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和碗状结构的纳米过渡金属分子催化剂。在铑催化的酮与三取代硅烷的硅氢加成反应中，将它们与其他常见的膦配体进行了比较。在24℃下的动力学研究表明，在铑催化剂体系中加入碗状膦配体，硅氢加成反应的速率分别提高了154、31和28倍。此外，在均相催化剂体系中，存在金属聚集和沉淀导致催化剂分解和催化活性的相当大的损失的持续问题。Pd黑的形成是已知Pd催化剂容易聚集和形成Pd黑的典型实例，尽管它们在有机合成中实现了多种有用的反应。为了克服均相Pd催化剂的这一固有问题，我们以醇类的有氧氧化为探针反应，探索了一类新型的Pd催化剂。我们发现了一种新的催化剂系统，即使在空气中，抑制钯黑的形成，并与高底物催化剂的摩尔比（S/C：大于1000）在醇的氧化。在甲苯中，80℃下Pd（OAc）_2催化空气（气球）氧化醇类化合物的反应中，2，3，4，5-四苯基取代的吡啶衍生物及其在吡啶环3-位上的高枝晶单元是一种优良的配体。与结构相关的吡啶配体比较发现，2，3，4，吡啶环3-位上的5-四苯基苯基取代基有效地抑制了Pd黑的形成，长时间保持催化活性，以高产率得到作为产物的醛或酮。

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.