Group of Conghuan, Institute of physics and chemistry, Chinese Academy of Sciences: the application of phosphine ligands derived from the framework of anthracene photodimers in palladium catalyzed coupling reaction

Lead design of new ligands is an enduring research topic in the development of transition metal catalytic reactions, because ligands can adjust the properties of metal centers, so that the catalyst has high selectivity and wide range of substrate applications Although there is a long history of research on the photodegradation of anthracene [4 + 4], the synthesis and application of anthracene [4 + 4] are still lacking The unique structure of anthracene [4 + 4] photodegradation for the design of new ligands has not been reported Recently, the research group of Conghuan, Institute of physics and chemistry, Chinese Academy of Sciences, has made new progress in the design of novel phosphine ligands for palladium catalyzed coupling reactions (org Lett 2019, DOI: 10.1021/acs.orglett.9b02414), based on the previous research on the synthesis of conjugated macrocycles using anthracene [4 + 4] photodimers (j.am Chem SOC 2016, 138, 11144; angelw Chem Int ed 2019, 58, 3943) ）。
About researcher Cong Huan, project portfolio: Cong Huan, graduated from Peking University in 2006 (Tutor: academician Xi Zhenfeng), obtained a doctor's degree from Boston University in 2011 (Tutor: Professor John A Porco), and engaged in postdoctoral research at MIT and Caltech from 2011 to 2015 (Tutor: Gregory C Fu Professor), in 2015, he was selected into the 11th batch of "youth thousand talents plan" of the Organization Department of the CPC Central Committee and incorporated into the Institute of physical and chemical technology of the Chinese Academy of Sciences to carry out independent research The research direction is photochemical synthesis of functional organic molecules, which has won academic honors such as "thiemechemistry journals Award" (2017) of Germany and "excellent youth fund" (2019) of Foundation Committee Leading scientific research achievements: the mono phosphine ligands derived from anthracene photo dimer are applied to palladium catalyzed coupling reactions Among the published ligands, the mono phosphine ligands are particularly effective for palladium catalyzed coupling reactions, which are characterized by the need for substituents with larger steric hindrance on the phosphorus atom, so as to improve the stability of the catalyst and promote the reduction elimination step of the catalytic cycle Using the rigid framework of anthracene [4 + 4] photo dimer, the author designed a new type of phosphine ligand containing anthracene photo dimer, and the synthesis process was simple A kind of air stable phosphine ligand dianthphos was synthesized from commercial raw materials through two steps (Figure 1) Fig 1 The preparation process of partial monophosphonic ligands and monophosphonic ligands dianthphos (source: org Lett.) the author selected 1-benzyl-pyrazole, 4-bromoquinoline and 5-bromo-2-aminopyrimidine, which represent different heterocyclic structures and electronic densities, as substrates for miyoura Boration reaction to evaluate the practicability of ligands (Fig 2) The results showed that the complexation of dianthphos with pdg4 dimer could effectively promote the boration of three substrates under the condition of low catalyst loading (0.5 mol% PD) It is worth noting that compared with the published ligands containing more alkyl substituents with higher electronic and steric hindrance, dianthphos has a better catalytic effect These results show the effectiveness of the design of the unique rigid anthracene photodimer ligands Fig 2 Optimization reaction by ligand evaluation (source: org Lett.) in order to clearly characterize PD precatalyst containing ligand dianthphos, the author uses the single crystal obtained for X-ray crystallography analysis (Fig 3) It is observed that the center of PD (II) is a slightly distorted plane quadrilateral, and the phosphorus atom combines with palladium atom, forming a trans structure with palladium atom and nitrogen atom The conformation of dianthphos is that its two phenyl substituents are far away from the large framework of anthracene photodimer Fig 3 The X-ray crystal structure (ortep) (source: org Lett.) of the pre catalyst dianthphos-pd G4 Through the expansion of the substrate (Fig 4), the author found that a variety of common heterocycles can produce the target boration products with high yield, which shows that the reaction has excellent heterocycle substrate compatibility Figure 4 Substrate expansion (source: org Lett.) later, the author synthesized the key intermediates of pharmacological active molecules and found that the boration products can be obtained in high yield under standard conditions (Figure 5) Fig 5 Further studies on the synthesis and application of pharmacologically active molecules (source: org Lett.) have found that dianthphos can not only catalyze the miyaara boration reaction of heterocyclic substrates, but also carry out palladium catalyzed Suzuki miyaara coupling, Negishi coupling and carbonyl α coupling reaction after slightly modifying the standard conditions (solvent or base) (Fig 6) Fig 6 The application of dianthphos in palladium catalyzed coupling reaction (source: org Lett.) a one pot miyaara boration / Suzuki coupling method (Fig 7), which can realize carbon carbon bond coupling between different heteroaromatic ring substrates by using PD dianthphos catalytic system, further proves the practicability of the monophosphonic ligand dianthphos Figure 7 Application of dianthphos in a pot of miyaara boration / Suzuki coupling reaction (source: org Lett) The research results were recently published in organic letters (DOI: 10.1021 / ACS Org lett 9b02414) Wang Xin, Ph.D student of Institute of physics and chemistry, and Liu Weigang, postdoctoral student, were the co first authors of this paper The research work was supported by the Chinese Academy of Sciences, the national key R & D plan, the National Natural Science Foundation and the director's fund of the Institute of physics and chemistry 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