DOI: 10.1002/cctc.201200288 The Origin of the Activity of Amine-Functionalized Metal–Organic Frameworks in the Catalytic Synthesis of Cyclic Carbonates from Epoxide and CO 2 Tristan Lescouet, [a] CØline Chizallet, [b] and David Farrusseng* [a] The conversion of carbon dioxide into bulk chemicals at lower energy cost is a scientific and technological challenge. [1, 2] Acid–base-pair catalysts are interesting for such applications because they can promote concerted reactions. The adsorption of CO 2 occurs on the basic sites to form activated species; then, the epoxide coordinates onto the neighboring acidic site and ring-opening occurs by nucleophilic attack of the activat- ed species. One example of rationally designed acid–base cata- lysts is amine-functionalized mesoporous Ti(Al)-SBA-15. [3] Rat- nasamy and co-workers reported a “volcanic plot” of the reac- tion rate as a function of amine basicity, in which secondary amines showed the optimum reactivity. They suggested that CO 2 is too-weakly activated on primary amines, whereas it is too-strongly adsorbed onto tertiary amines. Hence, moderate CO 2 -adsorption onto amine-functionalized solid acids appears to provide good candidates as catalyst for this reaction. It is generally acknowledged that metal–organic frameworks (MOFs) are appropriate materials for designing single-site acid– base catalysts. [4–6] In a spectroscopic study on MOFs, Gascon et al. showed the functionalization of MOF-5 by an amino sub- stituent (2-amino-1,4-benzenedicarboxylate), also known as IRMOF-3. The amine group acted as an electron donor (Lewis base) on CO 2 . [7] This “amino effect” on CO 2 -adsorption has been experimentally observed on various MOFs and was later confirmed by ab initio calculations. [8–11] The concept of concert- ed reactions on acid–base MOFs has been reported by Baiker and co-workers in the synthesis of propylene carbonate with amine-containing mixed-linker MIL-53 (co-catalyzed by tetraal- kylammonium halides). [12] A turnover frequency (TOF) of 400 h À1 was measured under solvent-free conditions. Another significant example is the activity of amine-functionalized UiO- 66 in the cross-aldol reaction reported by De Vos and co-workers. [13] Hence, we anticipated that the use of MOFs that contain acid–base pairs, such as a Brønsted acid MOF that is function- alized with NH 2 , could lead to potential catalyst candidates for the synthesis of carbonate from CO 2 . Herein, we elucidate the role of the NH 2 -functionalization of MIL-68(In)-NH 2 [14] as a catalyst for the synthesis of styrene car- bonate from styrene oxide and CO 2 . Surprisingly, we show by using ab initio calculations and spectroscopic investigations that the modification of the electronic structure of the inor- ganic component by ligand-substitution has a much-larger impact on the activation of CO 2 than the amine substituents. MIL-68(In) and MIL-68(In)-NH 2 were prepared by precipita- tion reactions of indium nitrate and terephthalic acid or amino- terephthalic acid in DMF. [15] X-ray diffraction, surface areas, DRIFT analysis, and the 1 H NMR spectra were in agreement with previous reports (see the Supporting Information). These results confirmed that the MOFs were empty of any organic solvent or occluded reactants. MIL-68(In) and MIL-68(In)-NH 2 were tested in the synthesis of carbonate (Scheme 1). This evaluation was performed in a glass vial at 150 8C under CO 2 pressure (8 bar). The results are reported in Table 1 and compared with blank experiments that were conducted without the catalyst and tet- ramethylammonium bromide, which is a known active- and se- lective homogeneous catalyst. [16] The conversion of styrene oxide was clearly enhanced by NH 2 -functionalisation: It in- [a] T. Lescouet, Dr. D. Farrusseng University of Lyon Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON) UMR 5256 CNRS, 2 Av. Albert Einstein 69626 Villeurbanne (France) Fax: (+ 33)(0)4 72 33 53 99 E-mail : david.farrusseng@ircelyon.univ-lyon1.fr [b] Dr. C. Chizallet IFP Energies nouvelles Rond-point de l’Øchangeur de Solaize, BP3 69360 Solaize (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200288. Scheme 1. Synthesis of styrene carbonate from styrene oxide. Table 1. Catalytic activity. Catalyst Conversion of styrene oxide [b] [%] TOF [b] [h À1 ] blank 8 – tetramethylammonium bromide 87 0.782 MIL-68 (In) [a] 42 0.544 MIL-68 (In) [a] 36 0.466 MIL-68(In)-NH 2 [a] 74 1.059 MIL-68(In)-NH 2 [a] 68 0.973 MIL-68(In)-NH 2 [a] 70 1.002 MIL-68(In)-NH 2 (recycled) 53 0.758 [a] Independent catalytic tests; [b] conversion and TOF calculated after 8 h. ChemCatChem 0000, 00, 1 – 4  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim &1& These are not the final page numbers! ÞÞ