The dendron/dendrimer size was found to strongly influence properties of catalysts based on such macromolecules. Here, we assessed the dendritic effect of third generation pyridylphenylene dendrons (G3) immobilized on magnetic silica and loaded with Pd species in Suzuki-Miyaura reactions of Br-arenes and phenylboronic acid as compared with the second generation dendron (G2) based catalyst. A comprehensive analysis allows decoupling the dendron influence from other parameters identifying a strong positive dendritic effect (higher activity with G3 based composite), attributed to a larger available space and to a greater number of coordinating groups in the G3 to host reacting molecules and stabilize catalytic species. A “local Pd leaching” mechanism for the Suzuki-Miyaura reaction, which occurs in the dendron environment of the catalyst, provides an excellent catalytic activity. This finding along with easy magnetic separation (a remarkable catalytic stability in five consecutive catalytic cycles) make such systems promising for other cross-coupling reactions.

发现树枝状/树枝状大分子的尺寸强烈影响基于此类大分子的催化剂的性能。在这里，我们评估了溴代芳烃和苯基硼酸的Suzuki-Miyaura反应中第三代吡啶基亚苯基树枝状分子（G3）固定在磁性二氧化硅上并负载了Pd的树突作用，与第二代树枝状（G2）基催化剂相比。全面的分析可以将树突的影响与其他参数解耦，从而确定强的正树突效应（基于G3的复合材料具有更高的活性），这归因于更大的可用空间和G3中更大的配位基团，以容纳反应分子并稳定催化作用种类。Suzuki-Miyaura反应的“局部Pd浸出”机理，发生在催化剂的树枝状环境中，提供出色的催化活性。这一发现以及容易的磁分离（在五个连续的催化循环中具有显着的催化稳定性）使得此类系统有望用于其他交叉偶联反应。