Expedient synthesis of E -hydrazone esters and 1 H -indazole scaffolds through heterogeneous single-atom platinum catalysis

Abstract

A heterogeneous Pt single-atom catalyst promotes E-selective synthesis of hydrazones en route to bioactive 1H-indazoles.

Insights into the Mechanism of n-Hexane Reforming over a Single-Site Platinum Catalyst

“…[9][10] However, typically in most application of SSCs, the scientists always focused on some small molecule reactant due to the lack of an ensemble of active metal atoms adjacent to the noble metal single atom. [11][12] Hence, investigating the reaction mechanism of a large probe molecule on SSCs and designing a novel catalytic material are the goal of our studies to accelerate the development of next generation SSCs. [4][5][6][7][8][9] Catalytic reforming of linear hydrocarbons is one of the petroleum refining processes for upgrading light hydrocarbon feedstocks, [13] involving dehydrocyclization, isomerization, and dehydrogenation.…”

Reduction of the Diazo Functionality of α-Diazocarbonyl Compounds into a Methylene Group by NH3BH3 or NaBH4 Catalyzed by Au Nanoparticles

“…In case of using an excess of reducing agent, a side catalytic pathway operates that reduces the α-diazocarbonyl compounds into the corresponding hydrazones. This work exemplifies the unique catalytic behavior of Au nanoparticles relative to other supported metallic noble metals such as Pt [ 20 ], where the reductive pathway of the formation of hydrazones occurs exclusively.…”

“…As noted earlier in Scheme 3 , hydrazones are formed exclusively in the Pt 1 /CeO 2 -catalyzed reaction of α-diazocarbonyl compounds using three molar equivalents of ammonia borane in MeOH [ 20 ]. We emphasize that in case of using an excess of reducing agent in our Au/TiO 2 -catalyzed transformation, the corresponding hydrazones were seen as minor products.…”

“…For instance, in the reduction of substrate 1a , we observed the following. Using 0.5–0.6 molar equivalents of NaBH 4 (≈100% excess in terms of hydride equivalents), hydrazone 4a [ 20 ] was observed in 8% yield relative to product 3a . With 1.2 molar equivalents, 4a is formed in 25% relative yield and with three molar equivalents in 38% ( Scheme 4 ).…”

“…The catalyst can be recycled at the end of each reaction by simple filtration and then reused after being washed with dichloromethane and dried in the oven at 90 °C for 2 h. We were able to perform five consecutive catalytic runs with the same batch of catalyst without observing any obvious deterioration in terms of yields. We emphasize herein the unique nature of our catalytic system, as it known [20] that in the analogous treatment of α-diazocarbonyl compounds with three molar equivalents of NH3BH3 under single-atom platinum on ceria catalysis conditions (Pt1/CeO2), the corresponding hydrazones are formed instead, as seen in Scheme 3. The amounts of boron hydride reagents that are necessary to achieve a quantitative reduction indicate that one hydride equivalent from either NH 3 BH 3 or NaBH 4 is required; thus, the second hydrogen atom on the product arises from the protic solvent (methanol).…”