Research on R3Si and R3C Ions in Solution

Counterions used in research on R3Si+ and R3C+ ions in solution 

Anion Sb2Fn (30), which is often used in carbenium ion investigations, represents an example for a counterion with delocalized negative charge. [87,97] However, 30 cannot be used in silylium ion chemistry since trialkylsilylhalides do not dissociate into R3Si+X ion-pairs in superacid media. [18] Corey proposed the perchlorate anion (31) as a suitable counterion [85] and Lambert used it in many of his investigations. [80-84] However, Olah and co-workers showed that 

Lambert and co-workers chose to work with tetrakis(pentafluorophenyl)borate (33, TPFPB ). [7-10] A crystal structure analysis of the triethylsilyl cation in toluene solution with TPFPB as counterion revealed that the closest cation-anion contact distance is 4.18 A, which is well outside the range of van der Waals distances suggesting that counterion coordination to R3Si+ is no longer a problem with anions such as 33. [7] 

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