Functionalisation of the MOF-808 framework as a versatile catalyst for fine chemicals synthesis (thesis data)

MOFs, particularly MOF-808 are potentially greener and more sustainable catalysts for synthetically useful reactions due to their chemical versatility. MOF-808 can be tuned into a bifunctional catalyst due to the ease with which its formate ligands can be exchanged with functionalised ones. With this in view, two MOF-808 materials were synthesised, in Zr and Hf forms: MOF-808(Zr/Hf) and MOF-808(Zr/Hf)-XL. MOF-808(Hf/Zr) has the ideal framework, while MOF-808(Zr/Hf)-XL is synthesised with a stoichiometric excess of benzenetricarboxylate linker, BTC. The MOFs were post-synthetically modified with three sulfonated ligands, 3-{(4-methoxyphenyl)thio}propane-1-sulfonate, 3-(di-tert-butylphosphino)propane-1-sulfonate and 2-(4-pyridyl)ethanesulfonate. After installing these ligands, they were metalated with Pd (II) or Ir(III) complexes.
Pd-MOF catalysts were successfully used to isomerise terminal alkenes. They were also tested in Suzuki-Miyaura coupling reactions where aryl bromides were coupled with different boronic acids or esters. Coupling of aryl chlorides with boronic acids using thioether-based MPTPS-MOF-808-Pd catalysts gave no conversion of the desired products. However, phosphine-based DTBPPS-MOF-808 catalysts gave products highlighting the need of a bulky, more electron donating ligand for this reaction. Testing Hf and Zr MOFs in the coupling of more challenging substrates resulted in low yields of the products when DTBPPS-MOF-808(Zr)-Pd was used. However, using DTBPPS-MOF-808(Hf)-Pd improved yields significantly.
MOF-808(Hf) was tested in borrowing hydrogen amine synthesis of N-alkylating anilines with secondary alcohols. In coupling 4-chloroaniline with a challenging alcohol, 1-(4-fluorophenyl)ethanol using both MOF-808(Hf) and MOF-808(Hf)-XL, MOF-808(Hf)-XL gives better selectivity and PESA was selected for the scope of the reaction, such that PESA-MOF-808(Hf)-XL-Ir was the catalyst of choice for alcohols with electron neutral to electron withdrawing groups. EXAFS indicates that the Ir remains in dispersed, rather than nanoparticle form. Reaction of electron-rich alcohols with anilines gave CC coupled products as the main or only product when catalysed by PESA-MOF-808(Hf)-XL-Ir. Remarkably, MOF-808(Hf) and especially PESA-MOF-808(Hf)-Ir gave good yields of N-alkylated products via borrowing hydrogen.