Selective formation of a coordinatively unsaturated metal complex at a surface: a SiO(2)-immobilized, three-coordinate ruthenium catalyst for alkene epoxidation.
Selective formation of a coordinatively unsaturated metal complex at a surface: a SiO(2)-immobilized, three-coordinate ruthenium catalyst for alkene epoxidation.
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DOI：
10.1002/anie.200700980
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发表时间：
2007-09
影响因子：
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通讯作者：
Mizuki Tada;Rudy Coquet;J. Yoshida;Mutsuo Kinoshita;Y. Iwasawa
中科院分区：
文献类型：
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作者：
Mizuki Tada;Rudy Coquet;J. Yoshida;Mutsuo Kinoshita;Y. Iwasawa
金属配合物在载体表面上的固定化仍然是均相和非均相催化之间的跨学科领域中的最新技术水平，而不管以可控方式设计固定化金属配合物的长期挑战，其目前在各种催化化学合成的实践中受到很多关注。[1]固定化金属络合物催化剂的潜力强烈地依赖于载体表面的性质，这可以导致类似均相络合物不表现出的显著的速率提高和新的催化性能。[1，2]在金属络合物催化的均相反应中，有人提出配位饱和的金属络合物（前体）消除配体并转化为具有不饱和金属中心的活性络合物，由于其在溶液中的低稳定性，其不能被分离并容易发生聚集，导致催化活性的损失。[3]另一方面，金属络合物在氧化物载体表面上的附着提供了孤立的单位点金属络合物。[1，4，5]该技术的目的不仅是金属络合物的简单表面固定，而且还在溶液中难以实现的表面上选择性地产生独特的活性结构和反应性。[2]在这里，我们报告的合成一种新的三配位不饱和钌配合物的SiO2表面的一种新的策略和催化性能，该系统。将单体对伞花烃配位的钌N-磺酰基-1，2-乙二胺配合物[6]拴在SiO2上，我们发现与O2/异丁醛（IBA）的放热反应促进了对伞花烃配体的化学计量消除，从而在表面的三配位不饱和钌配合物上形成中间氧化剂，该中间氧化剂对烯烃环氧化具有活性。
Immobilization of metal complexes on support surfaces is still the state of the art in the interdisciplinary field between homogeneous and heterogeneous catalysis, irrespective of long-term challenges of designing immobilized metal complexes in a controllable manner, which is currently receiving much attention in practice for a variety of catalytic chemical syntheses.[1] The potential of immobilized metal-complex catalysts strongly depends on the nature of the support surface, which can result in significant rate enhancement and novel catalytic performance that analogous homogeneous complexes do not exhibit.[1, 2] In homogeneous reactions catalyzed by metal complexes, it is suggested that a coordinatively saturated metal complex (precursor) eliminates a ligand and is converted to an active complex with an unsaturated metal center, which, because of its low stability in solution, cannot be isolated and readily undergoes aggregation leading to loss of catalytic activity.[3] On the other hand, attachment of metal complexes on the surface of oxide supports provides isolated single-site metal complexes.[1, 4, 5] The aim of this technique is not only the simple surface immobilization of metal complexes, but also the selective creation of unique active structures and reactivity on surfaces that are difficult to achieve in solution.[2] Here we report the synthesis of a novel three-coordinate unsaturated Ru complex on an SiO2 surface by a new strategy and the catalytic performance of this system. A monomeric pcymene-coordinated ruthenium N-sulfonyl-1, 2-ethylenediamine complex [6] was tethered on SiO2, and we found that exothermic reaction with O2/isobutyraldehyde (IBA) promoted stoichiometric elimination of a p-cymene ligand to form an intermediate oxidant on a three-coordinate unsaturated ruthenium complex at the surface, which is active for alkene epoxidation.