Characterization of phenylene-bridged hybrid mesoporous materials incorporating arenetricarbonyl complexes (–C6H4Me(CO)3–; Me = Cr, Mo) and their catalytic activities
Graphical abstract
Highlights
► Unique inorganic–organic hybrid mesoporous materials incorporating arenetricarbonyl complexes were successfully prepared by a simple CVD treatment of HMM-ph. ► Arenetricarbonyl complexes were stably constructed on HMM-ph by using phenylene moieties as the “framework ligand”. ► These complexes exhibited catalytic performance in polymerization and dehydrochlorination within heterogeneous systems.
Introduction
For the past several decades, siliceous mesoporous materials have attracted considerable attention in terms of their potential applications as an adsorbent and catalyst support as well as fillers for chromatography [1], [2], [3]. The anchoring of organometallic complexes on their surfaces as well as the incorporation of heteroatoms such as Ti-, Cr- and Mo-atoms within their frameworks are promising ways of designing unique catalysts and photocatalysts [3], [4], [5], [6], [7], [8], [9], [10]. On the other hand, recently, the synthesis of mesoporous materials which have bridged organic moieties, i.e., –CH2CH2–, –CHCH– and –C6H4–, within their silica frameworks has been achieved by using organosilanes [(R′O)3Si–R–Si(OR′)3] as a precursor [11], [12], [13], [14], [15]. The direct utilization of fascinating framework organic moieties within these inorganic–organic hybrid mesoporous materials (HMM) has been intensively studied in various research fields. For example, light-harvesting and light-emitting systems have been designed by a combination of HMM and organic dyes as guest molecules [16], [17]. Solid-acid and solid-base catalysts have also been prepared by the post-synthetic direct modification of framework organic moieties with sulfuric acid (–SO3H) and amino (–NH2) groups, respectively [18], [19], [20]. In line with such work, our group has previously reported the direct utilization of organic moieties (–C6H4– = phenylene (ph)) within HMM as a “framework ligand”, i.e., the construction of arenetricarbonyl complexes (–phMe(CO)3–; Me = Cr, Mo, W) by chemical vapor deposition (CVD) treatment of phenylene-bridged hybrid mesoporous materials (HMM-ph) with corresponding metal hexacarbonyls at elevated temperatures [21], [22]. Coelho et al. have also reported the synthesis of the same type of complexes by liquid phase treatment of HMM-ph and their catalytic performances for the epoxidation of olefins [23], [24].
In the present study, HMM-ph functionalized by arenetricarbonyl chromium and molybdenum complexes (HMM-phMe(CO)3; Me = Cr, Mo) have been prepared by the CVD method and characterized in detail with various spectroscopic methods. Attention has been focused on a clear determination of the local structure of –phMe(CO)3– (Me = Cr, Mo) complexes by XAFS measurements. Furthermore, the catalytic performance of HMM-phMe(CO)3 (Me = Cr, Mo) has been investigated by the polymerization of phenylacetylene as well as the dehydrochlorination of 2-chloro-2-methylbutane as model reactions in heterogeneous systems.
Section snippets
Materials
Octadecyltrimethylammonium chloride, phenylacetylene, and 2-chloro-2-methylbutane were purchased from Tokyo Kasei Kogyo Co., Ltd. Chromium hexacarbonyl (Cr(CO)6), benzene tricarbonyl chromium (C6H6Cr(CO)3), molybdenum hexacarbonyl (Mo(CO)6), and 1,4-bis(triethoxysilyl) benzene were obtained from Aldrich. Dry acetonitrile, dry chloroform, dry tetrahydrofuran and HCl (37%) were obtained from Nacalai Tesque Inc. All chemicals were used without further purification.
Synthesis of HMM-ph and HMM-phMe(CO)3 (Me = Cr, Mo)
HMM-ph was synthesized in
Characterization of HMM-ph and HMM-phMe(CO)3 (Me = Cr, Mo)
Fig. 1 shows the UV–vis absorption spectra of HMM-ph before and after CVD treatment with Mo(CO)6 and chloroform solution of the reference complexes. The peak position of C6H6Mo(CO)3 was quite different from that of Mo(CO)6. A typical absorption peak at around 325 nm (Fig. 1(b)) can be assigned to the metal–phenyl intramolecular charge transfer transition of the arenetricarbonyl metal complex [26], [27]. In the case of HMM-ph, only the absorption peak due to the π–π* transition of the framework
Conclusions
Unique inorganic–organic hybrid mesoporous materials which incorporate arenetricarbonyl chromium and molybdenum complexes (–phMe(CO)3–) within the framework of the mesopores have been successfully prepared by CVD treatment of HMM-ph with Cr(CO)6 and Mo(CO)6. The local structures of these complexes were investigated in detail by UV–vis, FT-IR and XAFS measurements. HMM-phMe(CO)3 (Me = Cr, Mo) showed catalytic activity for the polymerization reaction of phenylacetylene as well as
Acknowledgements
The present work is supported by a Grant-in-Aid for Scientific Research (KAKENHI) from Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 21550192). X-ray absorption measurements were performed at the BL-12C facility of the Photon Factory at the High-Energy Acceleration Research Organization (KEK) in Tsukuba, Japan (No. 2007G658). X-ray adsorption experiments were also performed at the BL-01B1 facility of SPring-8 at the Japan Synchrotron Radiation Research Institute
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