Research group of Guan bingtao, Nankai University: new progress in catalytic application of alkali metal complexes

Transition metal catalysts, including rare earth and tetra group metal catalysts, are widely used in organic synthesis, fine chemical industry, polymerization and energy industry, and play an important role However, most of the transition metals are less in the earth's crust, and the catalysts are expensive They are easy to remain in the products and produce toxicity to organisms and the environment Therefore, more and more chemists pay attention to the transition metal or main group metal catalysts which are rich in the earth's crust and have little element toxicity Some alkali metal and alkaline earth metal complexes have the same electronic configuration and similar reactivity as rare earth and four group metals, and they have the advantages of rich reserves, low price and no element toxicity However, compared with the wide application of rare earth and tetra group metal complexes, the synthesis of alkali metal and alkali earth metal complexes is faced with the problems of poor stability of complexes, easy to occur ligand exchange, single type of ligands and so on Recently, guanbingtao Research Lab of metal organic chemistry of Nankai University has made important progress in the field of alkali metal and its complex catalytic reaction, realizing the addition reaction of alkylpyridine and diarylmethane to Styrene Catalyzed by complex salts of amino potassium and zinc potassium (angelw Chem Int ed 2018, 57, 1650-1653; angelw Chem Int ed doi: 10.1002/anie.201713165) Brief introduction of research group of researcher Guan bingtao the research group of researcher Guan bingtao was founded in October 2012 They hope to use the main group metal complexes to realize the transition metal catalysis function At the beginning of the establishment of the research group, they decided to start with alkali metal and alkaline earth metal elements, and determined the purpose of developing alkali metal and alkaline earth metal chemistry: referring to the reactivity of rare earth and four group metal complexes, based on the new structure design, synthesis and catalytic reaction of alkali metal and alkaline earth metal complexes At present, there are 5 doctoral students, 3 master students and 2 undergraduate students in the research group The research direction of the research group: (1) organic chemistry of alkali metals, alkaline earth metals and rare earth metals; (2) design and synthesis of organometallic complexes and their catalytic application in organic synthesis and polymerization; (3) catalytic functionalization of inert chemical bonds Brief introduction of researcher Guan bingtao, a distinguished researcher and doctoral supervisor of the State Key Laboratory of elemental organic chemistry, Nankai University In 2003, he graduated from Zhengzhou University with a bachelor's degree in Applied Chemistry; in 2004, he was admitted to the school of chemistry and molecular engineering of Peking University, where he was engaged in the functionalization of transition metal catalyzed inert C-O bond under the guidance of Professor Shi Zhangjie, and obtained a doctor's degree in Science in 2009; later, he joined the research group of Hou Zhaomin, researcher of RIKEN, engaged in rare earth metals In 2012, he joined the State Key Laboratory of elemental organic chemistry of Nankai University to carry out the research on the synthesis and catalytic application of alkali metal, alkaline earth metal and rare earth metal complexes In 2012, it was selected into Tianjin Youth thousand talents project, and in 2014, it was selected into the "youth top talents" project of the central organization department Research achievements: the addition reaction of C-H bond of alkylpyridylbenzyl C-H bond to Styrene Catalyzed by amino potassium is a kind of direct, efficient and high atom economic reaction Because of its reliability, high efficiency and ideal atom economy, Br? Nsted base catalyzed carbon carbon bond formation reactions, such as aldol condensation, Mannich and Michael addition reactions, have been widely used in organic synthesis However, the substrates for these reactions are limited to compounds containing relatively acidic hydrogen atoms (PKA = 18 – 25), such as aldehydes, ketones, malonic acids, and nitroalkane derivatives For compounds containing weaker acidic hydrogen atoms, such as esters, nitriles, amides and aromatic heterocyclic alkyls (PKA > 30), the reaction usually requires a strong base of stoichiometry to undergo deprotonation and then nucleophilic reaction The early work of pines and knockel realized the addition of styrene to nitrile, ketone, imine, lactam and aromatic heterocyclic alkyl compounds catalyzed by potassium TERT butanol In recent years, Kobayashi and other research groups have reported the addition reaction of hydroxy, β - unsaturated carbonyl compounds with nitriles, imines, amides and aromatic heterocyclic alkyl compounds catalyzed by amino potassium or potassium hydride At present, the range of nucleophile substrates for this kind of reactions is limited to compounds with acid hydrogen atoms, while electrophilic reagents are limited to compounds with polar and weak polar unsaturated chemical bonds Functionalization of C-H bond of pyridyl benzyl is an important synthesis method of pyridyl derivatives The pre transition metal can realize the catalytic addition reaction of alkylpyridine and common olefins (Fig 1a) However, for alkylpyridines with both ortho pyridine C-H and benzyl C-H bonds, the pre transition metal