Development and Application of Transition-metal Molecular Catalysts having Nano-structure

我们已经成功地开发了具有树枝状大分子和碗状结构的纳米级过渡金属分子催化剂。将它们与其他常见的膦配体在Rg催化的酮与三取代硅烷的硅氢加成反应中进行了比较。在24℃下的动力学研究表明，具有碗状膦配体的Rh催化剂体系实现了154、31和28倍的硅氢加成反应。此外，在均相催化剂体系中，金属的聚集和沉淀导致催化剂的分解和催化活性的大量损失是一个长期存在的问题。Pd黑的形成就是一个典型的例子，尽管Pd催化剂在有机合成中实现了许多有用的反应，但它们很容易聚集并形成Pd黑。为了克服均相Pd催化剂的这一固有问题，我们探索了一种新型的Pd催化剂，采用醇类的好氧氧化作为探针反应。我们发现了一种新的催化剂体系，在醇的氧化反应中，即使在空气中也能抑制Pd黑的生成，并且具有较高的底剂与催化剂摩尔比(S/C：1000以上)。具有2，3，4，5-四苯基苯基的新型吡啶衍生物及其3-位较高的树枝状结构单元在80℃的钯催化甲苯中醇的空气(气球)氧化反应中发现，Pd(OAc)_2是优良的配体。与结构相关的吡啶配体相比，在吡啶环的3-位引入2，3，4，5-四苯基苯基可以有效地抑制Pd黑的生成，使催化活性长时间保持，从而高产率地生成醛或酮。

We have successfully developed nano-sized transition-metal molecular catalysts having dendrimers and bowl-shaped structures. They were compared with other common phosphine ligands in the rhodium-catalyzed hydrosilylation of ketones with a trisubstituted silane. A kinetic study at 24℃ indicated that a rhodium catalyst system with the bowl-shaped phosphine ligands realized 154,31, and 28 times faster hydrosilylation reaction. Furthermore, in homogeneous catalyst system, there is a persistent problem that metal aggregation and precipitation cause catalyst decomposition and considerable loss of catalytic activity Pd black formation is a typical example Pd catalysts are known to easily aggregate and form Pd black, although they realize a wide variety of useful reactions in organic synthesis. In order to overcome this intrinsic problem of homogeneous Pd catalysis, we explored a new class of Pd catalyst with adopting aerobic oxidation of alcohols as a probe reaction. We found a new catalyst system that suppresses the Pd black formation even under air and with a high substrate to catalyst molar ratio (S/C : more than 1000) in oxidation of alcohols. The novel pyridine derivatives having 2,3,4,5-tetraphenyiphenyl substituent and its higher dendritic unit at the 3-position of pyridine ring were found to be excellent ligands with Pd(OAc)_2 in the palladium-catalyzed air (balloon) oxidation of alcohols in toluene at 80℃ Comparison with structurally related pyridine ligands revealed that introduction of the 2,3,4,5-tetraphenylphenyl substituent at the 3-position of pyridine ring effectively suppresses the Pd black formation, maintaining the catalytic activity for a long time to give aldehydes or ketones as products in high yields.