Deng Liang group of Shanghai Institute of organic chemistry made progress in activating nitrogen with organometallic compounds

Nitrogen is the main component of the atmosphere, and the development of efficient catalytic conversion from nitrogen to nitrogen-containing compounds under mild conditions is one of the important challenges in synthetic chemistry Nitrogen has high bond energy (945 kJ / mol) and low reactivity In the ammonia industry, the activation and transformation of nitrogen need high temperature and high pressure In contrast, some transition metal complexes can coordinate nitrogen under mild conditions, which makes it possible to develop the activation and transformation methods of nitrogen molecules under mild conditions After decades of research, almost all of the transition metal molecular nitrogen complexes have been reported However, the further study of nitrogen molecular functionalization starting from the molecular nitrogen complexes mainly focuses on the fourth to the eighth group of transition metals, while the later study of transition metal molecular nitrogen complexes is basically blank This is mainly due to the large electronegativity of these post transition metals and the inability of the density of d electron cloud in the metal center to effectively feed back to the coordination nitrogen molecules, which results in the low activation of nitrogen molecules and the difficulty of functionalization Recently, Deng Liang's research group in the State Key Laboratory of organometallic chemistry, Shanghai Institute of organic chemistry, Chinese Academy of Sciences, has effectively realized the transformation from cobalt molecular nitrogen complexes to silyldiazene complexes by introducing nitrogen heterocyclic carbene ligands with strong electron donating ability It provides a new idea for the design of post transition metal complex catalyst which can efficiently catalyze the activation and transformation of nitrogen Figure 1 Synthesis of Nitrogen Heterocyclic Carbene iron molecular nitrogen complexes (source: chem EUR J 2016, DOI: 10.1002/chem.201603390) Deng Liang, research group of State Key Laboratory of metal organic chemistry, Shanghai Institute of organic chemistry, Chinese Academy of Sciences, has been committed to the study of small molecule activation promoted by low coordination low-cost iron cobalt complexes In the previous work, they have realized the synthesis of high spin monovalent iron nitrogen complexes [(icy) 3Fe (I) (N2)] [BPH 4] and high spin zero valent iron nitrogen complexes [(icy) 3Fe (0) (N2)] with cyclohexylcarbene (icy) as the ligand, and found that zero valent iron nitrogen complexes can be converted into divalent iron nitrogen complexes in solution (Fig 1) Among them, the infrared stretching vibration frequency (1841cm-1) of nitrogen nitrogen bond in zero valent iron molecular nitrogen complex is the lowest one reported so far, indicating the potential of Nitrogen Heterocyclic Carbene with strong electron donating ability in nitrogen molecular coordination activation (chem EUR J 2016, 22, 14162) On this basis, they carried out the research of cobalt molecular nitrogen complexes, and realized the synthesis of negative monovalent cobalt bis (molecular nitrogen) complexes and the functionalization reaction of coordination nitrogen molecules (j.am.chem.soc 2018, 140, 2239-2250) (Fig 2) Figure 2 Synthesis and transformation of Nitrogen Heterocyclic Carbene cobalt complexes (source: J am Chem SOC 2018, DOI: 10.1021/jacs.7b11660) It is found that the zero valent cobalt nitrogen complex [(icy) 3Co (0) (N2)] can be reduced by alkali metal to obtain the negative monovalent cobalt bis (molecular nitrogen) complex m [(icy) 2CO (- 1) (N2) 2] (M = k, Rb, CS) The nitrogen molecules in these negative monovalent cobalt bis (molecular nitrogen) complexes can be partially converted to hydrazine under the action of protonic acid with a yield of 24-30% (relative to cobalt); the reaction with R3 SiCl (r = me, ET) can achieve 1% of nitrogen molecules, This is the first post transition metal diazene complex prepared directly by nitrogen functionalization In the presence of kc8 and me 3sicl, the nitrogen-containing groups in the complex [(icy) 2CO (II) (ƞ 2-ME 3sinnsime 3)] can be converted to n (sime 3) 3 with high yield On this basis, they further developed the reduction silicification of nitrogen molecules catalyzed by Heterocyclic Carbene cobalt complexes, with a ton value of 120, which is higher than the reported 3D metal catalytic system This work expands the application of post transition metal in nitrogen activation and transformation, and has guiding significance for the design of new post transition metal catalytic system The above research work was supported by NSFC, the Ministry of science and technology, the strategic pilot project of Chinese Academy of Sciences (class B) and the State Key Laboratory of organometallic chemistry Corresponding author: researcher Deng Liang