Structural investigations of functionalized mesoporous silica-supported palladium catalyst for Heck and Suzuki coupling reactions
Structural investigations of functionalized mesoporous silica-supported palladium catalyst for Heck and Suzuki coupling reactions
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DOI：
10.1016/j.jcat.2004.09.005
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发表时间：
2004-11
影响因子：
7.3
通讯作者：
Ken-ichi Shimizu;Soichi Koizumi;Tsuyoshi Hatamachi;H. Yoshida;S. Komai;T. Kodama;Y. Kitayama
中科院分区：
文献类型：
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作者：
Ken-ichi Shimizu;Soichi Koizumi;Tsuyoshi Hatamachi;H. Yoshida;S. Komai;T. Kodama;Y. Kitayama
FSM-16介孔二氧化硅负载的巯基丙基硅氧烷Pd（II）配合物（Pd-SH-FSM）已被证明是一种活性、稳定和可回收的多相催化剂，用于4-溴苯乙酮与丙烯酸乙酯的Heck反应和4-溴苯甲醚与苯基硼酸的Suzuki反应。通过XRD、TEM、UV-vis、PdK-edge XANES/EXAFS和PdLIII-edge XANES等手段对反应前后Pd-SH-FSM中Pd物种的结构进行了表征，并与无定形二氧化硅负载的巯丙基硅氧烷Pd（II）配合物的结果进行了比较（Pd-SH-SiO2）、未改性的FSM-16负载的Pd（OAc）2（Pd-FSM）和先前报道的非均相催化剂（Pd沸石和Pd/C）。Pd物种在反应过程中的聚集行为很大程度上取决于载体。在Heck和Suzuki反应后的Pd-SH-FSM上，与硫配体配位的Pd（II）物种是主要的Pd物种，连同小的Pd簇作为次要物种，并且催化剂重复使用而没有明显的活性损失。在Pd-SH-SiO2上，相对大量的Pd（II）物种在Suzuki反应后转化为Pd簇。在无配体的Pd-FSM上，大部分Pd聚集形成Pd金属颗粒。回收催化剂的活性顺序（Pd-SH-FSM> Pd-SH-SiO2> Pd-FSM）表明，硫配体上的Pd（II）络合物和可能的小Pd簇比Pd金属颗粒更具有活性。 结果表明，在尺寸受限的介孔中引入硫配体可以有效地防止配位Pd络合物的聚集，从而使Pd-SH-FSM具有高的耐久性和循环利用特性。Pd络合物通过Pd聚集的失活对于常规Pd催化剂是显著的; Pd沸石中的[Pd（NH3）4]2+络合物和Pd/C上的PdO纳米团簇在Heck和Suzuki反应后变为反应性较低的金属颗粒或团簇。
FSM-16 mesoporous silica-supported mercaptopropylsiloxane Pd(II) complex, Pd-SH-FSM, has been shown to act as an active, stabile, and recyclable heterogeneous catalyst for the Heck reaction of 4-bromoacetophenone with ethyl acrylate and for the Suzuki reaction of 4-bromoanisole with phenylboronic acid. The structure of the Pd species in Pd-SH-FSM before and after the reaction was well characterized by a combination of XRD, TEM, UV–vis, Pd K-edge XANES/EXAFS, and Pd LIII-edge XANES, and the results were compared with those of a amorphous silica-supported mercaptopropylsiloxane Pd(II) complex (Pd-SH–SiO2), unmodified FSM-16-supported Pd(OAc)2(Pd-FSM), and previously reported heterogeneous catalysts (Pd zeolite and Pd/C). The aggregation behavior of Pd species during the reaction greatly depends on the support. On Pd-SH-FSM after Heck and Suzuki reactions, Pd(II) species coordinated to the sulfur ligands were the main Pd species together with small Pd clusters as minor species, and the catalyst was reused without marked loss in the activity. On Pd-SH–SiO2, relatively large numbers of the Pd(II) species were converted to Pd clusters after the Suzuki reaction. On ligandless Pd-FSM, most of the Pd was aggregated to form Pd metal particles. The activity order of the recycled catalysts (Pd-SH-FSM > Pd-SH–SiO2> Pd-FSM) indicates that the Pd(II) complexes on the sulfur ligands and possibly the small Pd clusters are more active than Pd metal particles. It is concluded that the sulfur ligands in the size-restricted mesopore are effective for preventing the aggregation of coordinated Pd complexes, and this results in high durability and recycling characteristic of the Pd-SH-FSM. The deactivation of the Pd complex via Pd aggregation was significant for the conventional Pd catalysts; [Pd(NH3)4]2+complexes in Pd zeolite and PdO nanoclusters on Pd/C were changed to less reactive metal particles or clusters after Heck and Suzuki reactions.