Reactions of Fluoroalkanes with Mg−Mg Bonds: Scope, sp³C−F/sp²C−F Coupling and Mechanism

Abstract

sp C-F Bonds of fluoroalkanes (7 examples; 1°, 2° and 3°) undergo addition to a low-valent Mg-Mg species generating reactive organomagnesium reagents. Further reactions with a series of electrophiles results in a net C-F to C-B, C-Si, C-Sn or C-C bond transformation (11 examples, diversity). The new reactivity has been exploited in an unprecedented one-pot magnesium-mediated coupling of sp C-F and sp C-F bonds. Calculations suggest that the sp C-F bond activation step occurs by frontside nucleophilic attack of the Mg-Mg reagent on the fluoroalkane.

Defluorosilylation of Industrially Relevant Fluoroolefins Using Nucleophilic Silicon Reagents

“…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 . Strong M—F interactions provide a large thermodynamic driving force for the reaction and can also play a role in determining the selectivity of which C−F bond reacts …”

“…2a reacts with hexafluoropropene or trifluoropropene but only at high temperature (100 8 8C) over long reaction periods. 2b did not react with hexafluoropropene despite heating for several days at (12),N ÀMgÀN90.04 (10). 2b:M g ÀN2.0040(15) and 2.0615 (16), MgÀ Si 2.6022(9), NÀMgÀN9 1.28 (6).…”

“…[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. [13] Herein, we extend our studies to nucleophilic magnesium and lithium silyl reagents and demonstrate ap rocedure for the selective sp 2 and sp 3 CÀFb ond functionalization of industrially relevant fluoroolefins.T he method is synthetically straightforward being free from additives or transition metals and in the case of the lithium-based nucleophiles proceeds with high yields,h igh selectivity and high atomefficiency under mild conditions.…”

Defluorosilylation of trifluoromethane: upgrading an environmentally damaging fluorocarbon

“…1,16 Despite this, our group has in recent years demonstrated the C-F activation of simple fluoroalkanes using aluminium and magnesium nucleophiles. 17,18 Furthermore, the groups of Shibata and Martin have both reported C-F activation of a range of fluoroalkanes using group 1 metal silyl nucleophiles. 19,20 We also recently reported the defluorosilylation of industrially relevant hydrofluoroolefins (HFOs) with simple silyl lithium reagents, 21 and in this work we sought to extend the methodology to HFCs.…”

“…A classical, direct S N 2 attack by 1ÁPMDETA at HCF 3 was calculated to proceed via TS4 (see ESI †) (DG 4 ‡ = 53.8 kcal mol À1 ). A 'frontside S N 2' approach was also considered, as this mechanism has been proposed to operate with highly fluorophilic nucleophiles, 18,33 and the highenergy TS5 (see ESI †) (DG 5 ‡ = 44.7 kcal mol À1 ) was found. We were unable to find a transition state for difluorocarbene formation from PMDETAÁLiCF 3 .…”