SN2 fluorination reactions in ionic liquids: a mechanistic study towards solvent engineering.
In the catalysis of S(N)2 fluorination reactions, the ionic liquid anion plays a key role as a Lewis base by binding to the counterion Cs(+) and thereby reducing the retarding Coulombic influence of Cs(+) on the nucleophile F(-). The reaction rates also depend critically on the structures of ionic liquid cation, for example, n-butyl imidazolium gives no S(N)2 products, whereas n-butylmethyl imidazolium works well. The origin of the observed phenomenal synergetic effects by the ionic liquid [mim-(t)OH][OMs], in which t-butanol is bonded covalently to the cation [mim], is that the t-butanol moiety binds to the leaving group of the substrate, moderating the retarding interactions between the acidic hydrogen and F(-). This work is a significant step toward designing and engineering solvents for promoting specific chemical reactions.
Department of Applied Chemistry, Kyunghee University, Yongin, Gyeoggi 446-701, Korea.
Young-Ho
YH
Oh
Hyeong Bin
HB
Jang
Suk
S
Im
Myoung Jong
MJ
Song
So-Yeon
SY
Kim
Sung-Woo
SW
Park
Dae Yoon
DY
Chi
Choong Eui
CE
Song
Sungyul
S
Lee