catalyst preferentially performs the catalytic alkylation of pyridine C-H bonds (Fig 1b) Recently, the research team of Guan bingtao of Nankai University found that the catalytic addition reaction of pyridine benzyl C-H bond and styrene can be successfully realized by hexamethyldisilazylamine potassium (khmds) (Fig 1c) Compared with rare earth and tetra group metal cation complexes, khmds has different selectivity and reactivity, and has the following advantages: (1) the catalyst is a commercial reagent, which is cheap and easy to obtain; (2) the reaction occurs selectively in the C-H bond of pyridylbenzyl; (3) for the third-order C-H bond with large steric hindrance The bond also has good reactivity and can be used in the synthesis of pyridine benzyl substituted derivatives These advantages can make alkylpyridine Alkylation Catalyzed by amino potassium become an economic and efficient synthesis method The preliminary mechanism study shows that the deprotonation equilibrium of amino potassium to alkylpyridine is the key to the good selectivity of the reaction Fig 1 The alkylation of C-H bond at the position of pyridyl benzyl (source: angelw Chem Int.ed 2018, 57, 1650-1653) the addition of diarylmethane benzyl C-H bond to Styrene Catalyzed by the complex of zinc and potassium salts diarylmethane structure widely exists in drug molecules and natural products; compounds containing diarylmethane structure usually have unique physiological activities The C-H bond of diarylmethanylbenzyl has certain acidity and good reactivity Therefore, deprotonation and further nucleophilic substitution or addition reactions under strong base conditions can realize the functionalization of diarylmethane (Fig 2a) In addition, under the action of transition metal catalyst, diarylmethane can undergo coupling reaction or oxidative coupling reaction (Fig 2B, c) These reactions usually require stronger conditions, equivalent or more strong bases or oxidants Therefore, it is of great significance to develop the synthesis method of diaryl alkanes under mild conditions Based on the alkylation of alkylpyridylbenzyl C-H with Styrene Catalyzed by amino potassium, the author tried to extend this reaction type to other weak acid compounds The pKa value of benzyl hydrogen of diphenylmethane is very close to that of benzyl hydrogen of alkylpyridine, so the author first used khmds as catalyst to try the reaction of diphenylmethane and styrene Khmds can make the reaction happen but the efficiency is low Heating at 70 ℃ for 12 hours, the reaction only realizes one catalytic cycle (10 mol% catalyst, yield 11%) However, when KBN and Zn (HMDS) 2 were mixed as catalysts, the yield increased to 88% under the same conditions There was no secondary alkylation and oligomerization of styrene When KBN is slowly added to the benzene or toluene solution of Zn (HMDS) 2, the red color of KBN will disappear slowly with time, and finally a white solid will be produced Through the NMR characterization of the white solid, we found that it is completely consistent with the NMR data of KZN (HMDS) 2bn complex, which is the product of deprotonation of toluene with KZN (HMDS) 3 reported by Mulvey et al The single crystal structure of zn-k complex shows that K and Zn are bridged by two N atoms, and benzyl group is connected with Zn Such a bridged structure may have an important influence on the performance of the catalyst Further substrate expansion experiments show that all kinds of diarylmethane and styrene derivatives can well realize the catalytic addition reaction (Fig 2D) The preliminary mechanism study shows that the C-H bond breaking of diphenylmethane benzyl is the decisive step of the reaction In summary, the research team realized the first catalytic addition reaction of biarylmethylbenzyl C-H bond and styrene The complex of zinc potassium salt prepared from benzyl potassium and amino zinc has unique catalytic activity Since there is no need for alkali and oxidant, the reaction represents a practical and atom economical method for the synthesis of diaryl alkanes At present, the further catalytic application and related mechanism research of zinc potassium complex are in progress Fig 2 The functionalization of C-H bond at the benzyl position of diarylmethane (source: angelw Chem Int ed doi: 10.1002/anie.201713165) was recently published on angelw.chem Int ed 2018, 57, 1650 – 1653; angelw Chem Int ed 10.1002/anie.201713165 The research work was supported by the "national high level talents special support program" of the Central Organization Department, the National Natural Science Foundation of China, Tianjin Natural Science Foundation, Nankai University and the State Key Laboratory of elemental organic chemistry In addition, the research group of Guan bingtao of Nankai University will recruit 1-2 postdoctors, with an annual salary of 300000-400000 before tax, and can enjoy a one-time living allowance of 50000 yuan from Tianjin Please pay attention to the official website of Nankai University in the near future for specific requirements and policies Dr graduates who wish to have experience in the operation of rare earth and alkaline earth metal complexes and who wish to engage in the research of metal complexes synthesis and catalytic application should contact Mr Guan bingtao (email: guan@nankai.edu.cn, Tel: 022-23509170) 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 CBG information, chembeango app, chembeango official microblog, CBG wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the domestic representative research group, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.