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

我们已经成功开发了具有树状大分子和碗状结构的纳米过渡金属分子催化剂。它们与其他常见的膦配体在铑催化酮与三取代硅烷的硅氢化反应中进行了比较。24℃下的动力学研究表明，含碗状膦配体的铑催化剂体系的硅氢化反应速度分别提高了154倍、31倍和28倍。此外，在均相催化剂体系中，金属聚集和沉淀导致催化剂分解和催化活性损失较大是一个长期存在的问题，钯黑的形成是一个典型的例子，钯催化剂虽然在有机合成中实现了各种有用的反应，但众所周知，钯催化剂容易聚集并形成钯黑。为了克服均相钯催化的固有问题，我们探索了一类以醇为探针反应的好氧氧化钯催化剂。我们发现了一种新的催化剂体系，即使在空气条件下，在高底物与催化剂的摩尔比（S/C：大于1000）下，也能抑制醇氧化过程中Pd黑的形成。以2,3,4,5-四苯基取代基及其在吡啶环3位的较高枝状单元为配体的新型吡啶衍生物在80℃钯催化甲苯气（球）氧化醇的过程中，与结构相关的吡啶配体比较表明，在吡啶环3位引入2,3,4,5-四苯基苯基取代基可有效抑制Pd黑的生成。长时间保持催化活性，以高收率得到醛类或酮类产物。

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.