In recent years, the unique physicochemical properties of free genes of main group elements have become an important research field of modern chemistry. Because of their high chemical activity, the main group of free radical species with one or more single electrons play an important role in the activation of small molecules and the construction of functional materials. Through the strategies of large steric hindrance ligands and electron delocalization, many boron containing single or multi radical compounds have been stably separated. On the contrary, there are few reports about heavy 13 group elements. Alkene cation ([C = C]? +) and double cation [C = C] 2 + are important intermediates in organic synthesis, which can be stably separated, but the main group metal alkene cation radicals are not stable. Recently, Wang Xinping's group of Nanjing University reported that the first case of cationic free radical and double cation of gallium diene was stabilized and separated by Nitrogen Heterocyclic Carbene.
Figure 1. Synthesis of cationic radicals and anions
As shown in Fig. 1, through single electron oxidation and two electron oxidation of gallium diene compound 2, we can respectively obtain gallium diene cation radical compound 2? + [barf4] - and double cation compound 22 + ([barf4] -) 2. The crystal structure of the compound was determined by single crystal diffraction (Fig. 2). The configuration of free radical cation 2? + is similar to compound 2. The gallium atom is planar triangle and two gallium atoms are coplanar with two adjacent silicon atoms and two carbon atoms. The length of GA GA bond in 2? + is longer than that in 2? + which is consistent with the fact that the double bond of gallium diene is oxidized to lose one π electron and the bond order becomes 1.5. The configuration of double cation 22 + is quite different from that of 2 and 2? +. Although the two gallium atoms are still in the plane triangle shape, the surfaces formed by the two gallium centers and the three connected atoms are no longer coplanar, but have a dihedral angle of 73.77 °. The GA – GA bond length (2.5508?) in 22 + is also in the single bond range. In addition, the above compounds were characterized by EPR, UV spectrum and theoretical calculation. It is found that the spin density of the cation radicals is mainly distributed on two gallium atoms (Fig. 2c, 2D).
Fig. 2. Crystal structure of compounds 2? + [barf4] - (a) and 22 + (b); EPR spectrum (c) and electron spin density distribution (d) of 2? + [barf4] - in room temperature solution.
It is found that the 2? + [barf4] - digalalene cation radical salt has high chemical activity. The product [2-h] + [barf4] - obtained by reaction with tributyltin shows the reactivity of gallium radical. Interestingly, the structure characterization and theoretical calculation show that the compound is a cationic salt with Ga-Ga and ga-h single bonds, while similar boron compounds are the adducts of dibornene and hydrogen protons. Free radical salt 2? + [barf4] - reacts with sulfur to form the first double cation compound 3 containing step like ga4s4 nucleus, which may be used as a single molecular precursor for the synthesis of gallium sulfide.
Figure 3. Study on the reactivity of cationic radical salt 2? + [barf4] -
The results were published in the recent Angewandte Chemie International Edition. The first authors of this paper are Feng Zhongtao, Ph.D. student of Nanjing University, Professor Tan Gengwen (currently working at Suzhou University) and Professor Wang Xinping as co correspondents of this paper.
Original text (scan or press QR code for a long time, and then go to the original page after identification): stable radical category and division of an n ‐ Hetrocyclic carbene stabilized digallene: synthesis, characterization and reactivitityzhonggtao Feng, Yong Fang, Huapeng Ruan, Yue Zhao, Gengwen Tan, * Xinping Wang * angel. Chem. Int. ed., 2020, DOI: 10.1002/ane.202000051
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