进的性能，例如吸附物触发的开/关孔隙率切换。[7]与扩展网络不同，在扩展网络中，溶剂可及的空隙通过刚性共价框架固体连接，该固体由离散的有机笼组成，主要通过相对较弱的分散力聚集。预测这种弱聚集材料的晶体结构是固态化学领域的一个长期挑战，[8]，并且在该领域，本质上与从其构建单元估计分子固体的最终孔隙率相关，因为不同的多晶型物可以提供具有显着不同表面积的固体。 [9]因此，报道的多孔有机固体的例子相对较少。[1d]然而，Cooper 和 Mastalerz 实验室最近的工作表明，可以通过晶体工程策略和合成加工来改变此类材料的孔隙率。[5a, 10] 在此，我们描述了一种新型、永久多孔、形状持久的笼状分子 (C1) 的合成和表征，该笼状分子完全由 热力学上稳定的碳-碳键，分子式为 C112H62O2（方案 1）。此外，我们证明了两种结晶多晶型物 C1a 和 C1b 的动力学控制途径，它们具有显着不同的 N2 孔隙率：多晶型物 C1a 对 N2 无孔，多晶型物 C1b 提供 1153 m2 g-1 的 BET 表面积。分子 C1 是通过两个刚性、 炔烃封端的结构单元（方案 1；2）。此类反应通常使用化学计量过量的铜试剂进行，已广泛应用于大环合成中。 [11]笼状前体化合物 2 可以由三足结构单元 4-[三（4-碘苯基）甲基]苯酚[12]通过连续苯酚甲基化、Sonogashira 偶联和甲硅烷基脱保护反应精制而成，三步收率达 53%。[13]最终的自偶联步骤在高稀释条件下使用大量过量的催化剂进行，以最大限度地提高动力学产物 C1 的产率。考虑到所涉及的键的不可逆性质以及笼合成过程中一个不正确的键形成步骤将引导反应形成低聚物这一事实，C1 的产率 (20%) 是引人注目的。该反应需要三个 Eglinton 自偶联反应，没有分离出其他主要产物。 C1 的能量最小化结构最好被描述为一个扭曲的三棱柱，其内部垂直和水平直径分别为 13.5 和 12。 [14]
Microporous materials are of significant interest owing to their central role in gas storage, separation processes, and catalysis.[1–4] Recently, microporous molecular solids composed of discrete, shape-persistent organic cages have received growing attention [1] because they possess unique properties that set them apart from conventional, extended network materials, such as zeolites,[2] metal–organic frameworks,[3] and covalent organic frameworks.[4] For example, molecular solids are readily solution-processable,[5] provide facile access to multicomponent materials by mix-and-match synthesis,[6] and, by virtue of their noncovalent intermolecular packing, can exhibit advanced properties, such as adsorbatetriggered on/off porosity switching.[7] Unlike extended networks, where solvent-accessible voids are linked through rigid covalent framework solids composed of discrete organic cages predominantly aggregate by relatively weak dispersion forces. Predicting the crystal structures of such weakly aggregating materials is a long-standing challenge in solid-state chemistry,[8] and is, in this field, inherently coupled to estimating the ultimate porosity of a molecular solid from its building units, as different polymorphs can afford solids with dramatically different surface areas.[9] Accordingly, relatively few examples of porous organic solids have been reported.[1d] Nevertheless, recent work from the laboratories of Cooper and Mastalerz have demonstrated that the porosity of such materials can be modified through crystal engineering strategies and synthetic processing.[5a, 10] Herein we describe the synthesis and characterization of a novel, permanently porous, shape-persistent cage molecule (C1) that is constructed entirely from thermodynamically robust carbon–carbon bonds and has the molecular formula C112H62O2 (Scheme 1). Furthermore, we demonstrate kinetically controlled access to two crystalline polymorphs C1a and C1b that possess dramatically different N2 porosities: polymorph C1a, which is nonporous to N2, and polymorph C1b, which affords a BET surface area of 1153 m2 gÀ1.Molecule C1 was synthesized by Eglinton homocoupling of two rigid, alkyne-terminated building units (Scheme 1; 2). Such reactions, which are often conducted with a stoichiometric excess of copper reagents, have been widely employed in macrocycle synthesis.[11] The cage precursor, compound 2, can be elaborated from a tripodal building block, 4-[tris (4-iodophenyl) methyl] phenol,[12] by sequential phenol methylation, Sonogashira coupling, and silyl deprotection reactions in 53% yield over three steps.[13] The ultimate homocoupling step proceeds under high-dilution conditions with a large excess of catalyst to maximize the yield of the kinetic product C1. The yield of C1 (20%) is remarkable given the irreversible nature of the bonding involved and the fact that one incorrect bond formation step during cage synthesis will direct the reaction towards the formation of oligomers. No other major products are isolated in this reaction that requires three Eglinton homocoupling reactions. The energy-minimized structure of C1 is best described as a distorted triangular prism with internal vertical and horizontal diameters of 13.5 and 12, respectively.[14]