scholarly journals The Reaction of Hydrogen Halides with Tetrahydroborate Anion and Hexahydro-Closo-Hexaborate Dianion

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3754
Author(s):  
Igor E. Golub ◽  
Oleg A. Filippov ◽  
Natalia V. Belkova ◽  
Lina M. Epstein ◽  
Elena S. Shubina
Keyword(s):  
Dft Calculations ◽  
Nucleophilic Substitution ◽  
Solvent Effects ◽  
Lewis Acids ◽  
Hydrogen Halides ◽  
Hydride Ion ◽  
Low Degree ◽  
Successive Substitution ◽  
Electron Deficiency ◽  
Ab Initio Dft

The mechanism of the consecutive halogenation of the tetrahydroborate anion [BH4]− by hydrogen halides (HX, X = F, Cl, Br) and hexahydro-closo-hexaborate dianion [B6H6]2− by HCl via electrophile-induced nucleophilic substitution (EINS) was established by ab initio DFT calculations [M06/6-311++G(d,p) and wB97XD/6-311++G(d,p)] in acetonitrile (MeCN), taking into account non-specific solvent effects (SMD model). Successive substitution of H− by X− resulted in increased electron deficiency of borohydrides and changes in the character of boron atoms from nucleophilic to highly electrophilic. This, in turn, increased the tendency of the B–H bond to transfer a proton rather than a hydride ion. Thus, the regularities established suggested that it should be possible to carry out halogenation more selectively with the targeted synthesis of halogen derivatives with a low degree of substitution, by stabilization of H2 complex, or by carrying out a nucleophilic substitution of B–H bonds activated by interaction with Lewis acids (BL3).

Tropylium Salt Promoted Hydroboration Reactions: Mechanistic Insights via Experimental and Computational Studies

2021 ◽  
Author(s):  
Nhan Nu Hong Ton ◽  
Binh Khanh Mai ◽  
Thanh Vinh Nguyen
Keyword(s):  
Dft Calculations ◽  
Lewis Acids ◽  
Experimental Studies ◽  
Cross Coupling ◽  
Computational Studies ◽  
Metal Free ◽  
Hydride Abstraction ◽  
Novel Method ◽  
Tropylium Salts

Abstract: Hydroboration reaction of alkynes is one of the most synthetically powerful tools to access organoboron compounds, versatile precursors for cross coupling chemistry. This type of reaction has traditionally been mediated by transition metal or main group catalysts. Herein, we report a novel method using tropylium salts, typically known as organic oxidants and Lewis acids, to efficiently promote the hydroboration reaction of alkynes. A broad range of vinylboranes can be easily accessed via this metal-free protocol. Similar hydroboration reactions of alkenes and epoxides can also be efficiently catalyzed by the same tropylium catalysts. Experimental studies and DFT calculations suggested that the reaction follows an uncommon mechanistic paradigm, which is triggered by a hydride abstraction of pinacolborane with tropylium ion. This is followed by a series of <i>in situ</i> counterion-activated substituent exchanges to generate boron intermediates that promote the hydroboration reaction.

scholarly journals Nucleophilic C–H functionalization of arenes: a new logic of organic synthesis

2017 ◽  
Vol 89 (8) ◽  
pp. 1195-1208 ◽  
Author(s):  
Oleg N. Chupakhin ◽  
Valery N. Charushin
Keyword(s):  
Electron Transfer ◽  
Green Chemistry ◽  
Nucleophilic Substitution ◽  
Organic Synthesis ◽  
Nucleophilic Substitution Of Hydrogen ◽  
Metal Free ◽  
Hydride Ion ◽  
Electrochemical Modeling ◽  
Leaving Groups ◽  
Concept Change

AbstractDirect metal-free C–H functionalization of arenes with nucleophiles is a new chapter in the chemistry of aromatics. Comprehensive studies on nucleophilic substitution of hydrogen in arenes (the SNH reactions), including mechanisms, intermediates, mathematic and electrochemical modeling, kinetics, electron-transfer, etc. have shown that this is not the hydride ion, but C–H proton is departed, and this process is facilitated by the presence of an appropriate oxidant or an auxiliary group. The SNH reactions, as a part of the general C–H functionalization concept, change the logic of organic synthesis. They open new opportunities, avoiding incorporation of good leaving groups or other auxiliaries in an aromatic ring, as a prefunctionalization step, thus providing a better correspondence to the principles of green chemistry.

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