Multistep Engineering of Synergistic Catalysts in a Metal–Organic Framework for Tandem C–O Bond Cleavage

Abstract

Cleavage of strong C−O bonds without breaking C−C/C−H bonds is a key step for catalytic conversion of renewable biomass to hydrocarbon feedstocks. Herein we report multistep sequential engineering of orthogonal Lewis acid and palladium nanoparticle (NP) catalysts in a metal−organic framework (MOF) built from (Al−OH) n secondary building units and a mixture of 2,2′-bipyridine-5,5′dicarboxylate (dcbpy) and 1,4-benzenediacrylate (pdac) ligands (1) for tandem C−O bond cleavage. Ozonolysis of 1 selectively removed pdac ligands to generate Al 2 (OH)(OH 2 ) sites, which were subsequently triflated with trimethylsilyl triflate to afford strongly Lewis acidic sites for dehydroalkoxylation. Coordination of Pd(MeCN) 2 Cl 2 to dcbpy ligands followed by in situ reduction produced orthogonal Pd NP sites in 1-OTf-Pd NP as the hydrogenation catalyst. The selective and precise transformation of 1 into 1-OTf-Pd NP was characterized step by step using powder Xray diffraction, transmission electron microscopy, thermogravimetric analysis, inductively coupled plasma mass spectrometry, infrared spectroscopy, and X-ray absorption spectroscopy. The hierarchical incorporation of orthogonal Lewis acid and Pd NP active sites endowed 1-OTf-Pd NP with outstanding catalytic performance in apparent hydrogenolysis of etheric, alcoholic, and esteric C−O bonds to generate saturated alkanes via a tandem dehydroalkoxylation−hydrogenation process under relatively mild conditions. The reactivity of C−O bonds followed the trend of tertiary carbon > secondary carbon > primary carbon. Control experiments demonstrated the heterogeneous nature and recyclability of 1-OTf-Pd NP and its superior catalytic activity over the homogeneous counterparts. Sequential engineering of multiple catalytic sites in MOFs thus presents a unique opportunity to address outstanding challenges in sustainable catalysis.

Advances in Versatile Nanoscale Catalyst for the Reductive Catalytic Fractionation of Lignin

“…[142a,145] For example, the hierarchical incorporation of Pd NPs and orthogonal Lewis acid on a mixed ligand MOF favoured 1-OTfÀ Pd NP (Figure 11b) with excellent hydrogenolysis activity towards alcoholic, etheric, and esteric CÀ O bonds. [145] Pd NPs, also stabilized by a decorated CeÀ MOF, were two-fold higher activity than that of Pd NPs decorated CeO 2 , selective hydrogenolysis of aryl ethers under mild temperature and pressure conditions. [146] MOF-supported single-site catalysts are also a type of potential lignin hydrogenolysis catalysts.…”

“…b) Lewis acid and Pd NP sites in 1-OTfÀ Pd NP . [145] Reused with permission. Copyright 2020, American Chemical Society.…”

“…Copyright 2012, American Association for the Advancement of Science. b) Lewis acid and Pd NP sites in 1-OTfÀ Pd NP [145]. Reused with permission.…”

Metal–Organic Framework-Based Solid Acid Materials for Biomass Upgrade

“…The sacrificial linker is another effective tool to produce defective sites in MOFs. For instance, ozone can selectively break the C=C bond of ozone-active ligands (e.g., 4,4′-stilbene-dicarboxylic acid (H 2 STI) or 1,4-phenylenediacrylic acid (H 2 PDAC)) among MOFs, resulting in the formation of linker-cleaved defects [56]. As an example, H 2 STI and 4,4′-azobenzene-dicarboxylic acid (H 2 AZO, an inert ligand toward ozone) were adopted as mixed linkers to build a multivariate MOF featured with the classical Zr 6 cluster.…”

Palladium and Copper: Advantageous Nanocatalysts for Multi-Step Transformations

“…PdNPs were prepared by reduction of palladium hexafluoroacetylacetonate (Pd(hfac) 2 ) with formaldehyde, giving small nanoparticles (1.1-2.9 nm) that were deposited on alumina via atomic layer deposition [101]. The catalytic reaction in ionic liquid ( (20 bar) [102]. The as-prepared material was highly active for tandem dehydroalkoxylationhydrogenation of ethers, alcohols and esters to form saturated alkanes under smooth conditions by C-O bond cleavage (10 examples, 61-99% yields).…”