Photoinduced reversible structural transformation and selective oxidation catalysis of unsaturated ruthenium complexes supported on SiO2.
Photoinduced reversible structural transformation and selective oxidation catalysis of unsaturated ruthenium complexes supported on SiO2.
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DOI：
10.1002/anie.200803122
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发表时间：
2008-11
影响因子：
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通讯作者：
Mizuki Tada;Yusaku Akatsuka;Yong Yang;Takehiko Sasaki;Mutsuo Kinoshita;Ken Motokura;Y. Iwasawa
中科院分区：
文献类型：
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作者：
Mizuki Tada;Yusaku Akatsuka;Yong Yang;Takehiko Sasaki;Mutsuo Kinoshita;Ken Motokura;Y. Iwasawa
的SiO2负载的Ru络合物的光照射被发现，以促进选择性地形成两个不同的，新颖的不饱和Ru结构的表面上，依赖于O2或N2气氛，不同的Ru H部分的取向。这些结构之一，由于适当的钌H构象，催化的选择性光氧化的环烷烃与O2。这两个表面结合的不饱和钌配合物在不同的气氛下通过不同波长的光激发进行可逆的结构相互转换。在非均相催化剂表面上，由于反应物的可及性有限，通常可以使用在均相溶液中难以分离的新型配位不饱和金属结构来开发速率增强和新的催化策略。金属络合物附着在表面上导致其稳定化并防止聚集和分解。最近，我们通过与SiO2结合的对苯乙烯基三甲氧基硅烷偶联，在SiO2表面制备了一种新型的三配位不饱和钌配合物。该不饱和钌配合物对异丁醛和氧气的混合物催化烯烃环氧化反应具有很高的催化活性。然而，钌配合物是惰性的选择性氧化饱和烃与O2作为唯一的氧化剂，这可能是更重要的，从实际使用的观点作为催化剂。使用N-磺酰基-1，2-乙二胺-Ru络合物（A）和对苯乙烯基三甲氧基硅烷官能化的SiO2制备SiO2负载的Ru络合物（B）（方案1，支持信息1）。B的局部配位结构与A相似。在N2气氛下，B经紫外光照射（1> 275 nm），可使对伞花烃配体从钌配合物中化学计量消除。在N2下光照射B 2小时后，在溶液中检测到87%的游离对伞花烃（表1），得到配位不饱和Ru络合物C2。对伞花烃的消除也通过C固态魔角旋转（MAS）NMR光谱证明（图1）。X射线光电子能谱（XPS）揭示在消除对伞花烃时Ru 3d 5/2的结合能从B的282.0 eV移动到C2的282.2 eV（表1和支持信息2）。Ru 3d ~（5/2）结合能的变化表明表面Ru配合物在光照射下带正电。然而，在B和C2中Cl 2 p与Ru 3 p 3/2的XPS信号强度的相似比率表明负载的Ru络合物C2保留Cl配体。Ru K边X射线吸收近边结构（XANES）光谱信号的变化也很明显（见辅助信息3）。Ru K边扩展X射线吸收精细结构（EXAFS）光谱分析显示了两种配位，Ru O（N）和Ru Cl，键级为3.2和1.0，键距为（2.10 0.01）及（2.38 0.01），分别（参见支持信息4），其证实了XPS所建议的Cl的保留，并且还表明通过氧与Ru的表面配位，同时通过硅烷偶联进行固定。3C固态NMR光谱表明，有机二胺配体在光诱导的对伞花烃消除过程中被保留（图1）。B在O2气氛下的光照射（1> 275 nm）也导致对伞花烃配体的解离（表1，图1，方案1），但得到不同的结构C1，如通过与C2非常不同的UV/维斯光谱所证明的（图2）。在N2下产生的C2的光谱在可见光区域显示出两个信号，分别位于468 nm和696 nm处（图2d），而在O2下产生的C1的光谱在517 nm左右有一个信号（图2 e）。然而，C1的XPS Ru 3d 5/2信号（在282.2eV处）、固态NMR谱和Ru K边EXAFS谱与C2的几乎相同。值得注意的是，Cl和C2可逆地相互转化：Cl通过在N2下的光照射（I> 275 nm）转化为C2，并且C2通过在O2下的光照射（I> 370 nm）转化为Cl（图2 e-h）。O2 [*] Dr. M. Tada，Y.赤冢博士杨，M.木下博士Motokura，Prof. Dr. Y.东京大学研究生院理学研究科岩泽化学系7-3-1，Hongo，文京区，Tokyo 113-0033（Japan）.传真：（+ 81）3-5800-6892电子邮件：iwasawa@chem.s.u-tokyo.ac.jp
The photoirradiation of a SiO2-supported Ru complex was found to promote the selective formation of two different, novel unsaturated Ru structures on the surface, dependent on an O2 or N2 atmosphere, differing in the orientation of an Ru H moiety. One of these structures, owing to an appropriate Ru H conformation, catalyzed the selective photooxidation of cycloalkanes with O2. The two surface-bound unsaturated Ru complexes undergo reversible structural interconversion by photoexcitation at different wavelengths under different atmospheres. On heterogeneous catalyst surfaces, owing to the limited accessibility of reactants, rate-enhancement and new catalytic strategies can often be developed using novel, coordinatively unsaturated metal structures, which are hard to isolate in homogeneous solutions. Attachment of metal complexes onto a surface results in their stabilization and prevents aggregation and decomposition. Recently, we produced a novel three-coordinate unsaturated ruthenium complex on a SiO2 surface by coupling with SiO2-bound