Dendrimer-Stabilized Metal Nanoparticles as Efficient Catalysts for Reversible Dehydrogenation/Hydrogenation of N-Heterocycles

Abstract

Nanoparticles (Pd, Pt, Rh) stabilized by G4OH PAMAM dendrimers and supported in SBA-15 (MNPs/SBA-15 with M = Pd, Pt, Rh) were efficiently used as catalysts in the acceptorless dehydrogenation of tetrahydroquinoline/indoline derivatives in toluene (release of H) at 130 °C. These catalysts are air stable, very active, robust, and recyclable during the process. The reverse hydrogenation reaction of quinoline derivatives (H storage) was also optimized and successfully performed in the presence of the same catalysts in toluene at 60 °C under only 1 atm of hydrogen gas. Such catalysts may be essential for the adoption of organic hydrogen-storage materials as an alternative to petroleum-derived fuels. Hot filtration test confirmed that the reaction follows a heterogeneous pathway. Moreover, PdNPs/SBA-15 was an excellent catalyst for the direct arylation at the C-2 position (via C-H activation) of indole in water in the presense of a hypervalent iodine oxidant. Thus, a one-pot dehydrogenation/direct arylation cascade reaction between indoline and an arylated agent was efficaciously performed in water, demonstrating the potential of the system to catalyze tandem heterogeneous/homogeneous processes by choice of the appropriate oxidant/reductant.

Metal–Organic Frameworks for the Exploitation of Distance between Active Sites in Efficient Photocatalysis

“…The acceptorless dehydrogenation of N‐heterocycles is an important reaction in organic synthesis, which also has potential in the storage of hydrogen . This reaction is usually carried out under thermal conditions, and recently shown possible to be catalyzed under visible light . The mechanism study revealed the multistep nature of the dehydrogenation process (Supporting Information, Figures S91, S92), which is suitable for the systematic study of MOFs with variable distance profiles.…”

Nanocatalosomes as Plasmonic Bilayer Shells with Interlayer Catalytic Nanospaces for Solar‐Light‐Induced Reactions

“…Previously, the benchmark two‐step highly endothermic AD‐reactions of tetrahydroquinolines (THQs) have been carried out with metal‐based homogeneous catalysts which are rarely recyclable and usually air‐sensitive, with heterogeneous noble‐metal NP based catalysts under unavoidable harsh conditions (temperature >135 °C, reaction time >24 h) and requiring additional oxidizers, bases, and hydrogen‐acceptors and also with few photocatalysts which are complicated to synthesize, requiring high furnace temperatures (ca. 1250 °C) under toxic ammonia flow, have narrow light absorption profile and take long reaction times using high catalyst amounts . Impressively, Pt‐Au‐based NCat demonstrated very clean AD reaction (yield >99 %) within short reaction time (ca.…”

Iridium‐Catalyzed Hydrogenation and Dehydrogenation of N‐Heterocycles in Water under Mild Conditions

“…Liquid organic hydrogen carriers (LOHCs) have been indeed proposed asc onvenient ands afe solutions for hydrogen storage. [6] Only very few homogeneous catalytic systemsc an both hydrogenate/dehydrogenate Nheterocycles. Heterogeneousc atalytic systems can in general be recovered and reused, but they require rather high temperatures compared to homogeneous catalysts.…”

“…This result prompted us to investigate the catalytic performance of these complexes in the hydrogenation/dehydrogenation of N-heterocycles. 80 8Cw as selected as the temperature to further investigate the catalyst loading (Table 1, entries [6][7][8][9]. Several experimentalp arameters were screened and optimized.…”

“…The reverse reaction was possible under milder conditions (60 8C, 1bar H 2 ). [6] Only very few homogeneous catalytic systemsc an both hydrogenate/dehydrogenate Nheterocycles. The first example of homogeneous catalysts capable of carrying out both hydrogenation and dehydrogenation of N-heterocycles was reported by Yamaguchi etal.…”