In Situ Generation of Silyl Anion Species through Si−B Bond Activation for the Concerted Nucleophilic Aromatic Substitution of Fluoroarenes

Abstract

In situ generated silyl anion species enable the concerted nucleophilic aromatic substitution of fluoroarenes. Model DFT calculations indicated that addition of a base to a silylborane would thermodynamically form a silyl borate complex and then kinetically release a silyl anion species through Si−B bond cleavage, and that the in situ generated silyl anion equivalent would further react with a fluoroarene through a concerted nucleophilic aromatic substitution pathway with an activation barrier of ca. 20 kcal/mol to afford the silylated product with a large energy gain. Experiments confirmed that the defluorosilylation reaction took place smoothly at room temperature simply upon mixing fluoroarenes with commercially available silylborane and NaOtBu. Radical scavenger and radical clock reaction experiments provide further evidence for the in situ generation of the silyl anion.

Activation of the Si–B interelement bond related to catalysis

“…Similarly, NaOtBu-mediated defluorosilylation of fluoroarene with Me 2 PhSi-Bpin was reported by Wang, Uchiyama, and coworkers (Scheme 141, bottom). 160 The concerted nucleophilic aromatic substitution pathway was supported by DFT calculations.…”

Palladium-catalysed C–F alumination of fluorobenzenes: mechanistic diversity and origin of selectivity

“…12 An alternative method to prepare uorinated building blocks from uorobenzenes is C-F bond functionalisation. A number of non-catalysed, photo-catalysed and transition metal catalysed methods for the borylation, [13][14][15][16][17][18][19][20] magnesiation, [21][22][23][24] alumination [25][26][27][28] and silylation [29][30][31][32][33] of uorobenzenes have emerged in recent years. The advantage of these approaches is that they form new C-B, C-Mg, C-Al and C-Si bonds respectively, allowing access to main group intermediates that can be used in onwards reactions.…”

Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

“…[5][6][7] In contrast, s-block silyl anions (M-SiR 3 ;M= Li, Na, K) have been invoked as intermediates in highly efficient methods for the defluorosi-lylation of sp 2 C À Fbonds of fluoroarenes and terminal sp 3 C À Fb onds of fluoroalkanes. [8][9][10][11] In related studies we,a nd others,h ave shown that main group nucleophiles are exceptional reagents for the CÀFfunctionalisation of fluoroarenes, fluoroalkenes and fluoroalkanes. [12][13][14][15][16][17] Strong M-F interactions provide al arge thermodynamic driving force for the reaction and can also play arole in determining the selectivity of which C À Fbond reacts.…”

“…Despite the importance of this work, the reactions have low efficiency, they rely on the combination of copper(I) catalyst at modest loading (5 mol %), high temperatures (100 °C) and employ stoichiometric quantities of main group reagents (R 3 Si‐Bpin or B 2 pin 2 ; R=alkyl, pin=pinacolato) . In contrast, s‐block silyl anions (M‐SiR 3 ; M=Li, Na, K) have been invoked as intermediates in highly efficient methods for the defluorosilylation of sp 2 C−F bonds of fluoroarenes and terminal sp 3 C−F bonds of fluoroalkanes . In related studies we, and others, have shown that main group nucleophiles are exceptional reagents for the C−F functionalisation of fluoroarenes, fluoroalkenes and fluoroalkanes .…”