Abstract
Zn-containing metal-organic frameworks have been used for the first time as heterogeneous catalysts in the amination of C-Cl bonds. The use of extended bis(pyrazolate) linkers can generate highly porous architectures, which favor the diffusion of amines to the confined spaces with respect to other imidazolate frameworks with narrower pore windows. The N4Zn nodes of the Zn-reticular framework show comparable activity to state-of-the-art homogeneous Zn amination catalysts, avoiding the use of basic conditions, precious metals, or other additives. This is combined with long-term activity and stability upon several reaction cycles, without contamination of the reaction product.
Highlights
C-N couplings involving the addition of N-H groups to C-Cl bonds in N-heterocycles are important reaction steps during the assemble of high value-added molecules
It seems plausible that when using ZnBDP, the rapid diffusion and confinement of the amination substrates inside the large metal-organic frameworks (MOFs) pores favors the course of the reaction, without the diffusion limitations towards the inner active sites occurring in ZIF-8
The larger Zn-bis(pyrazolate) cavities favor the transport of the substrate molecules inside the ZnBDP pores, where they access the inner active sites, as shown by the calculated diffusivities of the substrates in both MOFs
Summary
C-N couplings involving the addition of N-H groups to C-Cl bonds in N-heterocycles are important reaction steps during the assemble of high value-added molecules. The yield of the 4-aminated pyridine product after 72h of reaction increases in the order: ZIF-8 (26%) < ZnBDP (51%) < Zn(NO3)[2] (82%), for the same catalyst mass (see Figure 2a).
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