Alternative selective oxidation pathways for aldehyde oxidation and alkene epoxidation on a SiO2-supported Ru-monomer complex catalyst.
Alternative selective oxidation pathways for aldehyde oxidation and alkene epoxidation on a SiO2-supported Ru-monomer complex catalyst.
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DOI：
10.1021/ja9079513
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发表时间：
2010-01
影响因子：
15
通讯作者：
Mizuki Tada;Satoshi Muratsugu;Mutsuo Kinoshita;Takehiko Sasaki;Y. Iwasawa
中科院分区：
文献类型：
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作者：
Mizuki Tada;Satoshi Muratsugu;Mutsuo Kinoshita;Takehiko Sasaki;Y. Iwasawa
我们制备了一种新型的负载在SiO(2)表面上的Ru单体络合物，它对醛的选择氧化和O(2)对烯烃的环氧化反应具有很高的活性。通过FT-IR、固体核磁共振、漫反射UV/Vis、XPS、Ru K边EXAFS和密度泛函计算等手段对催化剂的结构进行了表征，证明了Ru络合物前体的p-伞花烃配体后面形成了孤立的、不饱和的Ru中心。在SiO(2)上的位置隔离的Ru单体络合物在醛和烯烃的选择性氧化方面取得了巨大的吨(周转数)；例如，在常温下选择性异丁醛(IBA)氧化的吨数为38,800,000吨，反式二苯乙烯环氧化的吨数为2,100,000吨，据我们所知，这是金属络合物催化剂中最高的吨之一。我们还发现，IBA底氧化的活化能为48kJ mol(-1)，比反式二苯乙烯环氧化的活化能99kJ mol(-1)容易得多，反式二苯乙烯的存在完全抑制了IBA的氧化。用选择性氧化途径的能量分布解释了从IBA氧化到反式二苯乙烯环氧化的选择性氧化途径的转换，导致反式二苯乙烯优先配位到表面的Ru-络合物上。这一方面揭示了IBA/O(2)选择环氧化烯烃的高效催化剂的起源。
We have prepared a novel Ru-mononer complex supported on a SiO(2) surface by using a Ru-monomer complex precursor with a p-cymene ligand, which was found to be highly active for the selective oxidation of aldehydes and the epoxidation of alkenes using O(2). The structure of the supported Ru catalyst was characterized by means of FT-IR, solid-state NMR, diffuse-reflectance UV/vis, XPS, Ru K-edge EXAFS, and DFT calculations, which demonstrated the formation of isolatedly located, unsaturated Ru centers behind a p-cymene ligand of the Ru-complex precursor. The site-isolated Ru-monomer complex on SiO(2) achieved tremendous TONs (turnover numbers) for the selective oxidation of aldehydes and alkenes; e.g. TONs of 38,800,000 for selective isobutyraldehyde (IBA) oxidation and 2,100,000 for trans-stilbene epoxidation at ambient temperature, which are among the highest TONs in metal-complex catalyzes to our knowledge. We also found that the IBA sole oxidation with an activation energy of 48 kJ mol(-1) much more facile than the trans-stilbene epoxidation with an activation energy of 99 kJ mol(-1) was completely suppressed by the coexistence of trans-stilbene. The switchover of the selective oxidation pathways from the IBA oxidation to the trans-stilbene epoxidation was explained in terms of energy profiles for the alternative selective oxidation pathways, resulting in the preferential coordination of trans-stilbene to the Ru-complex at the surface. This aspect gives an insight into the origin of the efficient catalysis for selective epoxidation of alkenes with IBA/O(2).