p-styryltrimethoxysilane. The unsaturated Ru complex was highly active for selective alkene epoxidation using a mixture of isobutyraldehyde and O2. However, the Ru complex was inactive for selective oxidation of saturated hydrocarbons with O2 as a sole oxidant, which may be more important from the viewpoint of practical use as a catalyst. A SiO2-supported Ru complex (B) was prepared using a N-sulfonyl-1,2-ethylenediamine–Ru complex (A) and pstyryltrimethoxysilane-functionalized SiO2 (Scheme 1, Supporting Information 1). The local coordination structure of B was similar to that of A. Ultraviolet irradiation (l> 275 nm) of B under N2 was found to cause the stoichiometric elimination of a coordinated p-cymene ligand from the supported Ru complex. 87% of free p-cymene was detected in a solution after the photoirradiation of B under N2 for 2 h (Table 1) affording the coordinatively unsaturated Ru complex C2. The elimination of p-cymene was also evidenced by C solid-state magic-angle spinning (MAS) NMR spectroscopy (Figure 1). X-ray photoelectron spectroscopy (XPS) revealed a shift in binding energy of Ru 3d5/2, on elimination of p-cymene, from 282.0 eV for B, to 282.2 eV for C2, (Table 1 and Supporting Information 2). The shift in the binding energy of Ru 3d5/2 indicates that the surface Ru complex is positively charged by the photoirradiation. However, the similar ratio of the XPS signal intensities for Cl 2p to Ru 3p3/2 in B and C2 indicates that the supported Ru complex C2 retains a Cl ligand. A change was also evident in the Ru K-edge X-ray absorption near-edge structure (XANES) spectroscopic signal (see Supporting Information 3). Ru K-edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis revealed two coordinations, Ru O(N) and Ru Cl, with bond orders of 3.2 and 1.0 , and bond distances of (2.10 0.01) and (2.38 0.01) , respectively (see Supporting Information 4), which confirms the retention of Cl, suggested by XPS, and also indicates surface coordination to Ru by oxygen, alongside the immobilization by silane coupling. C solid-state NMR spectroscopy indicated that the organic diamine ligand was retained during photoinduced p-cymene elimination (Figure 1). Photoirradiation (l> 275 nm) of B under an O2 atmosphere also resulted in dissociation of a p-cymene ligand (Table 1, Figure 1, Scheme 1) but afforded a different structure, C1, as evidenced by a very different UV/Vis spectrum to that of C2 (Figure 2). The spectrum for C2, produced under N2, shows two signals in the visible-light region, at 468 nm and 696 nm (Figure 2d), whereas that for C1, produced under O2, has one signal, at around 517 nm (Figure 2e). However, the XPS Ru 3d5/2 signal (at 282.2 eV), solid-state NMR spectrum, and Ru K-edge EXAFS spectrum of C1 were almost the same as those of C2. Notably, C1 and C2 are interconverted reversibly: C1 was converted into C2 by photoirradiation (l> 275 nm) under N2, and C2 was converted into C1 by photoirradiation (l> 370 nm) under O2 (Figure 2e–h). Neither O2 [*] Dr. M. Tada, Y. Akatsuka, Dr. Y. Yang, M. Kinoshita, Dr. K. Motokura, Prof. Dr. Y. Iwasawa Department of Chemistry, Graduate School of Science The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan). Fax: (+ 81)3-5800-6892 E-mail: iwasawa@chem.s.u-tokyo.ac.jp