DOI: 10.1002/cctc.201000133 A Covalently Immobilized Triphenylphosphine Rhodium Complex: Synthesis, Characterization, and Application in Catalytic Olefin Hydrogenation Lei Wang, [a, b] Mingjun Jia, [b] Sankaranarayanapillai Shylesh, [a] Thomas Philippi, [a] Andreas Seifert, [c] Stefan Ernst, [a] Anand Pal Singh, [d] and Werner R. Thiel* [a] Introduction Heterogenization of homogeneous single-site catalysts on solid support materials allows combining the superior activities and selectivities of homogeneous with the simple recovery of heterogeneous catalysts. Heterogenized catalysts can also be used in fixed- or flow-bed reactors, which additionally simplify process development. Therefore, such systems have extensive- ly been studied during the past two decades. [1] Olefin hydrogenation is an industrially important reaction. For more than 100 years chemists have used heterogeneous catalysts based on noble metals on various supports. [2] Homo- geneous hydrogenation catalysis was developed in the 1960s and is reviewed frequently. [3] Triphenylphosphine is one of the most important and widely used ligands for transition metal- based homogeneous catalysts. Wilkinson’s catalyst (RhCl- (PPh 3 ) 3 ) was the first homogeneous catalyst that could effi- ciently catalyze the hydrogenation of alkenes, [4] whereas Pd(PPh 3 ) 4 and other triphenylphosphine palladium compounds are widely used for catalytic C ÀC coupling reactions. [5] Thus, the immobilization of triphenlyphosphine and its complexes on solid supports is one way to generate active and stable het- erogeneous catalysts. [6] By using halogenated and cross-linked polystyrene as the starting material, a series of polymers containing phosphines as functional groups have been prepared. [7] These polymers can then act as ligands to bind catalytically active metal sites. However, the solvent-dependent swelling of these resins often is a drawback for applications in catalysis. On the other hand, silicas have been widely used as supports for catalytically active sites. They exhibit, depending on the preparation proce- dure, excellent mechanical and chemical stability, and extreme- ly high surface areas defined by their porous structure. The crucial point is the interaction between the support and the catalyst, which is in the case of polymer-grafted systems a strong C ÀC bond. For grafting on inorganic supports, the link- ing group has to be chosen carefully to guarantee an irreversi- ble linkage of the active sites. Because the surface Si ÀOH groups of the silica support are the only reactive sites available for grafting the catalyst, the degrees of freedom in the ligand synthesis are limited. Therefore only a few examples have been published in the literature, wherein phosphines have been bound covalently to a silica surface. Shyu et al. prepared (EtO) 3 Si À(CH 2 ) 3 ÀPPh 2 functionalized MCM-41 and treated this hybrid material with RhCl(PPh 3 ) 3 . The resulting heterogenized catalyst exhibited a higher activity in the hydrogenation of ole- fins than its homogeneous analogue. [8] Crudden et al. grafted a functionalized cationic rhodium complex involving a bidentate phosphine to minimize leaching onto mesoporous molecular sieves, and found this material being highly active for olefin A trimethoxysilane functionalized triphenylphosphine was co- ordinated to rhodium(I) and the resulting rhodium complex was covalently bound to a mesoporous SBA-15 support. The catalytic activity of this hybrid material was studied for the hy- drogenation of 2-cyclohexen-1-one and compared with the corresponding homogeneous catalyst. According to the 31 P- MAS NMR data, the catalytically active species was stable against oxidation; no structural change could be detected after exposing it to air for more than two months. Transmis- sion electron microscopy (TEM) measurements on the used catalyst confirmed that the rhodium species was also stable against reduction to the metal because the formation of rhodi- um nanoparticles during the catalysis could be excluded. The kinetic curves of the recycled system confirmed that this hybrid catalyst shows excellent activity, selectivity, stability, and reusability, and is truly heterogeneous in the hydrogenation re- action. [a] L. Wang, Dr. S. Shylesh, T. Philippi, Prof. Dr. S. Ernst, Prof. Dr. W. R. Thiel Fachbereich Chemie, Technische Universität Kaiserslautern Erwin-Schrçdinger-Str. Geb. 54, 67663, Kaiserslautern (Germany) Fax: (+ 49) 631-2054676 E-mail : thiel@chemie.uni-kl.de [b] L. Wang, Prof. Dr. M. Jia Key Laboratory of Surface and Interface Chemistry of Jilin Province College of Chemistry, Jilin University Changchun, 130012 (China) [c] Dr. A. Seifert Technische Universität Chemnitz, Institut für Chemie Straße der Nationen 62, 09111 Chemnitz (Germany) [d] Dr. A. P. Singh Inorganic and Catalysis Division, National Chemical Laboratory Dr. Homi Bhabha Road, Pashan, Pune 411 008 (India) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201000133. ChemCatChem 2010, 2, 1477 – 1482  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1477