New progress has been made in the study of regional selective hydroamine methylation reactions

Organic amines are an important class of chemical intermediates, widely used in the synthesis of pesticide medicine, biologically active natural products and functional material monomers and other chemicals. Hydroamine methylation of olefins is an important tandem carbonylation reaction that can directly synthesize organic amines in a pot with 100% atomic economy. However, in the current hydroamine methylation reaction, there are expensive rhodium and ruthenium metals in the homogeneous catalytic system that are difficult to reuse, the reaction efficiency of the duplex catalytic process is low, and the regional selective hydrogenamine methylation of heterophase catalysis is rarely reported. Therefore, there is an urgent need to design efficient multiphase catalysts for hydroamine methylation reactions to obtain excellent yield, selectivity and reusability.

The Research Group of State Key Laboratory of Homocyclic Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, has long been committed to the study of heterogeneous carbonylation reactions (Green Chem., 2018, 20, 3457; Chin. J. Chem., 2019, 37, 139; Green Chem., 2019, 21, 4040; Adv. Synth. Catal., 2020, 362, 2348;J. Catal., 2021, 401, 321)。

Recently, based on the concept of homogeneous heterogeneous fusion catalysis, the research group created a new polymer catalyst for in situ encapsulating single-atom rhodium, Rh@CPOL-DPMphos&p-3vPPh3, using DPMphos and p-3vPPh3 as copolymers, and applied it to the polyphasic hydroamine methylation reaction of olefins for the first time, and obtained the corresponding product amines with good to excellent yield and straight-chain selectivity. The limiting effect of the multistage pores in the polymer catalyst and the coordination effect of the bisphosphine ligand DPMphos synergistically promoted the improvement of hydroamine methylation activity and regional selectivity, and no loss of rhodium was detected during the recycling of the polymer catalyst.

Figure I. Biphosphine copolymer encapsulated single-atom Rh catalysts in situ for polyphase hydroamine methylation reactions

Solid-state 13C and 31P MAS NMR indicate that p-3vPPh3 and DPMphos successfully polymerized to prepare the catalyst of interest. The N2 suction and desorption curve indicates that the polymer catalyst has a large specific surface area and a multi-stage pore structure. The TGA curve indicates that the polymer catalyst has good thermal stability.

Figure II. Rh@CPOL-DPMphos&p-3vPPh3 catalysts for 13C MAS NMR(a), 31P MAS NMR(b), N2 aspiration desorption (c), TGA(d) characterization

HR-TEM and Abreaction-corrected HAADF-STEM characterization showed that in fresh and reused polymer catalysts, the active species Rh was encapsulated in a single-atom form in a biphosphine copolymer, demonstrating that the polymer catalysts had good thermal stability and reusability.

Figure III. HR-TEM and Abreaction-corrected-HAADF-STEM characterization of fresh (a and b) and post-reuse (c and d) Rh@CPOL-DPMphos&p-3vPPh3 catalysts

The above research provides ideas for the design of highly selective heterogeneous catalysts and promotes the development of the concept of homogeneous multiphase fusion catalysis.

The relevant research results are published onlineChemical Communications(DOI: 10.1039/d2cc02469a)Above. Dr. Kang Zhao is the first author of the paper, and Researcher Cui Xinjiang and Researcher Shi Feng are co-corresponding authors.

The above work has been supported by the National Natural Science Foundation of China and the Natural Science Foundation of Gansu Province. (Source: Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences)

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