Coordinatively Unsaturated Hf-MOF-808 Prepared via Hydrothermal Synthesis as a Bifunctional Catalyst for the Tandem N-Alkylation of Amines with Benzyl Alcohol

Abstract

The modulated hydrothermal (MHT) synthesis of an active and selective Hf-MOF-808 material for the N -alkylation reaction of aniline with benzyl alcohol under base-free mild reaction conditions is reported. Through kinetic experiments and isotopically labeled NMR spectroscopy studies, we have demonstrated that the reaction mechanism occurs via borrowing hydrogen (BH) pathway, in which the alcohol dehydrogenation is the limiting step. The high concentration of defective −OH groups generated on the metallic nodes through MHT synthesis enhances the alcohol activation, while the unsaturated Hf 4+ , which acts as a Lewis acid site, is able to borrow the hydrogen from the methylene position of benzyl alcohol. This fact makes this material at least 14 times more active for the N -alkylation reaction than the material obtained via solvothermal synthesis. The methodology described in this work could be applied to a wide range of aniline and benzyl alcohol derivates, showing in all cases high selectivity toward the corresponding N -benzylaniline product. Finally, Hf-MOF-808, which acts as a true heterogeneous catalyst, can be reused in at least four consecutive runs without any activity loss.

Quantification of Linker Defects in UiO-Type Metal–Organic Frameworks

“…After 15 min on a shaker, the sample was centrifuged and transferred to a sample holder. Other methods for digestion of Zr-based MOFs may also be applied (see refs − and refs therein).…”

Carbon-efficient conversion of natural gas and natural-gas condensates to chemical products and intermediate feedstocks via catalytic metal–organic framework (MOF) chemistry

“…Nevertheless, the interaction of alcohols with Brønsted acids, the formation of adsorbed/grafted alkoxides, catalytic dehydration of methanol to DME, ethanol to diethylether and ethylene, and t -butanol to isobutene have been studied in some detail. 124,125 These studies, chiefly by Gates and co-workers, 126 have been with MOFs that present well-defined Al( iii )- or Zr( iv )-oxy, hydroxy species (rods (Al) or clusters (Zr)) as nodes, 126–129 e.g. MIL-53(Al) (Al.KKEYFWRCBNTPAC.MOFkey-v1.rna), 130 MIL-68(Al), 131 UiO-66 (Zr.KKEYFWRCBNTPAC.MOFkey-v1.fcu), 30 hcp-UiO-66, 132 NU-1000, 24 Al-AIM-NU-1000, 133 and MOF-808 (Zr.QMKYBPDZANOJGF.MOFkey-v1.spn); 25 see Fig.…”

Polymer–metal–organic framework self-assembly (PMOFSA) as a robust one-step method to generate well-dispersed hybrid nanoparticles in water

“…Such solids are currently among the most studied MOF systems due to their versatility and good stability and have demonstrated their interest in catalytic and biomedical applications, among others. [31][32][33] Zr trimesate MOF-808 is a representative Zr-MOF due to its large 3D porosity and acidic metal sites. It can be noted that some of us recently succeeded in the production of well-defined monodispersed MOF-808 in aqueous solutionbased solvents.…”