Synthesis

As mentioned at the beginning of the Catalytic Strategy section, the first step of this work is to obtain MOFs with –OH groups. While the mimetic approach consists in reproducing already-known materials, the second method, which consists in creating defects, can be employed by testing the different synthesis routes. Indeed, it is known that the purity of the crystal depends on the reaction kinetics. If the kinetics is increased, the number of crystal defects is increased as well. With this in mind, different synthesis routes were tested.

x Solvothermal Synthesis (IRMOF-1 solvo)

Here the synthesis is performed according to the process reported by Sabo et al. ¹²⁸. DEF is used as solvent. In view of obtaining a product of high purity, the metallic nitrate precursor is tetrahydrated and there is no base. The synthesis is carried out in a Teflon-lined stainless-steel autoclave at 373 K for 20 h. The solid is filtered off, washed and finally exchanged with CHCl3. Finally, the material is evacuated and handled in a glove box for transfer into a Schlenk-type vessel.

x Slow Precipitation Synthesis (IRMOF-1 basf)

The preparation of this IRMOF-1 follows the procedure reported by Mueller et al. ⁵⁶. DMF is used as solvent. Here the reaction is carried out in a glass reactor equipped with a reflux condenser and a Teflon-lined stirrer. After 7 h of stirring at 403 K, the solid is filtered off, washed three times with DMF and dried at 403 K under

vacuum for 3 h. Here the precursor is Zn(NO3)2.6H2O and the reaction takes place without a base.

x Fast Precipitation Synthesis (IRMOF-1 pre)

IRMOFs can also be obtained by the precipitation procedure designed by Huang et al. ⁴⁸. Here the reaction takes place instantaneously at room temperature after the dropwise addition of Et3N. After 90 min. of stirring, the powder is filtered and washed three times with DMF and heated at 403 K overnight under dry air flow. This procedure is extended to the synthesis of the isoreticular compounds IRMOF-3, Zn- MOF-8 and Zn-MOF-10 by using 2-aminoterephthalic acid, naphthalene-2,6- dicarboxylic acid and biphenyl-4,4’-dicarboxylic acid, respectively ¹²⁶.

This procedure is also used for the creation of defects by uncoordinated ligands. The precipitation takes place in a mixture of o-toluic acid and benzenedicarboxylic acid (bdc). Three samples are prepared with toluic acid : bdc ratios equal to 2.5, 5, and 10 wt.% in order to yield ZnIRMOF-1 (2.5), ZnIRMOF-1 (5) and ZnIRMOF-1 (10), respectively.

x Synthesis of MOF-69 Family

MOF-69s are the hydrated forms of IRMOF structures. They are obtained by the protocol reported by Loiseau et al. ⁵⁰. The difference between an IRMOF and an MOF-69 comes from the addition of deionized water during the reaction. In this case, the structure of MOF-69c is Zn3(OH)2(bdc)2•2DEF. This experimental procedure is extended to the synthesis of MOF-69a and b with biphenyl-4,4’-dicarboxylic acid and naphthalene-2,6-dicarboxylic acid, respectively.

x Reference Materials and Catalysts

MIL-53(Al) was purchased from Aldrich (Basolite A100). The acid forms of beta (H-BEA, Si/Al=13.75) and mordenite (H-MOR, Si/Al=10) zeolites are obtained from the commercial Na forms (Fluka) by ammonium exchange followed by calcination treatment. The ion exchange is carried out with a 10 wt.% solution of

during 3 h. This procedure is repeated twice. Both AlCl3 (Aldrich 99.9 %), and ZnCl2

(Alfa Aesar, anhydrous, 98+ %) are used as received, as reference Lewis acids.

Table 8: Summary of MOF samples synthesized and used as catalysts in this study.

Sample Name Basic

Structure Linker Synthesis Method Reference

IRMOF-1 solvo IRMOF-1 H2bdc Solvothermal ¹²⁸

IRMOF-1 basf IRMOF-1 H2bdc Basf procedure ⁵⁶

IRMOF-1 pre IRMOF-1 H2bdc Fast precipitation ⁴⁸

ZnIRMOF-1

(2.5) IRMOF-1 H2dbc + 2-methyl toluic acid (2.5%) Fast precipitation this study ZnIRMOF-1 (5) IRMOF-1 H2dbc + 2-methyl toluic acid (5%) Fast precipitation this study ZnIRMOF-1 (10) IRMOF-1 H2dbc + 2-methyl toluic acid (10%) Fast precipitation this study MOF-69A MOF-69 biphenyl-4,4’-dicarboxylic acid Solvothermal this study MOF-69B MOF-69 naphthalene-2,6-dicarboxylic acid Solvothermal this study

MOF-69C MOF-69 H2bdc Solvothermal ⁵⁰

IRMOF-3 pre IRMOF-3 2-aminoterephthahlic acid Fast precipitation this study Zn-MOF-8 MOF-69 naphthalene-2,6-dicarboxylic acid Fast precipitation this study Zn-MOF-10 MOF-69 biphenyl-4,4’-dicarboxylic acid Fast precipitation this study

x Alkylation

The alkylation reactions take place in an autoclave with autogenous pressure.

They are carried out in n-decane with an aromatic : t-BuCl molar ratio of 2:1. The catalytic sample (30 mg) is activated at 403 K under vacuum. After 2 h, the solid is recovered by filtration at room temperature. The reaction mixtures are analyzed by gas chromatography with an HP 6890N equipped with an HP-5 capillary column (30 m length). The toluene conversion is calculated by taking into account the initial concentration (100% excess). Identification of the different isomer configurations is performed by GC-MS (HP 6890 equipped with HP-5/HP-1 capillary columns, an HP 5973 quadrupole detector - ionic impact at 70 eV, and NIST02 library).

Figure 56: Example of alkylation reaction and different products obtained at 100°C after two hours with their kinetic diameters [Å].

Two experiments are necessary to confirm that the reactions take place heterogeneously with no leaching. First of all, the reaction is carried out at room temperature. Then, fresh reactants are added to the liquids recovered from the reaction mixture and a new reaction run is performed.