Professor Jin Liqun and Professor Hu Xinquan of Zhejiang University of technology research team: Study on the cobalt catalyzed hydrosilylation of martensite promoted by rigid pyridine-cycloalkylimine ligands

Introduction alkenylsilane is an important organic synthetic block with good stability, low toxicity and easy preparation Among many preparation methods, transition metal catalyzed hydrosilylation of alkynes is the most direct and the most efficient one In the hydrosilylation of terminal alkynes, how to control the chemical selectivity of the reaction has always been a difficulty, because the silicon reagent can be added with alkynes to form the corresponding α - alkenylsilane, β - (E) alkenylsilane and β - (z) alkenylsilane However, there are only a few reports about the hydrosilylation of alkynes and phenylsilanes catalyzed by cobalt, and there are few examples of using bidentate nitrogen ligands in such reactions Therefore, based on the rigid pyridylcycloalkylimine ligands developed by his research group, the author has carried out the study of cobalt catalyzed hydrosilylation and made a new breakthrough, with the reaction of ton as high as 4950 Recently, Professor Jin Liqun and Professor Hu Xinquan of Zhejiang University of technology published the research results in org Lett (DOI: 10.1021/acs.orglett 9b02244) Hu Xinquan's research team has been working on the development of new ligands and transition metal complexes for homogeneous catalysis A series of bidentate and tridentate nitrogen ligands were developed on the basis of pyridylcycloalkylimine framework It was found that these ligands have the advantages of stabilizing catalyst and improving reaction selectivity in ethylene polymerization system At present, this ligand has been successfully used in PD catalyzed coupling reaction and reduction Heck reaction to construct C-C bond with high efficiency and selectivity Recently, the team has also made some progress in hydrogen transfer reactions catalyzed by cheap metals See adv synth Catalyst 2016, 358, 2642; chem Commun 2017, 53, 4124; Beilstein J org Chem 2017, 13, 213; chem Commun 2018, 54, 5752; org Chem Front 2018, 5, 2484; adv synth Catalyst 2018, 360, 3038; org Lett 2019 doi: 10.1021/acs.orglett.9b0224 Brief introduction to Professor Jin Liqun, distinguished professor of "Qianjiang scholar" in Zhejiang Province, Professor of Zhejiang University of technology, doctoral supervisor He graduated from Wuhan University in 2007 with a bachelor's degree, and obtained a doctor's degree from Wuhan University in 2012 After two years of postdoctoral research at the University of California, San Diego, the United States, he joined the school of chemical engineering of Zhejiang University of technology in 2015 The main research direction is the development of new efficient transition metal complexes and their application in homogeneous catalytic reactions At present, he has published more than 20 high-level academic papers as the first author and corresponding author, including SCI Adv., J am Chem SOC., angelw Chem Int ed and chem SCI., etc.; participated in the compilation of one monograph; twice obtained reaxy PhD prize Research achievements: alkenylsilane is an important organic synthetic block because of its good stability, low toxicity and easy preparation Among many preparation methods, transition metal catalyzed hydrosilylation of alkynes is the most direct and the most efficient one In hydrosilylation of terminal alkynes, how to control the selectivity of α -, β - (E) and β - (z) addition has always been a difficulty In recent years, Deng Liang, Thomas, Lu Zhan, Huang Zheng, Ge, wangelin and Yang Yong and other domestic and foreign research groups have successfully controlled the selectivity of the reaction by using different ligands However, there are only a few reported examples about the selectivity of addition of terminal alkyne to phenylsilane (Fig 1) Fig 1 hydrosilylation of terminal alkyne (source: org Lett.) the author first used phenylacetylene and phenylsilane as raw materials, CO (OAC) 2 as catalyst precursor, and reacted in THF With L3 as ligand, the target product can be selectively obtained with α / β (E) = 90 / 10 Since then, the author has investigated the pyrimidine ligands with different substituents, mainly from the perspective of steric hindrance Finally, when L5 is used as the ligand, the selectivity reaches 95 / 5 Then, the optimal ligands were used to expand the substrate The alkyne can obtain high yield and selectivity, and the halogen-containing substrate has no side reactions such as dehalogenation Sensitive sensory groups such as hydroxyl, amino, cyano, carbonyl, aldehyde and ester groups can also be well compatible For heterocyclic, endoalkyne and alkyl, alkyne type substrates, the yield and selectivity are moderate to excellent (Fig 2) Fig previous reports on the development of diyne substrate (source: org Lett.) show that different silanes have a great influence on the reaction in hydrosilylation Two different silicon reagents, phenylsilane and diphenylsilane, are usually studied in different systems Interestingly, the same ligand L5 was used to try the reaction of diphenylsilane as hydrosilylation reagent It was found that the reaction can also proceed smoothly after increasing the catalytic amount and temperature, and the conversion and selectivity are generally excellent (Fig 3) Fig 3 diphenylsilane is the substrate of hydrosilylation reagent (source: org Lett.) later, the author studied the practicability of the reaction and found that the yield and selectivity of the reaction can also be well maintained in the amplification experiment What's more interesting is that alkenylsilane product 2A can also be used as a good hydrosilylation reagent to react with phenylacetylene in the same system This method is expected to be used in the construction of chiral silicon compounds After adjusting the ratio of substrate, the system can be used to synthesize trisubstituted dienyl silane in one pot In the experiment of reducing the amount of catalyst, even if the amount of catalyst is reduced to 0.02 mol%, the reaction can be carried out well, and the selectivity of the reaction is also maintained The ton is as high as 4950, which is the highest so far in the cobalt catalyzed hydrosilyne end reaction (Figure 4) Fig 4 practical study (source: org Lett.) in order to explore the coordination of ligands and cobalt, the author used 1.2 equivalent ligands to react with cobalt acetate, and obtained the single crystal culture of the complex The crystal structure of the complex was determined as three metal nuclei by XRD: the linear trinuclear structure with one molecule of cobalt acetate as the overseas Chinese Association when the two molecules of cobalt acetate matched with the ligand 1:1 The complex can be used as catalyst for hydrosilylation, which shows that it has catalytic activity In order to prove whether the trinuclear cobalt complex is really the catalyst or catalyst precursor of the reaction, the author has carried out a kinetic study The results show that the catalyst activity of in situ synthesis is significantly higher than that of CO1, in other words, CO1 is not the active species in the reaction Interestingly, the addition of ligands in CO1 system to m: l = 1:1.2, the reaction rate is in good agreement with that of in situ system This shows that cobalt complexes are dissociated in the system Later, the author tried to adjust the ratio of cobalt acetate to ligand to obtain other crystal structures Unfortunately, no crystal structure other than trinuclear cobalt has been obtained (Fig 5) Fig 5 crystal structure and reaction kinetics of Trinuclear cobalt (source: org Lett.) in a word, the author reported a case of hydrosilylation of alkynes catalyzed by cobalt promoted by pyrimidine bidentate nitrogen ligands, resulting in a very high product of alkenylsilane with Markovian addition The system has a wide range of substrate applicability, with ton up to 4950 And through the study of reaction kinetics, the author has carried on some explorations to the mechanism This achievement was recently published in organic letters (DOI: 10.1021 / ACS Orglett 9b0254) The authors of this paper are: Zong Zhijian, Yu Qianwen, Sun Nan, Hu Baoxiang, Shen Zhenlu, Hu Xinquan and Jin Liqun The above research work was supported by the National Natural Science Foundation of China (21773210, 21603190 and 21776260) and the basic scientific research business expense project of Zhejiang University (rf-b2019005) Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism 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